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Life history of Teretriosoma nigrescens Lewis (Coleoptera: Histeridae) and its ability to suppress populations of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae)
J. srored Prod. Res. Vol. 21. No. 3, pp. 115-118, Printed in Great Britain.
1985
0022-474X/85 $3.00 + 0.00 Pergamon Press Ltd
LIFE HISTORY OF TERETRIOSOMA NIGRESCENS LEWIS (COLEOPTERA: HISTERIDAE) AND ITS ABILITY TO SUPPRESS POPULATIONS OF PROSTEPHANUS TRUNCATUS (HORN) (COLEOPTERA: BOSTRICHIDAE) D. P.
&ES
Storage Department, Tropical Development and Research Institute, London Road, Slough SL3 7HL, U.K. (Received 19 February 1985)
Abstract-The life history and behaviour of Teretriosoma nigrexens Lewis are typical of a histerid predator, but only 2, instead of the expected 3, larval instars were recorded. At 27”C, 70% r.h. development from oviposition to adult emergence took about 8 weeks. In 24 h at 27”C, 70% r.h., T. nigrescens adults and larvae, respectively, consumed on average up to 1.7 and 3.5 Prosrephanus rruncarus (Horn) larvae. After 7 weeks, 10 T. nigrescens adults prevented populations of 25, 50, 75 and 100 P. truncatus from increasing, while controls increased at least IO-fold. Grain moisture contents of between 8.514% had little effect on predatory efficiency.
INTRODUCTION
Records, held at the Tropical Development and Research Institute, indicate an association of Teretriosoma nigrescens Lewis (Coleoptera: Histeridae), first described by Lewis (1906) with Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) infesting maize in traditional farmers’ stores in Mexico and Honduras. It has been found also in association with Lyctus brunneus (Stephens) [Coleoptera: Lyctidae]. P. truncates was, until recently, confined to Central and parts of South America, being sometimes a serious pest of farm-stored maize cobs (Wright, 1984; Giles and Leon, 1975). Recently it has been introduced into Tanzania, East Africa, becoming there a pest of major importance of both maize and cassava (Dunstan and Magazini, 1981; Hodges et al., 1983). The present investigation was undertaken to obtain a brief description of the life history and biology of T. nigrescens and to evaluate its effectiveness as a predator of P. truncatus. MATERIALS
AND
METHODS
Predator life history and biology
Studies of the life history and biology of T. nigrescens were made by general observation of it in cultures of its prey, P. truncatus, infesting American No. 3 maize at 27°C 70% r.h., maintained in a constant temperature and humidity (c.t.h.) room. The number of larval instars was estimated by measuring the head width of 50 mixed age larvae. Rate of consumption of prey larvae
The number of P. truncatus larvae eaten per T. nigrescens adult or larvae in 24 h was investigated. Test chambers were used, prepared from 9 cm dia plaster of Paris disks made using a disposable plastic Petri dish as a mould. Into each disk was cut a 4.5 cm dia circular channel 0.5 cm deep by 0.3 cm wide which was widened at six equidistant positions to 0.5 cm. Before filling the channels with coarse maize flour, 1 predator adult or large larva and, at a rate of 1 per channel widening, between 1 and 6 full to half grown prey larvae were added to each test chamber. To prevent insect escape, test chambers were sealed with a Petri dish lid held in place with an elastic band. The prepared chambers were incubated for 24 h at 27°C 70% r.h., after which the numbers of live prey remaining in each chamber were counted. The treatments were replicated 20 times with either adult or larval predators. Control treatments, with no predators, were replicated 3 times. 115
116
D. P.
&ES
Population trends
Ten adult predators and 25, 50, 75 and 100 adult prey were added to 500cm3 capacity jars containing 150 g of American No. 3 maize, equilibrated for 1 week at 27°C 70% r.h. As P. truncatus has difficulty in attacking loose maize (Cowley et al., 1980) a 2 cm layer of glass beads (5 mm dia) was carefully poured over the grain. The jars were sealed with filter paper and wax and incubated at 27°C 70% r.h. in a c.t.h. room for 7 weeks, after which the number of adult insects present were counted. Three replicates of each prey density with or without predators were used. Inzuences of’ relative humidity
Fifty prey adults were added, as before, to 150 g of American No. 3 maize at 8.5, 10 or 12% moisture content, maintained in incubators at 27°C and 30, 38, and 55% r.h. respectively, over glycerol solutions (Braun and Braun, 1958; Hubbard et al., 1975) and also at 14% moisture content equilibrated at 27°C 70% r.h. in a c.t.h. room. Three replicates of each moisture content with or without 10 adult predators were used. These were incubated for 9 weeks and examined as above.
