Suitability of exotic and native lady beetle eggs (Coleoptera: Coccinellidae) for development of lady beetle larvae

Predation upon lady beetle (Coleoptera: Coccinellidae) eggs in the field is most often instances of egg cannibalism by larvae or adults while the majority of the remaining predation events upon coccinellid eggs is done by other species of Coccinellidae. Thus the recent introduction and establishment of Harmonia axyridis in the US could negatively affect native species of Coccinellidae via egg predation. However, little is known regarding the suitability of interspecific coccinellid eggs as a food source for larval development. In this study, it was found that native first or third instar Coleomegilla maculata and Olla v-nigrum larvae were incapable of surviving to the adult stage when provided solely exotic H. axyridis eggs. In stark contrast, H. axyridis larvae survived equally well when cannibalizing eggs or eating eggs of either native species. When C. maculata and O. v-nigrum were grouped as ‘native’ and compared with the exotic H. axyridis, more native eggs were attacked than exotic eggs and a higher percentage of eggs was attacked by H. axyridis larvae. Native and exotic larvae attacked a similar percentage of native eggs but native larvae attacked significantly fewer exotic eggs than did exotic larvae. These data suggest that H. axyridis may prey upon the eggs of these native species, when encountered in the field, compared with the likelihood of the native species preying upon H. axyridis eggs. Therefore, eggs of the native species C. maculata and O. v-nigrum will continue to be subjected to cannibalism and also to possible predation by other native species and the exotic H. axyridis.     

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.     

Predation on Colorado Potato Beetle Eggs by Generalist Predators in Research and Commercial Potato Plantings

Field studies quantified predation on Colorado potato beetle [Leptinotarsa decemlineata(Say)] eggs and determined the relationship between predation and egg mass abundance in research and commercial potato plantings in eastern North Carolina. Predator exclusion experiments were conducted weekly in research plantings. In addition, egg mass density and predation on egg masses were monitored throughout the season in research plots and commercial potato fields. Predation was an important source of mortality for Colorado potato beetle eggs. Survivorship of eggs exposed to predators was consistently, significantly lower than survivorship of eggs protected from predation. Averaged over 2 years, the mean survivorship of eggs protected from predation was 69%, compared with 26% survivorship of eggs exposed to predation. Regression analysis failed to detect any relationship between egg mortality due to predation and egg abundance. These results imply that efforts to reduce Colorado potato beetle populations selectively will not be offset by an according decline in abundance of natural enemies and therefore should be fully compatible with naturally occurring biological control.     

Predation of Colorado potato beetle eggs by a polyphagous ladybeetle in the presence of alternate prey: potential impact on resistance evolution

The influence of prey choice on the predation of a target prey item by a polyphagous insect predator was investigated in field plot studies. The target prey consisted of eggs of the Colorado potato beetle (CPB), Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), and the predator was the 12‐spotted ladybeetle, Coleomegilla maculata Lengi (Coleoptera: Coccinellidae). Eggs of the European corn borer (ECB), Ostrinia nubilalis Hübner (Lepidoptera: Pyralidae), and nymphs and adults of the green peach aphid, Myzus persicae Sulzer (Homoptera: Aphididae), comprised the alternative prey choices. The objectives of these studies were to: (1) examine predation in a multiprey scenario likely to occur in an agroecosystem, and (2) use the data to simulate the impact of predator‐induced mortality on the evolution of resistance to Bt‐transgenic plants in the target herbivore. Simulations of the rate of resistance evolution were carried out using a deterministic genetic model. Experiments were performed using potato field plots planted in a manner reflecting a 25% or 50% non‐transgenic refuge. CPB eggs were infested so as to mimic the densities of resistant and susceptible populations that might occur in commercial Bt‐transgenic plantings. Densities of predators and alternate prey species were chosen to represent those that might typically occur in potato crops in the eastern USA. Simulation results indicated that when ECB eggs were present, predation on CPB eggs either became inversely spatially density‐dependent, or increased significantly in a density‐dependent manner. When aphids were present, predation became positively density‐dependent. Model simulations predicted that ECB egg presence is beneficial, in that resistance was delayed by up to 40 pest generations (as compared to the scenario with CPB as the only prey), while aphid presence accelerated resistance evolution by 18 generations. Results suggest that resistance management strategies should take into account the composition of prey species available to generalist predators typically present, so as to best delay pest adaptation to Bt‐toxins.     

