Herbivorous Ladybird Beetle Research Articles

A solanum beetle on a fabaceous weed: Possible rapid progress of adaptation to a novel host‐plant in a geographical context

AbstractOur knowledge on how the local distribution pattern of ordinary and novel hosts promotes or hinders the progress of adaptation to the novel hosts by phytophagous insects is limited. The herbivorous ladybird beetle Henosepilachna vigintioctopunctata (Coleoptera: Coccinellidae) depends mainly on solanaceous plants as hosts; the major wild host of this beetle species in Java, Indonesia, is Solanum torvum. However, in several regions of Southeast Asia, including Java, H. vigintioctopunctata also occurs on the introduced fabaceous weed, Centrosema molle. Circumstantial evidence indicates that the use of C. molle by beetles became frequent in the very early 2000s in East Java. In the present study, based on laboratory and field data obtained from 2003 to 2005, we evaluated the degree of adaptation to C. molle by H. vigintioctopunctata populations from East Java and documented the geographic pattern of host‐plant distribution in East Java. Laboratory experiments revealed that the beetles from East Java possessed the highest degree of adaptation to C. molle among the beetle populations thus far investigated, suggesting that the adaptation to C. molle by beetles proceeded quite rapidly in East Java in the early 2000s. Meanwhile, field surveys showed that the habitats in East Java consisted of mosaics with sites where only C. molle was distributed and sites where C. molle and solanaceous plants co‐occurred. We discussed the role of such geographical structure of habitats in promoting the rapid adaptation of H. vigintioctopunctata to C. molle in East Java.

Smad on X is vital for larval-pupal transition in a herbivorous ladybird beetle

Insect development is regulated by a combination of juvenile hormone (JH) and 20-hydroxyecdysone (20E). Production of both JH and 20E is regulated by transforming growth factor-β (TGFβ) signaling. TGFβ can be classified into two branches, the Activin and Bone Morphogenetic Protein (BMP) pathways. In Drosophila melanogaster, BMP signaling is critical for JH synthesis, whereas Activin signal is required to generate the large pulse of 20E necessary for entering metamorphosis. However, to which extent the roles of these signals are conserved remains unknown. Here we studied the role of an Activin component Smad on X (Smox) in post-embryonic development in a defoliating ladybird Henosepilachna vigintioctopunctata. RNA interference (RNAi)-aided knockdown of Hvsmox inhibited larval growth, and impaired larval development. All Hvmyo RNAi larvae arrested at the fourth-instar larval stage. Moreover, knockdown of Hvsmox delayed gut and Malpighian tubules remodeling. Furthermore, the expression of a JH biosynthesis gene (Hvjhamt), a JH receptor gene HvMet and a JH response gene HvKr-h1 was greatly enhanced. Conversely, the expression levels of an ecdysteroidogenesis gene (Hvspo), a 20E receptor gene (HvEcR) and six 20E response genes (HvBrC, HvE74, HvE75, HvE93, HvHR3 and HvHR4) were significantly lowered. Knockdown of HvMet partially restored the negative phenotypes in the Hvsmox RNAi beetles. Our results suggest that Smox exerts regulative roles in JH production, ecdysteroidogenesis and organ remodeling, thus contributing to modulate the larva-pupa-adult transformation in H. vigintioctopunctata.

Cryptic local adaptation of the herbivorous ladybird beetle Henosepilachna pustulosa in the ability to use the thistle Cirsium boreale

AbstractLocal adaptation to different host plants is important in the diversification of phytophagous insects. Thus far, much evidence of the local adaptation of insects with respect to host use at the physiological level has been gathered from systems involving less mobile insects and/or divergent hosts such as plants belonging to different families or genera. On the other hand, the prevalence of such local adaptation of insects with moderate or high dispersal ability to the intraspecific variation of herbaceous hosts is largely unknown. In the present study, we examined the occurrence and degree of local adaptation of the herbivorous ladybird beetle Henosepilachna pustulosa (Kôno) (Coleoptera: Coccinellidae) to its primary host, the thistle Cirsium boreale Kitam. (Asteraceae), through reciprocal laboratory experiments using beetles and thistles from three locations with a range of approximately 200 km. Concerning the larval developmental ability, obvious patterns of local adaptation to the thistles from respective natal locations were detected, at least in some combinations of beetle populations. Similar tendencies were detected concerning adult feeding acceptance, although the statistical support was somewhat obscure. Overall, our results indicate that the degree of local adaptation of insect species with moderate dispersal ability to conspecific herbaceous hosts is occasionally as strong as that involving less mobile insects and/or heterospecific hosts, indicating the potential of such cryptic local adaptation to promote ecological/genetic differentiation of phytophagous insect populations.

