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Simyra dentinosa freyer (Lepidoptera: Noctuidae): A candidate for biological control of leafy spurge (Euphorbia esula L.) in the United States
BIOLOGICAL CONTROL
2, 78-85 (1992)
Simyra dentinosa Freyer (Lepidoptera: Noctuidae): A Candidate for Biological Control of Leafy Spurge (Euphorbia esula L.) in the United States P. PECORA , R. SOBHIAN,AND
M. CRISTOFARO
USDA Agricultural Research Service, European Biological Control Laboratory, BP 4168-Agropolis II, 34092 Montpellier Cedex 5, France Received August 12,199l; accepted March 18, 1992
Dunn, personal communication), and Euphorbia seguierana Necker and Euphorbia helioscopia L. in northern Greece (Rizza and Pecora, unpublished data; Campobasso, 1979, personal communication). Damage to Euphorbia spp. by larvae of S. dentinosa (Fig. 2c) is primarily on budding or flowering shoots. One of the host plants, E. uirgata var. orientalis, is an entity of leafy spurge (E. es&a L. “complex”). This is a noxious weed of Eurasian origin that has become a serious problem in rangelands, pastures, and other noncropland areas in North America, infesting about one million hectares. Leafy spurge becomes an irreversibly dominant weed, displacing useful forage plants on rangelands. It also is poisonous, producing an irritant that causes dermatitis in humans and animals (Kingsbury, 1964). Cattle usually refuse leafy spurge as food unless it is given to them in weedy hay, or unless better forage is not available. Several insect species have been evaluated and introduced as biological control agents against leafy spurge in North America (Harris et al., 1985; Pecora and Dunn, 1990). S. dentinosa was selected to provide an additional agent for the biological control of leafy spurge. Bionomical and host specificity studies were conducted at the U.S. Department of Agriculture laboratory in Rome, Italy, and its substation in Thessaloniki, Greece, from 1982 to 1988.
The biology and host specificity of Simyra dentinosa Freyer (Lepidoptera: Noctuidae) were studied from 1982 to 1988 in the field and laboratory in northern Greece and from 1986 to 1988 in the laboratory in Rome, Italy. Adults emerge from the middle of March to the end of April. Young larvae (instar l-4) are gregarious; the fifth and sixth instars are solitary. Larval development requires 30 days. Larvae feed on budding or flowering Euphorbia plants and prevent or reduce seed production. Mature larvae leave their host plant to pupate and overwinter in silken cocoons, which they make in cell-like spaces of twisted and dry leaves of various thistles. The larvae are parasitized by Cotesia sp. (Hymenoptera: Braconidae) and Exorista sp. (Diptera: Tachinidae). Neonate larvae hatched from eggs in the laboratory were tested on plants of 55 species or varieties in 17 families. Complete development of the larvae occurred on only 11 of 24 Euphorbia spp., including E. es&a, which originated from Nebraska. S. dentinosa is recommended as a candidate for biological control of E. esula in North America, where in the absence of its Old World parasites it should be very effective in reducing populations of Euphorbia spp. o 1992 Academic P~ISS, IN. KEY WORDS: Weed control; classical biological control; host specificity; insecta; phytophagous.
INTRODUCTION
MATERIAL
The genus Simyra Ochsenheimer 1816 belongs to the family Noctuidae, subfamily Apatelinae, order Lepidoptera. Simyra includes 15 species, at least 6 of which are palearctic (Poole, 1989). One species (Simyra henrici (Grote)) is reported from the nearctic region (Decker and Maddox, 1971). Simyra dentinosa is widely distributed in southeastern Europe, northern Asia Minor, Israel, southern Russia, southern Siberia, and central Asia (Fig. 1) (Spuler, 1908; Heinicke, 1965). Larvae (Fig. 2d) have been found on Euphorbia myrsinites L. in Macedonia (Thurner, 1964), Euphorbia virgata Waldstein and Kitaibel var. orientalis Boissier in Afganistan and Turkey (P. H. 1049-9644192
$5.00
Cowright 0 1992 hy Academic Press, Inc.
AND
METHODS
The insects used in this study were collected on E. seguierana in the hills 1 to 2 km north of Volvi Lake, 60 km east of Thessaloniki, Greece. The habitat was an overgrazed pasture along a dry river bed, with very dry and sandy soil. The climatic conditions, cold winters and hot, dry summers, favored the growth of E. seguierana and thistles (Cardus spp., Onopordum spp., and Centaurea spp.). Life History Adult emergence. To obtain information on the period of emergence of adults, 160 mature larvae collected 78
on May 21, 1982, were placed in a 30 X 30 X 30-cm screen cage in the Thessaloniki laboratory and provided with fresh bouquets of E. seguierana until all pupated. From these pupae, 130 were left undisturbed outdoors until the following spring when the first adults emerged. The remaining pupae were then moved to a 130 X 80 X 70-cm screen cage. Thirty pupae from the original larvae were kept in a climatic cabinet at 8 k 1°C from the end of September 1982 to mid March 1983 and then were moved to a laboratory and kept at ambient temperature until adults emerged. Additional data on the adult emergence of S. dentinosa were obtained at the Rome laboratory during 1987 and 1988. Adults that emerged during 1987 originated from eggs collected in Greece during mid April 1986, and reared in quarantine on potted plants of E. seguierana at 18.24 4 5.Ol”C, and 59.34 * 29.62% RH. Of the 41 pupae obtained, 21 were kept in individual cardboard containers in an outdoor insectary. The remaining 20 pupae were removed from their silken cocoons and divided equally into two 15 X 15 X 20-cm plastic containers provided with 6 to 8 cm of cornmeal. These containers were
kept in a climatic cabinet (15 + 1’C) from mid June until early November, and then moved to the outdoor insectary until adult emergence. The adults that emerged in 1988 originated from a colony of larvae that was reared on E. seguierana in Greece during the summer of 1987 and whose pupae (n = 128) had been sent to the Rome laboratory at the end of February 1988. Another colony of 80 larvae was reared on leafy spurge and E. seguierana outdoors during 1987; all of the pupae from these larvae were kept outdoors. Oviposition. S. dentinosa lays eggs in masses on the lower side of Euphorbia leaves. To determine whether there is any relation between leaf size and number of eggs per mass, 28 egg masses were collected in the field at the end of April 1983. Number of eggs per mass and percentage of leaf surface covered with eggs were recorded. To investigate egg production in captivity, newly emerged adults were held in the following containers: 1 . Transparent plastic tubes (n = lo), 22 cm in diameter and 50 cm high, provided with two holes (15 cm in
80
PECORA,
SOBHIAN,
AND
CRISTOFAKO
TABLE 1 Emergence
of
Simyra dentinosa Adults under Different Conditions during 1983,1987,
Year
No. pupae
1983 1983 1987 1987 1988 1988
130” 3ob 21’ 2od 128’ SO
No. (%) adults emerged 12 7 8 5 37 20
PP YY PP PP PY PP
27 13 5 7 29 14
66 6’3 $6 d$ $6 66
(40%) (66%) (62511 (60%) (51%) (44.7%)
and
1988
No. (‘;#I adults with malformed wings
Period of adult emergence
12 VP 14 66 (31%) 2 PP 2 66 (30%) 1 PV 3 (36 (30%) 3 PY 4 66 (58.31 5 YP .3 SC3 (12%) la (2.9%)
March 20-30 April 5518 April 15-30 April 23-30 April 1-21 March X0-April 1 5
u Pupae kept outdoors at the Thessaloniki laboratory. b Pupae kept in a climatic chamber at 8 f 1°C from September 1982 to March 1983 and then transferred to a laboratory at ambient temperature. ’ Pupae kept outdoors at the Rome laboratory. d Pupae taken out of the silken cocoons, placed in containers with a layer of cornmeal in a climatic chamber at 15 * 1°C from June to November 1986, and then removed outdoors. ’ Pupae kept outdoors at the Thessaloniki and Rome laboratories. ’ Pupae kept outdoors at the Rome laboratory.
