Control of black cutworm, Agrotis ipsilon (Lepidoptera: Noctuidae), with entomogenous nematodes (Nematoda: Steinernematidae, Heterorhabditidae)

JOURNAL

OF INVERTEBRATE

PATHOLOGY

52, 427-435 (1988)

Control of Black Cutworm, Agrotis ipsilon (Lepidoptera: with Entomogenous Nematodes (Nematoda: Steinernematidae, Heterorhabditidae) J. L. CAPINERA’, Department

D. PELISSIER,

of Entomology,

Colorado

G. S. MENOUT, State

University,

Ft.

Noctuidae),

AND N. D. EPSKY’ Collins,

Colorado

80523

Received February 20, 1988; accepted April 27, 1988 Various species and strains of entomophagous nematodes were assessed in the laboratory for their potential to infect black cutworm larvae, Agrotis ipsilon: Steinernema felriae (= Neoaplectana carpocapsae) strains Mexican and Kapow, S. bibionis and Heterorhabditis heliothidis. Based on LD5,, values, rates of mortality, and storage considerations, S. felriae Mexican strain was chosen for additional evaluation. When incorporated into wheat-bran pellets and calcium alginate capsules, nematode dauerlarvae were able to escape and cause infection of cutworms, but wheatbran pellets allowed more rapid escape. Cutworms consumed wheat-bran pellets as readily as corn seedlings, but more readily than calcium alginate capsules. Addition of wheat bran to calcium alginate capsules did not enhance consumption by cutworms. Field studies suggested no value of wheat-bran bait formulation, relative to aqueous suspension, for delivering nematodes. Significant reduction in corn seedling damage by cutworms in plots inoculated with aqueous suspension of dauerlarvae was demonstrated. Application of nematodes at rates of about 5 x 105/m2 provided over 50% reduction in plant damage in some treatments. 0 1988 Academic PESS, Inc. KEY WORDS: Steinernema; Heterorhabditis; cutworm; bait; susceptibility.

INTRODUCTION

dwelling insects have not been controlled successfully with steinernematids or heterorhabditids. Here we report results of studies designed to assess the potential for nematode suppression of black cutworm, Agrotis ipsilon (Lepidoptera: Noctuidae). Black cutworm is a polyphagous insect which attacks crops throughout the central United States, sometimes causing severe loss (Apple, 1967). Lepidopterans are among the insects most susceptible to infection by steinernematids and heterorhabditids, and the larval stages of black cutworm generally occur below ground; thus, it would seem to be an especially suitable target for biological suppression by entomophagous nematodes.

In the last several years, interest in entomogenous nematodes as biological control agents has increased (Gaugler, 1981). A number of factors are involved, but certainly the improved mass rearing of steinernematids and heterorhabditids (Bedding, 1981) and exemption from FIFRA restrictions by the United States Environmental Protection Agency (Nickle and Welch, 1984) are among the more important developments. While numerous insects are reported to be susceptible to infection (Laumond et al., 1979; Gaugler, 1981) practical use thus far has largely been limited to environments favorable for nematode survival. Attempts to control foliage-feeding insects have been disappointing, while soil-inhabiting insects are more suitable targets (Gaugler, 1981). With few exceptions (e.g., Lossbroek and Theunissen, 1985), however, even soil-

MATERIALS

AND METHODS

General Methods

Black cutworms were obtained from J. C. Reese, Kansas State University, and cultured on black cutworm artificial diet (Bio-Serve, Inc., Franktown, New Jersey) using the methods of Reese et al. (1972).

’ Present address: Department of Entomology and Nematology, University of Florida, Gainesville, Florida 32611. 427

0022-201 l/88 $1.50 Copyright All rights

0 1988 by Academic Press, Inc. of reproduction in any form reserved.

