Deep phylogeographical structure and parallel host range evolution in the leaf beetle Agelasa nigriceps

To understand the mechanisms behind the diversification of herbivorous insects through insect–plant interactions, it is important to know how the insects change their diet breadth in response to environmental changes. In this study, we investigated the phylogeographical pattern of the leaf beetle Agelasa nigriceps to infer the evolutionary history of its host range. While this beetle commonly uses Actinidia arguta (Actinidiaceae) as a host plant, it has been recorded recently on Pterostyrax hispidus (Styracaceae), which is now increasing in abundance at some localities in Japan due to the indirect effects of high population size of a mammalian herbivore. Considerable variation among populations in the ability of Ag. nigriceps to use P. hispidus suggests that P. hispidus is a newly acquired host plant for this beetle. Phylogenetic analyses using mitochondrial DNA sequences and amplified fragment length polymorphism (AFLP) revealed a high degree of phylogeographical structure in Ag. nigriceps throughout Japan, which is consistent with the hypothesis that several glacial refugia existed in the Japanese archipelago. In contrast, no genetic structure associated with the host plants was detected. Both the mitochondrial DNA and AFLP analyses showed that populations that can use P. hispidus are polyphyletic. These results and geographical variation in host use suggest that the host range expansion to a novel host, P. hispidus, is a very recent and possibly ongoing phenomenon and has occurred independently in several regions. Our study illustrates that the host range of herbivorous insects can evolve repeatedly in response to similar environmental changes.     

Evidence for host race formation in the leaf beetle Galerucella lineola

We examined preference and performance of four Finnish Galerucella lineola F. populations on alder and willow. In standardized two‐choice laboratory feeding trials with alder and willow, only two naturally alder‐associated G. lineola populations accepted alder. Two conspecific willow‐associated populations preferred willow. These preferences seem to be unstable, however, because they can be modified by the beetles’ experience. Thus, there probably is not a complete host preference‐based isolation of alder‐ and willow‐associated G. lineola beetles in nature. In performance experiments, larvae of all four populations survived better on willow than on alder. This may indicate that willows are the ancestral hosts for G. lineola. Nevertheless, larvae of the two alder‐associated G. lineola populations survived better on alder than larvae of the two willow‐associated populations. On the other hand, larvae of the two willow‐associated populations survived better on willow than larvae of the two alder‐associated populations. This performance trade‐off suggests that G. lineola encounters different selective pressures on alders and willows. On both of them, selection probably disfavours those G. lineola genotypes that are the most successful and abundant on alternative hosts. This may reduce the effects of gene flow that is likely to occur as a consequence of incomplete host preference‐based isolation of alder‐ and willow‐associated G. lineola populations. Data from pupal weights support the idea that alder‐ and willow‐associated G. lineola populations may be genetically differentiated. Pupae of the two alder‐associated populations were heavier than those of the willow‐associated populations irrespective of whether larvae had fed on alder or on willow. Overall, our results indicate host race formation in G. lineola. This process may be enforced by the variable abundance of alders and willows in local communities.     

Geographic variation in oviposition choice of a leaf beetle: the relationship between host plant ranking, specificity, and motivation

The degree of adaptation of herbivorous insects to their local flora is an important component of the evolutionary processes that lead to host plant specialization in insects. In this study we investigated geographic variations in the oviposition preference of the leaf beetle Oreina elongata Suffrian (Coleoptera: Chrysomelidae: Chrysolini) in relation to differences in host plant specialization, in the field. We focused on the mechanisms of host choice and asked whether potential differences among populations are due to variations in host plant ranking and/or host plant specificity. We performed a combination of simultaneous choice and sequential no‐choice experiments with two of the major host plants of the beetle [Cirsium spinosissimum (L.) and Adenostyles alliariae (Gouan) (Asteraceae)]. The results suggested that spatial variation in host plant specialization has resulted in differences between populations in some aspects of the oviposition choice of O. elongata, while other aspects seem unaffected. We found no variation in host plant ranking among populations, as estimated in simultaneous choice tests. In contrast, the sequential no‐choice test indicated that host plant specificity was lower in a population that never encountered the highest ranked plant in the field. This finding agreed with our expectations, and we discuss our results in relation to the commonly used hierarchical threshold model. The results suggested that the mechanism for the differences in specificity is the variation among populations in the general motivation to oviposit, rather than quantitative differences in relative preference for the two hosts. We stress that it is essential to establish which of the two mechanisms is most important, as it will affect the probability of evolutionary change in host plant ranking.     

