Intra‐ and interspecific interactions between aphidophagous ladybirds: the role of prey in predator coexistence

Cannibalism (CANN) and intraguild predation (IGP) may provide energy and nutrients to individuals and eliminate potential competitors. These negative competitive interactions could also affect the coexistence of predatory species. The co‐occurrence of aphidophagous ladybird species in crops creates opportunities for CANN and IGP, especially when aphids become scarce. The Lotka–Volterra model predicts the coexistence of two species if intraspecific competition is stronger than interspecific interference interactions. Cycloneda sanguinea L. and Eriopis connexa (Germar) (both Coleoptera: Coccinellidae) coexist in sweet pepper crops in La Plata (Argentina) consuming mainly Myzus persicae (Sulzer) (Hemiptera: Aphididae). The present study used laboratory experiments to estimate levels of CANN and IGP by adults and larvae on eggs, and by adults on larvae, in both the presence and absence of prey (i.e., M. persicae), to explain the effect of prey on coexistence of these two predators. Levels of CANN by C. sanguinea and E. connexa were high in the absence of aphids, and decreased when prey was present. Intraguild predation was bidirectional and asymmetric. Adults and larvae of E. connexa were more voracious IG predators of C. sanguinea than vice versa, the former being the stronger IG predator and interference competitor. Eriopis connexa always won when larvae of the same instar were compared, whereas the larger larva always won when larvae were of different instars, regardless of species. In the presence of prey, CANN by both species decreased, but IGP by E. connexa on C. sanguinea remained high, suggesting that E. connexa could displace C. sanguinea via interspecific interference competition. Other factors potentially affecting the coexistence of C. sanguinea and E. connexa in sweet pepper crops are discussed.     

Bitrophic toxicity of Cry1Ac to Cycloneda sanguinea,a predator in Brazilian cotton

Insect predators are exposed to the Cry1Ac toxin in Bt cotton fields through several pathways. In this study, we investigated the effects of activated Cry1Ac added to a diet on Cycloneda sanguinea (L.) (Coleoptera: Coccinellidae), which is one of the main predators of non‐target pests in Brazilian cotton. Direct bitrophic exposure of C. sanguinea to Cry1Ac was done by feeding beetles with Aphis gossypii (Glover) (Hemiptera: Aphidae) sprayed with 500 μg per ml Cry1Ac solution. Larval and pupal survival, development time, aphid consumption, and adult longevity were recorded daily. Couples within the same experimental treatment were paired and numbers of eggs laid and hatched per female were recorded daily. Net replacement rate was calculated for each female. During development, a C. sanguinea larva consumed on average 1.8 μg of activated Cry1Ac. No significant differences due to Cry1Ac were observed for any of the response variables, except aphid consumption. Larvae receiving Cry1Ac consumed more aphids than larvae receiving distilled water alone. Additional statistical analyses were conducted to evaluate independence of responses, and for the independent responses, a simple meta‐analysis was conducted to test the null hypothesis that all responses were zero. Nearly all of the response variables were statistically independent. Two pairs of responses were not independent, but the associated multivariate tests were not significant. The meta‐analysis suggested that all effects were not different from random variation around zero and no cumulative effects could be detected. Our results indicated that bitrophic exposure to activated Cry1Ac is likely to have little or no adverse ecological effect on C. sanguinea.     

Interactions between an introduced and indigenous coccinellid species at different prey densities