428

CAPINERA

Larval instars were determined by measuring head capsule width with an ocular micrometer (Archer and Musick, 1977). Nematodes were obtained from two sources. Steinernema feltiae (= Neoaplectana carpocapsae) Mexican strain, Steinernema bibionis SN strain, and Heterorhabditis heliothidis were provided by Biosis (Palo Alta, California). S. feltiae Kapow strain was provided by J. E. Lindegren, (U.S. Department of Agriculture, Fresno, California). The black cutworms were propagated and used for culture of the aforementioned nematodes, as well as for control studies. Propagation of nematodes was accomplished using standard culture techniques (Dutky et al., 1964) followed by minimal storage of dauerlarvae (less than 1 month) in 0.1% formaldehyde at 6”-7°C with oxygenation. Greater wax moth, Galleria mellonella (L.) (Lepidoptera: Pyralidae) was cultured using the methods of Dutky et al. (1962) and used for bioassay of nematode activity. Susceptibility to Different Strains of Nematodes

Species and

Black cutworm susceptibility to the various nematode species and strains was evaluated on moist filter paper and in soil. The filter paper method is commonly used as a rapid means of efficacy assessment, but the latter technique is more realistic for black cutworm, which spends much of its life cycle in soil. For filter paper tests, standard Petri dishes (9 x 2.5 cm) were lined with 2 fdter papers (Whatman No. 1). moistened with 1 ml of water. Infective juvenile (dauerlarvae) nematodes were applied in 1 ml of formalin (0.1%) solution, sprayed in a circle from the center of the Petri dish. We waited 1 hr to allow the nematodes to disperse and then one seventh instar larva was placed directly on the filter paper. The experiment cannot be conducted with several cutworms per Petri dish because of their cannibalistic behavior. Petri dishes were

ET AL.

placed in polyethylene bags to prevent dessiccation. Nematodes were applied at the rate of 0 (control), 5, 50, or 500 per Petri dish except in the case of H. heliothidis where a higher rate was needed; we applied 0,50,500, or 5000 nematodes per container for H. heliothidis. Ten cutworms were tested for each dose/substrate combination. Petri dishes were maintained at 25°C in an incubator. For soil tests, a sandy loam (60% sand, 20% silt, 20% clay) was used. One larva was placed at the bottom of the Petri dish and the dish filled with 100 g of moistened soil (8 ml of water/100 g of dry soil). The soil was autoclaved between each experiment so that we had the same type of soil for each species and strain of nematodes tested. We allowed 1 hr for the cutworm to settle in the soil before the nematodes were applied on the soil surface in a volume of 2 ml of water. Dishes were inoculated with dauerlarvae as in the filter paper tests. Mortality of the insects was recorded 24, 48, 72,96, and 120 hr after treatment. Dead insects were removed and set on individual emergence traps to verify the mortality was due to nematode infection. A regression analysis program (MSTAT Probit, Nissen, 1982) was used to determine the lethal dosage (LD,,), or dosage which kills 50% of a population for each nematode. Suitability of Baits for Dispensing Nematodes

Calcium alginate capsules and wheatbran pellets were evaluated as nematode carriers. Calcium alginate capsules are described by Kaya and Nelsen (1985) and were prepared by Plant Genetics, Inc. (Davis, California) using our nematodes. Each capsule contained approximately 1100 nematodes (ca. 20/mg), except as noted below in the feeding behavior test. In some tests wheat bran (5% by wt) was included in the calcium alginate capsules. Wheat-bran bait pellets were prepared from (1) wheat bran-wheat flour (50% each), (2) locust bean gum (1 g/100 ml of

BLACK

CUTWORM

CONTROL

WITH

ENTOMOGENOUS

NEMATODES

429

water), and (3) corn oil. Preparation involved suspending nematodes in gum solution and mixing the three components in the following amounts: (1) 20 g, (2) 20 ml, and (3) 2 ml. The mixture was passed through a food mill and broken into pieces manually to provide pellet structure. Nematodes were incorporated into wheat-bran bait pellets at 20 or 40 nematodes/mg. Amount of bait in comparison studies was varied to provide approximately equal numbers of nematodes irrespective of bait substrate. Escape of nematodes from pellets and capsules. To determine whether it is necessary for insects to feed on the pellets and capsules to release the nematodes, or whether they can disperse freely, observations were made on escape of nematodes in Petri dishes containing moist filter paper. Petri dishes containing several of each bait were wrapped in Parafilm to ensure high humidity and held at 25°C. Observations were made with a stereomicroscope after 6, 24, and 96 hr. Observations and a bioassay also were conducted to verify nematode activity and to determine whether soil type influenced escape of nematodes from capsules. Prepupae of greater wax moth were used as assay organisms and exposed for 5 days to soil in 40-ml cups which had previously held either pellets or capsules for 48 hr. Pellets were buried in agricultural soil, while capsules were buried in sterilized agricultural soil, untreated agricultural soil, or dairy compost (aged manure and straw). Capsules containing and lacking wheat bran were evaluated. Five containers, each with a single wax moth larva, were incubated at 25°C for each treatment.

