The effects of diet on herbivory by a predaceous lady beetle

We hypothesize that herbivory by predators is affected by the complexity of their diet. Coleomegilla maculata larvae fed prey – Acyrthosiphon pisum or Ostrinia nubilalis eggs – consumed two to three times more plant tissue (pinto beans) than those fed a mixed diet (containing pollen substitute and prey-based components). Simple, prey-only diets appear to lack plant-based nutrients important to this predator.     

Ontogenetic shifts in the functional response and interference interactions of Rhyacophila dorsalis larvae (Trichoptera)

1. Ontogenetic shifts in predator behaviour can affect the assessment of food‐web structure and the development of predator–prey models. Therefore, it is important to establish if the functional response and interference interactions differ between life‐stages. These hypotheses were tested by (i) comparing the functional response of second, third, fourth and fifth larval instars of Rhyacophila dorsalis, using three stream tanks with one Rhyacophila larva per tank and one of 10 prey densities between 20 and 200 larvae of Chironomus sp.; (ii) using other experiments to assess interference within instars (two to five larvae of the same instar per tank), and between pairs of different instars (one, two or three larvae per instar; total predator densities of two, four or six larvae per tank). 2. The first hypothesis was supported. The number of prey eaten by each instar increased with prey density, the relationship being described by a type II model. The curvilinear response was stronger for fourth and fifth instars than for second and third instars. Mean handling time did not change significantly with prey density, and increased with decreasing instar number from 169 s for fifth instars to 200 s for second instars. Attack rate decreased progressively with decreasing instar number. Handling time varied considerably for each predator–prey encounter, but was normally distributed for each predator instar. Variations in attack rate and handling time were related to differences in activity between instars, fourth and fifth instars being more active and aggressive than second and third instars, and having a higher food intake. 3. The second hypothesis was partially supported. In the interference experiments between larvae of the same instar or different instars, mean handling time did not change significantly with increasing predator density, and attack rate did not change for second and third instars but decreased curvilinearly for fourth and fifth instars. Interference between some instars could not be studied because insufficient second instars were available at the same time as fourth and fifth instars, and most third instars were eaten by fourth and fifth instars in the experiments. Prey capture always decreased with decreasing attack rate. Therefore, interference reduced prey consumption in fourth and fifth instars, but not in second and third instars. The varying feeding responses of different instars should be taken into account when assessing their role in predator–prey relationships in the field.     

Evaluation of dietary effects of transgenic corn pollen expressing Cry3Bb1 protein on a non-target ladybird beetle, Coleomegilla maculata

A transgenic corn event (MON 863) has been recently developed by Monsanto Company for control of corn rootworms, Diabrotica spp. (Coleoptera: Chrysomelidae). This transgenic corn event expresses the cry3Bb1 gene derived from Bacillus thuringiensis (Berliner), which encodes the insecticidal Cry3Bb1 protein for corn rootworm control. A continuous feeding study was conducted in the laboratory to evaluate the dietary effect of MON 863 pollen expressing the Cry3Bb1 protein on the survival, larval development, and reproductive capacity of the non-target species, Coleomegilla maculata DeGeer (Coleoptera: Coccinellidae). First instar C. maculata (less than 24 h old) and newly emerging adults (less than 72 h old) were fed individually on a diet mixture containing 50% of MON 863 pollen, non-transgenic (control) corn pollen, bee pollen (a component of normal rearing diet), or potassium arsenate-treated control corn pollen. In the larval tests, 96.7%, 90.0%, and 93.3% of C. maculata larvae successfully pupated and then emerged as adults when fed on MON 863 pollen, non-transgenic corn pollen, and bee pollen (normal rearing) diets, respectively. Among the larvae completing their development, there were no significant differences in the developmental time to pupation and adult emergence among the transgenic corn pollen, non-transgenic corn pollen, and bee pollen diet treatments. All larvae fed on arsenate treated corn pollen diet died as larvae. For tests with adults, 83.3%, 80.0%, and 100% of adult C. maculata survived for the 30 days of the test period when reared on diets containing 50% of MON 863 pollen, non-transgenic corn pollen, and bee pollen respectively. While the adult survival rate on MON 863 pollen diet was significantly less than that on the bee pollen diet, there was no significant difference between the MON 863 and non-transgenic corn pollen treatments. During the period of adult testing, an average of 77, 80, and 89 eggs per female were laid by females fed on the MON 863 pollen, control corn pollen, and bee pollen, respectively; no significant differences were detected in the number of eggs laid among these treatments. These results demonstrate that when offered at 50% by weight of the dietary component, transgenic corn (MON 863) pollen expressing Cry3Bb1 protein had no measurable negative effect on the survival and development of C. maculata larvae to pupation and adulthood nor any adverse effect on adult survival and reproductive capacity. Relevance of these findings to ecological impacts of transgenic Bt crops on non-target beneficial insects is discussed.     