RESULTS Predator life history and biology T. nigrescens is a typical histerid in appearance and behaviour. The adults, about 3 mm long, were observed to live for almost 3 months at 27°C preying on juvenile stages of P. truncatus. The relatively large eggs (1.1 x 0.5 mm) laid singly amongst the commodity, hatch in approx 7 days at 27°C. The larvae are campodeiform, 2-3 mm long on eclosion, with a flattened head bearing large sickle-shaped mandibles. The head and prothorax are heavily sclerotized. Head capsule measurements (Fig. 1) indicate two larval instars instead of the usual three (Hinton, 1945) suggesting, perhaps, that the missing instar may occur within the egg. Each instar lasts about 10 days at 27°C. The fully grown larva, 1.0-l .2 cm long, uses its mandibles to fashion a cell from a suitable crevice within a grain and pupates. Larval cells were also constructed in the plaster of Paris of the experimental chambers. The pupal stage lasted approx 3 weeks at 27°C and development from oviposition to adult emergence was approx 8 weeks. Rate of consumption of prev lanlae P. truncatus larvae were eaten by both larval and adult P. truncatus (Table 1). The larvae ate twice as many (up to 3.5 per day) as did adults (up to 1.7 per day). No prey mortality occurred in the controls. Population trends
Numbers of prey declined in all treatments containing predators, whereas numbers in controls increased by at least lo-fold (Table 2).
Head
Fig. 1. Head
widths
wdth
of a population
/mm
of T. nigrescens larvae.
Population
suppression
by a predator
117
Table 1. Mean number ( * SD) of P. rruncatus larvae eaten by T. nigrescens adults or larvae in 24h at 27°C 70% r.h. Initial no. of
No. eaten
P. trunentw
by larvae
I
0.83 f 1.42 f 1.74 f 2.55 f 3.50 f 3.37 +
2 3 4 5 6
No. eaten
by adults
0.38 0.77 1.24 1.67 1.40 1.83
0.68 f 0.80 f 0.90 f 0.91 * 1.70 * 1.55 +
0.48 0.89 0.97 0.95 1.34 1.82
Table 2. Growth in 7 weeks of various woulations of P. truncates infestina maize at 27”C, 70% r.h. with or without the ;nitial addition of 10 T. nigrescensadults Final number of adult insects (mean f SD) Initial No. of
No predators
P. truncatus
P. truncafus
25 50 75 100
317 * 700 f 1029 5 1013 f
101.08 177.08 74.85 122.45
With predators P. truncatus
11 * 37 * 39 * 76 f
2.08 4.73 4.93 21.55
T. nigrescens
11 * 16 f 18 f 22 *
2.52 2.52 5.86 4.73
Influence of relative humidity on predation
While T. nigrescens was able to prevent any increase in numbers of P. truncatus at all moisture contents tested (Table 3), predator numbers increased significantly only at 14% moisture content. In the controls, numbers of P. truncatus increased faster on maize at 14% moisture content than at 8.5% moisture content. Table 3. Effect of grain moisture content on the predatory ability of 10 T. nigrescens adults on 50 P. rruncatw adults over 9 weeks infesting maize at 27”C, 70% r.h. Final number of adult insects (mean f SD) Grain m.c. (%) 14 12 10 8.5
r.h. (%)
No predators
70 55 38 30
853 f 242 * 203 + 117+
P. rruncatus
528.66 123.89 65.75 10.58
With predators P. truncatus
23 f 15 * 22* 17 +
15.10 13.75 11.52 6.51
T. nigrescens
17 f 10 * 10 f 11 +
4.36 2.65 1.53 3.21
CONCLUSIONS Under these experimental conditions, both adults and larvae of T. nigrescens were effective predators of P. truncatus. Predator larvae probably each consume up to 60 prey larvae (at 2-3 per day) in order to complete their development. As P. truncatus is such a serious pest, even on maize with a very low moisture content [9x] (Hodges et al., 1983), the ability of T. nigrescens to survive and remain an effective predator of this species under dry conditions may be of considerable practical value. Unlike many other Histeridae, some Teretrinae, including Teretriosoma sp., are usually associated with wood boring Bostrichidae and Lyctidae (Hinton, 1945). This habitat is usually much drier than that normally inhabited by the Histeridae, and T. nigrescens may therefore be pre-adapted for life in dry grains. The possibility that the first larval instar is passed inside the egg may be an adaptation to reduce mortality of young larvae in dry conditions. As P. truncatus spreads and becomes established in new areas, other Histeridae, presently associated with wood boring insects may turn to exploit this new arrival. As P. truncatus has great difficulty in clinging to loose individual grains (Cowley et al., 1980) it is a much more serious pest of cob maize than shelled maize. To be realistic, therefore, any future work should be carried out on maize cobs. The species is only one member of a complex of pests infesting maize cobs in Tanzania (Hodges et al., 1983) and although the most serious of pests it should not be considered in isolation. Further work is in progress to study the interaction of T. nigrescens within this pest complex on maize cobs.