wheat-bran pellet, capsule with bran, and capsule without bran, in a Petri dish lined with moist filter paper. Nematodes (20OO/pellet; 1lOO/capsule) were present in baits. We tested 10 cutworms in each treatment on each of three dates. In Test 2, a no-choice test, sixth or seventh instar larvae were presented with one wheat-bran bait, one capsule with bran, or one capsule lacking bran individually set in a Petri dish lined with moist filter’ paper. Nematodes were present at the same rate as in Test 1 and tests were replicated as in Test 1. In Test 3, a single cutworm larva was provided with a choice between one corn seedling (1-2 leaves) or one wheat-bran pellet (200 mg average, no nematodes). The sixth to seventh instar larva was presented with the seedling planted in moist vermiculite, and bait was placed on the vermiculite surface, in a 150-ml cup. We tested 10 larvae in each of three replicates. In tests 1 to 3 we recorded consumption 3 and 24 hr after treatment. The consumption was noted as:

Feeding Behavior of Cutworms in Relation to Baits Three separate studies were conducted to assess black cutworm feeding behavior in choice and no-choice situations. In Test 1, a choice test, a single sixth or seventh instar black cutworm larva was provided with a choice between a single

Field Studies

0 = no feeding: 0.5 = bait, capsule, or corn seedling partially consumed; 1 = bait or capsule eaten completely, or corn seedling cut (at ground level). Mortality was assessed in Test 2 at 2, 3, 4, and 5 days post-treatment. Data were analyzed with one-way analysis of variance (ANOVA) followed by Duncan’s multiple range test to separate means for Tests 1 and 2 (Zar, 1984). Data were analyzed with Student’s t test for Test 3.

In 1986 and 1987 we investigated the use of S. feltiae Mexican strain in different formulations for suppressing black cutworm damage to seedling corn in small plot field experiments at Fort Collins, Colorado. The experimental units were plots (60 x 80 cm) of agricultural soil (40% sand, 26%

430

CAPINERA

silt, 34% clay). Plots were hand planted with field corn, with two rows and 10 seeds in each row. The seeds were planted at 5cm intervals with 20 cm separating the rows. The lo-cm-high galvanized steel barrier was placed around each plot to a depth of 3 cm. Vaseline was applied in a band around the inside upper 2 cm of the barrier to discourage escape of larvae. Plots were infested when the corn was in the four- to six-leaf stage, with 10 fourth instar larvae placed along the center line of the plot. Plots also were covered with birdnetting to prevent avian predation of cutworm larvae. The 1986 study was established on July 7, with soil at approximately l&20% moisture. The temperature was fairly low during the days following the experiment, often overcast, and the soil temperature (5 cm deep) did not surpass 22°C at noon. The experimental design was completely randomized, with four replicates of six treatments: (1) calcium alginate capsules with bran, (2) capsules without bran, (3) wheat-bran pellets, (4) aqueous suspension of nematodes, (5) control with nematodefree wheat-bran pellets, and (6) control (no treatment). Nematodes were applied at one dosage (88,000 nematodes/row, equivalent to 5.35 x lo5 nema/m2), on the row, approximately 3 cm deep. For the calcium alginate capsules (treatments 1 and 2), this resulted in an application of seven capsules between each seedling (77 capsules/row). For the wheat-bran pellets (treatments 3 and 5), this resulted in an application of one pellet between each seedling (11 baits/row). For the aqueous suspension (treatment 4) this resulted in 1 ml sprayed between each seedling from a squeeze-bottle containing a lOOml suspension (800,000 nematodes). Infestation with fourth instar cutworms was done immediately following inoculation with nematodes. Treatments were evaluated by recording both the number of plants damaged and type of plant damage. Plant damage was classified into three composite damage cat-

ET AL.

