Effects of host variety on blue willow beetle Phratora vulgatissima performance

Phratora vulgatissima adults exhibit feeding preferences among willow varieties, yet little is known of the effects of willow variety on larval and adult performance. The effects of host variety on adult fitness and fecundity as well as on larval mortality and development were studied under laboratory conditions for 35 willow varieties. The host variety significantly affected the number of days that adults survived and the rates of weight change. On average, males lost weight and females gained weight. The total number of eggs, eggs day¹, eggs clutch^?1 and the length of the oviposition period were also significantly affected by willow variety. Progeny from eggs laid by adults fed on the different willow varieties showed significant differences in days to pupation and pupal weight when subsequently reared on Salix × dasyclados or on the same variety as fed to the adults. However, there was no correlation between these parameters on S. × dasyclados and the variety fed to adults. The willow variety fed to larvae significantly affected larval mortality (four varieties caused 100% mortality), the shape of larval growth curves (as measured by predicted final weight and time to half the final weight), the number of days to pupation and pupal weight. There were significant positive correlations between previously determined adult P. vulgatissima feeding preferences of the 35 willow varieties and the following: number of eggs laid, length of the oviposition period, larval mortality and development and change in adult weight. There was a considerable degree of variation in these correlations and some varieties did not follow the general trend indicated by the size or sign of particular correlations, for example, having a high feeding preference ranking yet few eggs laid, low larval weight and longer time to pupation. The differences found between varieties for adult and larval performance in conjunction with previously established feeding preferences offer great potential for utilising plant resistance to P. vulgatissima as a means of strategic control. Despite the general correlation of feeding preference and performance parameters, the results found here suggest that it appears to be possible for plant breeders to circumvent this trend.     

Relationship between adult and larval host plant selection and larval performance in the generalist moth, Trichoplusia ni

Adult oviposition preferences are expected to correlate with host plant suitability for the development of their offspring. For most lepidopteran species, this is particularly important as the hatching neonate larvae of many species are relatively immobile. Thus, the site of oviposition chosen by a female adult can greatly influence the probability of survival for her offspring. In the present study, we investigated the oviposition preference of adult Trichoplusia ni moths for six plant species to determine whether they could accurately rank the suitability of the plants for larval development. We also compared oviposition preferences to neonate larval acceptance and preference to determine whether the adult host range matched that of larval diet breath. Our results indicate that in two-choice and no-choice tests adult T. ni were able to rank the plants accurately, with the exception of anise hyssop. However, when given a choice of all six plants together, they laid more eggs on a plant that was not suitable for larval survival. Larvae accepted and fed on all plants in no-choice tests, and accurately ranked them according to larval performance. We conclude that neonate larvae are better able than adults to rank plants according to larval performance, and that larval diet breadth is wider than the range of plants accepted by adults. We also provide a discussion of the reduced accuracy of adult oviposition preference with increased plant choices.     

Adult beetles compensate for poor larval food conditions

Life history traits of herbivores are highly influenced by the quality of their hosts, i.e., the composition of primary and secondary plant metabolites. In holometabolous insects, larvae and adults may face different host plants, which differ in quality. It has been hypothesised that adult fitness is either highest when larval and adult environmental conditions match (environmental matching) or it may be mainly determined by optimal larval conditions (silver spoon effect). Alternatively, the adult stage may be most decisive for the actual fitness, independent of larval food exposure, due to adult compensation ability. To determine the influence of constant versus changing larval and adult host plant experiences on growth performance, fitness and feeding preferences, we carried out a match–mismatch experiment using the mustard leaf beetle, Phaedon cochleariae. Larvae and adults were either constantly reared on watercress (natural host) or cabbage (crop plant) or were switched after metamorphosis to the other host. Growth, reproductive traits and feeding preferences were determined repeatedly over lifetime and host plant quality traits analysed. Differences in the host quality led to differences in the development time and female reproduction. Egg numbers were significantly influenced by the host plant species experienced by the adults. Thus, adults were able to compensate for poor larval conditions. Likewise, the current host experience was most decisive for feeding preferences; in adult beetles a feeding preference was shaped regardless of the larval host plant. Larvae or adults reared on the more nutritious host, cabbage, showed a higher preference for this host. Hence, beetles most likely develop a preference when gaining a direct positive feedback in terms of an improved performance, whereby the current experience matters the most. Highly nutritious crop plants may be, in consequence, all the more exploited by potential pests that may show a high plasticity in reproduction and feeding preferences.     

