Effect of microsporidian infection in Lacanobia oleracea (Lep., Noctuidae) on prey selection and consumption by the spined soldier bug Podisus maculiventris (Het., Pentatomidae)

Abstract:  The predatory behaviour of Podisus maculiventris was investigated when this bug was presented with Lacanobia oleracea larvae infected with the microsporidian pathogen Vairimorpha necatrix . In choice tests, adult predatory bugs attacked V. necatrix -infected L. oleracea prey in similar numbers to uninfected larvae. Exposure to infected prey during nymphal development increased the rate at which adult bugs attacked diseased L. oleracea larvae. Fifth instar P. maculiventris nymphs, however, attacked infected prey in the majority of cases (>80% of occasions). Consumption of healthy and infected prey was measured for both adult and nymphal bugs. Over the course of 1 week, the mean number of V. necatrix -infected prey eaten by P. maculiventris adults (7.0 ± 0.82) was approximately twice the number of uninfected prey consumed (3.8 ± 0.42). Similarly, the number of prey larvae attacked by the bug over the course of the final nymphal stadium was also increased, with 2.9 ± 0.42 uninfected larvae eaten as opposed to 4.9 ± 0.27 V. necatrix -infected prey. However, small-scale investigations into the rate of P. maculiventris reduced small populations of L. oleracea indicated that the combination of the predator and pathogen would produce, at best, an additive effect.     

Genetic variation in field and laboratory populations of the spined soldier bug,Podisus maculiventris

The predatory spined soldier bug, Podisus maculiventris (Say) (Heteroptera: Pentatomidae), is an economically important and highly valued biological control agent. There is substantial information on the biology, ecology, behavior, and rearing of this stink bug. However, virtually nothing is known of its genetic variation, in natural or domesticated populations. To address this lacuna, we used amplified fragment length polymorphism (AFLP) to assess the genetic variability of field and laboratory populations. Four AFLP universal primer combinations yielded a total of 209 usable loci. The AFLP results showed greater genetic variability between populations from Missouri and Mississippi (both USA), and relatively low variability within Missouri populations. We infer little genetic isolation among Missouri field populations and within laboratory populations, but a significant genetic isolation between Missouri and Mississippi populations.     

Impact of inbreeding on performance of the predator Podisus maculiventris

Effects of inbreeding on the development and reproduction of the predatory pentatomid Podisus maculiventris were assessed throughout 30 generations following introduction in the laboratory. Developmental and reproductive fitness of two mildly inbred lines did not differ dramatically from that of a reference population. In most generations, egg weight, egg hatch and developmental rate of nymphs were greater in the reference strain than in both inbred strains, but fecundity and longevity did not differ among strains. In the 30th generation, fecundity of all strains had dropped to about half of that observed in the 15th generation, which was presumably related to non-genetic factors. There were consistent differences among strains for adult body weight and size, indicating heritable variation. A positive relationship between weight at day 14 and humeral width of P. maculiventris females was found, but neither of these parameters was associated with total fecundity. In the 30th generation, predators from both inbred lines had generally similar predation capacities to those from the reference population. No significant relationship could be detected between body weights and predation rates of either nymphs or adults. The use of inbreeding to minimize selective adaptation during rearing or to select for favourable traits in P. maculiventris is discussed.     

The control of Malpighian tubule secretion in a predacious hemipteran insect, the spined soldier bug Podisus maculiventris (Heteroptera, Pentatomidae)

Spined soldier bugs, Podisus maculiventris, are heteropteran insects that feed voraciously on other insects, particular the soft bodied larval forms of Lepidoptera and Coleoptera. The response of P. maculiventris Malpighian tubules (MTs) to serotonin and known diuretic and antidiuretic peptides has been investigated, and is compared with that of MT from the hematophagous and phytophagous heteropteran bugs Rhodnius prolixus and Acrosternum hilare, respectively. A CRF-related peptide diuretic hormone (DH) from the termite Zootermopsis nevadensis (Zoone-DH) stimulated MT secretion, which was reversed by a member of the CAP_2b family of peptides from A. hilare (Acrhi-CAP_2b-2), an antidiuretic effect. Serotonin had no effect on secretion, neither did a representative calcitonin-like DH, kinin, tachykinin-related peptide, and an antidiuretic factor from the mealworm Tenebrio molitor (Tenmo-ADFb) in both P. maculiventris or A. hilare. Serotonin is a DH in R. prolixus, and its lack of effect on MT from P. maculiventris and A. hilare suggests this is an adaptation to hematophagy. On the other hand, the antidiuretic activity of members of the CAP_2b family in all three bugs is consistent with this being a heteropteran feature rather than a specialism for hematophagy.     