egories: leaf feeding (holes), cut leaves, and cut plant (ground level). Corn plants were observed for damage (24,48, and 72 hr after treatment. The experiment was not run longer because of no apparent increase in damage after this time and initiation of black cutworm pupation. Damage data were evaluated by one-way analysis of variance (Zar, 1984). No infection data were obtained from the field, as we observed some mortality but could not recover many of the cutworms from the plots. Black cutworm larvae are cannibalistic. Soil samples were collected 48 hr after treatment to verify nematode activity with a susceptible host bioassay. Samples were collected in the four plots of treatments 1, 2,3, and 4 at two locations each at about 4 and 8 cm from the row; the four subsamples were mixed together to form a single 200-g sample/plot. The samples were set in Petri dishes, kept moist, inoculated with one wax moth larva (fourth instar), and placed in an incubator at 25°C. We checked for mortality at 72 hr; dead larvae were set on emergence traps. The 1987 studies used the same plot technique and nematode application rate, but treatments focused on aqueous suspensions rather than bait methods of nematode application. Studies were initated on June 30. Soil temperatures were higher than in the 1986 study, reaching a maximum of 25°C at noon; soil moisture was similar. Treatments in the 1987 study were (1) aqueous nematode suspension incorporated at a 3-cm depth (surface incorporation) at the time of cutworm inoculation; (2) surface incorporation, but with the nematodes applied 4 days prior to cutworm release (June 26), (3) aqueous suspension incorporated at a lo-cm depth (injection) at the time of cutworm inoculation; (4) injection, but with the nematodes applied 4 days in advance of cutworm release, and (5) control (no nematodes). There were six replicate plots for each treatment. Data were

BLACK

CUTWORM

CONTROL

WITH

ENTOMOGENOUS

431

NEMATODES

analyzed with one-way ANOVA and orthogonal contrasts. Composite soil samples were taken from each plot to determine nematode activity, as in 1986, except they were taken at 72 hr post-treatment (7 days post-nematode application in the case of treatments 2 and 4). Wax moth larvae @/dish) were exposed to the soil samples.

tensive screening is necessary. The soil tests certainly are more similar to field conditions. When assessing which nematode to use for field studies on black cutworm control, S. feltiae Kapow strain might appear to be the obvious choice based on the filter paper and soil tests, where it caused rapid mortality. However, we observed that S. feltiae Kapow was difficult to store, with viability RESULTS AND DISCUSSION dissipating rapidly after 1 month. Since Susceptibility to Species and Strains storage would probably be required in either field research or in attempts at actual Nematodes differed in the rate at which they killed black cutworm larvae (Table 1). crop protection, the Kapow strain was rejected from further study. S. feltiae caused high levels of mortality Both S. feltiae Mexican strain and S. biwithin 48 hr, but it was necessary to wait 72 bionis appeared to be more suitable than H. hr to obtain data adequate for probit analheliothidis. S. feltiae was chosen over S. ysis in the case of S. bibionis and H. hebibionis because it inflicted mortality more liothidis. S. feltiae Kapow was the only rapidly. All subsequent tests employed S. nematode to give high levels of control feltiae Mexican strain. within 24 hr (70% mortality on filter paper, 90% in soil). Suitability of Baits for Dispensing Method of evaluation (filter paper vs soil) Nematodes seemed to influence determination of LD,, (Table l), but not in a consistent manner. Both wheat-bran pellets and calcium alFor Steinernema spp., addition of soil (and ginate capsules induced infections, but efa third dimension: depth), seemingly di- fectiveness varied among delivery systems. luted the nematodes, resulting in higher Within 6 hr, nematodes were observed LD,, values. However, the reverse was moving freely on the surface of wheat-bran true for H. heliothidis, were LD,, values pellets and dispersing over the moist filter apparently were lower for soil. paper. Under the same conditions, nemaAlthough neither the filter paper nor soil todes were not observed escaping from the test probably simulates field conditions ac- capsules, even after 96 hr. In agricultural curately, each has advantages. In particusoil, nematodes were observed on the soil lar, the ease of evaluating nematodes with surface within 24 hr when inoculated with the filter paper unit is attractive when ex- pellets. All wax moth larvae were infected TABLE LABORATORY