diameter) in the walls covered with plastic screen, covered on top with nylon organdy, and placed over potted plants in the greenhouse at 18.62 + 4.23”C and 54.93 -t 33.56% RH. One or two pairs of moths were confined in each. 2. Sleeve cages (n = 15), 15 cm in diameter and 30 cm high, of black nylon organdy enclosing one or two stems. Seven of these caged plants were kept in quarantine, and the remainder were kept outdoors. One to three females and one or two male moths were confined in each cage. 3. Wooden cages (n = 4) (35 x 35 x 45 cm) were covered on top with a metal screen, containing a potted plant, and kept in the laboratory garden. Two to four females and one to three males were confined in each cage. 4. Plastic screen cages (n = 2) 2 X 2 X 2 m placed in the laboratory garden containing two plastic pots (55 cm in diameter) with several E. seguieruna plants in bud and flower stages. Bouquets of various fresh wild flowers, collected in the laboratory garden, and vials containing a honey solution were added to provide food. Eight to twelve females and seven to nine males were released in each cage. 5. Cages of nylon organdy (n = 5), 65 cm in diameter and 80 cm high, placed over plastic pots (55 cm in diameter) containing E. seguierana in bud and flower stages. Bouquets and a honey solution were placed at the bottom of each cage. One or two pairs of moths were confined in each cage. These trials started at the beginning of April and ended on May 6. Eggs laid in the cages were inspected daily to determine their incubation period. Larval instars. Eggs were placed on potted E. seguierana plants outdoors in Thessaloniki. The eggs were checked daily for hatching, and the development of larvae was followed until pupation occurred.
Pupation site in field. Mature larvae feeding on their host plants were watched until they stopped feeding and left their host plant. These larvae (n = 3) were followed until they pupated. Parasites. Parasitization of S. dentinosa was determined from 50 larvae of various stages collected on May 28,1982. The larvae of each stage were caged separately in the Thessaloniki laboratory. Fresh bouquets of E. seguierana were provided every 3 or 4 days until the larvae pupated or died. Another sample of 47 mature larvae was collected on May 28 and caged with fresh bouquets as above and was inspected daily for emergence of parasites. In addition, field observations on the oviposition behavior of a tachinid fly attacking mature larvae on two E. seguierana plants were conducted during the first week of June 1987. Twenty larvae randomly collected on June 3, 1987, were inspected for eggs. Furthermore, another 13 larvae infested with eggs of the tachinid tly were inspected under a microscope, and the number of eggs and their position on the bodies of the larvae were recorded. These larvae were kept in cardboard containers (1 larva per container) and provided with fresh bouquets of E. seguierana until pupation. The number of tachinid flies that emerged from these larvae was recorded. Host Specificity Tests The host range of S. dentinosa was assessed by exposing neonate larvae to 55 plant species or varieties in 17 families. Heywood’s Flowering Plants of the World (1978) was used as a guide in drafting the test plant list, which included species closely related to Euphorbia spp. (order Euphorbiales), other orders of the superorder Rosidae, representatives of economically important plants in the Rosidae, and host plants associated with other species of Simyra (Tables 4-6).
Simyra
dentinosa
FOR BIOLOGICAL CONTROL OF LEAFY SPURGE
81
82
PECORA.
SOBHIAN. AND
TABLE 2
ceived 20 first instar larvae. The tested plant species or varieties, as well as the plant control, were replicated twice. The caged larvae were left undisturbed and fresh plants were replaced when necessary by removing the larvae on the new plants. The silken webs formed by groups of larvae between two successive molts were removed for measurement of head capsules to determine the number of instars that developed on the various test plants. The experiments were conducted in quarantine at the Rome laboratory under natural day length and ambient temperature during April through May 1986. During 1987, testing was conducted on representatives of economically important plants and host plants known to be attacked by other species of Simyra.
Developmental Parameters for Simyra dentinosa Larvae Reared on Euphorbia at Ambient Temperature in Thessaloniki Larval instar”
2 No. days between molts
Approx length of larvae (mm)
% Width of head capsule (mm J
I,1 L2 L3 L4 L5 L6
6.0 5.0
1.5-2.0 4.5-5.0
0.43 0.62
4.0
9.0
0.95
5.0 5.0 5.0
15.0 22.0 28.0
1.4 2.0 3.2
CRISTOFARO
’ n = 10 larvae/&tar
Oviposition Larval Survival Tests
Test
An oviposition test was conducted with adults that emerged in the laboratory during 1983. On March 10, 1983, ten potted leafy spurge plants from Nebraska and Montana and five E. seguierana plants were confined in a screen cage (130 X 80 X 70 cm). A smaller screen cage (with an open side) containing the pupae was placed in the middle of the cage with the test plants, so emerging adults could move freely onto the exposed plants. The number of eggs laid was recorded.
Two survival tests were conducted with neonate larvae reared from eggs collected at the end of March and beginning of April 1986 and 1987. In one experiment (Test A), individual first instars were placed in a 500~cc aerated cardboard cup provided with a paper towel in the bottom to absorb excess humidity and covered with a plastic lid. A bouquet of fresh leaves of each test plant was placed in each cup and replaced twice per week. As old bouquets were removed from the cups, they were inspected to record feeding and the number of dead larvae. For each test plant, 10 larvae were used and distributed into as many cups. Since larvae of S. dentinosa are gregarious until the fifth instar, a more natural experiment (Test B) using groups of neonate larvae distributed over potted plants caged in transparent plastic tubes 20 cm in diameter and 50 cm high was conducted. Each potted plant re-
RESULTS
Life History Adult. Adults emerged from the middle of March until the end of April. Adults that originated from pupae kept outdoors emerged from 1 to 2 weeks earlier than adults reared from pupae kept in a climatic cabinet. The sex ratio was about 1:l (99 females and 95 males). From
TABLE 3 Development and Survival of Simyra dentinosa Larvae on Euphorbia spp Daily leaf consumption (mm’) per larva” Euphorbia
spp.