Taste sensitivity and divergence in host plant acceptance between adult females and larvae of Papilio hospiton

On the island of Sardinia the lepidopteran Papilio hospiton uses Ferula communis as exclusive host plant. However, on the small island of Tavolara, adult females lay eggs on Seseli tortuosum, a plant confined to the island. When raised in captivity on Seseli only few larvae grew beyond the first–second instar. Host specificity of lepidopterans is determined by female oviposition preferences, but also by larval food acceptance, and adult and larval taste sensitivity may be related to host selection in both cases. Aim of this work was: (i) to study the taste sensitivity of larvae and ovipositing females to saps of Ferula and Seseli; (ii) to cross‐compare the spike activity of gustatory receptor neurons (GRNs) to both taste stimuli; (iii) to evaluate the discriminating capability between the two saps and determine which neural code/s is/are used. The results show that: (i) the spike responses of the tarsal GRNs of adult females to both plant saps are not different and therefore they cannot discriminate the two plants; (ii) larval L‐lat GRN shows a higher activity in response to Seseli than Ferula, while the opposite occurs for the phagostimulant neurons, and larvae may discriminate between the two saps by means of multiple neural codes; (iii) the number of eggs laid on the two plants is the same, but the larval growth performance is better on Ferula than Seseli. Taste sensitivity differences may explain the absence of a positive relationship between oviposition preferences by adult females and plant acceptance and growth performance by larvae.     

Greater impact of host plant species on oviposition of a willow leaf beetle <Emphasis Type="Italic">Plagiodera versicolora</Emphasis> Laicharting (Coleoptera: Chrysomelidae) during the adult stage than in developing larval stage

In some herbivorous insects, such as Coleoptera and aphids, not only the host species of larvae, but also those of adults should be considered as key determinants of potential fecundity because oviposition is affected by the quality of host species during both larval and adult stages. This study examined the relatively greater impact on host species of the larval or adult stage on oviposition of the willow leaf beetle Plagiodera versicolora Laicharting (Coleoptera: Chrysomelidae). We conducted an experiment using a 2 × 2 experimental design, in which either of two different host plant species was fed in larval and adult stages. Females fed on a locally unavailable host Salix eriocarpa in the adult stage did not lay any eggs, but those fed on the locally available host S. babylonica laid 67–75 eggs on average, irrespective of larval host species. Such reproductively inactive females fed S. eriocarpa as an adult host recovered reproductive activity within 3 weeks after changing the host species to S. babylonica. This result indicated that the host species fed in the adult stage had a greater impact on oviposition than in the larval stage.     

Intra-plant host selection, oviposition preference and larval survival of Chrysophtharta agricola (Chapuis) (Coleoptera: Chrysomelidae: Paropsini) between foliage types of a heterophyllous host