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

Local 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.     

Spatio-temporal abundance of flushing leaves shapes host selection in the willow leaf beetle, Plagiodera versicolora

In the willow leaf beetle, Plagiodera versicolora (Laicharting) (Coleoptera: Chrysomelidae), food resources available for adults are severely restricted by leaf toughness, which increases with age. Nevertheless, females require their own food almost all their life in order to produce eggs. In this paper, we have focused our attention on the spatio-temporal abundance of flushing leaves and have examined its effect on host-plant selection by adults among four co-occurring willow species ( Salix chaenomeloides , Salix eriocarpa , Salix integra , and Salix serissaefolia ) (Salicaceae) by field observations and experiments at two spatial scales. Among the various factors associated with this, the amount of new leaf production contributed maximally to variation in adult abundance. By conducting two experiments, we confirmed that the adults preferentially flew towards willow trees with abundant flushing leaves. Furthermore, we detected substantial seasonal changes in new leaf abundance and realized fecundity in the field, and a strong positive correlation was observed between them. Availability of adult food resources limited the reproductive performance of adults, particularly in mid-summer when only S. serissaefolia produced a few new leaves. These results supported the substantial effect of new leaf abundance on adult abundance in the field. Thus, we concluded that adult feeding is a critical factor that shapes the host-plant selection of P. versicolora and determines its seasonal occurrence through the dispersal and settlement of adults.     

Asymmetric local adaptation to host plants (Cirsium spp.) by the phytophagous ladybird beetle Henosepilachna niponica and its implications

Divergent host specialization by phytophagous insects is often detected as local adaptation and is thought to have played an important role in their diversification even within an ecological specialist. The phytophagous ladybird beetle Henosepilachna niponica Lewis (Coleoptera: Coccinellidae) predominantly depends on thistles (Cirsium spp., Asteraceae). The distribution of H. niponica occupies multiple areas dominated by different thistle species. This implies the possibility of the occurrence of host-associated divergent specialization of H. niponica. In this study, we investigated the pattern of host-use ability of three allopatric H. niponica populations (Aomori, Iwate, and Yamagata) on three thistle species – Cirsium alpicola Nakai, Cirsium nipponicum (Maxim.) Makino, and Cirsium tonense Nakai – under laboratory conditions. The results displayed asymmetric local adaptation by the beetles. The adults and larvae of the Aomori population showed sufficient acceptance and performance on C. nipponicum and C. tonense, the hosts of the Iwate and Yamagata populations, respectively. On the other hand, the Iwate and Yamagata populations fed small amounts of and performed poorly on C. alpicola, the host of the Aomori population. In contrast, the adults from all the populations clearly preferred feeding on C. nipponicum or C. tonense to C. alpicola. We concluded that the small but significant population differentiation and asymmetric local adaptation by beetles to congeneric host plant species could be a sign of the earliest stage of population divergence by divergent natural selection, given that these divergences will act as ‘immigrant inviability’ and ‘habitat isolation’ at least asymmetrically when these populations come into contact.     