Coccinella septempunctata L. (Coleoptera: Coccinellidae), a Palearctic coccinellid, has established and rapidly spread throughout the United States. This quantitative examination of larval interactions between C. septempunctata and Coleomegilla maculata (DeGeer) (Coleoptera: Coccinellidae), a Nearctic coccinellid, was conducted under controlled prey densities. Larvae of both coccinellid species are affected by a limited diet [one pea aphid per day Acyrthosiphon pisum (Harris) (Homoptera: Aphididae)] compared with an excess diet (>20 aphids per day). Larval survival decreased from 86 to 63% in C. maculata and from 84 to 33% in C. septempunctata; mean preimaginal developmental time increased from 20.6 to 26.7 days in C. maculata, and from 18.1 to 32.0 days in C. septempunctata. Additionally, on one aphid per day, mean adult weight was reduced from 12.39 to 9.79 mg in C. maculata, and from 39.57 to 14.44 mg in C. septempunctata. Interspecific interactions, favoring C. septempunctata over C. maculata at a␣low prey density (one aphid per day), take the form of␣reduced survival of C. maculata compared with C.␣septempunctata (14 versus 66%). Reduced survival of␣C. maculata may be the result of competition for aphids or intraguild predation by C. septempunctata on C.␣maculata. No interspecific interactions (measured as effects on larval survival, preimaginal developmental time, and adult weight) were observed between larvae of these two species at a high prey density (>20 aphids per predator per day). Received: 15 September 1997 / Accepted: 20 May 1998     

Conservation of two predator species for biological control ofChrysophtharta bimaculata (Col.: Chrysomelidae) in tasmanian forests

Chrysophtharta bimaculata (Olivier) (Coleoptera: Chrysomelidae) is a major defoliator of regeneration eucalypt trees in Tasmania causing a significant reduction in height and diameter increment of trees which reduces wood volume per hectare. A study to conserve and enhance the efficiency of coccinellid species chieflyCleobora mellyi (Mulsant) (Coleoptera: Coccinellidae), and the cantharid,Chauliognathus pulchellus (Macleay) (Coleoptera: Cantharidae), for the biological control ofC. bimaculata was conducted in young regeneration forests in southern Tasmania from 1991–92. Cantharid adults and coccinellid adults and larvae feed onC. bimaculata eggs and, to a lesser extent, young larvae. The study found that coccinellids were more active throughout the egg and early (1^st and 2^nd) stage ofC. bimaculata. The cantharid, however was active only during the egg stage of the prey and then disappeared from the plantation. The coccinellids were therefore the most useful predators, but their population declined when the prey reached the 3^rd and 4^th stages. As shortage of food may account for this decline, supplementary food was provided in the form of sucrose sprays or sugar granules at a feeding station. This resulted in the retention of both predators and particularly the coccinellids and enhanced their efficacy.     

Use of odours by Cycloneda sanguinea to assess patch quality

Adult ladybirds are likely to encounter various species of prey when foraging for oviposition sites. Optimal oviposition theory predicts that females should lay eggs in those sites that are the most suitable for offspring development. Therefore, factors that directly affect offspring mortality, such as the presence of predators and food, are expected to play an important role in the assessment of patch profitability by ladybird predators. Using a Y‐tube olfactometer, we tested whether the predatory ladybird Cycloneda sanguinea L. (Coleoptera: Coccinellidae) can use volatile cues to assess patch profitability and avoid predator‐rich patches. We assessed the foraging behaviour of C. sanguinea in response to odours associated with tomato plants infested with a superior prey, Macrosiphum euphorbiae Thomas (Homoptera: Aphididae), and with an inferior prey, Tetranychus evansi Baker and Pritchard (Acari: Tetranychidae), in the presence or absence of the heterospecific predator Eriopis connexa Mulsant (Coleoptera: Coccinellidae). Females of C. sanguinea significantly preferred plants infested by M. euphorbiae to plants infested by T. evansi and avoided odours emanating from plants on which E. connexa females were present. Our results show that C. sanguinea use volatile cues to assess patch profitability and to avoid patches with heterospecific competitors or intraguild predators.     

Effects of augmentative releases of the coccinellid, Adalia bipunctata, and of insecticide treatments in autumn on the spring population of aphids of the genus Dysaphis in apple orchards