Effects of sequential mating by males on reproductive output of the stinkbug predator, Podisus nigrispinus

Reproductive output of the stinkbug predator Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) was investigated as a function of the number of matings that the male had made with a range of females. After being placed with a female, virgin males were most likely to mate within 12 hours, while non-virgin males were most likely to mate within 12–24 hours. Although males lost weight during their first mating, the weights of mated and unmated males were not significantly different throughout their lifetime. Longevity was significantly greater for unmated males (36.0 days) than for mated males (29.8 days). Survival curves for both mated and unmated males were Type II. The capacity of males to transfer sperm to virgin females was not affected by previous matings. From 65.7 to 76.4% of eggs were viable and 206.7 to 274.6 nymphs were produced per female. Regardless of the number of matings that the male had made, females that had mated only once exhausted their stored sperm progressively and produced an increasing proportion of infertile eggs, which peaked at the end of their lives. These results show that P. nigrispinus females need more than one mating to maintain fertility, but their performance is not affected by the number of previous matings that the male has made or by male weight. Thus, the strategy of pairing with males multiple times improved production efficiency by increasing output and reducing food waste in mass production systems. This is achieved by temporarily pairing females at intervals of about 20 days during their entire lifetime.     

Suppression of Colorado potato beetle infestation by pheromone-mediated augmentation of the predatory spined soldier bug, Podisus maculiventris (Say) (Heteroptera: Pentatomidae)

1 Hardware and protocols were tested to enable individual growers and insectary operators to mass-produce predatory spined soldier bugs (SSBs), Podisus maculiventris (Say) (Heteroptera: Pentatomidae: Asopinae), for augmentative biological control. Using pheromone-based technology, an average of 1775 female SSBs (potentially as many as 1.6 million offspring) were captured each year during 2–3 weeks in early spring. 2 Data for the first 2 years of a 3-year project to use SSB for biological suppression of the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), verified earlier research showing that augmentation of SSB (～5 nymphs/plant) can significantly suppress CPB infestations. In the third year, wild SSBs were transferred directly from pheromone traps to mid-plot nursery cages having a mesh size chosen to retain the adult predators but allow their offspring to escape. Pheromone dispensers were placed peripherally to promote dispersal of young predators and immigration of new wild spined soldier bug adults. Pheromone-mediated augmentation using porous nursery cages and pheromone dispensers was less labour-intensive than earlier methods, and resulted in significantly improved potato yield. 3 Trapping SSB adults early in the spring protects them from parasitization by tachinid flies and scelionid wasps that use the pheromone to facilitate host-finding. The compatibility of pheromone-mediated predator augmentation/conservation with implementation of transgenic plants, imidacloprid insecticide, and other biocontrol methods is discussed.     

Developmental response of the beneficial predator Podisus maculiventris to change in dietary ascorbic acid concentration

We report here the effects of a range of ascorbic acid concentrations (0.07, 0.3, 3.0, and 30.0 g l^?1) in artificial diets on growth rates, adult weights, fecundity, and survival over two generations of the predatory stink bug, Podisus maculiventris (Say) (Heteroptera: Pentatomidae). Overall, a dietary level of 3.0 g l^?1 gave the shortest developmental times over two generations. The likelihood of egg hatch at one ascorbic acid concentration compared to another concentration suggested that egg hatch increased as the concentration of ascorbic acid increased from 0.07 to 3.0 g l^?1 and then declined from 3.0 to 30.0 g l^?1. The combination of the maximum egg oviposition at 0.3 and 3.0 g l^?1, egg hatch at 3.0 g l^?1, and survival at 0.07 and 0.3 g l^?1 suggests an overall superior performance at a concentration between 0.3 and 3.0 g l^?1. Depletion of ascorbic acid below 3.0 g l^?1 or addition of ascorbic acid above 3.0 g l^?1 lowered the likelihood of egg hatch, which became more pronounced in the second generation. This is consistent with previously published information for phytophagous insects.     