1

COMPARISON OF DIFFERENT STRAINS AND SPECIES OF NEMATODES FOR BLACK CONTROL USING MOIST FILTER PAPER OR SOIL SUBSTRATE@

Steinernema feltiae Substrate Filter paper Soil Filter paper Soil

(hr) 48 48 72 72

Kapow

Mexican

1 16 -

9 486 -

Note. Values given are LD,, obtained using probit analysis. a (-) Indicates no response or data inadequate for probit analysis

Steinernema bibionis 83 210

CUTWORM

Heterorhabditis heliothidis 1916 -I79

432

CAPINERA

when exposed to this soil. Nematodes were not observed on the soil surface although 80 and 20% of the larvae became infected when placed in compost-containing cups which formerly held capsules containing bran and not containing bran, respectively. Less infection occurred in agricultural soil: 0 and 20% infection with and without bran, respectively. No infection occurred in sterile soil. Although not exhaustively tested, it is evident that nematodes do not rapidly escape from capsules; this is consistent with a report by Kaya et al. (1987). Soil microorganisms may degrade capsules, increasing the rate of nematode escape. Feeding Behavior of Cutworms in Relation to Baits In both choice (Test 1) and no-choice (Test 2) tests, black cutworm larvae consumed more wheat-bran pellets than calcium alginate capsule (Table 2). Initially, capsules lacking bran were consumed more readily, but this difference disappeared by 24 hr. Mortality appeared to proceed slightly more quickly where larvae consumed wheat-bran pellets. This is not surTABLE

2

MEAN CONSUMPTION RATINGS“ OF BLACK CUTWORM LARVAE IN CHOICE (TEST 1) AND NO-CHOICE (TEST 2) BAIT TESTS AND WHERE PREFERRED BAIT WAS COMPARED TO A SUSCEPTIBLE HOST PLANT (TEST 3)

A

ET AL.

prising considering the higher consumption rate and higher nematode inoculation. However, by 5 days post-treatment there were no statistically significant differences in mortality, with larvae exhibiting 100, 96, and 76% mortality when they consumed pellets, capsules without bran, or capsules with bran, respectively. When larvae were offered a choice between the wheat-bran pellets and seedling corn they did not discriminate significantly. The ability of infective nematodes to escape rapidly from wheat-bran pellets, and the tendency for larvae to consume pellets more readily than calcium alginate capsules, suggested that pellets would be a superior bait formulation. Unfortunately, the pellets were not more attractive than corn seedlings, suggesting that high application rates might be necessary under field conditions. Field Studies There were no significant differences in leaf feeding, number of plants with cut leaves, number of plants cut, or total number of plants exhibiting damage in the 1986 trials by ANOVA. On average, however, plots not receiving bait or nematodes were most damaged (38% exhibiting damage) while plots receiving nematodes in aqueous suspension were least damaged (20%). so

Time (hr) 3

t

24 40

Test 1 Wheat-bran pellet Capsules WI bran Capsules w/o bran Test 2 Wheat-bran pellet Capsules WI bran Capsules w/o bran Test 3 Wheat-bran pellet Corn seedling

0.70a 0.08~ 0.28b

0.95a 0.43b 0.53b

0.63a 0.08c 0.37b

0.92a 0.68b 0.6Ob

0.43a 0.32a

0.82a 0.77a

“. Wheat-bran

pellets

0 Nematode

suspension

nematodes

?i 0 L

l Contra’

F

HOURS

a Means followed by the same letter are not significantly different by Duncan’s new multiple range test (Tests 1 and 2) or Student’s t test (Test 3) (P < 0.05).

with

AFTER

’

TREATMENT

FIG. 1. Percentage of corn seedlings damaged by black cutworm larvae in field plots receiving three nematode treatments, 1986.