Facilitated predation through interaction between life stages in the stinkbug predatorperillus bioculatus (Hemiptera: Pentatomidae)

Competitive interactions in arthropod predators are well-known, but positive interactions have received less attention. The two-spotted stinkbugPerillus bioculatus often feeds gregariously on leaf beetle larvae and caterpillar prey. Consequences of prey sharing amongP. bioculatus conspecifics of dissimilar size (instar) was studied using Colorado potato beetle (CPB) prey. Rearing second-instar (N2) nymphs ofP. bioculatus with an N5 conspecific facilitated early feeding on L4 CPB larvae (a difficult prey to handle by N2 nymphs but not by N5’s), thus increasing survival and accelerating development. One in every 20 cases ofP. bioculatus foraging in the field was accounted for by pairs or small groups of mostly feeding individuals. CPB egg masses and L4’s represented a disproportionate number of cases of aggregated feeding byP. bioculatus, compared to feeding singly. Small CPB larvae decreased in the diet of aggregated stinkbugs compared to L4 larvae and egg masses, suggesting that sharing these prey may be favorable or unavoidable. In a field test measuring residence/survival of N2’s limited to L4 prey, the N2’s rate of residence/survival increased significantly when large nymphs acting as food providers were also present. The function of communal feeding inP. bioculatus is discussed, as well as the potential for greater impact on prey density that may be expected from tolerance to opportunistic feeding by conspecifics in slightly gregarious predators.     

Comparative Prey Suitability ofOstrinia nubilalisEggs andAcyrthosiphon pisumforColeomegilla maculata

The effects ofOstrinia nubilalis(Hübner) (Lepidoptera: Pyralidae) eggs andAcyrthosiphon pisum(Harris) (Homoptera: Aphididae), when provided as single prey species and in combination, on life history characteristics ofColeomegilla maculataDeGeer (Coleoptera: Coccinellidae) larvae and adults were quantified. Preimaginal development was not influenced by the larval prey regime; development at 26 ± 1°C was completed in approximately 13.5 days onO. nubilaliseggs,A. pisum,orA. pisumalternated daily withO. nubilaliseggs. The resulting adults weighed 13.0, 10.7, and 12.5 mg when reared onO. nubilaliseggs,A. pisum,andA. pisumalternated daily withO. nubilaliseggs, respectively. Eighteen percent of the individuals died when reared onA. pisum,28% died when reared onO. nubilaliseggs, and 22% died when fedA. pisumalternated daily withO. nubilaliseggs. Seven adult diet combinations, based on diet regimes of larvae and adults, did not cause significant differences in preoviposition period, interoviposition period, and the number of days on which eggs were laid. Total fecundity was influenced both by larval and adult diet. The diet that resulted in highly fecund females wasA. pisumalternated daily withO. nubilaliseggs for larvae andO. nubilaliseggs for adults. FemaleC. maculatafedO. nubilaliseggs had the highest intrinsic rate of increase and net reproductive rate.     

Negative dietary effects of Colorado potato beetle eggs for the larvae of native and introduced ladybird beetles