Performance of leaf beetle larvae on sympatric host and non-host plants

Studies asking the ability of insects to utilize novel host plants often use novel hosts that are allopatric with the insect population under investigation. However, since the outcomes of species interactions are often site-specific, such studies cannot tell us whether a plant would actually be used by a given insect population if the plant grew sympatrically with it. We therefore performed a quantitative genetics experiment to analyse the performance of larvae of the leaf beetle Oreina elongata Suffrian (Coleoptera: Chrysomelidae, Chrysomelinae) on two host and three non-host plants, collected from a site where insects and plants co-occur in the Western Alps. When raised on the non-host Petasites albus (L.), larvae were able to survive equally well as on the two hosts, Adenostyles alliariae (Gouan) and Cirsium spinosissimum (L.), whereas they did not survive on the two other non-hosts, Peucedanum ostruthium (L.) and Rumex alpinus L. On P. albus, growth rate was slightly lower and development time slightly longer than on the two hosts. We found a genotype by environment interaction only for growth rate but not for development time and survival. However, the shape of the reaction norms of growth rates suggests that it is unlikely that selection could favour the inclusion of P. albus into the host range of the study population.     

Differential herbivory of the specialist beetle Stolas punicea on chemical phenotypes of its host Mikania micrantha

We assessed the preference of two populations of the specialist beetle Stolas punicea, on plants from three phytochemically differentiated geographical mosaics of the American weed Mikania micrantha. Our results show a significant geographic variation in host preference in S. punicea that could affect its success as a biocontrol agent.     

Response of the elm leaf beetle to host plants induced by oviposition and feeding: the infestation rate matters

We investigated by olfactometry and feeding‐ and oviposition‐choice‐tests how the highly specialised elm leaf beetle, Xanthogaleruca luteola Müller (Coleoptera: Chrysomelidae), responds to conspecifically induced defences in the field elm Ulmus minor Miller (Ulmaceae). While egg deposition of the beetle induced elms to release volatiles attractive to the egg parasitoid Oomyzus gallerucae Fonscolombe (Hymenoptera: Eulophidae), feeding alone did not. In the present study, females of the elm leaf beetle showed preferences for the odours of twigs induced by low egg deposition and feeding over odours from uninfested twigs. In contrast, heavy infestation rendered elm odours less attractive to the beetles. Feeding and oviposition bioassays revealed an oviposition preference for leaves from uninfested twigs when compared to locally infested leaves. However, beetles preferred to feed upon systemically induced leaves compared to uninfested ones. The different preferences of the elm leaf beetle during host plant approach might be explained by a strategy that accounts for both gaining access to high quality nutrition and avoiding competition or parasitism.     

The genetic architecture of a niche: variation and covariation in host use traits in the Colorado potato beetle

The genetic basis of host plant use by phytophagous insects can provide insight into the evolution of ecological niches, especially phenomena such as specialization and phylogenetic conservatism. We carried out a quantitative genetic analysis of multiple host use traits, estimated on five species of host plants, in the Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae). Mean values of all characters varied among host plants, providing evidence that adaptation to plants may require evolution of both behavioral (preference) and post-ingestive physiological (performance) characteristics. Significant additive genetic variation was detected for several characters on several hosts, but not in the capacity to use the two major hosts, a pattern that might be caused by directional selection. No negative genetic correlations across hosts were detected for any 'performance' traits, i.e. we found no evidence of trade-offs in fitness on different plants. Larval consumption was positively genetically correlated across host plants, suggesting that diet generalization might evolve as a distinct trait, rather than by independent evolution of feeding responses to each plant species, but several other traits did not show this pattern. We explored genetic correlations among traits expressed on a given plant species, in a first effort to shed light on the number of independent traits that may evolve in response to selection for host-plant utilization. Most traits were not correlated with each other, implying that adaptation to a novel potential host could be a complex, multidimensional 'character' that might constrain adaptation and contribute to the pronounced ecological specialization and the phylogenetic niche conservatism that characterize many clades of phytophagous insects.     