Evidence for intraguild predation by Podisus maculiventris on a ladybeetle, Coleomegilla maculata: Implications for biological control of Colorado potato beetle, Leptinotarsa decemlineata

The potential for intraguild predation (IGP) between larval and adult life stages of twopolyphagous arthropod predators common in NorthAmerican agroecosystems was studied in thelaboratory. Predators examined were the spinedsoldier bug, Podisus maculiventris Say,and the twelve-spotted ladybeetle, Coleomegilla maculata Lengi. A shared preyitem, eggs of the Colorado potato beetle (CPB),Leptinotarsa decemlineata Say, was alsoprovided to the predators, both to provide analternate food source and to quantify theimpact of IGP on the potential for pestsuppression by these two predators. Experimentswere conducted on single potato leaves inplastic cup arenas, and, subsequently, in cagesenclosing whole potato plants. IGP occurredasymmetrically, with P. maculiventrisadults and nymphs only attacking C. maculata larvae. Even though ladybeetle adultswere generally smaller than soldier bug adults,they were never preyed upon. This appears to bethe first documented case of a coccinellidshowing differential larval and adult immunityto attack by a larger invertebrate predator.The impact of IGP, when it did occur, on CPBegg consumption was equivocal. IGP did notconsistently influence levels of predation onthe eggs. Conversely, even when IGP did notoccur, predation on CPB eggs by both predatorstogether did not increase significantly overlevels inflicted by either predator alone. Theimplications for biological control of CPB bythese predators, which are being considered foraugmentative release in potato and tomato cropsin the United States, are discussed.     

Temperature influence on the reproduction of Podisus nigrispinus, a predator of the noctuid larva Alabama argillacea

The influence of temperature on thereproduction and longevity of Podisusnigrispinus (Dallas) (Heteroptera:Pentatomidae) fed with Alabamaargillacea (Hübner) (Lepidoptera:Noctuidae) larvae was studied. This predatorwas reared at constant temperatures of 20, 23,25, 28, 30 and 33 ± 0.2 °C, all atrelative humidity of 60 ± 10%, and aphotoperiod of L:D 14:10. Fecundity of P.nigrispinus at the various temperatures rangedfrom 401.2 (33 °C) to 841.3 (28 °C) eggs/female. The preoviposition,oviposition peak, and declining ovipositionperiods of P. nigrispinus were affectedby temperature [preoviposition period: 4.0 (33 °C) to 13.2 (20 °C) days;duration of oviposition peak period: 9.0 (33 °C) to 33.0 (20 °C) days; andduration of declining oviposition period: 16.0(33 °C) to 46.0 (20 °C) days].Longevity of females and males of P.nigrispinus ranged from 28.4 (33 °C) to88.6 (20 °C) days, and from 42.7 (33 °C); to 114.3 (20 °C) days,respectively. These data are useful in relationto the development of population dynamicsmodels to underpin programmes of biologicalcontrol.     

Chemical cues from Spodoptera litura larvae elicit prey-locating behavior by the predatory stink bug, Eocanthecona furcellata

Two chemical compounds eliciting prey-locating behavior of the predatory stink bug, Eocanthecona furcellata, were isolated from solvent extracts of Spodoptera litura larvae and identified. A hexane eluted fraction from silica gel chromatography of the solvent extracts of S. litura larvae was attractive to E. furcellata nymphs when assayed with a linear track olfactometer. The hexane fraction was found to contain n-pentadecane (2500 ng/larva), n-tetracosane (54 ng/larva), n-heptadecane (41 ng/larva), n-heptacosane (61 ng/larva), n-nonacosane (147 ng/larva), n-hentriacontane (200 ng/larva) and squalene (323 ng/larva). The synthetic n-pentadecane was attractive to the bugs, although its activity was slightly lower than that of the hexane fraction. A mixture of synthetic n-pentadecane and the other six hydrocarbons was also attractive, although no improved attractiveness was observed by the addition of the latter compounds. On the other hand, a 15%-ether-in- hexane eluted fraction from silica gel chromatography stimulated bugs to display a proboscis-protruding behavior. A neutral-layer fraction of the 15% fraction, which contained E-phytol (480 ng/larva), also elicited this behavior. Synthetic E-phytol had the same effect on the predators as the neutral-layer fraction.     