Some observations on the food of larvae of Procladius bellus (Diptera: Chironomidae)

Analysis of the gut contents of Procladius bellus (Loew) larvae collected in field samples indicated that it was a detrivitore‐omnivore. The observed dietary change from first and second instars (detritivore‐herbivores) to third and fourth instars (omnivores) did not suggest a change in feeding behaviour from detritivore to predator, but rather that the animal material was consumed along with larger detrital material. Small detrital material (1–15 μm) was an important dietary component and detritus in general contributed 50–70% of the overall diet. Diatoms and green algae contributed 15–20%, while blue‐green algae contributed about 10%. Animal material contributed about 5% to second and third instar larvae and 20% to fourth instar larvae.     

Instar-specific defense ofColeomegilla maculata lengi (Col.: Coccinellidae): Influence on attack success of the intraguild predatorChrysoperla rufilabris (Neur.: Chrysopidae)

We conducted a laboratory study of the behavioural interactions between larval stages of the lady beetleColeomegilla maculata lengi Timberlake and an intraguild predator, the lacewingChrysoperla rufilabris Burmeister. Ladybird susceptibility to predation by third instarC. rufilabris is age-specific and influenced by larval defensive strategies. First and second instars ofC. maculata were captured more consistently by chrysopid larvae than third and fourth instars. Young coccinellids generally exhibit escape reactions (dropping, fleeing, retreating) but, do not survive after being caught by lacewings. In addition to escape reactions, older larvae may actively defend themselves by wriggling or biting, even after being pierced. The proportion of physical interactions that resulted in coccinellid death was significantly lower for older instars (<2%) than for first (35%) and second (19%) instars. Capture efficiency byC. rufilabris was related to the coccinellid-chrysopid size ratio. Dropping off the leaves, the most common defensive behaviour displayed by coccinellid larvae, contributed to reduce overall mortality of first instars to a level similar to the one observed for older stages. However, lacewings were able to prevent coccinellid dropping by impaling and holding their prey in the air, or by falling with the ladybirds to the ground where they continued their attack.     

Importance of predation by Coleomegilla maculata larvae in the natural control of the corn earworm in sweet corn

The corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) is a serious pest of many crops in North America, particularly sweet corn. The larvae of Coleomegilla maculata (DeGeer) (Coleoptera: Coccinellidae) are the most frequently observed predators of H. zea eggs in sweet corn. Companion cropping strategies have been developed to augment densities of C. maculata in sweet corn plantings. In this study, the importance of predation by C. maculata larvae was evaluated in experiments when larval abundance was manipulated using hand removal and physical exclusion. In 2003 and 2004, sentinel H. zea eggs were exposed on corn for 48 h. Egg mortality was 13.8% greater in the treatment where C. maculata larvae were present. In 2004 and 2005 eggs were exposed on corn under the same hand removal and physical exclusion techniques and monitored at 3-h intervals for 24 h to directly observe predation on sentinel eggs. Coleomegilla maculata larvae were the most frequently observed predators of the eggs, accounting for 45.9% of 85 total observed predation events in the control. Whereas in the treatment where C. maculata larvae were reduced, egg survival was 26.13% greater and only 37 total predation events were observed. All pest eggs were eliminated from individual ears 22.1% more often when C. maculata larvae were present at natural densities indicating that predation by this predator stage lessens crop damage by H. zea. The results of this study suggest that C. maculata larvae are an irreplaceable source of natural mortality for H. zea eggs on sweet corn.     