118
D. P.
REES
Acknowledgements-The author wishes to thank Dr D. G. H. Halstead for confirmation of the identity of T. nigrescens, Dr R. H. Smith and Dr D. C. Howard for assistance and advice during work undertaken at the University of Reading, and Dr R. J. Hodges for his constructive criticism of the manuscript.
REFERENCES Braun J. V. and Braun J. D. (1958) Relationship between relative humidity and specific gravity of glycerol solutions. Corrosion 14, 117-I 18. Cowley R. J., Howard D. C. and Smith R. H. (1980) The effect of grain stability on damage caused by Prosfephanus truncatus (Horn) and three other beetle pests of stored maize. J. stored Prod. Res. 16, 15-78. Dunstan W. R. and Magazini I. A. (1981) Outbreaks and new records. Tanzania. The larger grain borer on stored products. FAO Plant Protection Bulletin, 29, 8(t81.
Giles P. H. and Leon 0. S. (1975) Investigation of problems in farm-stored maize in Nicaragua. Proc. 1st Int. Prod. Ent., Savannah, Hinton H. E. (1945) The Histeridae associated with stored products. Bull. ent. Res. 35, 309-340. Hodges R. J., Dunstan W. R., Magazini I. and Golob P. (1983) An outbreak of Prosfephanus truncatus (Horn) Bostrichidae) in East Africa. Prot. Ecol. 5, 183-194. Hubbard J. E., Earle F. R. and Senti R. I. R. (1975) Moisture relations in wheat and corn. Cereal Chem. Lewis G. (1906) New species of Histeridae and notices of others. Ann. Msg. nat. Hisr. 17, 401-402. Wright V. E. (1984) World distribution of Prostephanus truncatus. GASGA Workshop on ihe larger Prostephanus truncatus. TPI, Slough 24-25 February 1983. GTZ, Eschbom, 1984. pp. 11-16.
Conf. Stored
(Coleoptera: 34, 422433.
grain borer
1985
0022-474X/85 $3.00 + 0.00 Pergamon Press Ltd
LIFE HISTORY OF TERETRIOSOMA NIGRESCENS LEWIS (COLEOPTERA: HISTERIDAE) AND ITS ABILITY TO SUPPRESS POPULATIONS OF PROSTEPHANUS TRUNCATUS (HORN) (COLEOPTERA: BOSTRICHIDAE) D. P.
&ES
Storage Department, Tropical Development and Research Institute, London Road, Slough SL3 7HL, U.K. (Received 19 February 1985)
Abstract-The life history and behaviour of Teretriosoma nigrexens Lewis are typical of a histerid predator, but only 2, instead of the expected 3, larval instars were recorded. At 27”C, 70% r.h. development from oviposition to adult emergence took about 8 weeks. In 24 h at 27”C, 70% r.h., T. nigrescens adults and larvae, respectively, consumed on average up to 1.7 and 3.5 Prosrephanus rruncarus (Horn) larvae. After 7 weeks, 10 T. nigrescens adults prevented populations of 25, 50, 75 and 100 P. truncatus from increasing, while controls increased at least IO-fold. Grain moisture contents of between 8.514% had little effect on predatory efficiency.