Euphorbia seguierana E. uirgata (Oregon) E. uirgata (Wyoming) E. uirgata (Montana) E. uirgata (Nebraska) E. dendroides E. peplus E. cyparissias E. Iucida E. maculata E. helioscopia E. sphathulata a b ’ d
No. larvae surviving as”
(J? + SD)
LII
LIII
LIV
LV
LVI
P
No. days to pupal stage” Cx i SD)
110.01 & 8.53” 110.86 f 6.55” 86.62 f 3.67’ 91.42 + 7.45* 94.29 IL 3.56’.’ 101.47 iz 1.66”,’ 9i.67 Ifr 2.33b,’ 93.10 z!I 3.40b,’ 95.08 f 0.24h,’ 130.12 +- 4.14d 130.30 rf 5.60d 106.29
8 8 8 8 9 5 10 10 8 8 10 3
5 6 6 6 6 4 3 8 6 6 7 1
5 6 6 6 6 4 2 8 6 6 7 1
5 5 5 6 6 4 2 7 4 4 4
s s 5 5 6 3 2 5 3 :i :i
5 s 5 5 6 3 2 s 3 3 3
39.40 -t 1.57” 31.50 ?I 1.00* 32.05 * l.O@ 31.40 t 1.34* 32.16 t 0.75h 45.38 5 3.03’ 35.50 t 4.94a,h 31.00 * 0.70 38.11 I< t 2.13” 47.33 f 4.04’ 54.1:i + 4.61d
1
1
I
aid
No. larvae (!&) surviving to pupal stage 18 15 13 20 12 5 5 14 10 3 3 2
Means in the same column followed by the same letter are not significantly different (P = 0.05) (Student Newman-Keuls test). Single larvae/cut replicated 10 times. Twenty larvae/potted plant replicated twice. One larva reached the pupal stage; no analysis was performed.
(45.0) (37.5) (32.5) (50.0) (30.0) (12.5) (12.5) (35.0) (25.0) ($5) (7.5) (5.0)
83
Simyra dentinosa FOR BIOLOGICAL CONTROL OF LEAFY SPURGE
TABLE 4 Species of Euphorbia Related to Leafy Spurge That Were Evaluated for Host Suitability for
Sim.va dentinosa
Order (family)
Genus
Subgenus
Species
Common name
Euphorbiales (Euphorbiaceae)
Euphorbia
Esula
*Euphorbia seguierana Necker-Greece *E. uirgata Waldstein and Kitaibel-Nebraska *E. uirgata Waldstein and Kitaibel-Wyoming *E. uirgata Waldstein and Kitaibel-Montana ‘E. uirgata Waldstein and Kitaibel-Oregon *E. dendroides L. *E. cyparissias L. *E. peplus L. *E. lucida Waldstein and Kitaibel “E. helioscopia I,. E. characias L. E. lathyris L. E. enigua L. *E. spathulatu De Lamarck E. rigida van Bieberstein E. marginata Pursh E. antisyphilitica Zuccar E. tirucalli L. E. milii Desmoulins *E. maculata L. E. supina Rafinesque-Schmaltz E. serpyllifolia Persoon E. heterophylla L. E. pulcherrima Willdenow Codieaum variegatum Blume Mercurialis annua L. Ricinus communis L.
Leafy spurge Leafy spurge Leafy spurge Large spurge Leafy spurge Tree spurge Cypress spurge Petty spurge Spurge Wartweed Mediterranean spurge Caper spurge Dwarf spurge
Agaloma Euphorbium Chamaesyce
Poinsettia
Ghostweed Candelilla Milkbush Christ thorn
Paintleaf Poinsettia Croton Annual mercury Castor bean
* Plant species on which Simyru dentinosa larvae completed their life cycle.
40 to 66% of the pupae emerged as adults, from 2.9 to 58.3% of which were malformed (Table 1). Adults lived 4 to 10 days in the laboratory, during which time they remained mostly inactive and did not feed (Fig. 2a). Oviposition. Adults were not observed to mate and did not lay fertile eggs. Only one female laid unfertile eggs (total of 35) in the laboratory. Two females were dissected the day after their emergence; one harbored 85 and the other 350 eggs in the ovarioles. Ten newly emerged females dissected in 1988 had a mean of 345 f 54.2 eggs in their ovarioles. Simyra eggs were found on E. seguierana from the first week of April until the end of the month at Volvi Lake (Greece). They were relatively flat, disclike, or nearly circular, and measured 0.87 + 0.05 mm in diameter (range 0.76-0.96 mm) (n = 30). Freshly laid eggs (Fig. 2b) are light yellow but turn dark brown in 3 to 5 days. The eggs were laid en masse in irregular rows on the lower surface of single leaflets of E. seguierana. The number of eggs per mass ranged from 61 to 242 (n = 28) (X = 131+ 40.9 SD). No relationship was found between the size of a leaf and the number of eggs laid on it. For example, one egg mass with 242 eggs covered 60% of the leaf while another egg mass with 114 eggs covered 90% of the leaf. The incubation period of 150 freshly laid
eggs in the laboratory ranged from 16 to 19 days (temperature 20 4 3°C). Ninety-five percent of the eggs were fertile. Larval instars. There were 6 larval instars (Table 2). Larvae were extremely gregarious from the first to the fourth instar. Groups of 10 to 20 neonate larvae fed at the tops of budding or flowering shoots of E. seguierana and made a silken web in which they molted (Fig. 2~). After each molt the larvae moved to a new branch to feed and spin a new silken web. This procedure continued through the fourth instar. The fifth and sixth instar larvae were solitary (Fig. ad). In the laboratory, mature larvae left the plants and pupated in silken cocoons made among twisted paper or, if this material was not available, on the walls of the cardboard containers and plastic cylinders. Pupation site in field. Mature larvae leave their host plant, empty their gut, and search for pupation sites. These consist of twisted dry leaves of various thistles (e.g., Onopordum and Carduus spp.). Pupation occurs in a silken cocoon constructed in the cell-like space formed by the twisted leaf. Mortality factors. Two parasites, Cotesia sp. (Hymenoptera: Braconidae), and Exorista sp. (Diptera:
84
PECORA,
SOBHIAN.
AND
CRISTOFARO
TABLE 5 Plant Species Hosting Order
Family
Commelinales
Gramineae
Polygonales
Polygonaceae
Typhales
Typhaceae
Simyra spp.
Host plant genus/species
Common name
Triticum aestivum L. Secale cereale L. Phalaris canariensis L. Poa pratensis L. Dactylis glomerata L. Zea mays L. (sweet corn) Zea mays L. cv. Golden hybrid blend Zea mays L. cv. Marao Rheum rhabarbarum L. Fagopyrum tataricum Gaertner Typha latifolia L.