The impact of augmentative releases of indigenous predators and insecticide applications to control the autumn aphid forms of the genus Dysaphis (Homoptera: Aphididae), major pest insects on apple trees, was assessed in one-year field experiments in Switzerland. Eggs and larvae of the two-spot ladybird beetle Adalia bipunctata (L.) (Coleoptera: Coccinellidae) were released on 4-year old apple trees in various numbers at five different dates in autumn 1998 when sexuales of the aphids were present. Additionally, Pyrethrum HP was sprayed at the same five dates to compare the effectiveness of these augmentative releases to a commonly applied insecticide. Augmentative releases of larvae before mid-October significantly prevented the deposition of overwintering eggs by aphids of the genus Dysaphis and consequently reduced the number of hatched fundatrices in spring, 1999. There was a significant negative functional response among the number of released coccinellid larvae in autumn 1998 and the number of observed fundatrices on apple trees in spring 1999. Applications of Pyrethrum HP before mid-October were more effective than augmentative releases of larvae of A. bipunctata. The release of coccinellid eggs had no impact on the number of fundatrices of the genus Dysaphis in the next spring because they did not hatch due to bad weather conditions. The weather conditions in autumn seemed to have an impact on the autumn migration of the winged aphids back to their primary host. The prevention of egg deposition of aphids in autumn is a promising control strategy and deserves further exploration for practical use.     

Pea aphid dropping behavior diminishes foraging efficiency of a predatory ladybeetle

Antipredator defensive behaviors are a well‐studied and often crucial part of prey life histories, but little has been done to quantify how such behaviors affect natural enemies, their foraging, and their effectiveness as biological control agents. We explored how the generalist predatory coccinellid Harmonia axyridis Pallas (Coleoptera: Coccinellidae) affects the dropping behavior of the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), and in turn, how that defensive behavior affects the foraging efficiency of the predator. Experimental arenas that allowed or prevented pea aphid dropping were compared to determine how dropping influences the foraging of multiple life stages of H. axyridis: second instars, fourth instars, and adults. Dropping reduced predation on aphids by all ladybeetle life stages. Despite older predators inducing more dropping, aphid dropping reduced predation by approximately 40% across all ladybeetle life stages. Aphid dropping and predator consumption of aphids were both correlated with how much the predator moved, which also increased with predator life stage. We suggest that the high rates of dropping induced by H. axyridis and the subsequent decrease in H. axyridis foraging efficiency may partially explain why H. axyridis is less effective at controlling pea aphids than it is at controlling other aphid species that do not drop.     

Cornicle secretions of Uroleucon nigrotuberculatum (Homoptera: Aphididae) as the last bullet against lady beetle larvae

Aphids have evolved various defense strategies against natural enemies, including secretions from their cornicles. We assessed the defensive function of cornicle secretions by the goldenrod aphid, Uroleucon nigrotuberculatum (Olive), against larvae of the lady beetles Coccinella septempunctata bruckii Mulsant and Propylea japonica (Thunberg) (Coleoptera: Coccinellidae). The aphid secreted red droplets from its cornicles when attacked by the larvae. Two‐thirds of the C. septempunctata bruckii larvae and 46.7% of the P. japonica larvae that preyed on the aphids died before reaching the pre‐pupal stage. The secretions caused molting failure when smeared on the larvae's heads or glued to the larvae's mouthparts, killing 56.7% of C. septempunctata bruckii larvae and 36.7% of P. japonica larvae. Second instar larvae were affected most. About 40% of third and fourth instar larvae of C. septempunctata bruckii vomited soon after ingesting the aphids. In the field, up to 40% of first and second instar larvae were smeared with red secretions. Our results show that these cornicle secretions are an effective and active defense against earlier instars of coccinellid larvae.     

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.     

The effect of temperature on development and fecundityof Scymnus levaillanti

Development and fecundity of Scymnus levaillanti(Mulsant) were recorded at fiveconstant temperatures ranging from 15 to 35 ± 1 °C in 5 °C increments, 60 ± 5% RHand 16 h of artificial light (5000 Lux). Developmentaltime (egg to adult) of S. levaillantisignificantly decreased with increasing temperatures,ranging from 63.9 days at 15 °C to 11.1 days at35 °C. Development from egg to adult required305.2 DD above a developmental threshold estimated as11.7 °C. Oviposition periods lasted 86.5, 76.1,47.2, and 31.5 days at 20, 25, 30 and 35 °C,respectively. No eggs were deposited at 15 °C.Higher temperatures resulted in shorter generationtimes (T_O) and in decreased net reproductiverates (R_O) of the coccinellid. S.levaillanti kept at 30 °C produced 0.151females/female/day, the highest per capita rate ofpopulation growth (r_m). The `functional response'of larvae and adults of S. levaillanti matcheswell that described by Holling (1959) as Type 2.Daily number of eggs deposited by females increased toa plateau with increasing prey density. Resultsobtained here provide information about the biology ofS. levaillanti, and its feeding capacityindicates that it may act as an important control agent.     