INTRODUCTION
Records, held at the Tropical Development and Research Institute, indicate an association of Teretriosoma nigrescens Lewis (Coleoptera: Histeridae), first described by Lewis (1906) with Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) infesting maize in traditional farmers’ stores in Mexico and Honduras. It has been found also in association with Lyctus brunneus (Stephens) [Coleoptera: Lyctidae]. P. truncates was, until recently, confined to Central and parts of South America, being sometimes a serious pest of farm-stored maize cobs (Wright, 1984; Giles and Leon, 1975). Recently it has been introduced into Tanzania, East Africa, becoming there a pest of major importance of both maize and cassava (Dunstan and Magazini, 1981; Hodges et al., 1983). The present investigation was undertaken to obtain a brief description of the life history and biology of T. nigrescens and to evaluate its effectiveness as a predator of P. truncatus. MATERIALS
AND
METHODS
Predator life history and biology
Studies of the life history and biology of T. nigrescens were made by general observation of it in cultures of its prey, P. truncatus, infesting American No. 3 maize at 27°C 70% r.h., maintained in a constant temperature and humidity (c.t.h.) room. The number of larval instars was estimated by measuring the head width of 50 mixed age larvae. Rate of consumption of prey larvae
The number of P. truncatus larvae eaten per T. nigrescens adult or larvae in 24 h was investigated. Test chambers were used, prepared from 9 cm dia plaster of Paris disks made using a disposable plastic Petri dish as a mould. Into each disk was cut a 4.5 cm dia circular channel 0.5 cm deep by 0.3 cm wide which was widened at six equidistant positions to 0.5 cm. Before filling the channels with coarse maize flour, 1 predator adult or large larva and, at a rate of 1 per channel widening, between 1 and 6 full to half grown prey larvae were added to each test chamber. To prevent insect escape, test chambers were sealed with a Petri dish lid held in place with an elastic band. The prepared chambers were incubated for 24 h at 27°C 70% r.h., after which the numbers of live prey remaining in each chamber were counted. The treatments were replicated 20 times with either adult or larval predators. Control treatments, with no predators, were replicated 3 times. 115
116
D. P.
&ES
Population trends
Ten adult predators and 25, 50, 75 and 100 adult prey were added to 500cm3 capacity jars containing 150 g of American No. 3 maize, equilibrated for 1 week at 27°C 70% r.h. As P. truncatus has difficulty in attacking loose maize (Cowley et al., 1980) a 2 cm layer of glass beads (5 mm dia) was carefully poured over the grain. The jars were sealed with filter paper and wax and incubated at 27°C 70% r.h. in a c.t.h. room for 7 weeks, after which the number of adult insects present were counted. Three replicates of each prey density with or without predators were used. Inzuences of’ relative humidity
Fifty prey adults were added, as before, to 150 g of American No. 3 maize at 8.5, 10 or 12% moisture content, maintained in incubators at 27°C and 30, 38, and 55% r.h. respectively, over glycerol solutions (Braun and Braun, 1958; Hubbard et al., 1975) and also at 14% moisture content equilibrated at 27°C 70% r.h. in a c.t.h. room. Three replicates of each moisture content with or without 10 adult predators were used. These were incubated for 9 weeks and examined as above.
RESULTS Predator life history and biology T. nigrescens is a typical histerid in appearance and behaviour. The adults, about 3 mm long, were observed to live for almost 3 months at 27°C preying on juvenile stages of P. truncatus. The relatively large eggs (1.1 x 0.5 mm) laid singly amongst the commodity, hatch in approx 7 days at 27°C. The larvae are campodeiform, 2-3 mm long on eclosion, with a flattened head bearing large sickle-shaped mandibles. The head and prothorax are heavily sclerotized. Head capsule measurements (Fig. 1) indicate two larval instars instead of the usual three (Hinton, 1945) suggesting, perhaps, that the missing instar may occur within the egg. Each instar lasts about 10 days at 27°C. The fully grown larva, 1.0-l .2 cm long, uses its mandibles to fashion a cell from a suitable crevice within a grain and pupates. Larval cells were also constructed in the plaster of Paris of the experimental chambers. The pupal stage lasted approx 3 weeks at 27°C and development from oviposition to adult emergence was approx 8 weeks. Rate of consumption of prev lanlae P. truncatus larvae were eaten by both larval and adult P. truncatus (Table 1). The larvae ate twice as many (up to 3.5 per day) as did adults (up to 1.7 per day). No prey mortality occurred in the controls. Population trends
Numbers of prey declined in all treatments containing predators, whereas numbers in controls increased by at least lo-fold (Table 2).
Head
Fig. 1. Head
widths
wdth
of a population
/mm
of T. nigrescens larvae.