Common wheat Common rye Canary grass Spear grass Orchard grass Corn Corn Corn Rhubarb India wheat Cattail
Tachinidae), were reared from S. dentinosa found on E. seguierana near Volvi Lake. Parasitization due to Cotesia spp. ranged from 2.1 to 3.5%, while from 6.3 to 25% were parasitized by Exorista. Mature larvae of Cotesia were gregarious and spun a mass of silken cocoons away from the parasitized S. dentinosa larvae, from which 100 to 300 adults of Cotesia sp. emerged. A female Exorista sp. was observed ovipositing on a mature larva of S. dentinosa in the field. Five of 20 larvae collected on June 3, 1987, were infested with tachinid eggs. Of the stock of 13 infested larvae collected on June 6, nine were infested with one egg, two had two eggs, one had three eggs, and one had four eggs. One egg was found on the head capsule, one on the dorsal side, and the others on the ventral side of the larvae. All of these larvae, except one, pupated by June 10, and seven tachinid flies emerged between June 19 and 25. Effect of S. dentinosa on host plants. Feeding by S. dentinosa larvae took place during April and May in Greece when the host plant (E. seguierana) was in the bolting and blooming stages. Feeding occurred either on
Simvra species 5’. albovenosa S. albovenosa S. albovenosa S. albovenosa S. albovenosa S. albovenosa S. albovenosa S. albovenosa 8. buettneri S. buettneri S. albovenosa
and and and and and and and and
S. henrici S. henrici S. henrici S. henrici S. henrici S. henrici S. henrici S. henrici
and S. henrici
the terminal growth of young branches or on the apices of flowering shoots of spurge plants. In case of heavy infestation, S. dentinosa completely defoliated the plants, preventing seed production. During the second week of May 1983, near Serrai, northern Greece, 43 (11.3%) of a group of 380 plants of E. seguierana were almost completely destroyed by S. dentinosa; 10 to 75 larvae of various stages were found on each infested plant. During mid May 1984,28 (8%) of 350 plants of E. seguierana in the Serrai area were infested by 8 to 13 S. dentinosa larvae per plant. Host Specificity Test The larvae of S. dentinosa completed their development only on plants of the genus Euphorbia. Ten species of the suitable hosts are in the subgenus Esula and one is in the subgenus Chamaesyce. The mean of daily feeding for larvae which completed development was (1) not different on the biotype of leafy spurge from Oregon and E. dendroides L., (2) significantly higher on E. maculata
TABLE 6 Evaluated Plant Species Not Hosting Order
Family
Violaes Geraniales
Cistaceae Geraniaceae
Asterales
Linaceae Composite
Liamiales Fabales Sapindales Scrophulariales Polemoniales Capparales Gentianales
Labiatae Leguminosae Rutaceae Scrophulariaceae Convolvulaceae Cruciferae Asclepiadaceae
Rosales Liliales
Crassulaceae Iridaceae
Simyra dentinosa Genus/species
Common name
Helianthemum appenium L. Geranium rotundifolium L. Pelargonium zonale Aiton Linum usitatissum L. Cynara scolymus I.. Lactuca sativa L. Salvia splenders Ken-Gawler Medicago sativa L. Ruta graveolens L. Linaria vulgaris Miller Philip Ipomoea grandiflora Roxburg Alyssum argentum Allioni Asclepias syriaca L. Asclepias speciosa Torrey Sedum album I,. Iris sibirica I,.
Sun rose Cranesbill Storksbill Flax Artichoke Lettuce Scarlet sage Alfalfa Common rue Toadflax Moon flower Madwort Silkweed Milkweed Stonecrop Siberian iris
Simyra dentinosa FOR BIOLOGICAL CONTROL OF LEAFY SPURGE
L. and E. helioscopia, and (3) lower on leafy spurge plants from Wyoming, Montana, and Nebraska (Table 3). The value recorded for E. spathulata De Lamark was not analyzed because only 1 individual reached the pupal stage. Furthermore, of the 10 larvae tested on Helianthemum apenninum L. during 1986, two reached the third instar, causing moderate damage. During 1987 another 20 neonate larvae retested on H. apenninum did not feed and died within 4 days. Last, of 10 larvae tested on E. exigua L., 3 reached the second instar, with minimal feeding. The mean number of days required for larvae to pupate was significantly less on all North American specimens of leafy spurge and on E. cyparissias L. than on the control plant, E. seguierana. This value was significantly greater for E. dendroides, E. maculata, and E. helioscopia, and not significantly different for E. peplus L. and E. lucida Waldstein and Kitaibel. We assume that the longer time required for development of larvae on the control plant E. seguierana than on North American leafy spurge was due to the poorer condition of the E. seguierana plants from Greece. In oviposition tests, only one egg mass (48 eggs) was found on leafy spurge from Nebraska, and no eggs were found on E. seguierana, probably because these plants were not in good condition. Larvae that emerged from eggs laid on the North American plant fed and completed their development on these plants. DISCUSSION
S. dentinosa oviposited on and completed its development on leafy spurge plants from Nebraska. In addition, neonate larvae developed to pupation on leafy spurge plants, an important point in considering whether this moth should be introduced into the United States as a biological control agent. Laboratory testing also demonstrated that the host spectrum of S. dentinosa is restricted to plants of the genus Euphorbia. Although E. maculata and E. spathulata were suitable hosts for S. dentinosa under no-choice conditions, these species, which are sympatric with leafy spurge (Pemberton, 1985), would not necessarily be suitable hosts under natural conditions. To evaluate E. maculata and E. spathulata as hosts for S. dentinosa more closely, additional testing (i.e., oviposition and host recognition tests) is necessary before a final decision on its release in the United States is made. The following points suggest that S. dentinosa warrants serious consideration for additional host specificity testing:
85
1. There are no published records of S. dentinosa attacking plants of economic or social importance. 2. Published records indicate that S. dentinosa is associated only with plants in genus Euphorbia. 3. Most leafy spurge species tested from the United States were suitable hosts for S. dentinosa. 4. Damage caused by S. dentinosa larvae contributes to reduced seed production and photosynthetic surfaces of leafy spurge. 5. Since S. dentinosa occurs over a wide climatic range, different ecotypes should be available for introduction into the United States. ACKNOWLEDGMENTS We thank P. M. Marsh and N. E. Woodley, Systematic Entomology Laboratory, USDA-ARS, Washington, DC for identifying the Braconidae and the Tachinidae, respectively; F. Herard, A. Kirk, and L. Knutson, European Biological Control Laboratory, USDA-AR& Montpellier, France; N. Rees, Rangeland Weeds Laboratory, USDAARS, Bozeman, MT; E. Colonnelli, Institute of Zoology, University of Rome, Italy; and L. Wendell, Mission Biocontrol Laboratory, USDA, APHIS-PPQ, Mission, TX, for reviewing the manuscript; and M. Stazi and the staff of the Rome laboratory for technical support.
REFERENCES Decker, G. C., and Maddox, J. V. 1971. Observations on the bionomics of Simyra henrici. J. Econ. Entomol. 64, 117-122. Harris, P., Dunn, P. H., Schroeder, D., and Vonmoos, R. 1985. Biological control of leafy spurge in North America. Monogr. Ser. Weed Sci. Sot. Amer. 3, 79-92. Heinicke, W. 1965. Ergebnisse der Albanien-Expedition 1961 des Deutschen Entom. Inst., 31 Beitrag., Lepidoptera: Noctuidae. Beitr. Entomol. 15, 5-60; 503:632. Heywood, V. H. 1978. “Flowering Plants of the World.” Mayflower Books, New York. Kingsbury, J. M. 1964. “Poisonous Plants of the United States and Canada.” Prentice-Hall, Englewood Cliffs, NJ. Lerault, P. 1980. Systematic and synonymic list of the Lepidoptera of France, Belgium, and Corsica. Alexanor, Suppl., Vol. XI. Pecora, P., and Dunn, P. H. 1990. Insect association on leafy spurge in Europe: Implication for strategies for release of biological control agents in North America. In “Proceedings, VII Int. Symp. Biol. Contr. Weeds, Rome, Italy” (E. S. Delfosse, Ed.), pp. 75-82. Pemberton, R. W. 1985. Native plant consideration in the biological control of leafy spurge. In “Proceedings, VI Int. Symp. Biol. Contr. Weeds, Vancouver, Canada” (E. S. Delfosse, Ed.), pp. 3655390. Poole, R. 1989. “Lepidopterorum Catalogus” (new series). Fascicle 18. Spuler, A. 1908. Die Schmetterlinge Europas. I. Band. E. Schweizerbartsche Verlagsbuchhandlung, Stuttgart. Thurner, J. 1964. Die Lepidopterenfauna jugoslavisch Mazedonies. n.1 Prir. Muz. Skopje.
