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.     

Susceptibility of lady beetles (Coleoptera: Coccinellidae) to entomopathogenic nematodes

We investigated differential susceptibility of lady beetles to entomopathogenic nematodes, for two reasons: (1) to estimate potential nontarget effects on natural lady beetle populations, (2) to compare the susceptibility of exotic versus native lady beetle species. We hypothesize that successful establishment of some exotically introduced arthropods may be due, in part, to a lower susceptibility relative to competing native species. In laboratory studies, we compared the pathogenicity, virulence, and reproductive capacity of Heterorhabditis bacteriophora and Steinernema carpocapsae among two native (Coleomegilla maculata and Olla v-nigrum) and two successfully established exotic (Harmonia axyridis and Coccinella septempunctata) lady beetles, and a known susceptible lepidopteran host, Agrotis ipsilon. After 1 and 2 days of exposure to either nematode species, mortality of A. ipsilon was higher than in all lady beetles. Thus, we predict that nematode field applications would have significantly less impact on lady beetle populations than on a susceptible target pest. Additionally, the impact of soil-applied nematodes may be lower on lady beetles than on soil-dwelling hosts because the former spends relatively less time on the soil. Exotic lady beetles were less susceptible to nematode infection than native species. Reproductive capacity data also indicated lower host suitability in H. axyridis, but not in C. septempunctata. Overall, the hypothesis that low susceptibility to pathogens in certain exotic lady beetles may have contributed to competitive establishment was supported (especially for H. axyridis). Additional studies incorporating different hosts and pathogens from various geographic locations will be required to further address the hypothesis.     

Susceptibility of a native and an exotic lady beetle (Coleoptera: Coccinellidae) to Beauveria bassiana

The exotic multicolored Asian lady beetle, Harmonia axyridis, became established and recently spread across much of North America and southern Canada. In a habitat now used by both the invading H. axyridis and a native lady beetle, Olla v-nigrum, we discovered that the native lady beetle was commonly infected by Beauveria bassiana; whereas, the exotic H. axyridis, was not. Laboratory assays revealed that B. bassiana isolates collected from naturally infected O. v-nigrum were pathogenic to adult O. v-nigrum but not to adult H. axyridis. In contrast, the GHA strain of B. bassiana was not significantly pathogenic to O. v-nigrum nor H. axyridis. Late-season field collections revealed significantly higher B. bassiana infection of O. v-nigrum than H. axyridis. Our results lead us to hypothesize that low susceptibility of H. axyridis to B. bassiana (found to infect O. v-nigrum) may provide an intraguild advantage to H. axyridis over O. v-nigrum; this may also occur with other species of native lady beetles and other endemic entomopathogens in different habitats and regions.     

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.     

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.     

Barcode haplotype variation in north American agroecosystem lady beetles (Coleoptera: Coccinellidae)

DNA barcodes have proven invaluable in identifying and distinguishing insect pests, most notably for determining the provenance of exotic invasives, but relatively few insect natural enemies have been barcoded. We used Folmer et al.’s (1994) universal invertebrate primers and Hebert et al.’s (2004) for Lepidoptera, to amplify 658 bp at the 5′ end of the mitochondrial cytochrome oxidase c subunit I (COI) gene in five species of lady beetles from crop fields in six states in the US Mid‐Atlantic, Plains and Midwest: three native species, Hippodamia convergens Guérin‐Méneville, H. parenthesis (Say) and Coleomegilla maculata (De Geer); and two exotic species, Harmonia axyridis (Pallas) and Coccinella septempunctata Linnaeus. Sequence divergences within species were low, never exceeding 0.9% (Kimura 2‐parameter distances). Sequence divergences between the two Hippodamia species ranged from 14.7 to 16.4%, mirroring the relationships found for other arthropod taxa. Among the exotic species, C. septempunctata sequences were as variable as those of the three native species, while H. axyridis populations comprised a single haplotype. Limited data on two Coleomegilla subspecies, C. m. lengi Timberlake and C. m. fuscilabris (Mulsant), are consistent with their belonging to the same species, although morphological and reproductive data indicate that they represent separate species. Our results support the general utility of COI barcodes for distinguishing and diagnosing coccinellid species, but point to possible limitations in the use of barcodes to resolve species assignments in recently divergent sibling species.     