Intraguild responses of aphid predators on apple to the invasion of an exotic species, Harmonia axyridis

The effects of the invasion ofan exotic predator, Harmonia axyridis(Pallas) (Coleoptera: Coccinellidae), wereinvestigated using three experiments on theecology of aphid predators on apple. Oneexperiment, 1992, was collected prior to theH. axyridis invasion, and two others,1996 to 1997 and 1999 to 2000, were collectedafter the invasion. Except for one year, 1999,H. axyridis was the dominant coccinellid,replacing the formerly dominant Coccinellaseptempunctata L. (Coleoptera: Coccinellidae),another exotic species. The dominance of H. axyridis was greater among larvae thanamong adults. There was no apparent effect ofthe H. axyridis invasion on abundance ofthe predator, Aphidoletes aphidimyza(Rondani) (Diptera: Cecidomyiidae) and apossible positive effect on the abundance ofchrysopids (Neuroptera: Chrysopidae). Principal component analysis indicated thatalthough individual species were affected, theoverall effect of H. axyridis invasion onthe predator guild as a whole was negligible. The data indicate that the interaction betweenthe two exotic species, H. axyridis andC. septempunctata, may be allowing nativecoccinellids to become more abundant on applethan when C. septempunctata was thedominant coccinellid.     

Evaluation of some coccinellid species for the biological control of aphids in protected cropping

Four species of Coccinellidae, Adalia bipunctata (L.), Coccinella septem-punctata L., Coelomegilla maculata de G. and Cycloneda sanguinea L., were compared as predators of aphids on cucumbers and chrysanthemums. In laboratory feeding tests C. maculata and C. sanguinea proved the most voracious but the former could not remain on cucumber foliage long enough to be effective. The fecundity of C. sanguinea was the highest of those studied and a satisfactory laboratory rearing technique has been developed for this species.     

Effect of size,extraguild prey and habitat complexity on intraguild interactions: a case study with the invasive ladybird <Emphasis Type="Italic">Harmonia axyridis</Emphasis> and the hoverfly <Emphasis Type="Italic">Episyrphus balteatus</Emphasis>

Intraguild predation (IGP) is a widespread interaction between predatory arthropods, and is influenced by several factors. The harlequin ladybird, Harmonia axyridis (Coleoptera: Coccinellidae), has frequently been reported as an intraguild predator of other Coccinellidae, but little is known about its interactions with other aphidophagous predators, including syrphids. This study investigated the incidence of IGP between H. axyridis and Episyrphus balteatus (Diptera: Syrphidae), the most abundant hoverfly species in Europe and a commercially available aphid biocontrol agent. The influence of size, presence of extraguild prey and habitat complexity were investigated through laboratory experiments in Petri dishes and on potted broad bean plants. In both types of arenas, IGP between H. axyridis and E. balteatus was found to be asymmetric, with the coccinellid in the majority of cases being the intraguild predator. There was a significant effect of size on the frequency of IGP. The efficiency of H. axyridis as an intraguild predator increased with the developmental stage. Early instars of E. balteatus were the most vulnerable to IGP. Pupae of either species were not attacked. In the presence of extraguild prey, the frequency of IGP was substantially reduced. However, IGP still occurred, mainly in combinations of older larvae of H. axyridis with first or second instars of E. balteatus. The size of the arena affected the incidence of IGP in combinations with second instars of E. balteatus, but not in combinations with third instars. Field research is needed to elucidate the ecological relevance of IGP among these predators.     