Feeding damage by larvae of the mustard leaf beetle deters conspecific females from oviposition and feeding

Herbivorous insects may be informed about the presence of competitors on the same host plant by a variety of cues. These cues can derive from either the competitor itself or the damaged plant. In the mustard leaf beetle Phaedon cochleariae (Coleoptera, Chrysomelidae), adults are known to be deterred from feeding and oviposition by the exocrine glandular secretion of conspecific co-occurring larvae. We hypothesised that the exocrine larval secretion released by feeding larvae may adsorb to the surface of Chinese cabbage leaves, and thus, convey the information about their former or actual presence. Further experiments tested the influence of leaves damaged by conspecific larvae, mechanically damaged leaves, larval frass and regurgitant on the oviposition and feeding behaviour of P. cochleariae. Finally, the effect of previous conspecific herbivory on larval development and larval host selection was assessed. Our results show that (epi)chrysomelidial, the major component of the exocrine secretion from P. cochleariae larvae, was detectable by GC-MS in surface extracts from leaves upon which larvae had fed. However, leaves exposed to volatiles of the larval secretion were not avoided by female P. cochleariae for feeding or oviposition. Thus, we conclude that secretion volatiles did not adsorb in sufficient amounts on the leaf surface to display deterrent activity towards adults. By contrast, gravid females avoided to feed and lay their eggs on leaves damaged by second-instar larvae for three days when compared to undamaged leaves. Mechanical damage of leaves and treatment of artificially damaged leaves with larval frass or regurgitant did not affect oviposition and feeding of P. cochleariae. Since no adverse effects of previous herbivory on larval development were detected, we suggest that female P. cochleariae avoid Chinese cabbage leaves damaged by feeding larvae for other reasons than escape from competition or avoidance of direct negative effects that result from consuming induced plant material.     

Nitrogen homeostasis in a willow leaf beetle, Plagiodera versicolora, is independent of host plant quality

While foliar nitrogen (N) content of host plants depends on environmental conditions, N content of herbivorous insects may remain relatively constant due to homeostasis. However, it is unknown to what extent insects can maintain their body elemental composition against natural variation in host plant quality. The present study examined the performance and N content of a willow leaf beetle, Plagiodera versicolora Laicharting (Coleoptera: Chrysomelidae), when fed leaves of host willow, Salix eriocarpa Franchet et Savatier (Salicaceae), with varying nutritional status. Water content, toughness, and N content of willow leaves varied seasonally, and they affected performance of the leaf beetle. The leaf beetle achieved high performance when fed young leaves. On the other hand, the N content of the leaf beetle changed little, and it was independent of that of willow leaves, indicating strong N homeostasis of the leaf beetle. We discussed the function of N homeostasis in herbivorous insects in tritrophic level interactions.     

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

Our 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.     

Postmating isolation and genetically variable host use in ecologically divergent host forms of Neochlamisus bebbianae leaf beetles

Ecological speciation studies have more thoroughly addressed premating than postmating reproductive isolation. This study examines multiple postmating barriers between host forms of Neochlamisus bebbianae leaf beetles that specialize on Acer and Salix trees. We demonstrate cryptic isolation and reduced hybrid fitness via controlled matings of these host forms. These findings reveal host-associated postmating isolation, although a nonecological, 'intrinsic' basis for these patterns cannot be ruled out. Host preference and performance results among cross types further suggest sex-linked maternal effects on these traits, whereas family effects indicate their genetic basis and associated variation. Genes of major effect appear to influence these traits. Together with previous findings of premating isolation and adaptive differentiation in sympatry, our results meet many assumptions of 'speciation with gene flow' models. Here, such gene flow is likely asymmetric, with consequences for the dynamics of future ecological divergence and potential ecological speciation of these host forms.     

Contemporary evolution of host plant range expansion in an introduced herbivorous beetle Ophraella communa

Host range expansion of herbivorous insects is a key event in ecological speciation and insect pest management. However, the mechanistic processes are relatively unknown because it is difficult to observe the ongoing host range expansion in natural population. In this study, we focused on the ongoing host range expansion in introduced populations of the ragweed leaf beetle, Ophraella communa, to estimate the evolutionary process of host plant range expansion of a herbivorous insect. In the native range of North America, O. communa does not utilize Ambrosia trifida, as a host plant, but this plant is extensively utilized in the beetle's introduced range. Larval performance and adult preference experiments demonstrated that native O. communa beetles show better survival on host plant individuals from introduced plant populations than those from native plant populations and they also oviposit on the introduced plant, but not on the native plant. Introduced O. communa beetles showed significantly higher performance on and preference for both introduced and native A. trifida plants, when compared with native O. communa. These results indicate the contemporary evolution of host plant range expansion of introduced O. communa and suggest that the evolutionary change of both the host plant and the herbivorous insect involved in the host range expansion.     