Functional Response ofColeomegilla maculata(Coleoptera: Coccinellidae) to Colorado Potato Beetle Eggs (Coleoptera: Chrysomelidae)

A comparative study of the functional response ofColeomegilla maculataDeGeer (Coleoptera: Coccinellidae) fourth instars was conducted under laboratory, greenhouse, and field conditions. In the laboratory, individual larvae were placed in 9-cm petri dishes for 24 h, with 1, 3, 5, or 7 Colorado potato beetle (Leptinotarsa decemlineata[Say]) (Coleoptera: Chrysomelidae) egg masses. Each egg mass was standardized at 15 eggs. In the greenhouse and field,C. maculatalarvae were provided with an equivalent of 0.5 to 35L. decemlineataegg masses/m²of potato leaf. Fourth instars ofC. maculataexhibited a type II functional response toL. decemlineataeggs under laboratory, greenhouse, and field conditions. Predator search efficiency was inversely related with prey density. The maximum mean attack rate (8.7 eggs) byC. maculatalarvae in the field was about half the mean attack rate in the laboratory (17.6 eggs) and greenhouse (20.1 eggs). The difference in prey density between the laboratory and field seems to have been a major contributing factor in determining the rate of predation, whereas differences in environmental conditions (e.g., temperature and possible alternate food) may explain the differences observed in the predation rate in the greenhouse and field.     

Nutritional suitability of corn pollen for the predator Coleomegilla maculata (Coleoptera: Coccinellidae)

The nutritional suitability of corn pollen for the facultatively phytophagous predator Coleomegilla maculata was studied in the laboratory. Dry matter, organic matter, ash, crude protein, amino acid, and quercetin contents of pollen from 10 hybrids of field corn were determined. C. maculata were reared on pollen or aphids + artificial diet for their entire lives; larval duration, post-mortem adult dry weights, fecundity within 7 days of mating, and mortality rates were compared among the treatments. In another experiment, C. maculata larvae were reared on pollen; weight gained, pollen ingested, and frass produced were compared among instars. Also, consumption relative to increases in larval biomass and the efficiency with which larvae converted corn pollen into biomass were compared among instars. Beetles reared on aphids had greater weights and fecundity and a shorter larval duration relative to the pollen-fed beetles. The percentages of organic matter and ash in corn pollen were significantly correlated with C. maculata mortality, and we hypothesize that some micronutrient or phytochemical is at sub-optimal levels for C. maculata development in some of the pollens. We observed an increase in the conversion efficiency of pollen and a decrease in the consumption relative to biomass of C. maculata as the larvae aged, which suggests a physiological or behavioral alteration in the feeding behavior of C. maculata during the larval stage.     

Suitability of pollen sources for the development and reproduction of Coleomegilla maculata (Coleoptera: Coccinellidae) under simulated drought conditions

Laboratory experiments compared the nutritive value of various pollen sources for the development of Coleomegilla maculata DeGeer under conditions of continuous water availability and simulated drought. When water was continuously available, larval survival was not different from 100% on diets of frozen eggs of Ephestia kuehniella Zeller, corn pollen, sorghum pollen, or pulverized bee pollen, whereas survival of larvae was significantly reduced on the latter three diets in the simulated drought treatment. Pollen of cultivated sunflower, Helianthus annus L., proved fatal to both larvae and adults; its surface structure caused clumping and accumulation on the insect cuticle that led to death from exhaustion/desiccation in petri dishes. The Ephestia egg diet yielded shorter developmental times and heavier adult weights than any pollen diet in both treatments. The drought treatment increased developmental time on all diets with a significant treatment–diet interaction. Drought reduced the adult weight of females on the sorghum pollen diet, and that of both sexes on the bee pollen diet, again with a significant treatment–diet interaction. Initial water content was highest in corn pollen (36.8%), followed by Ephestia eggs (29.2%), sorghum pollen (25.3%), sunflower pollen (8.7%), and bee pollen (4.6%), but did not appear correlated with C. maculata larval survival on pollen sources under drought conditions. Reproductive adult females that received corn or sorghum pollen as a supplement to Ephestia eggs did not differ in fecundity or fertility from those fed only Ephestia eggs.     