Predation by adult and larval lady beetles (Coleoptera: Coccinellidae) on initial contact with lady beetle eggs

Na?ve adults and larvae of the native lady beetles Coleomegilla maculata (DeGeer), Cycloneda munda (Say), Hippodamia convergens Guérin-Méneville, Olla v-nigrum (Mulsant), and the exotic lady beetle Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) were tested for their initial response to eggs of these five lady beetle species and for egg consumption on first contact and after 3 h. Additionally, field-collected O. v-nigrum and H. axyridis adults were tested. C. maculata, H. axyridis, and O. v-nigrum adults responded similarly to all egg species on first contact. Higher numbers of C. munda adults did not eat C. maculata, H. convergens, and O. v-nigrum eggs on first contact compared with numbers that did eat C. munda and H. axyridis eggs. H. convergens adults always ate C. munda eggs but hardly ate H. axyridis eggs on first contact. Results showed that over the 3-h interval, egg predation by those predators feeding on first contact was always higher, except for adults and larvae of C. maculata, than for those that did not feed on first contact. Thus, acceptance of eggs on initial contact does impact egg survival. It is likely that eggs of all native species tested (i.e., C. maculata, C. munda, H. convergens, and O. v-nigrum), but not exotic H. axyridis eggs, are suitable food for C. maculata, H. convergens, and O. v-nigrum, whereas only C. munda eggs serve as suitable food for C. munda. In direct contrast, all egg species tested would likely serve as suitable food for the exotic H. axyridis.     

Variable correspondence of female host preference and larval performance in a phytophagous ladybird beetle Epilachna pustulosa (Coleoptera: Coccinellidae)

Genetic and environmental factors causing intraspecific variation of the thistle Cirsium kamtschaticum Ledeb. as a host plant of the phytophagous ladybird Epilachna pustulosa Kôno were investigated through simple food-choice tests and rearing of larvae. Two thistle clones (T1U₁ and T4H₂) were used, originally growing approximately 12 km apart. A previous study showed that adult female ladybirds preferred T1U₁ to T4H₂, and that larval performance was better on T1U₁, when leaves from the clones in situ were examined. The two clones retained their characteristics with respect to beetle preference after transplantation into a common garden. However, the difference between T1U₁ and T4H₂ with respect to larval performance was reduced after the transplantation. When leaves from shoots of T1U₁ exposed to different sunlight intensities were offered, adult female ladybirds did not show obvious preferences. Larval eclosion rates increased significantly with the increase in leaf sunlight intensity exposure. These results suggest strongly that both genetic and environmental factors are involved in interclonal variation of thistle quality in beetle preference and/or performance. It is suggested that the quality of thistle leaves for larval performance is largely affected by environmental factors, while leaf quality for beetle preference may be determined strictly by genetic factors. Under certain conditions, E. pustulosa females may behave maladaptively, preferring plants not appropriate for larval growth, or not choosing plants appropriate for the larval growth.     

Host plant suitability of a recently naturalized thistle Cirsium vulgare (Asteraceae) for a phytophagous ladybird beetle,Epilachna pustulosa (Coleoptera: Coccinellidae)

The phytophagous ladybird beetle, Epilachna pustulosa Kôno occurs mainly on the thistle Cirsium kamtschaticum Ledeb. In recent years, we have confirmed feeding and oviposition by E.pustulosa, and some degree of larval development of this beetle, on a naturalized congeneric thistle, Cirsium vulgare (Savi) Tenore. In this study, we assessed the host suitability of C.vulgare for E.pustulosa, using larval rearing and simple food choice tests, by comparing the performance on, and preference for, their legitimate host C.kamtschaticum. All experiments were initiated in July, when the utilization of C.vulgare by E.pustulosa became obvious. For larval performance, E.pustulosa showed a lower eclosion rate, shorter developmental duration and smaller body size when reared on C.vulgare than on C.kamtschaticum. Cirsium vulgare appeared to be a less adequate larval food than C.kamtschaticum. Adult feeding preference was altered seasonally; females preferred C.kamtschaticum to C.vulgare in a food choice test conducted in early July, whereas they showed the opposite preference in tests conducted in mid and late July. The utilization of C.vulgare by E.pustulosa appeared to be induced by qualitative deterioration of C.kamtschaticum leaves in July, which resulted in increased dispersion of adult beetles.     