A solanum beetle on a fabaceous weed: Host plant generalization and specialization are two sides of the same coin

AbstractInvestigations of the ongoing evolutionary change of host specificity, especially of that in the initial phase, contribute largely to our understanding of the mechanisms responsible for the diversification of phytophagous insects. However, empirical studies of this aspect in natural systems are very scanty. In the present study, we document the evolutionary change of the degree of adaptation to an introduced legume centro by adults and larvae of the herbivorous ladybird beetle Henosepilachna vigintioctopunctata (Fabricius), which depends normally on various solanaceous plants. Results obtained through experiments conducted in seven successive years revealed a fluctuating degree of adaptation, but with a gradual increase, to centro by H. vigintioctopunctata, showing a tendency towards host plant generalization. Of particular importance, our results suggest that both host plant specialization and generalization are possible evolutionary outcomes of a dynamic initial phase of ongoing host range expansion. In addition, results of quantitative genetic analyses on larval development and other circumstantial evidence suggested that the evolutionary trajectories to specialization/generalization are largely determined by ecological conditions rather than by the insects' intrinsic genetic architecture. We also discuss some special aspects of acquisition of, and adaptation to, novel hosts by H. vigintioctopunctata and other herbivorous beetles, of which adults also feed on plant leaves.

Local variation in the thistle species Cirsium grayanum affects its utilization by the herbivorous ladybird beetle Henosepilachna niponica

AbstractHost plants are the most critical environmental factor for phytophagous arthropods. Adaptation to a novel host will alter the distributional range of an herbivore to include the area the novel host covers, and might promote divergence between populations utilizing the old and new hosts. On the Oshima Peninsula, Hokkaido Island, northern Japan, the ladybird beetle Henosepilachna niponica (Lewis) (Coleoptera: Coccinellidae) usually occurs exclusively on the thistle Cirsium alpicola Nakai (Asteraceae), which is distributed in the southernmost part of the island, although some other Cirsium species often grow in sympatry. At least at one site (Assabu), however, H. niponica depends on another thistle, Cirsium grayanum (Maxim.) Nakai, the most abundant and widely distributed thistle species on the Oshima Peninsula. We examined adult feeding acceptance and preference, and larval performance, in two populations of H. niponica that utilize different species of thistles (the Assabu population occurs on C. grayanum; the Shiriuchi population, on C. alpicola) by testing three kinds of thistles (C. grayanum from Assabu, C. grayanum from Shiriuchi, and C. alpicola from Shiriuchi). Results strongly suggested that among the three plants tested, C. grayanum from Assabu was the most suitable host for H. niponica. We concluded that local differences in C. grayanum mainly explain why it is not used at Shiriuchi, but that there are also local differences in host use among the beetle populations, suggesting some degree of local adaptation. This suggests that different selective regimes associated with different host plants might promote divergence among beetle populations. We conclude that H. niponica is at present unlikely to expand its range to the whole range of C. grayanum.

Genetic architecture for normal and novel host-plant use in two local populations of the herbivorous ladybird beetle, Epilachna pustulosa.

Trade-offs in host-plant use are thought to promote the evolution of host specificity. However, usually either positive or no genetic correlations have been found. Whereas factors enhancing variation in overall viability have been claimed to mask negative genetic correlations, alternative hypotheses emphasize the sequential changes in genetic correlation in the course of host-range evolution. In this study, the genetic architectures of performances on different hosts were compared in two populations of the herbivorous ladybird beetle, Epilachna pustulosa, using three host plants, one being normal for both, one novel for only one population, and the other novel for both populations. The genetic correlations between larval periods on normal hosts were significantly positive whereas those between normal and novel hosts were not different from zero. There was no evidence for reduced genetic variation on the normal host-plants. These results suggest that the host-range is not restricted by the antagonistic genetic associations among exploitation abilities on different plant species, but rather that selection of different host-plants may improve the coordination between genes responsible for the use of different plants.

Conspecific thistle plant selection by a herbivorous ladybird beetle, Epilachna pustulosa

AbstractHost selection by Epilachna pustulosa Kôno (Coleoptera: Coccinellidae) was surveyed in an area of about 130 ares, focusing on the role of the spatial distribution pattern of the host plant, thistle Cirsium kamtschaticum Ledeb. (Asteraceae) and the environmental conditions of habitats where thistle plants were growing. A total of 198 thistle clones were found in the area studied, and approximately 40% showed some degree of E. pustulosa infestation by July. Eggs were only oviposited on thistle clones that were fed on by adults. Adult beetles and egg masses of E. pustulosa showed an aggregated distribution in the earlier season (June) among thistle clones. The distribution of adults became more random (but still aggregated) by the later season (July), along with an increase in the number of infested clones. Multiple logistic regression analyses revealed that clone size and soil moisture were consistently important for the beetle's choice of clones to feed on. The other logistic regression analyses indicated that thistle‐clone size and sunlight condition influenced egg distribution. Thistle clone selection by E. pustulosa changed with season from a rather strict selection in June to a more obscure one in July, expanding the range of thistle clones used as feeding and oviposition substrate.