Abstract 1 Paropsine chrysomelid beetles defoliate commercial eucalypt plantations in Australia. Adults and larvae feed on the same host, with the larval food source determined by the oviposition choice of females. Most eucalypt species are heterophyllous, with their foliage undergoing distinct morphological and chemical changes between adult and juvenile growth. 2 The intra‐plant foliage feeding and oviposition preference adults and the larval development of Chrysophtharta agricola were examined using adult and juvenile foliage of a heterophyllous plantation species, Eucalyptus nitens. The foliage types differ in chemistry, toughness, waxiness and timing of production. 3 In the field, feeding damage caused by adult beetles was 15% more frequent on adult foliage than on juvenile foliage; however, egg batches were three times more common on juvenile than on adult foliage. 4 Oviposition preference for juvenile foliage over adult foliage was confirmed in choice trials in the laboratory, with adult fecundity and longevity not significantly different between foliage types. 5 Larval survival, development time and subsequent pupal weight were also unaffected by foliage type, suggesting that neither foliage type is nutritionally superior for adults or for larvae. However, adult foliage was significantly thicker than juvenile foliage and this may prove a physical constraint to larval establishment. Biotic and abiotic factors (including interactions with natural enemies, competition, microclimate and mate location) that may affect patterns of host plant utilization are discussed.     

Oviposition,larval preference,and larval performance in two polyphagous species: does the larva know best?

It is expected that females preferentially oviposit on plant hosts that allow for optimal larval performance. However, this expectation contradicts empirical evidence where adults do not always choose the best host for their descendants. Recent evidence suggests that females’ host selection depends on the number of potential hosts. Females from oligophagous species seem to be able to choose an appropriate host in terms of larval performance, whereas in polyphagous species, adult oviposition preference is not related with larval performance. This suggests that larvae in polyphagous species could be taking a more active role in host selection than their mothers. Here, we evaluated the oviposition preference and the larval preference and performance of two polyphagous species of economic importance, Copitarsia decolora (Guenée) (Lepidoptera: Noctuidae: Cuculliinae) and Peridroma saucia (Hübner) (Lepidoptera: Noctuidae: Noctuinae), on eight species of cultivated plants. In laboratory and greenhouse choice assays, we tested adult preference for oviposition and larval preference at 1 and 24 h. Larval performance was measured in terms of survival to adulthood, length of larval period, and pupal weight. We found that both adult females and larvae actively choose their hosts and that the larval preference toward the hosts is related to the females’ preference in both herbivore species. However, the females and larvae did not preferentially select the host with the best larval performance, indicating that larval performance is not related to female or larval preference and that other selective pressures are influencing the choice of the host plant in these two species.     

Oviposition preference,larval performance and adaptation of Trichoplusia ni on cabbage and cotton

Most female herbivores ensure to lay eggs where their offspring can develop successfully. The oviposition preferences of females affect strategies in pest management. In this study, the performance of two cohorts of Trichoplusia ni larvae on cabbage and cotton (after they had been transferred from their original host plants) were investigated. The preferences of female moth ovipositing and larval feeding on these two host plants were observed. The results indicated that plants significantly affected oviposition preference of the female adults and development and survival of larvae of T. ni. All females preferred to lay eggs on cabbage than cotton regardless from which host they originated. The detrimental effects of cotton on the development and survival of T. ni larvae originated from cabbage (CaTn) increased with the increase of the larval age when they were transferred. In addition, the host plant change did not significantly affect the development and survival of larvae of T. ni originating from cotton (CoTn). Larvae of CaTn preferred cabbage plants as compared to cotton plants, whereas larvae of CoTn did not show a significant choice. Although the adult females preferred laying eggs on cabbage, they did not show preferences between cotton and cabbage in a Y‐tube olfactometer test. The hypothesis of oviposition preference and performance of larvae was supported by the results of CaTn, whereas they not supported by those from CoTn. Based on these results, the strategy to manage this serious pest was discussed.     

Butterfly oviposition preference is not related to larval performance on a polyploid herb