BLACK

CUTWORM

CONTROL

WITH

Temporal effects of some treatments are shown in Fig. 1 The soil collected from the nematode-inoculated plots (treatments 1,2, 3, and 4) and returned to the laboratory produced 0, 8, 50, and 75% infection, respectively, in the wax moth bioassay. Since the laboratory and field studies indicated that nematode suspensions were as promising, or more promising, than bait formulation, the latter treatments were deleted from 1987 evaluations. Reduction in number of treatments also allowed increase in number of replicates, and, potentially, better resolution of treatment effects. Analysis of the 1987 field study by ANOVA indicated that the nematode treatments failed to affect the proportion of plants undamaged, proportion cut, or composite damage rating 24 hr post-treatment (F = 0.66-0.77; N.S.), but significance was approached at 48 and 72 hr post-treatment (F = 1.86-2.75; 0.05 < P < 0.10 in five of six analyses). Trends in the proportion of plants damaged are shown in Fig. 2 for some treatments. Orthogonal comparison, contrasting the two injection treatments with the control, suggested a significant reduction in corn seedling damage at 48 hr (F = 8.91; P < 0.001) and at 72 hr (F = 7.53; P = O.Oll), but not at 24 hr (F = 0.86; P <

HOURS

AFTER TREATMENT

2. Percentage of corn seedlings damaged by black cutworm larvae in field plots receiving three nematode treatments, 1987. Treatments shown are those receiving nematodes on the same data as cutworms: treatments 1, 3, and 5 of text. FIG.

ENTOMOGENOUS

NEMATODES

433

0.10). Surface incorporation appeared to be less efficacious at 48 hr (F = 3.21; P = 0.085) and 72 hr (F = 3.04; P = 0.093), and not significant at 24 hr (F = 0.01; P c 0.10) by orthogonal contrast. The two injection treatments were very similar, as were the two surface incorporation treatments. It is not surprising that there might not be an immediate effect of the nematodes on corn seedling protection, since it frequently takes 24-48 hr for mortality to occur following infection with S. feltiue. Since initial consumption affects the latter evaluations as well, we also examined the change in damage ratings between 24- and 48-hr assessments, and between 48 and 72 hr. There was a significant difference in composite damage rating between 24 and 48 hr (F = 4.98; P < O.OOS), but significant treatment effects were not observed between 48 and 72 hr by ANOVA (F = 0.69; P < 0.10). Orthogonal contrasts also were conducted to assess the change in composite damage ratings between 24 and 48 hr. These analyses suggested highly significant levels of corn seedling damage suppression by injection of nematodes (F = 17.5; P < O.OOl), but only weakly significant protection by surface incorporation (F = 3.21; P = 0.08). On average, injection treatments reduced proportion of plants damaged by 52 and 57% at 48 and 72 hr, respectively. Surface incorporation similarly reduced damage by only 21 and 32%, respectively. When wax moth larvae were used in a bioassay to verify nematode activity, higher levels of infection were found in the treatments where nematodes and cutworms were applied on the same date; percentage infection was 82 and 72% for surface incorporated and injected nematodes, respectively. Where nematodes were applied 4 days prior to inoculation with cutworms, wax moth larval infection was 52 and 41% for surface incorporation and injection, respectively. Thus, nematode longevity may be a limiting factor in field use. Soildwelling arthropods consume entomogenous nematodes (Epsky et al., 1988); unfa-

434

CAPINERA

vorable abiotic conditions probably also act to reduce nematode abundance. CONCLUSION Black cutworm larvae are very susceptible to infection by steinernematid and heterorhabditid nematodes, but the biological characteristics of each nematode species and strain present unique potentials and problems. S. feltiue has long been regarded as having great potential for control of a number of pests (Laumond et al., 1979; Gaugler, 1981) and was chosen for these studies because it seemed most practical given the several operational constraints confronting users. Morris (1985) also determined that this nematode might be particularly useful against cutworms. Formulations which prolong longevity (Welch and Briand, 1961; Bedding, 1976; MacVean et al., 1982; Kaya and Nelsen, 1985; Shapiro et al., 1985) or enhance attractiveness (Poinar and Ennik, 1972) have not come into general use, although the rapid loss of efficacy reported herein, and elsewhere (Morris, 1987), suggests that improved formulations, or enhanced longevity, are necessary. In the case of black cutworm control, it would be highly desirable if nematodes applied for cutworm control in early spring could persist and also provide suppression of corn rootworm larvae, Diabrotica spp. (Coleoptera: Chrysomelidae), which hatch in late spring. The behavioral and ecological barriers that limit the potential use of S. feltiae for many hosts under natural conditions are absent below ground; soil is an ideal medium if longevity can be improved. S. feltiae occurs naturally in some soils, and may cause high levels of mortality (Beavers, et al., 1983) without supplemental release. Delivery of dauerlarvae to the environment inhabited by cutworms appears to be accomplished as readily by liquid as by pellet or capsule formulation. If a bait formulation was significantly more attractive than corn seedlings, there might be an advantage