Larval interactions in aphidophagous predators: effectiveness of wax cover as defence shield of Scymnus larvae against predation from syrphids

Small-sized predators in the aphidophagous guild of Aphis gossypii Glover colonies on hibiscus trees in Japan exploit aphids at low prey abundance. Scymnus (Pullus) posticalis Sicard beetles were the first predatory species to attack aphids in the spring, and their larvae co-occurred with larvae of Eupeodes freguens (Matsumura) syrphids in aphid-infested leaves of hibiscus for 3 weeks in absence of large-sized coccinellid predators. Larval interaction between Scymnus and syrphid predators was examined in relation to effectiveness of wax cover of Scymnus against predation from syrphids. Waxless first instar larvae were not protected but wax-covered larvae of second, third and fourth instars were protected from predation by syrphid larvae. The protection was lower in the second instar which has a thin wax cover and significantly higher in the third and fourth instars having a thick wax cover. In addition, larvae from which the wax was removed were significantly more vulnerable to predation. Vulnerability of Scymnus larvae to predation from syrphids was directly related to the thickness of wax cover. Results suggest that the wax cover of Scymnus larvae act as an effective defence mechanism against predation from syrphid larvae.     

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.     

多异瓢虫食物消耗与利用与其猎物棉蚜的寄主植物种类相关

【目的】猎物质量和类型在捕食者食物选择、消耗及营养转化过程中起着重要作用,植物的营养质量影响植食者的营养质量,进而植食者作为捕食者猎物的营养质量。为进一步了解植物-猎物-捕食者三营养层的相互作用,研究了寄主植物对捕食者食物消耗与利用的影响。【方法】在室内评价了多异瓢虫Hippodamia variegata (Goeze) 4龄幼虫和雌成虫取食和利用 5种不同葫芦科植物上的棉蚜 Aphis gossypii Glover的效率。【结果】多异瓢虫4龄幼虫和成虫均对南瓜Cucurbita moschata var. melonaeformis上的蚜虫取食量最高,而对瓢葫芦Lagenaria siceraria var. gourda上的蚜虫取食量最低。4龄幼虫取食哈密瓜 Cucumis melo var. cantalupensis上的蚜虫时,其相对生长率、食物利用率和食物转化率均达到最大,而雌成虫在取食黄瓜Cucumis sativus和搅瓜Cucurbita pepo var. medullosa上的蚜虫时,其相对生长率不存在显著差异,在取食黄瓜、瓢葫芦和搅瓜上的蚜虫时,其食物利用率和食物转化率也不存在显著差异。因此,哈密瓜上的瓜蚜更适宜作为多异瓢虫4龄幼虫的猎物,而黄瓜、瓢葫芦和搅瓜上的瓜蚜更适宜作为成虫的猎物。【结论】寄主植物种类与多异瓢虫对棉蚜的捕食效率相关,该结论为进一步利用昆虫的食性对害虫进行控制奠定理论基础。     

Non-crop vegetation associated with chili pepper agroecosystems promote the abundance and survival of aphid predators

Habitat manipulation has long been used as strategy to enhance beneficial insects in agroecosystems. Non-crop weed strips have the potential of supplying food resources to natural enemies, even when pest densities are low. However, in tropical agroecosystems there is a paucity of information pertaining to the resources provided by non-crop weeds and their interactions with natural enemies. In this study we evaluated (a) whether weeds within chili pepper fields affect the diversity and abundance of aphidophagous species; (b) whether there are direct interactions between weeds and aphidophagous arthropods; and (c) the importance of weed floral resources for survival of a native and exotic coccinellid in chili pepper agroecosystems. In the field, aphidophagous arthropods were dominated by Coccinellidae, Syrphidae, Anthocoridae, Neuroptera and Araneae, and these natural enemies were readily observed preying on aphids, feeding on flowers or extrafloral nectaries, and using plant structures for oviposition and/or protection. Survival of native Cycloneda sanguinea (Coleoptera: Coccinellidae) differed between plant species, with significantly greater survival on Ageratum conyzoides and Bidens pilosa. However, no evidence was gathered to suggest that weed floral resources provided any nutritional benefit to the exotic Harmonia axyridis (Coleoptera: Coccinellidae). This research has provided evidence that naturally growing weeds in chili pepper agroecosystems can affect aphid natural enemy abundance and survival, highlighting the need for further research to fully characterize the structure and function of plant resources in these and other tropical agroecosystems.     