2, 78-85 (1992)
Simyra dentinosa Freyer (Lepidoptera: Noctuidae): A Candidate for Biological Control of Leafy Spurge (Euphorbia esula L.) in the United States P. PECORA , R. SOBHIAN,AND
M. CRISTOFARO
USDA Agricultural Research Service, European Biological Control Laboratory, BP 4168-Agropolis II, 34092 Montpellier Cedex 5, France Received August 12,199l; accepted March 18, 1992
Dunn, personal communication), and Euphorbia seguierana Necker and Euphorbia helioscopia L. in northern Greece (Rizza and Pecora, unpublished data; Campobasso, 1979, personal communication). Damage to Euphorbia spp. by larvae of S. dentinosa (Fig. 2c) is primarily on budding or flowering shoots. One of the host plants, E. uirgata var. orientalis, is an entity of leafy spurge (E. es&a L. “complex”). This is a noxious weed of Eurasian origin that has become a serious problem in rangelands, pastures, and other noncropland areas in North America, infesting about one million hectares. Leafy spurge becomes an irreversibly dominant weed, displacing useful forage plants on rangelands. It also is poisonous, producing an irritant that causes dermatitis in humans and animals (Kingsbury, 1964). Cattle usually refuse leafy spurge as food unless it is given to them in weedy hay, or unless better forage is not available. Several insect species have been evaluated and introduced as biological control agents against leafy spurge in North America (Harris et al., 1985; Pecora and Dunn, 1990). S. dentinosa was selected to provide an additional agent for the biological control of leafy spurge. Bionomical and host specificity studies were conducted at the U.S. Department of Agriculture laboratory in Rome, Italy, and its substation in Thessaloniki, Greece, from 1982 to 1988.
The biology and host specificity of Simyra dentinosa Freyer (Lepidoptera: Noctuidae) were studied from 1982 to 1988 in the field and laboratory in northern Greece and from 1986 to 1988 in the laboratory in Rome, Italy. Adults emerge from the middle of March to the end of April. Young larvae (instar l-4) are gregarious; the fifth and sixth instars are solitary. Larval development requires 30 days. Larvae feed on budding or flowering Euphorbia plants and prevent or reduce seed production. Mature larvae leave their host plant to pupate and overwinter in silken cocoons, which they make in cell-like spaces of twisted and dry leaves of various thistles. The larvae are parasitized by Cotesia sp. (Hymenoptera: Braconidae) and Exorista sp. (Diptera: Tachinidae). Neonate larvae hatched from eggs in the laboratory were tested on plants of 55 species or varieties in 17 families. Complete development of the larvae occurred on only 11 of 24 Euphorbia spp., including E. es&a, which originated from Nebraska. S. dentinosa is recommended as a candidate for biological control of E. esula in North America, where in the absence of its Old World parasites it should be very effective in reducing populations of Euphorbia spp. o 1992 Academic P~ISS, IN. KEY WORDS: Weed control; classical biological control; host specificity; insecta; phytophagous.
INTRODUCTION
MATERIAL
The genus Simyra Ochsenheimer 1816 belongs to the family Noctuidae, subfamily Apatelinae, order Lepidoptera. Simyra includes 15 species, at least 6 of which are palearctic (Poole, 1989). One species (Simyra henrici (Grote)) is reported from the nearctic region (Decker and Maddox, 1971). Simyra dentinosa is widely distributed in southeastern Europe, northern Asia Minor, Israel, southern Russia, southern Siberia, and central Asia (Fig. 1) (Spuler, 1908; Heinicke, 1965). Larvae (Fig. 2d) have been found on Euphorbia myrsinites L. in Macedonia (Thurner, 1964), Euphorbia virgata Waldstein and Kitaibel var. orientalis Boissier in Afganistan and Turkey (P. H. 1049-9644192
$5.00
Cowright 0 1992 hy Academic Press, Inc.
AND
METHODS
The insects used in this study were collected on E. seguierana in the hills 1 to 2 km north of Volvi Lake, 60 km east of Thessaloniki, Greece. The habitat was an overgrazed pasture along a dry river bed, with very dry and sandy soil. The climatic conditions, cold winters and hot, dry summers, favored the growth of E. seguierana and thistles (Cardus spp., Onopordum spp., and Centaurea spp.). Life History Adult emergence. To obtain information on the period of emergence of adults, 160 mature larvae collected 78
on May 21, 1982, were placed in a 30 X 30 X 30-cm screen cage in the Thessaloniki laboratory and provided with fresh bouquets of E. seguierana until all pupated. From these pupae, 130 were left undisturbed outdoors until the following spring when the first adults emerged. The remaining pupae were then moved to a 130 X 80 X 70-cm screen cage. Thirty pupae from the original larvae were kept in a climatic cabinet at 8 k 1°C from the end of September 1982 to mid March 1983 and then were moved to a laboratory and kept at ambient temperature until adults emerged. Additional data on the adult emergence of S. dentinosa were obtained at the Rome laboratory during 1987 and 1988. Adults that emerged during 1987 originated from eggs collected in Greece during mid April 1986, and reared in quarantine on potted plants of E. seguierana at 18.24 4 5.Ol”C, and 59.34 * 29.62% RH. Of the 41 pupae obtained, 21 were kept in individual cardboard containers in an outdoor insectary. The remaining 20 pupae were removed from their silken cocoons and divided equally into two 15 X 15 X 20-cm plastic containers provided with 6 to 8 cm of cornmeal. These containers were
kept in a climatic cabinet (15 + 1’C) from mid June until early November, and then moved to the outdoor insectary until adult emergence. The adults that emerged in 1988 originated from a colony of larvae that was reared on E. seguierana in Greece during the summer of 1987 and whose pupae (n = 128) had been sent to the Rome laboratory at the end of February 1988. Another colony of 80 larvae was reared on leafy spurge and E. seguierana outdoors during 1987; all of the pupae from these larvae were kept outdoors. Oviposition. S. dentinosa lays eggs in masses on the lower side of Euphorbia leaves. To determine whether there is any relation between leaf size and number of eggs per mass, 28 egg masses were collected in the field at the end of April 1983. Number of eggs per mass and percentage of leaf surface covered with eggs were recorded. To investigate egg production in captivity, newly emerged adults were held in the following containers: 1 . Transparent plastic tubes (n = lo), 22 cm in diameter and 50 cm high, provided with two holes (15 cm in
80
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TABLE 1 Emergence
of
Simyra dentinosa Adults under Different Conditions during 1983,1987,
Year
No. pupae
1983 1983 1987 1987 1988 1988
130” 3ob 21’ 2od 128’ SO
No. (%) adults emerged 12 7 8 5 37 20
PP YY PP PP PY PP
27 13 5 7 29 14
66 6’3 $6 d$ $6 66
(40%) (66%) (62511 (60%) (51%) (44.7%)
and
1988
No. (‘;#I adults with malformed wings
Period of adult emergence
12 VP 14 66 (31%) 2 PP 2 66 (30%) 1 PV 3 (36 (30%) 3 PY 4 66 (58.31 5 YP .3 SC3 (12%) la (2.9%)
March 20-30 April 5518 April 15-30 April 23-30 April 1-21 March X0-April 1 5
u Pupae kept outdoors at the Thessaloniki laboratory. b Pupae kept in a climatic chamber at 8 f 1°C from September 1982 to March 1983 and then transferred to a laboratory at ambient temperature. ’ Pupae kept outdoors at the Rome laboratory. d Pupae taken out of the silken cocoons, placed in containers with a layer of cornmeal in a climatic chamber at 15 * 1°C from June to November 1986, and then removed outdoors. ’ Pupae kept outdoors at the Thessaloniki and Rome laboratories. ’ Pupae kept outdoors at the Rome laboratory.