The preference–performance hypothesis predicts that female insects maximize their fitness by utilizing host plants which are associated with high larval performance. Still, studies with several insect species have failed to find a positive correlation between oviposition preference and larval performance. In the present study, we experimentally investigated the relationship between oviposition preferences and larval performance in the butterfly Anthocharis cardamines. Preferences were assessed using both cage experiments and field data on the proportion of host plant individuals utilized in natural populations. Larval performance was experimentally investigated using larvae descending from 419 oviposition events by 21 females on plants from 51 populations of two ploidy types of the perennial herb Cardamine pratensis. Neither ploidy type nor population identity influenced egg survival or larval development, but increased plant inflorescence size resulted in a larger final larval size. There was no correlation between female oviposition preference and egg survival or larval development under controlled conditions. Moreover, variation in larval performance among populations under controlled conditions was not correlated with the proportion of host plants utilized in the field. Lastly, first instar larvae added to plants rejected for oviposition by butterfly females during the preference experiment performed equally well as larvae growing on plants chosen for oviposition. The lack of a correlation between larval performance and oviposition preference for A. cardamines under both experimental and natural settings suggests that female host choice does not maximize the fitness of the individual offspring.     

Oviposition and feeding preferences of a flower-feeding weevil,Coelocephalapion aculeatum, in relation to conspecific damage to its host-plant

The oviposition and feeding preferences ofCoelocephalapion aculeatum Fall (Coleoptera: Apionidae), a host specific florivore ofMimosa pigra L. (Mimosaceae), were studied in relation to conspecific damage to its hostplant. Adults ofC. aculeatum cease ovipositing in inflorescences when the egg load reaches a number consistent with the larval carrying capacity of the inflorescence. The basis for this oviposition deterrence was examined by offering inflorescences damaged by adult feeding alone, larval feeding alone and a combination of adult feeding and oviposition. Adults preferred to oviposit on inflorescences which are not damaged by either adult feeding, larval feeding, or oviposition. No evidence for the existence of an oviposition deterring pheromone (ODP) was found. I suggest that the ability of a single host inflorescence to support the development of many larvae causes selection for the use of these oviposition deterring cues which can convey more quantitative information about the level of previous infestation than can ODPs. Adults fed a similar amount on damaged compared to undamaged inflorescences. These results assisted in the design of host range testing trials and allows predictions to be made about the effectiveness of this insect as a biological control agent.     

Oviposition preferences and larval performance of a flower-feeding weevil,Coelocephalapion aculeatum, in relation to host development

The oviposition behaviour ofCoelocephalapion aculeatum Fall (Coleoptera: Apionidae), a host specific florivore exploiting an ephemeral resource, was studied in relation to host development. Immature inflorescences of its host, the weedMimosa pigra L. (Mimosaceae), were categorised into 5 developmental stages ranging from first appearance to one day before opening. The duration, weight, percent abortion, and nitrogen content of each stage were measured. Oviposition preferences ofC. aculeatum for all inflorescence stages were determined in multiple choice trials. Newly hatched, larvae were transferred into inflorescences of each stage to determine larval survival as a function of stage. Numbers of eggs laid into inflorescences generally correlated with larval survival except that oviposition was greater in stage 4 inflorescences than expected from the larval survival. Numbers of eggs laid into inflorescences generally correlated with their carrying capacity except that adults avoided stage 5 inflorescences in which larval survival was low. The evolution of oviposition preferences ofC. aculeatum appears to have been influenced by two opposing selective forces. The need to complete development before the inflorescence deteriorated would have selected for oviposition in young inflorescences. The greater availability of food and lower probability of abortion offered by older inflorescences would have selected for oviposition in these. The net outcome of these pressures has resulted in the observed oviposition strategy.     

Oviposition preference and larval performance of North American monarch butterflies on four Asclepias species