Effects of diet on development and reproduction of the predatory pentatomids Picromerus bidens and Podisus maculiventris

The effects of five diets (larvae of Galleria mellonella L., larvae of Spodoptera littoralis (Boisduval), eggs of Ephestia kuehniella Zeller, cysts of Artemia franciscana Kellogg and an artificial diet based on bovine meat) on development, survival and reproduction of two predatory stinkbugs, Picromerus bidens L. and Podisus maculiventris (Say), were studied in the laboratory. Both species successfully completed immature development on the foods offered, except for P. bidens on cysts of A. franciscana. Significant effects of diet on developmental duration were found in both species. Total developmental time from second instar to adult ranged from 25.0 to 41.5 days and from 18.7 to 46.0 days in P. bidens and P. maculiventris, respectively. Nymphal survival of P. maculiventris was superior to that of P. bidens on all diets tested. Nymphal survival of P. maculiventris was greater than 92% on all diets except on A. franciscana cysts, yielding only 50% survival to adulthood. Survival of P. bidens fed on eggs of E. kuehniella was higher than that of conspecifics fed on caterpillar prey or artificial diet (89% on flour moth eggs vs. 68 and 80% on G. mellonella and S. littoralis and only 50% on meat diet). Fresh weight of newly emerged females of both pentatomids was affected by the diet offered to the predators during their nymphal stage. Females of P. maculiventris produced viable eggs on all diets except on cysts of A. franciscana and had mean fecundities of 691, 436, 608 and 344 eggs per female on S. littoralis, G. mellonella, E. kuehniella eggs and the meat diet, respectively. Females of P. bidens laid eggs only on live prey with mean fecundities of 94 and 38 eggs per female on S. littoralis and G. mellonella, respectively. The results indicate a lower nutritional plasticity of P. bidens as compared with P. maculiventris. An erratum to this article can be found at     

Relationship between predation by Podisus nigrispinus and developmental phase and density of its prey,Plutella xylostella

This study evaluated the predation by Podisus nigrispinus (Dallas) (Hemiptera: Pentatomidae) at various densities of larvae and pupae of the pest Plutella xylostella (L.) (Lepidoptera: Plutellidae). We tested predator behavior of female P. nigrispinus at six experimental densities (1, 5, 10, 15, 20, or 25 prey items in a 1‐l transparent plastic container, replicated 15 times for each density) of both the fourth instar and pupae of P. xylostella. The number of prey consumed was monitored every 15 min for 12 h and was subsequently monitored at 24 h. Podisus nigrispinus females were weighed before and after the experiments to determine the effect of different densities of prey on their weight gain. Female predators had a Type‐II functional response, with attack rate estimated at 1.387 and 0.260 and a handling time of 0.091 and 0.183 h^?1 for larvae and pupae, respectively. Podisus nigrispinus consumed on average 10.9 larvae or 5.5 pupae in 24 h. Despite the similarity of the response type, P. nigrispinus preferred to feed on larvae, rather than on pupae.     

Infection by the microsporidium Vairimorpha necatrix (Microspora: Microsporidia) elevates juvenile hormone titres in larvae of the tomato moth, Lacanobia oleracea (Lepidoptera: Noctuidae)

The effects of infection by a microsporidium, Vairimorpha necatrix (Kramer), on the endogenous levels of juvenile hormones in tomato moth (Lacanobia oleracea L.) larvae were investigated. Levels of juvenile hormone II (JH II) were 10-fold greater in the infected larvae on day two of the sixth stadium but no significant difference was observed on day seven. Juvenile hormone I (JH I) was also detected in day two and day seven sixth instar infected larvae but was not detected in non-infected larvae. The duration of the fifth and sixth stadia was significantly longer for infected larvae when compared with non-infected larvae. No evidence was found to suggest that supernumerary moults are a feature of infection by V. necatrix in L. oleracea larvae. Experiments were performed to determine whether the elevation in JH levels, which probably prevents pupation, is an adaptive mechanism of the microsporidium for extending the growth phase of the host, thereby allowing increased spore production. A proportion of infected larvae were collected on days 9 and 24 of the sixth stadium and spore extracts prepared from each larva. These days represent the average duration of the sixth stadium required for uninfected larvae to reach pupation, and the average number of days that V. necatrix-infected larvae survive in the sixth stadium before dying from infection. The mean spore yields from infected larvae 24 days into the sixth stadium were significantly higher than the spore yields obtained from day nine sixth instar larvae. The hypothesis that V. necatrix manipulates host endocrinology (i.e. prolong the host larval state to maximise spore yield) is discussed in context with the results obtained.     