Complete mitochondrial genome of the seven-spotted lady beetle, Coccinella septempunctata (Coleoptera: Coccinellidae)

The complete mitochondrial genome (mitogenome) of the seven-spotted lady beetle, Coccinella septempunctata (Coleoptera: Coccinellidae), which is one of the best known insects capable of predation, is described with an emphasis on the noteworthy composition of the A+T-rich region. The C. septempunctata genome consists of 2 rRNAs, 22 tRNAs, 13 protein-coding genes, and 1 control region, designated as the A+T-rich region in insects. Along with an unusually long A+T-rich region (4469 bp), the 18,965-bp long C. septempunctata mitogenome was the largest in Coleoptera. The A+T-rich region is composed of a 2214-bp long non-repeat region composed of 80.17% A/T nucleotides and a 2256-bp long repeat region composed of 65.71% A/T nucleotides. The repeat region harbors 32 identical 70-bp long tandem repeats plus one 15-bp long incomplete first repeat. These repeat sequences may possibly have been caused by slipped-strand mispairing and unequal crossing-over events during DNA replication.     

Phytophagous preferences of the multicolored Asian lady beetle (Coleoptera: Coccinellidae) for autumn-ripening fruit

The objective of this study was to assess the potential pest status of Harmonia axyridis (Pallas) on autumn-ripening fruit. In autumn, H. axyridis has been observed feeding on pumpkins, apples, grapes, and raspberries in Minnesota. To determine whether H. axyridis can inflict primary feeding damage to fruit (i.e., breaking the skin of the fruit), we conducted laboratory feeding experiments with undamaged pumpkins, apples, grapes, and raspberries. The only fruit that H. axyridis was able to damage directly was raspberry. Laboratory choice tests were conducted to determine whether H. axyridis exhibits a preference between damaged and undamaged fruit, between cultivars of fruit, and between sugar water and water alone. For all fruits tested, H. axyridis showed a preference for damaged fruits over undamaged fruits. H. axyridis also exhibited a strong preference for sugar water over water alone. However, few differences were exhibited in preference between cultivars of fruit. In autumn, it seems that H. axyridis is an opportunist, taking advantage of previously damaged fruit, caused by other agents.     

Inheritance of lambda-cyhalothrin resistance in the predator lady beetle Eriopis connexa (Germar) (Coleoptera: Coccinellidae)

Lambda-cyhalothrin is a pyrethroid insecticide widely used to control pests in various crop ecosystems, in which the lady beetle occurs naturally. Therefore, lady beetle populations are exposed to lambda-cyhalothrin sprays that may foster tolerance to this insecticide. This study was conducted to confirm the occurrence of resistance in the lady beetle Eriopis connexa (Germar) (Coleoptera: Coccinellidae) to lambda-cyhalothrin and to characterize the inheritance of resistance after eight progressive selection with insecticide dosages based on the LD₅₀ determined for the F1 generation. Dose–mortality curves were determined for parental populations, F1 hybrids and backcross progenies. Parameters regarding the heritability of resistance to lambda-cyhalothrin in E. connexa allow estimating 10-fold increase in the initial LD₅₀ after 54.5 generations of successive selections. The resistance of E. connexa to lambda-cyhalothrin was characterized as autosomally inherited and incompletely dominant, and influenced by a major gene with possible influence of secondary genes. Additionally, the resistance in E. connexa varies from functionally dominant to functionally recessive depending on the dose used. These findings indicate that insecticide resistance in E. connexa can be selected in the field as determined for field-collected individuals, and subsequently enhanced under laboratory conditions. Its characterization presented here is an important step toward linking biological and chemical control within pest management regarding the lady beetle and lambda-cyhalothrin targeting different pest groups.     

Tumidusternus,a new genus of Aspidimerini from China (Coleoptera,Coccinellidae)

Tumidusternus gen. n., along with Tumidusternus fujianensis sp. n. (Coleoptera, Coccinellidae, Aspidimerini) from China is described and illustrated. A key to the tribe Aspidimerini is given.     