Learning affects prey selection in larvae of a generalist coccinellid predator

Under natural conditions, generalist predatory insects have to cope with a variety of potential prey species that are not all equally suitable. Under these circumstances, learning may be adaptive if it allows adjustment to variations in resource quality and availability. Under laboratory conditions, we examined the learning ability and memory in the prey selection process of larvae of the predatory coccinellid Coleomegilla maculata ssp. lengi Timberlake (Coleoptera: Coccinellidae). Using choice tests, we studied prey rejection behaviour of C. maculata fourth instars towards prey of different quality and we also tested the influence of hunger and prior experience with other food types on the prey rejection behaviour of coccinellid larvae. Coleomegilla maculata larvae gradually changed their behaviour and rejected low‐quality hosts more frequently, whereas high‐quality hosts were nearly always accepted. After 48 h, the learned behaviour appeared to be partially forgotten. Hunger and experience with other food types prior to the test had little effect on the gradual change of behaviour but the quality of the food ingested influenced the initial level of prey rejection. Our results demonstrate that (1) C. maculata larvae can adjust their prey selection behaviour with experience to reject progressively less suitable prey, and (2) previous experience with other prey types can influence their initial preference.     

Behavioral Response to Larval Tracks and the Influence of Tracks on Intraguild Scavenging by Coccinellid Larvae

A paired design was used to determine that Harmonia axyridis 4th instars were not influenced by the presence of conspecific larval tracks, but well-fed H. axyridis 4th instars spent less time on plants that contained tracks left by Coleomegilla maculata 4th instars. To determine if the presence of larval tracks influences intraguild scavenging by H. axyridis 4th instars, dead 4th instars were placed in Petri dishes that contained or did not contain larval tracks. The presence of larval tracks did not influence the feeding frequency or the amount of time before feeding. However, larvae dragged their pygopod on dish surfaces more frequently if the dish contained larval tracks. In addition, starved H. axyridis larvae were more likely to feed on the prey and dragged their pygopod less frequently than well-fed larvae.     

Potential for intraguild predation and competition among predatory Coccinellidae and Chrysopidae

In a laboratory study two coccinellid species, Coleomegilla maculata (DeGeer) and Harmonia axyridis Pallas, completed preimaginal development on lacewing eggs, Chrysoperla carnea Stephens or pea aphids, Acyrthosiphon pisum (Harris) in similar times. Preimaginal survival on C. carnea eggs was similar to survival on A. pisum for all stages of C. maculata and H. axyridis. Coccinellid adults that developed on C. carnea eggs were smaller than adults reared on A. pisum. Coccinella septempunctata L. did not complete preimaginal development on C. carnea eggs. Chrysoperla carnea preimaginal developmental time was approximately 20 days when fed either C. maculata eggs or A. pisum. Chrysoperla carnea fed C. maculata eggs developed into smaller adults, compared to adults reared as larvae on A. pisum, Ostrinia nubilalis (Hübner) eggs, or A. pisum alternated daily with O. nubilalis eggs. C. carnea did not complete preimaginal development on H. axyridis eggs. Cannibalism occurred more frequently between C. carnea third instars than between C. maculata fourth instars. When a C. carnea third instar was paired with a C. maculata fourth instar, more C. maculata were preyed upon by C. carnea, regardless of the herbivorous prey density. In the field these two predator species may negatively affect each other and reduce their suppression of pest densities.     