Population
suppression
by a predator
117
Table 1. Mean number ( * SD) of P. rruncatus larvae eaten by T. nigrescens adults or larvae in 24h at 27°C 70% r.h. Initial no. of
No. eaten
P. trunentw
by larvae
I
0.83 f 1.42 f 1.74 f 2.55 f 3.50 f 3.37 +
2 3 4 5 6
No. eaten
by adults
0.38 0.77 1.24 1.67 1.40 1.83
0.68 f 0.80 f 0.90 f 0.91 * 1.70 * 1.55 +
0.48 0.89 0.97 0.95 1.34 1.82
Table 2. Growth in 7 weeks of various woulations of P. truncates infestina maize at 27”C, 70% r.h. with or without the ;nitial addition of 10 T. nigrescensadults Final number of adult insects (mean f SD) Initial No. of
No predators
P. truncatus
P. truncafus
25 50 75 100
317 * 700 f 1029 5 1013 f
101.08 177.08 74.85 122.45
With predators P. truncatus
11 * 37 * 39 * 76 f
2.08 4.73 4.93 21.55
T. nigrescens
11 * 16 f 18 f 22 *
2.52 2.52 5.86 4.73
Influence of relative humidity on predation
While T. nigrescens was able to prevent any increase in numbers of P. truncatus at all moisture contents tested (Table 3), predator numbers increased significantly only at 14% moisture content. In the controls, numbers of P. truncatus increased faster on maize at 14% moisture content than at 8.5% moisture content. Table 3. Effect of grain moisture content on the predatory ability of 10 T. nigrescens adults on 50 P. rruncatw adults over 9 weeks infesting maize at 27”C, 70% r.h. Final number of adult insects (mean f SD) Grain m.c. (%) 14 12 10 8.5
r.h. (%)
No predators
70 55 38 30
853 f 242 * 203 + 117+
P. rruncatus
528.66 123.89 65.75 10.58
With predators P. truncatus
23 f 15 * 22* 17 +
15.10 13.75 11.52 6.51
T. nigrescens
17 f 10 * 10 f 11 +
4.36 2.65 1.53 3.21
CONCLUSIONS Under these experimental conditions, both adults and larvae of T. nigrescens were effective predators of P. truncatus. Predator larvae probably each consume up to 60 prey larvae (at 2-3 per day) in order to complete their development. As P. truncatus is such a serious pest, even on maize with a very low moisture content [9x] (Hodges et al., 1983), the ability of T. nigrescens to survive and remain an effective predator of this species under dry conditions may be of considerable practical value. Unlike many other Histeridae, some Teretrinae, including Teretriosoma sp., are usually associated with wood boring Bostrichidae and Lyctidae (Hinton, 1945). This habitat is usually much drier than that normally inhabited by the Histeridae, and T. nigrescens may therefore be pre-adapted for life in dry grains. The possibility that the first larval instar is passed inside the egg may be an adaptation to reduce mortality of young larvae in dry conditions. As P. truncatus spreads and becomes established in new areas, other Histeridae, presently associated with wood boring insects may turn to exploit this new arrival. As P. truncatus has great difficulty in clinging to loose individual grains (Cowley et al., 1980) it is a much more serious pest of cob maize than shelled maize. To be realistic, therefore, any future work should be carried out on maize cobs. The species is only one member of a complex of pests infesting maize cobs in Tanzania (Hodges et al., 1983) and although the most serious of pests it should not be considered in isolation. Further work is in progress to study the interaction of T. nigrescens within this pest complex on maize cobs.
118
D. P.
REES
Acknowledgements-The author wishes to thank Dr D. G. H. Halstead for confirmation of the identity of T. nigrescens, Dr R. H. Smith and Dr D. C. Howard for assistance and advice during work undertaken at the University of Reading, and Dr R. J. Hodges for his constructive criticism of the manuscript.
REFERENCES Braun J. V. and Braun J. D. (1958) Relationship between relative humidity and specific gravity of glycerol solutions. Corrosion 14, 117-I 18. Cowley R. J., Howard D. C. and Smith R. H. (1980) The effect of grain stability on damage caused by Prosfephanus truncatus (Horn) and three other beetle pests of stored maize. J. stored Prod. Res. 16, 15-78. Dunstan W. R. and Magazini I. A. (1981) Outbreaks and new records. Tanzania. The larger grain borer on stored products. FAO Plant Protection Bulletin, 29, 8(t81.
Giles P. H. and Leon 0. S. (1975) Investigation of problems in farm-stored maize in Nicaragua. Proc. 1st Int. Prod. Ent., Savannah, Hinton H. E. (1945) The Histeridae associated with stored products. Bull. ent. Res. 35, 309-340. Hodges R. J., Dunstan W. R., Magazini I. and Golob P. (1983) An outbreak of Prosfephanus truncatus (Horn) Bostrichidae) in East Africa. Prot. Ecol. 5, 183-194. Hubbard J. E., Earle F. R. and Senti R. I. R. (1975) Moisture relations in wheat and corn. Cereal Chem. Lewis G. (1906) New species of Histeridae and notices of others. Ann. Msg. nat. Hisr. 17, 401-402. Wright V. E. (1984) World distribution of Prostephanus truncatus. GASGA Workshop on ihe larger Prostephanus truncatus. TPI, Slough 24-25 February 1983. GTZ, Eschbom, 1984. pp. 11-16.
Conf. Stored
(Coleoptera: 34, 422433.
grain borer