Monarch butterflies, Danaus plexippus L. (Lepidoptera: Nymphalidae), occur world‐wide and are specialist herbivores of plants in the milkweed family (Asclepiadaceae). In North America, two monarch populations breed east and west of the continental divide in areas populated by different host plant species. To examine the population variation in monarch responses to different Asclepias species, we measured oviposition preference and larval performance among captive progeny reared from adult butterflies collected in eastern and western North America. Host plant use was evaluated using two milkweed species widely distributed in eastern North America (A. incarnata and A. syriaca), and two species common to western North America (A. fascicularis and A. speciosa). We predicted that exposure to different host plant species in their respective breeding ranges could select for divergent host use traits, so that monarchs should preferentially lay more eggs on, and larvae should perform better on, milkweed species common to their native habitats. Results showed that across all adult female butterflies, oviposition preferences were highest for A. incarnata and lowest for A. fascicularis, but mean preferences did not differ significantly between eastern and western monarch populations. Larvae from both populations experienced the highest survival and growth rates on A. incarnata and A. fascicularis, and we again found no significant interactions between monarch source population and milkweed species. Moreover, the average rank order of larval performance did not correspond directly to mean female oviposition preferences, suggesting that additional factors beyond larval performance influence monarch oviposition behavior. Finally, significant family level variation was observed for both preference and performance responses within populations, suggesting an underlying genetic variation or maternal effects governing these traits.     

Factors Influencing Host Plant Choice and Larval Performance in Bactericera cockerelli

Among the many topics of interest to ecologists studying associations between phytophagous insects and their host plants are the influence of natal host plant on future oviposition decisions and the mechanisms of generalist versus specialist host selection behavior. In this study, we examined the oviposition preferences, behavior and larval development of the tomato/potato psyllid, Bactericera cockerelli. By rearing psyllids with two distinct geographically-linked haplotypes on different host plants, we were able to examine the role of natal host plant and potential local adaptation on host plant usage. Choice bioassays among three host species demonstrated that psyllids from California had clear preferences that were influenced by natal plant. We further found that patterns in choice bioassays corresponded to observed feeding and movement responses. No-choice bioassays demonstrated that there is little to no association between development and host-plant choice for oviposition, while also indicating that host choice varies between haplotypes. These findings support the concept that mothers do not always choose oviposition sites optimally and also add support for the controversial Hopkins'' host selection principle.     

Asymmetry of larval diet breadth and oviposition preference in Leptinotarsa undecimlineata

The relationship between preference and performance was studied under laboratory conditions for larvae and adult females of Leptinotarsa undecimlineata (Stål) (Coleoptera: Chrysomelidae). Leptinotarsa undecimlineata feeds exclusively on Solanum lanceolatum L. (Solanaceae) in the centre of Veracruz, Mexico. A common sympatric species, Solanum myriacanthum Dunal, is not used as host. We conducted a series of laboratory experiments to detect reasons for the exclusive use of one host plant. Leptinotarsa undecimlineata larvae were reared under laboratory conditions on both plant species, Solanum lanceolatum and S. myriacanthum . Length of larval stages, pupal weight, and percent adult eclosion were compared, and larval preference for both Solanum species was tested. Upon eclosion, adult females were exposed to each of the plants, and the effect of larval diet on adult preference was determined. Oviposition on both Solanum species was observed in no-choice tests. Larvae showed no significant preferences for either plant species. Pupal weight, however, was significantly higher on S. lanceolatum . Female beetles significantly preferred S. lanceolatum leaves, and no effect of preimaginal conditioning was found. Females reproduced in lower numbers after feeding on S. myriacanthum , oviposition initiated later, and females laid fewer eggs than females fed with S. lanceolatum . No female accepted S. myriacanthum for oviposition. Results obtained suggest that the potential host breadth of L. undecimlineata is broader in larvae than in female beetles.     

Influence of Dietary Experience on the Induction of Preference of Adult Moths and Larvae for a New Olfactory Cue

In Lepidoptera, host plant selection is first conditioned by oviposition site preference of adult females followed by feeding site preference of larvae. Dietary experience to plant volatile cues can induce larval and adult host plant preference. We investigated how the parent’s and self-experience induce host preference in adult females and larvae of three lepidopteran stem borer species with different host plant ranges, namely the polyphagous Sesamia nonagrioides, the oligophagous Busseola fusca and the monophagous Busseola nairobica, and whether this induction can be linked to a neurophysiological phenotypic plasticity. The three species were conditioned to artificial diet enriched with vanillin from the neonate larvae to the adult stage during two generations. Thereafter, two-choice tests on both larvae and adults using a Y-tube olfactometer and electrophysiological (electroantennography [EAG] recordings) experiments on adults were carried out. In the polyphagous species, the induction of preference for a new olfactory cue (vanillin) by females and 3^rd instar larvae was determined by parents’ and self-experiences, without any modification of the sensitivity of the females antennae. No preference induction was found in the oligophagous and monophagous species. Our results suggest that lepidopteran stem borers may acquire preferences for new olfactory cues from the larval to the adult stage as described by Hopkins’ host selection principle (HHSP), neo-Hopkins’ principle, and the concept of ‘chemical legacy.’     