ET AL.

to baits because they could cause an aggregation of cutworms, enhancing infection. However, the nematodes seem to be relatively effective at dispersing short distances in soil, so this probably is not important. Baits remain of interest when subsurface applications are difficult due to damage to plants or because the target insects are surface-dwellers. Unprotected nematodes are unlikely to be effective in this situation. The results of the field studies compare favorably with other field suppression evaluations: strawberry root weevil, Nemotestes incomptus (Coleoptera: Curculionidae) (Georgis and Poinar, 1984); raspberry crown borer, Pennisetia marginata (Lepidoptera: Sesiidae) (Capinera et al., 1986); a citrus root weevil, Diuprepes abbreviutus (L.) (Coleoptera: Curculionidae) (Schroeder, 1987); Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) and sugarbeet wireworm, Limonius californicus (Coleoptera: Elateridae) (Toba et al., 1983); and crucifer flea beetle, Phyllotreta cruciferue (Coleoptera: Chrysomelidae) (Morris, 1987). The most directly comparable study, however, demonstrated superior protection of lettuce seedlings from a cutworm, Agrotis segetum (Lossbroek and Theunissen, 1985). The Agrotis study used Neoaplectana bibionis in sandy soil to achieve protection equivalent to insecticide. The heavier soil encountered in the studies reported herein are less suitable for nematodes. Also, we were unable to allow the study to continue for a protracted period of time, as was done in the Lossbroek and Theunissen (1985) study, because black cutworms develop very rapidly and were beginning to pupate. Nevertheless, if nematode survival can be improved, cutworms appear to be a suitable target for supplemental release to attain crop protection. ACKNOWLEDGMENTS This research was supported by Colorado Agricultural Experiment Station. The cooperation of BIOSIS and Plant Genetics is gratefully acknowledged.

BLACK

CUTWORM

CONTROL

WITH

REFERENCES APPLE, J. W. 1967. Insecticidal control of regular populations of black cutworms on corn. J. Econ. Entomol., 60, 1612-1615. ARCHER, T. L., AND MUSICK, G. J. 1977. Cutting potential of the black cutworm on tield corn. J. Econ. Entomol., 70, 745-747. BEAVERS, J. B., MCCOY, C. W., AND KAPLAN, D. T. 1983. Natural enemies of subterranean Diuprepes abbreviatus (Coleoptera: Curculionidae) larvae in Florida. Environ. Entomol., 12, 840-843. BEDDING, R. A. 1976. New methods increase the feasibility of using Neouplecfana sp. (Nematoda) for the control of insect pests. In “Proceedings of the 1st International Colloquium of Invertebrate Pathology,” pp. 250-254. Kingston. BEDDING, R. A. 1981. Low cost, in vitro mass production of Neouplectanu and Heterorhubditis species (Nematoda) for field control of insect pests. Nematologicu, 27, 109-l 14. CAPINERA, J. L., CRANSHAW, W. S., AND HUGHES, H. G. 1986. Suppression of raspberry crown borer, Penrzisetiu murginatu (Harris) (Lepidoptera: Sesiidae) with soil applications of Steinernemu feltiae (Rhabditida: Steinernematidae). J. Znvertebr. Pathol., 48, 257-258. DUTKY, S. R., THOMPSON, J. V., AND CANTWELL, G. E. 1962. A technique for mass rearing the greater wax moth (Lepidoptera: Galleriidae). Proc. Entomol. Sot. Wash., 64, 56-58. DUTKY, S. R., THOMPSON, J. V., AND CANTWELL, G. E. 1964. A technique for the mass propagation of the DD-136 nematode. J. Znsect Puthol., 6,417422. EPSKY, N. D., WALTER, D. E., AND CAPINERA, J. L. 1988. Potential role of nematophagous microarthropods as biotic mortality factors of entomophagous nematodes (Rhabditida: Steinemematidae, Heterorhabditidae). J. Econ. Entomol., 81, 821-825. GAUGLER, R. 1981. Biological control potential of neoaplectanid nematodes. J. Nemurol., 13,24I-249. GEORGIS, R., AND POINAR, G. O., JR. 1984. Field control of the strawberry root weevil, Nemocestes incomptus, by neoaplectanid nematodes (Steinemematidae: Nematoda). J. Znvertebr. Puthol., 43, 130131. KAYA, H. K., AND NELSEN, C. E. 1985. Encapsulation of steinernematid and heterorhabditid nematodes with calcium alginate: A new approach for insect control and other applications. Environ. Entomol., 14, 572-574. KAYA, H. K., MANNION, C. M., BURLANDO, T. M., AND NELSEN, C. E. 1987. Escape of Steinernema feltiue from alginate capsules containing tomato seeds. J. Nemutol., 19, 287-291. LAUMOND, C., MAULEON, H., AND KERMARREC, A. 1979. Donnes nouvelles sur le spectre d’hotes et le