Differential predation by Coleomegilla maculata on Colorado potato beetle strains that vary in growth on tomato

This study tests the hypothesis that the generalist predator Coleomegilla maculata DeGeer causes differential mortality of Colorado potato beetle, Leptinotarsa decemlineata (Say), larvae differing in their degree of genetic adaptation to tomato (Lycopersicon esculentum Mill.) as a host plant. Results of a series of laboratory experiments demonstrate that adult C. maculata can cause higher mortality to nonadapted than adapted Colorado potato beetle larvae. The extent of differential mortality caused by C. maculata depended on age of potato beetle larvae; presence of potato beetle eggs; whether or not the predator had a choice among prey items; and, in choice situations, the ratio of adapted to nonadapted potato beetle larvae. Although adult C. maculata have the potential to prey differentially on tomato-adapted and nonadapted Colorado potato beetle larvae in mixed populations, the magnitude of differential predation in a natural setting could be highly variable.     

Changes in digestive rate of a predatory beetle over its larval stage: Implications for dietary breadth

Prey and non-prey foods differ substantially in their suitability for zoophytophagous omnivores, but the relative quality of these foods depends on the stage-specific digestive capabilities of the organism in question. Quantitative (or real-time) PCR was used to amplify food-specific DNA and measure consumption rates and digestion efficiencies of four foods - two prey (Aphis glycines and Leptinotarsa decemlineata eggs) and two non-prey (Zea mays pollen and the yeast Saccharomyces cerevisiae) species - over different larval stages of Coleomegilla maculata. The amount of Z. mays pollen consumed increased as larvae aged, but not proportionately with larval size, such that consumption rates decreased uniformly with insect age. While aging larvae fed A. glycines had a similar pattern in their diminishing consumption rates, they consumed similar amounts of A. glycines regardless of age, suggesting a negative feedback mechanism for consumption of this species of aphids. Older larvae digested three of the four foods significantly more efficiently than younger larvae, the exception being larvae fed A. glycines which was digested at a similar rate throughout the larval stage. There was a significant effect of time on food quantity detected for all four species of food. We conclude that C. maculata expands its physiological capacity for digesting prey and non-prey foods as they age in order to better accommodate the increased nutritional needs of the older larvae. This strategy has important implications for the life history strategies of zoophytophagous insects and how they function within foods webs.     

Prey switching in Rhyacophila dorsalis (Trichoptera) alters with larval instar

1. Ontogenetic shifts in predator behaviour can affect the assessment of food‐web structure and the development of predator–prey models. Previous studies have shown that the diel activity pattern and functional response differed between larval instars of the carnivorous caddis, Rhyacophila dorsalis. The present study examines switching by larvae of R. dorsalis presented with different proportions of two prey types; either small (length 2–4 mm) and large (5–8 mm) Chironomus larvae for second, third, fourth and fifth instars of R. dorsalis; or Baetis rhodani (9–12 mm) and large Chironomus larvae for fourth and fifth instars. Experiments were performed in stream tanks with one Rhyacophila larva per tank and 200 prey arranged in nine different combinations of the two prey types (20 : 180, 40 : 160, 60 : 140, 80 : 120, 100 : 100, 120 : 80, 140 : 60, 160 : 40 and 180 : 20). Prey were replaced as they were eaten. A model predicted the functional response in the absence of switching and provided a null hypothesis against which any tendency to switch could be tested. 2. There was no prey switching in the second and third instars, with both instars always showing a preference for small over large Chironomus larvae. Prey switching occurred in the fourth and fifth instars. As the relative abundance of one prey type increased in relation to the alternative, the proportion eaten of the former prey changed from less to more than expected from its availability, the relationship being described by an S‐shaped curve. In the experiments with small and large Chironomus, the two instars switched to large larvae when their percentage of the total available prey exceeded 29% and 37% for fourth and fifth instars, respectively. In the experiments with Baetis and large Chironomus, both instars switched to Baetis larvae when their percentage of the total available prey exceeded 36%. 3. Non‐switching in second and third instars was related to their feeding strategies, both instars preferring smaller prey items. When the fourth and fifth instars foraged actively at night, they preferred larger over small Chironomus larvae, but when they behaved as ambush predators at dusk, they captured the more active Baetis larvae in preference to the more sedentary large Chironomus larvae and only switched to the latter when they were >64% of the available prey.     