Comparison of genetic variation in growth performance on normal and novel host plants in a local population of a herbivorous ladybird beetle, Epilachna vigintioctomaculata.

Local populations of herbivore species that display variation in host plant use are subject to natural selection for improved ability to use their own host species. Since natural selection changes the frequency of alleles that control host use, genetic variation in growth performance on host plants may change with each generation of selection. Therefore, within-population variations in the ability to use different hosts may reflect past selective forces. The present study reports the genetic variation in growth performance in a population of the herbivorous ladybird beetle, Epilachna vigintioctomaculata Motschulsky (Coccinellidae, Epilachninae) on both the normal host and a novel host. The present study found higher heritabilities for growth performance on the novel host than the normal host. The difference in heritabilities was caused by smaller among-family variance components on the normal host compared to those on the novel host. The results are compatible with the view that natural selection, which improved the ability of the population to use a particular host plant, has reduced genetic variation within that population in the ability to use that host plant. The pattern of reduced genetic variation in a population reared on the normal host observed in the present study is compared with that in another population, which showed local adaptation in the use of its own host plant. The effect of natural selection on differing host plant use on within-population genetic variation is discussed.

Population differentiation in host‐plant use in a herbivorous ladybird beetle, Epilachna vigintioctomaculata

Population differentiation in host‐plant use in a herbivorous ladybird beetle, <i>Epilachna vigintioctomaculata</i>

Genetic basis for established and novel host plant use in a herbivorous ladybird beetle, Epilachna vigintioctomaculata

AbstractGenetic trade‐offs in host plant use are thought to promote the evolution of host specificity. Experiments on a range of herbivorous insects, however, have found negative genetic correlation in host plant use in only a limited number of species. To account for the general lack of negative genetic correlation, recent hypotheses advocate that different stages in evolution of host use must be distinguished: initial performance on a novel host in comparison with the established host, and performance on both hosts after the insect population has interacted with both hosts for a long time. The hypotheses suggest that genetic correlation may not necessarily be negative at the initial stage. The present study examines growth performance on both the established and a novel host in a herbivorous ladybird beetle, Epilachna vigintioctomaculata Motschulsky (Coccinellidae, Epilachninae). The results show that traits of growth performance across hosts were positively or neutrally correlated, but there was no evidence of a negative genetic correlation. In addition, significant genetic variance of growth performance on each host was detected, suggesting that E. vigintioctomaculata can potentially respond to selection for increased performance on both plant species. These results and similar results from experiments on other herbivores suggest that host expansion may not be constrained genetically, at least at the initial stage of host range evolution.

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

AbstractIndividual variation in two species of host plants (thistle, Cirsium kamtschaticum, and blue cohosh, Caulophyllum robustum) of the herbivorous ladybird beetle Epilachna 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.

Genetic basis for different host use in Epilachna pustulosa, a herbivorous ladybird beetle

The genetic basis for different host plant use was studied in a herbivorous ladybird beetle, Epilachna pustulosa, that exhibits interpopulational variation in host plant utilization. It usually depends on thistle, but one of the local forms occurs on both thistle and blue cohosh, which differ at the infraclass taxonomic level. In this local population, genetic association between the developmental performance on the two plants was neutral, suggesting genetic independence across the host plants. The form of reaction norms indicated some changes in relative rank position. Genetic variation among individuals on each host plant was detected. These results suggest that different genotypes are selected on different host plants and that a substantial proportion of the overall phenotypic plasticity is contributed by genotype-dependent environmental effects.

Genetic basis for different host use in Epilachna pustulosa, a herbivorous ladybird beetle

Genetic basis for different host use in Epilachna pustulosa, a herbivorous ladybird beetle

Consequences of adult size for survival and reproductive performance in a herbivorous ladybird beetle

Abstract. A univoltine herbivorous ladybird beetle Epilachna niponica (Coleoptera: Coccinellidae) shows a large variation in adult size within a population. Large adults had higher survival from emergence to the reproductive season, and the size‐dependent adult survival was most apparent during hibernation. On the other hand, adult survival during pre‐hibernation contributed little to size‐dependent overall survival. Neither reproductive lifespan nor lifetime fecundity were a function of adult size, though large females produced larger size of egg batches. Size of adult beetles was significantly reduced by leaf damage to plants on which they grew up on larval stage. Since leaf herbivory increases through the season, late emerged adults that were subjected to food deterioration during the larval period were smaller than early‐emerged individuals.