Behavioral responses in prey location of the predatory stink bug, Eocanthecona furcellata, to chemical cues in the larvae of Spodoptera litura

Behavioral responses of the predatory stink bug Eocanthecona furcellata (Wolff) (Heteroptera: Pentatomidae) towards Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) larvae were observed in olfactometers. In single-and dual-tube olfactometers, adult bugs were observed to approach and stretch their proboscis toward the odor source. These types of behavior were also observed toward the control odor source in the dual-tube olfactometer. However, the frequency of these phases toward the control odor was significantly lower than that toward the odors from intact or dead larvae. The solvent extracts of larvae elicited these similar behavioral phases significantly more frequently and for significantly longer duration than the control. In a linear track olfactometer, E. furcellata nymphs were observed to be attracted to the fraction eluted with hexane from silica gel chromatography but proboscis-protruding behavior was not observed. The other fraction, 15%-ether-in-hexane from silica gel chromatography, elicited the proboscis-protruding behavior by a simple behavioral assay using a Pasteur pipette. These findings therefore indicate the presence of at least two different chemical cues in prey location.     

Interactions of Bacillus thuringiensis bioinsecticides and the predatory stink bug Podisus nigrispinus to control Plutella xylostella

The diamondback moth (DBM), Plutella xylostella (L.), is a major pest of brassica crops worldwide. Control of this pest is difficult because it rapidly develops resistance to synthetic and biological insecticides and because of the effects of insecticides on its natural enemies. Podisus nigrispinus (Dallas) is a predator that feeds on its prey, as well as on the host plants of its prey, and is an important biological control agent of DBMs. The aim of this study was to determine the susceptibility of P. xylostella larvae to two bioinsecticides: the HD1 strain of Bacillus thuringiensis (B. thuringiensis var. kurstaki) and the commercial product Agree^® (B. thuringiensis var. aizawai CG 91). In addition, the impact of these bioinsecticides on the P. nigrispinus consumption of DBM larvae and phytophagy was evaluated. Both the HD1 strain and Agree^® caused 100% mortality in P. xylostella larvae. P. nigrispinus nymphs fed only with kale leaves (Brassica oleracea var. acephala) sprayed with water, the HD1 strain, or Agree^® did not complete their nymphal development. When prey was also available, P. nigiripinus fed on kale leaves to obtain water. Both nymphs and adults of P. nigrispinus consumed greater numbers of DBM larvae, and fed less on kale leaves, when sprayed with the HD1 strain or Agree^®. These results suggest a positive interaction of B. thuringiensis‐based products and the predator P. nigrispinus in the control of P. xylostella larvae.     

Parasitism of Lacanobia oleracea (lepidoptera) by the ectoparasitic wasp, Eulophus pennicornis, disrupts the cytoskeleton of host haemocytes and suppresses encapsulation in vivo

Parasitism of Lacanobia oleracea larvae by the ectoparasitic wasp Eulophus pennicornis suppressed host haemocyte-mediated encapsulation of Sephadex DEAE A-25 beads in vivo. Beads dissected out of parasitized larvae had fewer haemocytes associated with them. Moreover, those haemocytes that were associated with the beads tended to retain a rounded configuration and rarely flattened. Similar results were obtained using in vitro encapsulation assays. SDS PAGE indicated that for parasitized and PBS injected larvae, there were some differences in the plasma proteins that bound to Sephadex DEAE A-25 beads, suggesting that parasitism-mediated changes to host plasma proteins might contribute to the differences in the encapsulation response occurring in these larvae. However, in vitro encapsulation assays using beads that had been pre-incubated in plasma from parasitized and unparasitized larvae, demonstrated that major differences in the extent of encapsulation did not occur. These results, plus in vitro haemocyte attachment and spreading assays, suggest that parasitism-mediated suppression of encapsulation is primarily due to reductions in the ability of host haemocytes to attach to (i.e., recognize) and flatten over non-self surfaces and other haemocytes. This proposal is corroborated by staining of actin in the haemocyte cytoskeleton by FITC-labelled phalloidin, which indicated that parasitism disrupts the formation of stress fibers and focal adhesions in plasmatocytes. By contrast, experimental injection of adult female wasp venom into unparasitized L. oleracea larvae had no significant effect on in vivo encapsulation responses or the haemocyte cytoskeleton. Arch. Insect Biochem. Physiol. 49:108-124, 2002. Published 2002 Wiley-Liss, Inc.     