Seasonal Changes in Habitat Preference by Coleomegilla maculata: Implications for Colorado Potato Beetle Management in Potato

Seasonal abundance, dispersal, and overwintering of the 12-spotted ladybird beetle, Coleomegilla maculata (DeGeer), in the mid-Atlantic states were investigated to assess the potential to manipulate the habitat of this predator to increase its impact on Colorado potato beetle, Leptinotarsa decemlineata (Say), management in commercial potato plantings. C. maculata populations were highest in corn fields through August, and overwintering aggregations were found most commonly in habitats adjacent to these fields. Although adult and larval populations of C. maculata were synchronized with first-generation potato beetle eggs and small larvae, they were concentrated in wheat rather than potato fields because most of the potato plants had not yet emerged when C. maculata adults dispersed from their overwintering sites. The subsequent generation of C. maculata tended to aggregate in corn rather than potato in late May and early June. Therefore, given the current mixture of crops as well as climatic and marketing limitations on planting date for potatoes, the potential for habitat manipulation to increase the impact of C. maculata on Colorado potato beetle management in potato in the mid-Atlantic states appears to be limited.     

Prey discrimination by a generalist coccinellid predator: effect of prey age or parasitism?

1. Patterns of prey discrimination by the generalist predatory coccinellid Coleomegilla maculata lengi Timb. (Coleoptera: Coccinellidae) were studied in relation to prey quality, under laboratory conditions. 2. Choice experiments were performed in which second‐ and fourth‐instar coccinellids had the choice between Trichoplusia ni (Lepidoptera: Noctuidae) eggs that were young or old, unparasitised or parasitised by Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae). 3. Coleomegilla maculata larvae did not exhibit any preference for parasitised or unparasitised eggs at a similar stage of development but always preferred younger eggs, regardless of whether or not they were parasitised. Furthermore, the percentage of rejection was higher and handling time longer on the less preferred egg type. Pre‐imaginal development time, food intake to reach adulthood, and survival of coccinellid immatures were altered when coccinellid larvae were fed with parasitised and old unparasitised eggs. 4. These results indicate that C. maculata larvae select eggs based on their stage of development regardless of parasitism, and that prey quality of aged prey is lower. 5. Fourth‐instar coccinellid larvae spent less time in patches containing solely parasitised old eggs, and their level of exploitation was greatly reduced, compared with homogeneous patches containing unparasitised young eggs. This suggests that C. maculata larvae respond to variable patch quality by using flexible decision rules that reflect the payoff of the patch.     

Effects of prey density, prey instar, and patch size on the development of the predatory mosquito, Toxorhynchites towadensis

Effects of prey density, prey instar, and patch size on the development of the predatory mosquito larva, Toxorhynchites towadensis, were investigated in the laboratory. Survivors of T. towadensis showed different developmental patterns in relation to prey age structure. All predatory larvae in containers with only second instar prey developed into the third instar. However, in several containers with fourth instar prey, mortality of predators was observed. During the third instar, no predatory larva died, but both prey density and prey instar significantly affected the survival of predators during their fourth instar. Large prey size promoted large predator adults, and predatory larvae which grew up in small surface containers responded by developing to large sizes than those in large containers. Larval developmental time of the predators differed in each treatment. During first and second instars, faster predator development was observed in containers with small surface areas and containing young prey individuals. However, when development was enhanced by the presence of old prey individuals, no surface effect was observed. The fastest predator development was observed with prey of mixed instars and high density. This study suggests that a small surface container containing prey of mixed instars and high density is suitable for development of predators.     