Influence of native and alien Prunus species and light conditions on performance of the leaf beetle Gonioctena quinquepunctata

The polyphagous beetle Gonioctena quinquepunctata Fabricius (Coleoptera: Chrysomelidae) is a serious leaf pest of the native European bird cherry, Prunus padus L., and the invasive alien black cherry, Prunus serotina Ehrh. (Rosaceae). In the shade, leaf damage is extensive in both species, whereas in full light, it is extensive in P. padus, but very low in P. serotina. We determined the influence of Prunus species and light conditions on differences in performance of both sexes of this folivore. In a laboratory experiment in which larvae were fed with leaves of a single species grown under particular light conditions, we measured larval, pupal, and adult mass, efficiency of conversion of ingested food (ECI), duration of development, total food eaten, and relative growth rate. In the field, we observed differences in beetle mass on shrubs of the two species growing under various light conditions. From the field observations, we hypothesised that leaves of the invasive P. serotina are not an equally good food source as leaves of P. padus for G. quinquepunctata, and the preference of these beetles for shaded shrubs is most favourable for their growth and development. Under laboratory conditions, we found that the beetle growth rate was not affected significantly by Prunus species or light conditions, despite the significant effect of light condition on the structure and chemical composition of Prunus seedlings. The lower ECI value for larvae feeding on sunlit leaves was compensated for by their higher level of consumption. In the field, adult insect mass was higher on P. padus than on P. serotina, and higher on sunlit shrubs of both species than on shaded ones. Under natural conditions, the mass of adult insects is probably also affected by other factors, such as predators and competition among folivores.     

Adaptive change and conservatism in host specificity in two local populations of the thistle-feeding ladybird beetle Epilachna niponica

We investigated geographic differences in the host specificity of Epilachna niponica Lewis (Coleoptera: Coccinellidae). The Yuwaku population feeds mainly on Cirsium matsumurae Nakai (Asteraceae) and secondarily on Cirsrium kagamontanum Nakai. The Asiu population, located 150 km away from the Yuwaku, feeds exclusively on C. ashiuense Yokoyama et T. Shimizu. Under laboratory conditions, we examined the differences between the two populations in adult feeding acceptance, adult feeding preference, and larval performance, using several closely related thistle species and varieties, including their native hosts. In the Asiu population, adult beetles clearly avoided the host of the Yuwaku population, C. kagamontanum, and no larvae were able to complete their development, whereas in the Yuwaku population, adults accepted and even preferred it to some other thistle species, and about 10% of first instar larvae became adults. This indicates that the Yuwaku population evolved its feeding preference and physiological adaptation to C. kagamontanum through a utilization of this low‐ranked host under natural conditions. Apart from C. kagamontanum, the two populations showed a similar host susceptibility pattern, indicating that this ladybird beetle has a conserved hierarchy in feeding preference and growth performance. We also observed adult leaf choice behavior when given different thistle species, and found that difference in biting rate after palpation determined the leaf areas consumed, implying that factors on the leaf surface played an important role in the choice.     

Relevance of visual and olfactory cues for host location in the mustard leaf beetle Phaedon cochleariae