diameter) in the walls covered with plastic screen, covered on top with nylon organdy, and placed over potted plants in the greenhouse at 18.62 + 4.23”C and 54.93 -t 33.56% RH. One or two pairs of moths were confined in each. 2. Sleeve cages (n = 15), 15 cm in diameter and 30 cm high, of black nylon organdy enclosing one or two stems. Seven of these caged plants were kept in quarantine, and the remainder were kept outdoors. One to three females and one or two male moths were confined in each cage. 3. Wooden cages (n = 4) (35 x 35 x 45 cm) were covered on top with a metal screen, containing a potted plant, and kept in the laboratory garden. Two to four females and one to three males were confined in each cage. 4. Plastic screen cages (n = 2) 2 X 2 X 2 m placed in the laboratory garden containing two plastic pots (55 cm in diameter) with several E. seguieruna plants in bud and flower stages. Bouquets of various fresh wild flowers, collected in the laboratory garden, and vials containing a honey solution were added to provide food. Eight to twelve females and seven to nine males were released in each cage. 5. Cages of nylon organdy (n = 5), 65 cm in diameter and 80 cm high, placed over plastic pots (55 cm in diameter) containing E. seguierana in bud and flower stages. Bouquets and a honey solution were placed at the bottom of each cage. One or two pairs of moths were confined in each cage. These trials started at the beginning of April and ended on May 6. Eggs laid in the cages were inspected daily to determine their incubation period. Larval instars. Eggs were placed on potted E. seguierana plants outdoors in Thessaloniki. The eggs were checked daily for hatching, and the development of larvae was followed until pupation occurred.
Pupation site in field. Mature larvae feeding on their host plants were watched until they stopped feeding and left their host plant. These larvae (n = 3) were followed until they pupated. Parasites. Parasitization of S. dentinosa was determined from 50 larvae of various stages collected on May 28,1982. The larvae of each stage were caged separately in the Thessaloniki laboratory. Fresh bouquets of E. seguierana were provided every 3 or 4 days until the larvae pupated or died. Another sample of 47 mature larvae was collected on May 28 and caged with fresh bouquets as above and was inspected daily for emergence of parasites. In addition, field observations on the oviposition behavior of a tachinid fly attacking mature larvae on two E. seguierana plants were conducted during the first week of June 1987. Twenty larvae randomly collected on June 3, 1987, were inspected for eggs. Furthermore, another 13 larvae infested with eggs of the tachinid tly were inspected under a microscope, and the number of eggs and their position on the bodies of the larvae were recorded. These larvae were kept in cardboard containers (1 larva per container) and provided with fresh bouquets of E. seguierana until pupation. The number of tachinid flies that emerged from these larvae was recorded. Host Specificity Tests The host range of S. dentinosa was assessed by exposing neonate larvae to 55 plant species or varieties in 17 families. Heywood’s Flowering Plants of the World (1978) was used as a guide in drafting the test plant list, which included species closely related to Euphorbia spp. (order Euphorbiales), other orders of the superorder Rosidae, representatives of economically important plants in the Rosidae, and host plants associated with other species of Simyra (Tables 4-6).
Simyra
dentinosa
FOR BIOLOGICAL CONTROL OF LEAFY SPURGE
81
82
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TABLE 2
ceived 20 first instar larvae. The tested plant species or varieties, as well as the plant control, were replicated twice. The caged larvae were left undisturbed and fresh plants were replaced when necessary by removing the larvae on the new plants. The silken webs formed by groups of larvae between two successive molts were removed for measurement of head capsules to determine the number of instars that developed on the various test plants. The experiments were conducted in quarantine at the Rome laboratory under natural day length and ambient temperature during April through May 1986. During 1987, testing was conducted on representatives of economically important plants and host plants known to be attacked by other species of Simyra.
Developmental Parameters for Simyra dentinosa Larvae Reared on Euphorbia at Ambient Temperature in Thessaloniki Larval instar”
2 No. days between molts
Approx length of larvae (mm)
% Width of head capsule (mm J
I,1 L2 L3 L4 L5 L6
6.0 5.0
1.5-2.0 4.5-5.0
0.43 0.62
4.0
9.0
0.95
5.0 5.0 5.0
15.0 22.0 28.0
1.4 2.0 3.2
CRISTOFARO
’ n = 10 larvae/&tar
Oviposition Larval Survival Tests
Test
An oviposition test was conducted with adults that emerged in the laboratory during 1983. On March 10, 1983, ten potted leafy spurge plants from Nebraska and Montana and five E. seguierana plants were confined in a screen cage (130 X 80 X 70 cm). A smaller screen cage (with an open side) containing the pupae was placed in the middle of the cage with the test plants, so emerging adults could move freely onto the exposed plants. The number of eggs laid was recorded.
Two survival tests were conducted with neonate larvae reared from eggs collected at the end of March and beginning of April 1986 and 1987. In one experiment (Test A), individual first instars were placed in a 500~cc aerated cardboard cup provided with a paper towel in the bottom to absorb excess humidity and covered with a plastic lid. A bouquet of fresh leaves of each test plant was placed in each cup and replaced twice per week. As old bouquets were removed from the cups, they were inspected to record feeding and the number of dead larvae. For each test plant, 10 larvae were used and distributed into as many cups. Since larvae of S. dentinosa are gregarious until the fifth instar, a more natural experiment (Test B) using groups of neonate larvae distributed over potted plants caged in transparent plastic tubes 20 cm in diameter and 50 cm high was conducted. Each potted plant re-
RESULTS
Life History Adult. Adults emerged from the middle of March until the end of April. Adults that originated from pupae kept outdoors emerged from 1 to 2 weeks earlier than adults reared from pupae kept in a climatic cabinet. The sex ratio was about 1:l (99 females and 95 males). From
TABLE 3 Development and Survival of Simyra dentinosa Larvae on Euphorbia spp Daily leaf consumption (mm’) per larva” Euphorbia
spp.