Factors influencing dispersal of larval Coleomegilla maculata from the weed Acalypha ostryaefolia to sweet corn

The polyphagous predator, Coleomegilla maculata (DeGeer) (Coleoptera: Coccinellidae), commonly oviposits on the native weed, Acalypha ostryaefolia Riddell (Euphorbiaceae), in and around Kentucky sweet corn fields. Cannibalism of eggs by C. maculata adults and larvae is drastically lower on A. ostryaefolia than on nearby sweet corn plants. We examined ovipositional preference of C. maculata for A. ostryaefolia plants or sweet corn plants, dispersal of larvae from A. ostryaefolia plants, capability for dispersal of larvae across bare soil (e.g., to nearby plants), ability of larvae to climb from ground level up A. ostryaefolia plants or sweet corn plants, and effect of A. ostryaefolia borders adjacent to sweet corn plots on C. maculata population density in sweet corn. The ovipositional preference study revealed that C. maculata laid more eggs on A. ostryaefolia than on corn. First-instar C. maculata that hatched from egg clusters on A. ostryaefolia dispersed predominantly by falling, rather than crawling, to the ground. Glandular trichomes on A. ostryaefolia petioles and stems apparently inhibited intraplant movement of first instars, resulting in those larvae falling directly from leaves to the ground. Some first instars were capable of moving at least 8 m across bare soil in 24 h. From the ground, significantly more first instars climbed sweet corn plants than climbed A. ostryaefolia plants. Significantly more larvae were present in sweet corn plots bordered by A. ostryaefolia plants than in sweet corn plots without an A. ostryaefolia border. These findings show that physical attributes of companion plants can significantly influence natural enemy populations on crop plants by affecting interplant dispersal of natural enemies.     

Effect of corn hybrids expressing the coleopteran-specific cry3Bb1 protein for corn rootworm control on aboveground insect predators

Field and laboratory studies were conducted to determine the effect of transgenic Bacillus thuringiensis (Bt) corn, Zea mays L. (YieldGard Rootworm), expressing the Cry3Bb1 protein on aboveground nontarget insect predators (minute pirate bug, ladybird beetles, and carabids). Visual counts of adult and immature Orius insidiosus (Say), Coleomegilla maculata (DeGeer), Hippodamia convergens Gurin-Meneville, and Scymnus spp. occurring in Bt corn and its non-Bt isoline were made at Manhattan, KS, in 2002 and at Manhattan and Scandia, KS, in 2003. No significant differences were found between the Bt corn and non-Bt isoline plots in the abundance (number per plant) of O. insidiosus, C. maculata, H. convergens, and Scymnus spp. Field predation on Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) egg masses was also observed during the silking stage of corn at Manhattan and Scandia in 2003. No significant differences were observed among treatments in predation rate for predators with chewing versus sucking mouthparts. Two laboratory studies determined the effect of Cry3Bb1 protein expressed in Bt corn pollen on C. maculata and carabids. The larvae of C. maculata were reared on Bt pollen, non-Bt pollen, or greenbugs, Schizaphis graminum (Rondani). The duration of larval and pupal stages, developmental time from egg hatch to adult emergence, percentage of survival, and elytra length were compared among treatments. There were no significant differences in developmental time of larvae fed pollen or greenbugs during their first two instars. However, significantly prolonged development of the third (1 d) and fourth instars (2 d) was observed for larvae fed greenbugs only. Total time for larval development was significantly longer for larvae that fed on greenbugs versus larvae fed on pollen. No significant differences were observed among treatments in the percentage of larvae that pupated or pupal stage duration. Larvae that fed on greenbugs had higher pupal and adult weights compared with pollen-fed larvae. However, pupal and adult weights did not vary between the Bt and non-Bt pollen treatments. No significant differences occurred in longevity and elytra length of beetles among all treatments. Two carabid species, Harpalus caliginosus F. and Harpalus pensylvanicus DeGeer, were reared on moistened dog food sprinkled with Bt or non-Bt corn pollen. No significant differences in mortality of H. caliginosus and H. pensylvanicus were detected among any of the treatments. There was no significant effect of Bt pollen on fecundity and egg viability of H. caliginosus. Our studies showed that YieldGard Rootworm had no effect on the selected coleopteran predators; therefore, this Bt corn hybrid could be used in an integrated pest management system.