Aphidophagous ladybird beetles (Coleoptera: Coccinellidae) are attracted to and feed heavily on aphids, but many species will also feed opportunistically on other prey that they encounter. In potatoes (Solanum tuberosum L.) in Washington State, USA, coccinellids feed on both green peach aphids (“GPA,” Myzus persicae Sulzer) and eggs of the Colorado potato beetle (“CPB,” Leptinotarsa decemlineata Say). The guild of aphidophagous ladybirds includes two native species, Hippodamia convergens Guérin-Méneville and Coccinella transversoguttata Brown. Recently, an introduced species, Coccinella septempunctata L., has invaded and apparently displaced its native congener. A second exotic, Harmonia axyridis Pallas, has colonized the area and is becoming more abundant. We compared larval development of each species on a monotypic diet of GPA, a monotypic diet of CPB eggs, or a mixed diet of both GPA and CPB eggs. Our goal was to answer two questions: (1) do larvae of the four ladybird species benefit from including CPB eggs in their diet and (2) do the four ladybird species differ in their ability to utilize CPB eggs as prey? No larva of any species completed development on a pure diet of CPB eggs, and survivorship was highest for all species when they fed on a pure diet of GPA. One native species, H. convergens, and one exotic species, H. axyridis, exhibited significantly lower survivorship on a mixed diet of both CPB eggs and GPA, compared to a pure GPA diet; H. axyridis also took longer to develop from egg to adult when both prey were provided. Survivorship of the two Coccinella spp. was not altered by the inclusion of CPB eggs with GPA, although CPB eggs lengthened the development time of C. transversoguttata. Adult size was not consistently affected by diet for any of the coccinellids. Overall, no ladybird species benefited from the inclusion of potato beetle eggs in its diet. The two Coccinella species responded similarly to the inclusion of CPB eggs, and so we would not expect any difference in the success of coccinellid larval development in potato fields following the replacement of C. transversoguttata by C. septempunctata. Hippodamia convergens and H. axyridis, the two species whose survivorship was depressed by combining CPB egg and aphid prey, were also the two species that consumed the greatest number of CPB eggs during successful larval development. A comparison of total egg consumption by each species cohort suggested that displacement of the other species by H. axyridis would not alter CPB biological control, because the higher per capita feeding rate by H. axyridis larvae compensated for individuals’ greater mortality risk on a diet including CPB eggs.     

Potential for the biological control ofLeptinotarsa decemlineata [Col.: Chrysomelidae] by the egg parasite,Edovum puttleri [Hym.: Eulophidae] in Maryland, 1981–84

The biological control potential ofEdovum puttleri Grissell, an exotic egg parasite ofLeptinotarsa decemlineata (Say), was examined in experimental potato plots. The parasite does not overwinter in Maryland, but through annual inoculative releases it consistently parasitized Colorado potato beetle (CPB) egg masses throughout the season. Approximately 50% of all egg masses collected were parasitized and maximum parasitism byE. puttleri occurred in egg masses produced by first generation adults.Edovum puttleri reproduced and maintained itself in potato plots for 15 weeks. The random sampling of CPB egg masses to evaluate the parasite in the field is described.      

Spatial distribution of interacting insect predators: Possible roles of intraguild predation and the surrounding habitat

Predator foraging behaviour affects the outcome of enemy–enemy interactions. Using a combination of fieldwork and laboratory experiments, we show that intraguild predation may be important in the field distribution of generalist predators that share a common prey: the eggs (and larvae) of the leaf beetle Phratora vulgatissima, a major insect pest in coppicing willow plantations. We focused on a species from the hoverfly genus Parasyrphus (Syrphidae), which may exhibit large temporal and spatial variation in density. Predator and prey densities were quantified in 40 field plots in willow plantations. The likelihood of finding hoverfly eggs declined with increasing densities of two predatory mirids, Orthotylus marginalis and Closterotomus fulvomaculatus, which exhibit less mobile behaviour similar to that of hoverfly larvae. The density of a more mobile predatory bug species, the anthocorid Anthocoris nemorum, was not associated with hoverfly occurrence. These results corroborate the hypothesis that less mobile predators should be stronger intraguild predators than mobilepredators. Further partial support for this hypothesis was obtained in the laboratory study where individual predators were presented with clutches of P. vulgatissima eggs containing one hoverfly egg: the less mobile C. fulvomaculatus and O. marginalis tended to consume the hoverfly egg more readily than the more mobile A. nemorum. However, most individuals of all three bug species consumed the egg of the potential competitor – the syrphid – within 24 h. The field study also showed that hoverfly occurrence was positively associated with the density of their prey and with the presence of nearby forests. We conclude that intraguild predation, abundance of prey and the surrounding habitat affect the distribution of hoverflies in this system and should be considered when developing biological control methods.     