Euphorbia seguierana E. uirgata (Oregon) E. uirgata (Wyoming) E. uirgata (Montana) E. uirgata (Nebraska) E. dendroides E. peplus E. cyparissias E. Iucida E. maculata E. helioscopia E. sphathulata a b ’ d
No. larvae surviving as”
(J? + SD)
LII
LIII
LIV
LV
LVI
P
No. days to pupal stage” Cx i SD)
110.01 & 8.53” 110.86 f 6.55” 86.62 f 3.67’ 91.42 + 7.45* 94.29 IL 3.56’.’ 101.47 iz 1.66”,’ 9i.67 Ifr 2.33b,’ 93.10 z!I 3.40b,’ 95.08 f 0.24h,’ 130.12 +- 4.14d 130.30 rf 5.60d 106.29
8 8 8 8 9 5 10 10 8 8 10 3
5 6 6 6 6 4 3 8 6 6 7 1
5 6 6 6 6 4 2 8 6 6 7 1
5 5 5 6 6 4 2 7 4 4 4
s s 5 5 6 3 2 5 3 :i :i
5 s 5 5 6 3 2 s 3 3 3
39.40 -t 1.57” 31.50 ?I 1.00* 32.05 * l.O@ 31.40 t 1.34* 32.16 t 0.75h 45.38 5 3.03’ 35.50 t 4.94a,h 31.00 * 0.70 38.11 I< t 2.13” 47.33 f 4.04’ 54.1:i + 4.61d
1
1
I
aid
No. larvae (!&) surviving to pupal stage 18 15 13 20 12 5 5 14 10 3 3 2
Means in the same column followed by the same letter are not significantly different (P = 0.05) (Student Newman-Keuls test). Single larvae/cut replicated 10 times. Twenty larvae/potted plant replicated twice. One larva reached the pupal stage; no analysis was performed.
(45.0) (37.5) (32.5) (50.0) (30.0) (12.5) (12.5) (35.0) (25.0) ($5) (7.5) (5.0)
83
Simyra dentinosa FOR BIOLOGICAL CONTROL OF LEAFY SPURGE
TABLE 4 Species of Euphorbia Related to Leafy Spurge That Were Evaluated for Host Suitability for
Sim.va dentinosa
Order (family)
Genus
Subgenus
Species
Common name
Euphorbiales (Euphorbiaceae)
Euphorbia
Esula
*Euphorbia seguierana Necker-Greece *E. uirgata Waldstein and Kitaibel-Nebraska *E. uirgata Waldstein and Kitaibel-Wyoming *E. uirgata Waldstein and Kitaibel-Montana ‘E. uirgata Waldstein and Kitaibel-Oregon *E. dendroides L. *E. cyparissias L. *E. peplus L. *E. lucida Waldstein and Kitaibel “E. helioscopia I,. E. characias L. E. lathyris L. E. enigua L. *E. spathulatu De Lamarck E. rigida van Bieberstein E. marginata Pursh E. antisyphilitica Zuccar E. tirucalli L. E. milii Desmoulins *E. maculata L. E. supina Rafinesque-Schmaltz E. serpyllifolia Persoon E. heterophylla L. E. pulcherrima Willdenow Codieaum variegatum Blume Mercurialis annua L. Ricinus communis L.
Leafy spurge Leafy spurge Leafy spurge Large spurge Leafy spurge Tree spurge Cypress spurge Petty spurge Spurge Wartweed Mediterranean spurge Caper spurge Dwarf spurge
Agaloma Euphorbium Chamaesyce
Poinsettia
Ghostweed Candelilla Milkbush Christ thorn
Paintleaf Poinsettia Croton Annual mercury Castor bean
* Plant species on which Simyru dentinosa larvae completed their life cycle.
40 to 66% of the pupae emerged as adults, from 2.9 to 58.3% of which were malformed (Table 1). Adults lived 4 to 10 days in the laboratory, during which time they remained mostly inactive and did not feed (Fig. 2a). Oviposition. Adults were not observed to mate and did not lay fertile eggs. Only one female laid unfertile eggs (total of 35) in the laboratory. Two females were dissected the day after their emergence; one harbored 85 and the other 350 eggs in the ovarioles. Ten newly emerged females dissected in 1988 had a mean of 345 f 54.2 eggs in their ovarioles. Simyra eggs were found on E. seguierana from the first week of April until the end of the month at Volvi Lake (Greece). They were relatively flat, disclike, or nearly circular, and measured 0.87 + 0.05 mm in diameter (range 0.76-0.96 mm) (n = 30). Freshly laid eggs (Fig. 2b) are light yellow but turn dark brown in 3 to 5 days. The eggs were laid en masse in irregular rows on the lower surface of single leaflets of E. seguierana. The number of eggs per mass ranged from 61 to 242 (n = 28) (X = 131+ 40.9 SD). No relationship was found between the size of a leaf and the number of eggs laid on it. For example, one egg mass with 242 eggs covered 60% of the leaf while another egg mass with 114 eggs covered 90% of the leaf. The incubation period of 150 freshly laid
eggs in the laboratory ranged from 16 to 19 days (temperature 20 4 3°C). Ninety-five percent of the eggs were fertile. Larval instars. There were 6 larval instars (Table 2). Larvae were extremely gregarious from the first to the fourth instar. Groups of 10 to 20 neonate larvae fed at the tops of budding or flowering shoots of E. seguierana and made a silken web in which they molted (Fig. 2~). After each molt the larvae moved to a new branch to feed and spin a new silken web. This procedure continued through the fourth instar. The fifth and sixth instar larvae were solitary (Fig. ad). In the laboratory, mature larvae left the plants and pupated in silken cocoons made among twisted paper or, if this material was not available, on the walls of the cardboard containers and plastic cylinders. Pupation site in field. Mature larvae leave their host plant, empty their gut, and search for pupation sites. These consist of twisted dry leaves of various thistles (e.g., Onopordum and Carduus spp.). Pupation occurs in a silken cocoon constructed in the cell-like space formed by the twisted leaf. Mortality factors. Two parasites, Cotesia sp. (Hymenoptera: Braconidae), and Exorista sp. (Diptera:
84
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TABLE 5 Plant Species Hosting Order
Family
Commelinales
Gramineae
Polygonales
Polygonaceae
Typhales
Typhaceae
Simyra spp.
Host plant genus/species
Common name
Triticum aestivum L. Secale cereale L. Phalaris canariensis L. Poa pratensis L. Dactylis glomerata L. Zea mays L. (sweet corn) Zea mays L. cv. Golden hybrid blend Zea mays L. cv. Marao Rheum rhabarbarum L. Fagopyrum tataricum Gaertner Typha latifolia L.