Beyond preference and performance: host plant selection by monarch butterflies,Danaus plexippus

The connection between adult preferences and offspring performance is a long‐standing issue in understanding the evolutionary and ecological forces that dictate host associations and specialization in herbivorous insects. Indeed, decisions made by females about where to lay their eggs have direct consequences for fitness and are influenced by interacting factors including offspring performance, defence and competition. Nonetheless, in addition to these attributes of the offspring, a female's choices may be affected by her own prior experience. Here we examined oviposition preference, larval performance and the role of learning in the monarch butterfly, Danaus plexippus, which encounters diverse milkweed host species across its broad range and over the course of migration. Monarch females consistently preferred to oviposit on Asclepias incarnata subspecies pulchra. This plant, however, was associated with poor caterpillar growth, low sequestration of toxins and the highest plant defences (latex and trichomes). We examined flexibility in this apparently maladaptive preference by testing the impact of previous experience and competition on preference. Experience laying on an alternative plant species enhanced preference for that species in contrast to A. i. pulchra. In addition, presence of a (competing) conspecific caterpillar on A. i. pulchra had a strongly deterrent effect and reversed host plant preferences. Thus, monarch butterflies exhibit preferences contrary to what would be expected based on offspring development and sequestered defences, but their preferences are altered by learning and competition, which may allow butterflies to shift preferences as they encounter diverse milkweeds across the landscape. Learning and perception of threats (i.e. competition or predation) may be critical for most herbivorous insects, which universally experience heterogeneity among their potential host plants.     

Host feeding experience affects host plant odour preference of the polyphagous leafminer Liriomyza bryoniae

Herbivorous insects use highly specific volatiles or blends of volatiles characteristic to particular plant species to locate their host plants. Thus, data on olfactory preferences can be valuable in developing integrated pest management tools that deal with manipulation of pest insect behaviour. We examined host plant odour preferences of the tomato leafminer, Liriomyza bryoniae (Kaltenbach) (Diptera: Agromyzidae), which is an economically important agricultural pest widespread throughout Europe. The odour preferences of leafminers were tested in dependence of feeding experiences. We ranked host plant odours by their appeal to L. bryoniae based on two‐choice tests using a Y‐tube olfactometer with five host plants: tomato, Solanum lycopersicum Mill.; bittersweet, Solanum dulcamara L.; downy ground‐cherry, Physalis pubescens L. (all Solanaceae); white goosefoot, Chenopodium album L. (Chenopodiaceae); and dead nettle, Lamium album L. (Lamiaceae). The results imply that ranking of host plant odours by their attractiveness to L. bryoniae is complicated due to the influence of larval and adult feeding experiences. Without any feeding experience as an adult, L. bryoniae males showed a preference for the airflow with host plant odour vs. pure air, whereas females did not display a preference. Further tests revealed that adult feeding experience can alter the odour choice of L. bryoniae females. After feeding experience, females showed a preference for host plant odour vs. pure air. Feeding experience in the larval stage influenced the choice by adults of both sexes: for males as well as females reared on bittersweet the odour of that plant was the most attractive. Thus, host feeding experience both in larval and/or adult stage of polyphagous tomato leafminer L. bryoniae influences host plant odour preference by adults.     

Intraspecific variability in host plant quality and ovipositionaI preferences in Eucheira socialis (Lepidoptera: Pieridae)

Abstract.