Heterogeneity of twoBeauveria bassiana strains revealed by biochemical tests,protein profiles and bio-assays ofLeptinotarsa decemlineata (Col.: Chrysomelidae) andColeomegilla macultata lengi (Col.: Coccinellidae) larvae

Biochemical profiles on API Rapid CH^* strips and protein profiles on polyacrylamide gels in the presence of sodium dodecyl sulfate were used to distinguish two strains of the entomopathogenic fungusBeauveria bassiana (Balsamo) Vuillemin, ARSEF 2991 and ATCC 44860. Next, the toxicity of these two strains was determined at concentrations of 10², 10⁴, 10⁶ and 10⁸ blastospores/ml on larvae of the Colorado potato beetleLeptinotarsa decemlineata Say (Coleoptera: Chrysomelidae) and of its predator, the spotted ladybird beetle,Coleomegilla maculata lengi Timberlake (Coleoptera: Coccinellidae). Both strains were highly toxic toL. decemlineata larvae. However, the two strains exhibited different levels of toxicity forC. maculata larvae: ARSEF 2991 was toxic, whereas ATCC 44860 caused little coccinellid larval mortality.

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Résumé Les profils biochimiques sur galeries API Rapid CH^* et les profils protéiques sur gels de polyacrylamide ont été utilisés pour distinguer deux souches du champignon entomopathogèneBeauveria bassiana (Balsamo) Vuillemin. La toxicité de ces deux souches a été déterminée à des concentrations de 10², 10⁴, 10⁶ et 10⁸ blastospores/ml sur des larves du doryphore,Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae) et de la coccinelle maculéeColeomegilla maculata lengi Timberlake (Coleoptera: Coccinellidae). Les deux souches deB. bassiana se sont avérées actives à l'égard des larves deL. decemlineata. Toutefois la souche ARSEF 2991 s'est avérée pathogène pour les larves deC. maculata, alors que la souche ATCC 44860 a provoqué une faible mortalité des larves.

     

The influence of natural enemies on brood production inIps typographus (Col. scolytidae) with special reference to egg-laying and predation byThanasimus formicarius (Col.: Cleridae)

The predatorThanasimus formicarius (L.) (Coleoptera, Cleridae) and its preyIps typographus (L.) (Coleoptera, Scolytidae) were studied in the laboratory and the field. In the laboratory, 11T. formicarius laid 71–132 eggs (mean=162) during 66–123 days. During this time they ate 66–132I. typographus adults per pair (male +female). The number of eggs laid per female was not correlated with life span or the number ofIps eaten. In the field, predation byT. formicarius larvae and other natural enemies onI. typographus brood was studied in the last year of an outbreak. Caged and uncaged spruce bolts attacked byI. typographus were used, and pairs ofT. formicarius were released in the cages. The treatments were: uncaged bolts, caged bolts withoutT. formicarius, caged bolts with 4T. formicarius pairs, and caged bolts with 8T. formicarius pairs. The productivity ofI. typographus was highest in the caged bolts withoutT. formicarius (mean=4.5 offspring/female) and lowest in the uncaged bolts (mean=0.9 offspring/female). The density ofI. typographus galleries was similar in the different treatments. Hence, the variation in productivity between treatments could not have been due to differences in the levels of intraspecific competition. There was no difference in bark beetle productivity or density ofT. formicarius larvae between bolts with 4 pairs ofT. formicarius and bolts with 8 pairs (mean=2.5 offspring/female). This indicates that some kind of interference occurred betweenT. formicarius individuals (e.g. cannibalism) and that a maximum level of predation was reached. Predation by larvae ofMedetera spp. (Diptera, Dolichopodidae),Thanasimus spp. and other beetles, and parasitism by wasps (Hymenoptera, Pteromalidae) probably caused the low productivity in the uncaged bolts.      

Larval oophagy in the ant <Emphasis Type="Italic">Amblyopone silvestrii</Emphasis> (Hymenoptera,Formicidae)

Summary Larvae pass through five instars in the temperate, subterranean ponerine ant, Amblyopone silvestrii. Field colonies displayed a large decrease in the number of eggs during mid-summer, despite the fact that queens maintained fully developed ovaries with mature eggs. Observations of laboratory colonies indicate that cannibalism by 1st and 2nd instar larvae caused this decrease in egg number. These instars consumed a total of 66–75% of eggs in the nest, with each larva consuming 2–3 eggs before molting to the 3rd instar. At that time the larvae began to feed on arthropods. The preferred prey of A. silvestrii consists of entire centipedes; the large size of these prey items relative to the size of early instar larvae makes it difficult for the larvae to feed on these prey. Additionally, workers of A. silvestrii do not engage in oral trophallaxis. Consequently, oophagy is a plausible method to feed these very small larvae.     