The relevance of visual and olfactory cues for host‐plant location is investigated in males and females of the oligophagous mustard leaf beetle Phaedon cochleariae Fabricius (Coleoptera: Chrysomelidae). Different objects are offered in a walking arena and the behaviour of beetles is observed. Beetles orient toward vertically or horizontally striped black and white pattern independent of stripe orientation. The results suggest that contrast facilitates orientation in the field, whereas the pattern itself may be less important for host location in dense vegetation. The response to green and yellow objects is tested to investigate discrimination abilities between young (green) and mature (yellow) leaves. Beetles prefer green over yellow independent of material (cardboard or leaves of Nasturtium officinale R. Br., Brassicaceae). Preference behaviour tested in a dual‐choice contact assay coincides with visual preferences, where adults prefer young, more nutritious leaves for feeding and oviposition. Furthermore, females discriminate between visual cues of green leaves and green cardboard, whereas males do not, indicating that females are more sensitive in colour discrimination. Differences in colour wavelength influence the choice of beetle behaviour more strongly than differences in intensity. Both sexes of P. cochleariae prefer volatiles of the host plant N. officinale, whereas only females respond to the main volatile compound 2‐phenylethyl isothiocyanate. Given a choice between visual and olfactory cues, males orientate towards the colour cues, whereas females do not show any preferences. In males, visual cues may thus override olfactory cues, whereas, in females, both are equally important, which may reflect different ecological requirements and/or physiological abilities.     

Biology and host range of Platyphora semiviridis, a leaf beetle evaluated as a potential biological control agent for Solanum mauritianum in South Africa

The South American tree Solanum mauritianum is a major environmental weed in the high-rainfall regions of South Africa and has been targeted for biological control. Potential agents included five species of the genus Platyphora, which were imported from South America in 1994. Platyphora species associated with Solanaceae reputedly have very specific habitat requirements and host plant preferences in the field. Despite this, host-specificity tests on one species, Platyphora semiviridis, revealed a broad physiological host range. Although laboratory tests showed that P. semiviridis is confined to Solanum species and cannot survive on solanaceous crops outside that genus, it developed on potato and cultivated eggplant (aubergine) as well as on 10 native South African Solanum species. With few exceptions, there were no consistent differences in survival and duration of development on these compared with S. mauritianum. Furthermore, at least six of these non-target species, including potato and eggplant, supported breeding colonies of the beetles in cages. During choice tests in both small and larger cages, P. semiviridis avoided potato but did not consistently discriminate between S. mauritianum, eggplant and six native solanums for larviposition. Despite these findings, P. semiviridis has never been recorded on either potato or eggplant in South America, where it was only observed to feed on S. mauritianum. Although there are several reasons why P. semiviridis is unlikely to attack non-target Solanum species in the field, it will not be released in South Africa because there are other imported agents which have displayed narrower physiological host ranges and which may be more effective.     

Host-plant use in the range expansion of the pine processionary moth, Thaumetopoea pityocampa

Abstract.  1. During range expansions of phytophagous insects, secondary or novel hosts may allow colonisation of areas without primary hosts. Because plant species often differ in their relative attractiveness and suitability for insects, insect preference for, and performance on, these hosts can determine recruitment potential in the current and future expansion areas.
2. This study explores the relative roles of female preference and larval performance in an important pine defoliator, Thaumetopoea pityocampa (Denis & Schiffermüller) (Lepidoptera, Notodontidae), which colonises three Pinus species at its current range margin in the Italian Alps: P. nigra (primary host), P. sylvestris (secondary host), and P. mugo (novel host).
3. Host use patterns in multiple insect populations were studied through choice and no-choice oviposition experiments in cages, field surveys of mixed stands, and laboratory and field monitoring of larval growth and mortality. It was predicted that a specific life-history trait – time limitation of short-lived females to lay a single batch of eggs – would act as a component of female performance, and lead to similar rates of host acceptance in no-choice settings.
4. In the choice experiment, P. nigra was accepted the most frequently while P. sylvestris was accepted the least frequently, confirming nest density patterns in the field. Contrary to prediction, females remained discriminating in no-choice settings in spite of time limitation. In contrast, relative growth rate (RGR) and mortality of larvae did not differ significantly among the three hosts, highlighting a discrepancy between female preference and larval performance.
5. Recruitment potential of T. pityocampa in future expansion into stands of P. sylvestris and P. mugo is evaluated by combining host quality, conservatism in oviposition behaviour, habitat suitability, and the opportunity for local adaptation.