• 1 This study investigates interactions between Eucheira socialis (Pieridae: Lepidoptera), a strict monophagous herbivore, on Arbutus xalapensis (Ericaceae), a host plant with few herbivores. This tight association of insect on plant has many attributes conducive to reciprocal rather than diffuse evolution.
• 2 An indirect way of testing plant–insect coevolutionary theories is to test for the necessary conditions for reciprocal evolution in ecological time. Two conditions for coevolution were studied: (1) host plants vary in their suitability for larval growth and development, and (2) ovipositing insects discriminate among these plants based on their relative suitability.
• 3 Large differences in host plant suitability were found and relative differences were consistent from year to year.
• 4 There was no evidence that female insects based their ovipositional decisions on relative tree quality, which implies that factors other than host plant quality are involved in the maintenance and evolution of oviposition behaviour in Eucheira.
• 5 Of seven factors known to influence ovipositional preferences of insects among plants independent of potential larval success, the most likely causal factor in this system is the ability of females to balance a time/energy budget for finding potential oviposition sites, discriminating among them, and actually ovipositing.

     

Choosy mothers pick challenging plants: maternal preference and larval performance of a specialist herbivore are not linked

1. Maternal preference is a dynamic process and interactions between preference and performance are fundamental for understanding evolutionary ecology and host association in insect–plant interactions. In the present study, the hypothesis of preference–performance was tested by offering solanaceous specialist Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae) larvae and adult females four plant congeners that ranged in suitability. 2. Larval feeding, development, oviposition, plant glycoalkaloids, and headspace volatiles in the four plant species were analysed to examine the extent of variation, which might explain performance–preference differences. 3. It was found that larval performance was mismatched with adult oviposition preferences. Adults laid more eggs on Solanum immite Dunal plants, which were poor hosts for larval development, feeding, and survival, compared to the other three Solanum species. 4. Chemical plant defenses, in general, did not correlate with performance or preference, but some plant volatiles may have played a role in resolving female choice. Glycoalkaloids such as solanine and chaconine were detected in similar amounts in preferred and non‐preferred hosts, but there was significantly more limonene in the headspace of S. immite than in S. tuberosum L. 5. The present findings suggest that we must consider the risk‐spreading hypothesis in cases where preference and performance are not positively correlated, particularly in specialist herbivores that can feed on a diversity of congener plants and may attempt to expand their exploits to other solanaceae species.     

Can the Geranium Bronze, <Emphasis Type="Italic">Cacyreus marshalli</Emphasis>, become a threat for European biodiversity?

Cacyreus marshalli Butler is an invasive species in many parts of Europe and Mediterranean area. In Europe, its larvae normally feed on pelargoniums. We investigated its potential to spread to native Geranium spp. and evaluated the conservation risks that such a shift would pose for both native geraniums and cohabitant butterflies. The host plant preferences of the Geranium Bronze were investigated under controlled conditions. Studies included both no-choice and multi-choice tests, respectively using 9 and 6 Italian native Geranium spp. Host plant preferences were evaluated by counting the number of eggs laid on individual plants and following butterfly development until adult emergence. Under no-choice conditions, at least one egg was recorded on each tested plant, except for G. phaeum L. All the plants on which oviposition occurred were fully suitable for larval development. The butterfly, however, clearly preferred three species, i.e. G. pratense L., G. sanguineum L. and G. sylvaticum L. for oviposition. In multi-choice trials, females laid at least one egg on all the tested plants, with a preference for G. pratense and G. sylvaticum. In presence of Pelargonium spp. plants, however, no oviposition was observed on any Geranium spp. We assessed offspring fitness measuring their wingspan. No statistical differences were detected in the wingspan between adults emerged from Geranium and Pelargonium. Cacyreus marshalli represents a potential threat for both native geraniums and for Geranium-consuming lycaenids, such as Aricia nicias Meigen and Eumedonia eumedon Esper.