Common wheat Common rye Canary grass Spear grass Orchard grass Corn Corn Corn Rhubarb India wheat Cattail
Tachinidae), were reared from S. dentinosa found on E. seguierana near Volvi Lake. Parasitization due to Cotesia spp. ranged from 2.1 to 3.5%, while from 6.3 to 25% were parasitized by Exorista. Mature larvae of Cotesia were gregarious and spun a mass of silken cocoons away from the parasitized S. dentinosa larvae, from which 100 to 300 adults of Cotesia sp. emerged. A female Exorista sp. was observed ovipositing on a mature larva of S. dentinosa in the field. Five of 20 larvae collected on June 3, 1987, were infested with tachinid eggs. Of the stock of 13 infested larvae collected on June 6, nine were infested with one egg, two had two eggs, one had three eggs, and one had four eggs. One egg was found on the head capsule, one on the dorsal side, and the others on the ventral side of the larvae. All of these larvae, except one, pupated by June 10, and seven tachinid flies emerged between June 19 and 25. Effect of S. dentinosa on host plants. Feeding by S. dentinosa larvae took place during April and May in Greece when the host plant (E. seguierana) was in the bolting and blooming stages. Feeding occurred either on
Simvra species 5’. albovenosa S. albovenosa S. albovenosa S. albovenosa S. albovenosa S. albovenosa S. albovenosa S. albovenosa 8. buettneri S. buettneri S. albovenosa
and and and and and and and and
S. henrici S. henrici S. henrici S. henrici S. henrici S. henrici S. henrici S. henrici
and S. henrici
the terminal growth of young branches or on the apices of flowering shoots of spurge plants. In case of heavy infestation, S. dentinosa completely defoliated the plants, preventing seed production. During the second week of May 1983, near Serrai, northern Greece, 43 (11.3%) of a group of 380 plants of E. seguierana were almost completely destroyed by S. dentinosa; 10 to 75 larvae of various stages were found on each infested plant. During mid May 1984,28 (8%) of 350 plants of E. seguierana in the Serrai area were infested by 8 to 13 S. dentinosa larvae per plant. Host Specificity Test The larvae of S. dentinosa completed their development only on plants of the genus Euphorbia. Ten species of the suitable hosts are in the subgenus Esula and one is in the subgenus Chamaesyce. The mean of daily feeding for larvae which completed development was (1) not different on the biotype of leafy spurge from Oregon and E. dendroides L., (2) significantly higher on E. maculata
TABLE 6 Evaluated Plant Species Not Hosting Order
Family
Violaes Geraniales
Cistaceae Geraniaceae
Asterales
Linaceae Composite
Liamiales Fabales Sapindales Scrophulariales Polemoniales Capparales Gentianales
Labiatae Leguminosae Rutaceae Scrophulariaceae Convolvulaceae Cruciferae Asclepiadaceae
Rosales Liliales
Crassulaceae Iridaceae
Simyra dentinosa Genus/species
Common name
Helianthemum appenium L. Geranium rotundifolium L. Pelargonium zonale Aiton Linum usitatissum L. Cynara scolymus I.. Lactuca sativa L. Salvia splenders Ken-Gawler Medicago sativa L. Ruta graveolens L. Linaria vulgaris Miller Philip Ipomoea grandiflora Roxburg Alyssum argentum Allioni Asclepias syriaca L. Asclepias speciosa Torrey Sedum album I,. Iris sibirica I,.
Sun rose Cranesbill Storksbill Flax Artichoke Lettuce Scarlet sage Alfalfa Common rue Toadflax Moon flower Madwort Silkweed Milkweed Stonecrop Siberian iris
Simyra dentinosa FOR BIOLOGICAL CONTROL OF LEAFY SPURGE
L. and E. helioscopia, and (3) lower on leafy spurge plants from Wyoming, Montana, and Nebraska (Table 3). The value recorded for E. spathulata De Lamark was not analyzed because only 1 individual reached the pupal stage. Furthermore, of the 10 larvae tested on Helianthemum apenninum L. during 1986, two reached the third instar, causing moderate damage. During 1987 another 20 neonate larvae retested on H. apenninum did not feed and died within 4 days. Last, of 10 larvae tested on E. exigua L., 3 reached the second instar, with minimal feeding. The mean number of days required for larvae to pupate was significantly less on all North American specimens of leafy spurge and on E. cyparissias L. than on the control plant, E. seguierana. This value was significantly greater for E. dendroides, E. maculata, and E. helioscopia, and not significantly different for E. peplus L. and E. lucida Waldstein and Kitaibel. We assume that the longer time required for development of larvae on the control plant E. seguierana than on North American leafy spurge was due to the poorer condition of the E. seguierana plants from Greece. In oviposition tests, only one egg mass (48 eggs) was found on leafy spurge from Nebraska, and no eggs were found on E. seguierana, probably because these plants were not in good condition. Larvae that emerged from eggs laid on the North American plant fed and completed their development on these plants. DISCUSSION
S. dentinosa oviposited on and completed its development on leafy spurge plants from Nebraska. In addition, neonate larvae developed to pupation on leafy spurge plants, an important point in considering whether this moth should be introduced into the United States as a biological control agent. Laboratory testing also demonstrated that the host spectrum of S. dentinosa is restricted to plants of the genus Euphorbia. Although E. maculata and E. spathulata were suitable hosts for S. dentinosa under no-choice conditions, these species, which are sympatric with leafy spurge (Pemberton, 1985), would not necessarily be suitable hosts under natural conditions. To evaluate E. maculata and E. spathulata as hosts for S. dentinosa more closely, additional testing (i.e., oviposition and host recognition tests) is necessary before a final decision on its release in the United States is made. The following points suggest that S. dentinosa warrants serious consideration for additional host specificity testing:
85
1. There are no published records of S. dentinosa attacking plants of economic or social importance. 2. Published records indicate that S. dentinosa is associated only with plants in genus Euphorbia. 3. Most leafy spurge species tested from the United States were suitable hosts for S. dentinosa. 4. Damage caused by S. dentinosa larvae contributes to reduced seed production and photosynthetic surfaces of leafy spurge. 5. Since S. dentinosa occurs over a wide climatic range, different ecotypes should be available for introduction into the United States. ACKNOWLEDGMENTS We thank P. M. Marsh and N. E. Woodley, Systematic Entomology Laboratory, USDA-ARS, Washington, DC for identifying the Braconidae and the Tachinidae, respectively; F. Herard, A. Kirk, and L. Knutson, European Biological Control Laboratory, USDA-AR& Montpellier, France; N. Rees, Rangeland Weeds Laboratory, USDAARS, Bozeman, MT; E. Colonnelli, Institute of Zoology, University of Rome, Italy; and L. Wendell, Mission Biocontrol Laboratory, USDA, APHIS-PPQ, Mission, TX, for reviewing the manuscript; and M. Stazi and the staff of the Rome laboratory for technical support.
REFERENCES Decker, G. C., and Maddox, J. V. 1971. Observations on the bionomics of Simyra henrici. J. Econ. Entomol. 64, 117-122. Harris, P., Dunn, P. H., Schroeder, D., and Vonmoos, R. 1985. Biological control of leafy spurge in North America. Monogr. Ser. Weed Sci. Sot. Amer. 3, 79-92. Heinicke, W. 1965. Ergebnisse der Albanien-Expedition 1961 des Deutschen Entom. Inst., 31 Beitrag., Lepidoptera: Noctuidae. Beitr. Entomol. 15, 5-60; 503:632. Heywood, V. H. 1978. “Flowering Plants of the World.” Mayflower Books, New York. Kingsbury, J. M. 1964. “Poisonous Plants of the United States and Canada.” Prentice-Hall, Englewood Cliffs, NJ. Lerault, P. 1980. Systematic and synonymic list of the Lepidoptera of France, Belgium, and Corsica. Alexanor, Suppl., Vol. XI. Pecora, P., and Dunn, P. H. 1990. Insect association on leafy spurge in Europe: Implication for strategies for release of biological control agents in North America. In “Proceedings, VII Int. Symp. Biol. Contr. Weeds, Rome, Italy” (E. S. Delfosse, Ed.), pp. 75-82. Pemberton, R. W. 1985. Native plant consideration in the biological control of leafy spurge. In “Proceedings, VI Int. Symp. Biol. Contr. Weeds, Vancouver, Canada” (E. S. Delfosse, Ed.), pp. 3655390. Poole, R. 1989. “Lepidopterorum Catalogus” (new series). Fascicle 18. Spuler, A. 1908. Die Schmetterlinge Europas. I. Band. E. Schweizerbartsche Verlagsbuchhandlung, Stuttgart. Thurner, J. 1964. Die Lepidopterenfauna jugoslavisch Mazedonies. n.1 Prir. Muz. Skopje.