Horizontal transmission of a microsporidium from the convergent lady beetle, Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae), to three coccinellid species of Nova Scotia

Convergent lady beetles, Hippodamia convergens Guérin-Méneville, are a popular choice for aphid control in North America. An unidentified microsporidium was found in H. convergens adults that were purchased from a commercial insectary in 2004. This study examined egg cannibalism and egg predation as a means of horizontal transmission of the unidentified microsporidium among H. convergens larvae and three coccinellid species found in Nova Scotia: Coccinella septempunctata (seven-spotted lady beetle), C. trifasciata perplexa (three-banded lady beetle), and Harmonia axyridis (multicolored Asian lady beetle). The microsporidium was transmitted with 100% efficiency when first instars fed on microsporidia-infected eggs. Mean spore count data from smear preparations of infected beetles suggest that the infection was as heavy in C. trifasciata perplexa (a native coccinellid) (11.2 ± 0.96 spores/100 μm²) as it was in H. convergens (the natural host) (12.8 ± 1.16) but lighter in the introduced species C. septempunctata (7.5 ± 0.65) and H. axyridis (0.8 ± 0.11). For all of the beetle species examined, larval development was significantly longer for microsporidia-infected individuals than for their uninfected cohorts. The microsporidium had no effect on larval mortality. Based on the results of this study, field-collected H. convergens should be examined for microsporidia and uninfected individuals should be used to rear individuals for release in biological control programs. However, this is unlikely to happen because H. convergens are relatively easy and inexpensive to collect from their overwintering sites for redistribution.     

A contribution to Asian Afidentula Kapur (Coleoptera,Coccinellidae, Epilachnini)

Two new species of Afidentula, Afidentula dentata sp. n. and Afidentula jinpingensis sp. n. are described from China. Afissa siamensis Dieke is moved to Afidentula comb. n.. All three species are described and illustrated, and a distribution map is given. A key to Asian species of Afidentula is updated. Diagnostic similarities and differences between Afidentula and Afidenta are discussed and illustrated.     

Bacteria in ovarioles of females from maleless families of ladybird beetles Adalia bipunctata L. (Coleoptera: Coccinellidae) naturally infected with Rickettsia,Wolbachia, and Spiroplasma

Ovarioles were found to be infected with Spiroplasma, Wolbachia, and Rickettsia in Adalia bipunctata females with maleless progeny in different natural populations. Ooplasm was infected with few Wolbachia bacteria. In ooplasm infected by Rickettsia, bacteria were present in small foci. Spiroplasmas were found encapsulated into ooplasm from the wider intercellular spaces between epithelial and oocyte cells. The cytoplasm of follicular epithelia infected with Rickettsia was heavily destroyed, but the nucleus was intact and free from bacteria. The essential feature of follicular epithelium cells from Spiroplasma and Wolbachia infected A. bipunctata females was inclusions of three types: crystalline, filaments, and concentric myelin-like lamellae. Observations of smears prepared from ovaries of A. bipunctata from natural populations revealed a low concentration of bacteria within a microscopy field (less 10 bacteria) in more than 90% of specimens, and only a few ovaries were heavily infected. Two different ways of bacterial invasion of the oocyte are suggested: Spiroplasma-like, through the intercellular spaces in the epithelium and Rickettsia-like, through the cytoplasm of follicular epithelium cells. Bacteria were not found in germarium zones and we suggest that each follicle is infected from haemolymph.     

Individual variation in two host plants of the ladybird beetle,Epilachna pustulosa (Coleoptera: Coccinellidae)

Individual variation in two species of host plants (thistle,Cirsium kamtschaticum, and blue cohosh,Caulophyllum robustum) of the herbivorous ladybird beetleEpilachna pustulosa was examined under laboratory conditions for their acceptability to adult beetles as a food resource, for adult preference and for larval performance. When clones of these plants were subjected to non-choice tests using posthibernating female beetles, there was found to be significant intraspecific variation among clones in terms of their acceptability, but interspecific variation was not detected. Significant intraspecific as well as interspecific variation were frequently detected in the two host plants when clones of these plants were subjected to choice tests using posthibernating female beetles; the magnitude of interspecific plant variation for beetle preference is not necessarily larger than that of intraspecific plant variation. Individual variation across plant species with respect to beetle larval performance was also significant. A positive correlation between adult preference and larval performance is suggested across the two taxonomically remote host plant species, thistle and blue cohosh, although this needs further investigation.