Effect of plant nutrition on aphid size,prey consumption,and life history characteristics of green lacewing

Plant quality can directly and indirectly affect the third trophic level. The predation by all the instars of green lacewing, Chrysoperla carnea （S.） （Neuroptera： Chrysopidae） on the cereal aphids, Rhopalosiphum padi （L.）, and Sitobion avenae （F.） at varying nitrogen fertilizer levels was calculated under laboratory conditions. Wheat plants were grown on four nitrogen fertilizer levels and aphids were fed on these plants and subsequently offered as food to the C. carnea. Aphid densities of 10, 30, and 90 were offered to first, second, and third instar larvae of green lacewing. Increased nitrogen application improved nitrogen contents of the plants and also the body weight of cereal aphids feeding on them. Aphid consumption by green lacewings was reduced with the increase in nitrogen content in the host plants of aphids. Predation of both aphid species by first, second, and third instars larvae of C. carnea was highest on aphids reared on plants with the lowest rate of fertilization, suggesting a compensatory consumption to overcome reduced biomass （lower aphid size）. Total biomass devoured by C. carnea on all nitrogen fertilizer treatments was not statistically different. Additionally, the heavier host prey influenced by the plant nutrition had an effect on the life history characteristics of green lacewings. The larval duration, pupal weight, pupal duration, fecundity, and male and female longevity were significantly affected by the level of nitrogen fertilization to the aphid＇s host plants, except for pupal duration when fed on S. avenae. This study showed that quantity of prey supplied to the larvae affects the prey consumption and thereafter the life history characteristics of green lacewings.     

Laboratory and field tests of predation on the cereal leaf beetle,Oulema melanopus (Coleoptera: Chrysomelidae)

The cereal leaf beetle (CLB), Oulema melanopus (L.) (Coleoptera: Chrysomelidae), is an invasive pest in North America recently reported in the Canadian Prairies. We performed a series of laboratory assays to identify potential predators and a field study to quantify predation of CLB eggs. In no-choice Petri dish assays, ground beetles (Carabidae), rove beetles (Staphylinidae), and several common lady beetle species (Coccinellidae) were the most consistent predators of eggs and larvae. Nabis spp. (Hemiptera: Nabidae) and wolf spiders (Araneae: Lycosidae) consumed many larvae, but did not consume eggs. Hippodamia spp., Coccinella septempunctata (L.) (Coleoptera: Coccinellidae), and Pterostichus melanarius (Illiger) (Coleoptera: Carabidae) also fed on CLB eggs on potted plants when an alternative food source was available, Sitobion avenae (Fabricius) (Hemiptera: Aphididae). In our field study, we found an average of 24.5% of sentinel eggs disappeared over a 24?h period, likely due to predation. Our results suggest that generalist predators can play an important role in the biological control of CLB, and warrant further study.     

Effects of conspecific and heterospecific competitors on feeding and oviposition of a predatory ladybird: a laboratory study

Abstract There are several examples of intraguild interactions among insect predators of aphids, but little is known regarding the effects of interactions on feeding and oviposition of individual competitors in a guild. In the laboratory, we determined the feeding and oviposition responses of a ladybird predator to its conspecific and heterospecific competitors in an aphidophagous guild. Gravid females of Menochilus sexmaculatus (Fabricius) (Coleoptera, Coccinellidae) reduced oviposition, but not feeding, when exposed to immobilised conspecific or Coccinella transversalis (Fabricius) (Coleoptera, Coccinellidae) individuals in the short‐term (3 h) and long‐term (24 h). Feeding and oviposition responses were not affected when M. sexmaculatus females were exposed to larvae or adults of Scymnus pyrocheilus Mulsant (Coleoptera, Coccinellidae) beetles or larvae of the syrphid fly Ischiodon scutellaris (Fabricius) (Diptera: Syrphidae). The ratio of eggs laid to numbers of aphids consumed by M. sexmaculatus females was also affected by the presence of conspecific or C. transversalis larvae. The results suggest that fecundity of this predator may be affected by both conspecific and heterospecific competitors in a patchy resource.