ENTOMOGENOUS

NEMATODES

435

parasitisme du nematode entomophage Neoaplectuna carpocupsue. Entomophaga, 24, 13-27. LOSSBROEK, T. G., AND THEUNISSEN, J. 1985. The entomogenous nematode Neoaplectanu bibionis as a biological control agent of Agrotis segetum in lettuce. Entomol. Exp. Appl., 39, 261-264. MACVEAN, C. M., BREWER, J. W., AND CAPINERA, J. L. 1982. Field tests of antidesiccants to extend the infection period of an entomogenous nematode, Neoaplectuna carpocupsae, against the Colorado potato beetle. J. Econ. Entomol., 75, 97-101. MORRIS, 0. N. 1985. Susceptibility of 31 species of agricultural insect pests to the entomogenous nematodes Steinernema feltiue and Heterorhubditis bucteriophoru. Canad. Entomol., 117, 40147. MORRIS, 0. N. 1987. Evaluation of the nematode, Steinernema feltiue Filipjev, for the control of the crucifer flea bettle, Phyllotretu cruciferue (Gaeze) (Coleoptera: Chrysomelidae). Canud. Entomol., 119, 95-101.

NICKLE, W. R., AND WELCH, H. E. 1984. History, development, and importance of insect nematology. In “Plant and Insect Nematodes” (W. R. Nickle, Ed.), pp. 627-653. Dekker, New York. NISSEN, 0. 1982. “MSTAT: A microcomputer program for the design, management, and analysis of agronomic research experiments (Version 3.Q.” Michigan State University, East Lansing, Michigan. POINAR, G. O., JR., AND ENNIK, F. 1972. The use of Neouplectanu carpocapsue (Steinernematidae: Rhabditoidea) against adult yellow jackets (Vespulu spp., Vespidae: Hymenoptera). J. Znvertebr. Puthol., 19, 331-334. REESE, J. C., ENGLISH, L. M., YONKE, T. R., AND FAIRCHILD, M. L. 1972. A method for rearing black cutworms. J. Econ. Entomol., 65, 1047-1049. SCHROEDER, W. J. 1987. Laboratory bioassays and field trials of entomogenous nematodes for control of Diuprepes ubbreviutus (Coleoptera: Curculionidae) in citrus. Environ. Entomol., 16, 987-989. SHAPIRO, M., MCLANE, W., AND BELL, R. 1985. Laboratory evaluation of selected chemicals and antidesiccants for the protection of the entomogenous nematode, Steinernema feltiue (Rhabditidae: Steinernematidae), against Lymuntria dispur (Lepidoptera: Lymantriidae). J. Econ. Entomol., 78, 1437-1441. TOBA, H. H., LINDEGREN, J. E., TURNER, J. E., AND VAIL, P. V. 1983. Susceptibility of the Colorado potato beetle and sugarbeet wireworm to Steinernemu feltiae and S. gluseri. J. Nematol., 15, 597-601. WELCH, H. E., AND BRIAND, L. J. 1961. Tests of the nematode DD-136 and an associated bacterium for control of the Colorado potato beetle, Leptinotersu decemlineuta (Say). Cunad. Entomol., 93, 75%763. ZAR, J. H. 1984. “Biostatistical Analysis,” 2nd ed. Prentice-Hall. Englewood Cliffs, New Jersey.