Activity enhancement of Zygogramma bicolorata,a biocontrol agent of Parthenium hysterophorus,by temperature regulated diapause aversion

Diapause is a unique strategy of dormancy in insects to avoid unfavourable conditions. The exotic beetle Zygogramma bicolorata, is an effective biological control agent of Parthenium hysterophorus in India, Adults diapause in soil during December to May. As a result, there is delay in its effectiveness on the plant that reaches to flowering and seed production by the time the beetle is able to build up its population after emerging from diapause. Therefore, a study was conducted to explore possibilities of diapause aversion by temperature regulation. Results indicated that exposure of newly emerged adults to heat treatment of 35°C and to low temperature of 10°C could reduce diapause in Z. bicolorata. The low temperature can also be used as a medium for the storage of the mass reared beetles for a long time without having negative effect on their longevity and fecundity.     

Potency of Bacillus thuringiensis and Bacillus subtilis against the cotton leafworm,Spodoptera littoralis (Bosid.) Larvae

The biological activities of two species of bacteria isolated from soil of cotton fields identified as Bacillus subtilis strain NRC313 (BS NRC313) and Bacillus thuringiensis strain NRC335 (BT NRC335) were evaluated against the third larval instar of the cotton leafworm, Spodoptera littoralis (Boisd.). The different entomopathogenic bacteria of BS NRC313and BT NRC335 contained 10 × 10⁸ cell/ml, and caused mortality of 100 and 97.3% for the above mentioned strains, respectively. Concentrations of 2.5 × 10⁸ to 10 × 10⁸ cell/ml of strains BS NRC313 and BT NRC335 were applied to the larvae: LC₅₀ were 3.3 × 10⁸ and 3.9 × 10⁸ cell/ml respectively. The influence of exposure to toxin concentrations manifested in terms of decreasing the adult emergence and prolongation of the generation period. The percentage of larvae that survived and succeeded to pupate increased by decreasing the concentration. The longevity of adult emergence that resulted from larvae treated with Bacillus subtilis were 6.0 ± 0.51 and 9.0 ± 0.63 days at 5 × 10⁸ and 2.5 × 10⁸ cell/ml, respectively compared with 9.8 ± 0.47 in control. The results indicated that Bacillus subtilis was more potent than Bacillus thuringiensis. Field applications of B. thuringiensis, B. subtilis and Reldan achieved 55.6, 67.4 and 89.4% reduction of the cotton leafworm larvae Spodoptera littoralis in clover plants under field conditions.     

The effect of prey size and prey density on the functional response,survival, growth and development of a predatory pentatomid bug,Podisus maculiventris say

Two experiments on the nymphal predation of Podisus maculiventris were conducted using Spodoptera litura larvae as prey. First experiment: The predator nymphs divided into three groups were reared individually from second instar to adult in a small vessel. Each nymph in the groups 1, 2 and 3 was allowed to attack the serially growing larvae (these were supplied at the rate of one per day) from 3-, 5- and 7-day old after hatching, respectively. The first prey used for the group 1 was so small that it was not only insufficient to satiate the predator but also was difficult to be searched out. But these disadvantages were soon recuperated due to the rapid growth of the prey and all nymphs could survive to adults. The survival rate of third and fourth instar nymphs in the group 3 was severely affected by vigorous counterattack of older prey larvae. Second experiment: The predator nymphs were individually reared either in a small vessel or in a large one at various rates of food supply (the prey larvae of 7-day old were used). The functional response curves obtained for each instar of the predator took a saturation type within a certain range of the prey density. The saturation level specific to each instar was generally higher for the predator reared in the large vessel than in the small one. The functional response of fourth and fifth instar nymphs was accelerated at a high prey density, viz. 16 larvae per vessel. Even at the low rate of food supply, viz. one larva per day per predator, the predator nymphs could survive to adults, but the size of resultant adults were abnormally small.