Response ofNabis roseipennis [Heteroptera: Nabidae] to Larvae of Mexican bean beetle,Epilachna varivestis [Col.: Coccinellidae]

Laboratory studies were done to measure predation by adult damsel bugs,Nabis roseipennis Reuter [Heteroptera: Nabidae], on 3^rd instar larvae of Mexican bean beetle (MBB),Epilachna varivestis Mulsant [Coleoptera: Coccinellidae], and to measure longevity and body weight of the nabids. In the 1^st experiment, field-collected nabids were isolated for 24h in 9 cm Petri dishes with lima bean foliage (Phaseolus lunatus L.) and were assigned to one of 3 prey treatments: either 4 3^rd-instar MBB larvae, 4 3^rd-instar larvae of boll weevil (BW),Anthonomus grandis Boheman [Coleoptera: Curculionidae], or 2 larvae of each species. No MBB larvae were attacked in either the MBB treatment or 2-species treatment. In contrast, BW larvae were attacked in both BW and 2-species treatments. Significantly more BW larvae were attacked in the BW treatment than in the 2-species treatment, and both were greater than the number of MBB larvae attacked. Nabids that did not attack prey lost weight during the 24 h, whereas those that attacked prey gained weight. In the 2^nd experiment, nabids that had attacked prey were isolated with lima foliage, and nabids that had not attacked prey were kept with MBB and lima foliage until an attack or death. In no instances were MBB attacked. Longevity and the pattern of weight loss did not differ between nabids that did or did not attack prey. We discuss possible reasons for the failure ofN. roseipennis to attack MBB larvae, as well as the implications for using nabids to influence pest populations in the field.      

Predation rates,survivorship and development ofPodisus maculiventris (Het.: Pentatomidae) on larvae ofLeptinotarsa decemlineata (Col.: Chrysomelidae) andPieris brassicae (Lep.: Pieridae), under field conditions

The mean predation rate per day and the effect of the prey on the development and survival of the various nymphal stages ofPodisus maculiventris (Say) were studied under field-cage conditions. Third instar larvae of the Colorado potato beetleLeptinotarsa decemlineata (Say) and the large white butterflyPieris brassicae (Linnaeus) were used as the prey. The results show that under climatic conditions similar to those occurring in the Thessaloniki region (N. Greece), the 5^th instar nymphs and the adults of the predatorP. maculiventris would be promising agents for the biological control of larvae ofL. decemlineata andP. brassicae.

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Résumé Des recherches de terrain ont été menées afin d'étudier le degré de prédation journalier et l'effet de la proie sur le développement et la survie des différents stades nymphaux deProdisus maculiventris Say en présence de larves du 3^e stade deLeptinotarsa decemlineata (Say) et dePieris brassicae (Linnaeus). Les résultats obtenus montrent que les nymphes du 5^e stade et les adultes du prédateur ont une importante activité prédatrice avec un taux de survie élevé quand ils se nourrissent aux dépens de larves du doryphore ou de la Piéride du chou. Par conséquent, il est très probable quePodisus pourrait être utilisé contre ces ravageurs dans des zones où les conditions climatiques sont proches de celles de la région de Thessaloniki (Grèce du Nord).

     

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.     

Parasitism ofLeptinotarsa decemlineata [Coleoptera: Chrysomelidae] byEdovum puttleri [Hymenoptera: Eulophidae] in different cultivars of eggplant

Experiments were conducted to quantify parasitism of Colorado potato beetle,Leptinotarsa decemlineata (Say), by the egg parasitoid,Edovum puttleri Grissell, on 3 different cultivars of eggplant,Solanum melongena L. Levels of parasitism were higher (P<0.05) on ‘Black Pride’ than on other cultivars. The percentage of egg masses that were parasitized was 1.2-fold higher (P<0.05) on ‘Black Pride’ than on ‘Harris Special’ and ‘White’. The number of eggs per mass that were parasitized was 1.3- and 1.4- fold greater (P<0.05) on ‘Black Pride’ than on ‘Harris Special’ and ‘White’, respectively. The percentage of eggs that were parasitized per mass and percentage of emerged adult parasitoids did not differ (P>0.05) among cultivars; between 2.1- to 2.6- fold more females than males emerged from eggs on all cultivars during the growing season.Edovum puttleri suppressed the 2nd generation ofL. decemlineata on ‘Black Pride’ and ‘Harris Special’, but did not suppress populations on ‘White’.      

Preliminary life table of the spotted tortoise beetle,Aspidomorpha miliaris (Coleoptera: Chrysomelidae) in Sumatra

From December, 1981 to February, 1982, a population study of the spotted tortoise beetle, Aspidomorpha miliaris, feeding on a shrub-like morning glory, Ipomea carnea, was conducted in Padang, Sumatra with the construction of a life table.

1. Dissection of oothecae collected from the field after hatching clarified that the average egg mass size was 43.4 and hatching rate was 25.0%. Causes for egg mortality included: parasitism by a wasp, Tetrastichus sp. A(Europhidae) (49.8% of eggs laid), predation (12.8%), disappearance of egg masses (5.3%) and hatching failure (7.1%). An ant, Dolichoderus bituberculatus, visiting the extrafloral nectaries of the host plnts was responsible for predation and disappearance of the egg masses. The ants again attacked the larvae and pupae.
2. Larvae showed a gregarious habit for almost the entire larval period. Survival rates between two successive instars were low and constant, ranging from 70 to 90%, but only 1.3% of final (5th) instars become pupae (six individuals). Since the growth of host plants was extremely rapid, shortage of food was rare in larval stages. The sudden drop in numbers after 5th instar may be due to predation and/or dispersal of matured larvae from the host plants for pupation.
3. Pupae were attacked by three species of parasitic wasps:Tetrastichus sp. C, Pediobius elasmi (Eulophidae) and Cassidocida aspidomorphae (Tetracampidae). Among the six pupae, two were parasitized, one died of disease and two disappeared. Out of 4078 eggs laid, only one emerged to adult.

     

Functional response of Chrysoperla carnea (Neuroptera: Chrysopidae) to Helicoverpa armigera (Lepidoptera: Noctuidae): Effect of prey and predator stages

Abstract Understanding predator–prey interactions has a pivotal role in biological control programs. This study evaluated the functional response of three larval instars of the green lacewing, Chrysoperla carnea (Stephens), preying upon eggs and first instar larvae of the cotton bollworm, Helicoverpa armigera Hübner. The first and second instar larvae of C. carnea exhibited type II functional responses against both prey stages. However, the third instar larvae of C. carnea showed a type II functional response to the first instar larvae of H. armigera, but a type III functional response to the eggs. For the first instar larvae of C. carnea, the attack rate on H. armigera eggs was significantly higher than that on the larvae, whereas the attack rate of the second instar C. carnea on H. armigera larvae was significantly higher than that on the eggs. For the third instar larvae of C. carnea, the attack rate on the larvae was 1.015 ± 0.278/h, and the attack coefficient on the eggs was 0.036 ± 0.005. The handling times of the third instar larvae on larvae and eggs were 0.087 ± 0.009 and 0.071 ± 0.001 h, respectively. The highest predation rate was found for the third instar larvae of C. carnea on H. armigera eggs. Results of this study revealed that the larvae of C. carnea, especially the third instar, had a good predation potential in controlling H. armigera eggs and larvae. However, for a comprehensive estimation of the bio‐control abilities of C. carnea toward H. armigera, further field‐based studies are needed.     

Oviposition behavior of Edovum puttleri, reared on two hosts, Leptinotarsa decemlineata and L. texana

Female Edovum puttleri Grissell [Hymenoptera: Eulophidae], reared from eggs of Leptinotarsa decemlineata (Say) or Leptinotarsa texana Schaeffer [Coleoptera: Chrysomelidae], were videotaped as they attacked egg masses of L. decemlineata containing 20 host eggs. We identified 15 components of ovipositional behavior. Parasitoids reared on L. texana attacked and oviposited in significantly more host eggs than did females reared on L. decemlineata. Ethometric analyses of behavioral transitions and a clustering analysis of 34 behavioral parameters showed that females reared on L. texana attacked the host egg mass in a different manner than those reared from L. decemlineata. It was concluded that differences were associated with the host species upon which they were reared. Contrary to previous reports, mortality of unparasitized hosts was caused by an ovipositor probe of short duration, which was not related to host-feeding.     

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.