Host‐associated genomic differentiation in congeneric butterflies: now you see it,now you do not

Ecotypic variation among populations may become associated with widespread genomic differentiation, but theory predicts that this should happen only under particular conditions of gene flow, selection and population size. In closely related species, we might expect the strength of host‐associated genomic differentiation (HAD) to be correlated with the degree of phenotypic differentiation in host‐adaptive traits. Using microsatellite and Amplified Fragment Length Polymorphism (AFLP) markers, and controlling for isolation by distance between populations, we sought HAD in two congeneric species of butterflies with different degrees of host plant specialization. Prior work on Euphydryas editha had shown strong interpopulation differentiation in host‐adapted traits, resulting in incipient reproductive isolation among host‐associated ecotypes. We show here that Euphydryas aurinia had much weaker host‐associated phenotypic differentiation. Contrary to our expectations, we detected HAD in Euphydryas aurinia, but not in E. editha. Even within an E. aurinia population that fed on both hosts, we found weak but significant sympatric HAD that persisted in samples taken 9 years apart. The finding of significantly stronger HAD in the system with less phenotypic differentiation may seem paradoxical. Our findings can be explained by multiple factors, ranging from differences in dispersal or effective population size, to spatial variation in genomic or phenotypic traits and to structure induced by past histories of host‐adapted populations. Other infrequently measured factors, such as differences in recombination rates, may also play a role. Our result adds to recent work as a further caution against assumptions of simple relationships between genomic and adaptive phenotypic differentiation.     

REPEATED REVERSALS OF HOST-PREFERENCE EVOLUTION IN A SPECIALIST INSECT HERBIVORE

A tree of mitochondrial DNA (mtDNA) haplotypes was constructed to estimate the number of evolutionary changes of host-plant preference needed to account for variation among 24 populations of the butterfly Euphydryas editha. Using 17 restriction endonucleases, 22 mtDNA haplotypes were found among 24 populations of this butterfly species. We allowed for the possibility of haplotypes to acquire particular preferences either from evolutionary change at their local sites or from migration to populations where those preferences occurred. After we had taken these estimates of migration into account, a minimum of 10 evolutionary changes of host preference (reduced from 22) was needed to explain the pattern of use of five host-plant genera among these populations. Analysis of allozyme variation among a partially overlapping set of populations also suggested multiple host shifts. Although genetic variation of host preference is largely responsible for interpopulation variation of diet, repeated reversals of preference evolution have occurred. However, host preferences were not distributed randomly with respect to phylogeny, and some tendency toward evolutionary conservation of preference also was indicated. The haplotype of E. editha most closely related to the sister species, E. chalcedona, used a principal host of E. chalcedona. Our results suggest that host shifts occur frequently in E. editha, are a result of both migration and local evolution, and have not been associated with speciation in these insects.     

HERITABILITY OF OVIPOSITION PREFERENCE AND ITS RELATIONSHIP TO OFFSPRING PERFORMANCE WITHIN A SINGLE INSECT POPULATION

Within a population of the butterfly Euphydryas editha that oviposits predominantly on two host species, heritable variation in postalighting oviposition preference was found. In a separate experiment, oviposition preference of adult females was found to be correlated with offspring performance (growth). There was a significant tendency for offspring to perform better on the host species that their female parent preferred. Analysis of the data showed that no single factor, neither maternal preference nor the host species on which the offspring were raised, accounted for any significant variation in larval performance. However, the effect of the interaction between host species and maternal preference on offspring performance was highly significant. These findings imply specialization in both oviposition preference and offspring performance by individuals within a single population. With present evidence, this preference-performance correlation is likely to be genetic. However, as in previous studies, other interpretations cannot be excluded.     

INCORPORATION OF A EUROPEAN WEED INTO THE DIET OF A NORTH AMERICAN HERBIVORE

Populations of the butterfly Euphydryas editha living within a 30 times 100–km region on the eastern slope of the Sierra Nevada range were compared for oviposition preference and ability of larvae to grow and survive on two host plants, Collinsia parviflora and Plantago lanceolata. Since its introduction approximately 100 years ago, P. lanceolata has been incorporated in the diet of E. editha in one of the study populations. The populations differed in oviposition preference; only the population that uses P. lanceolata contains some individuals that prefer P. lanceolata. Larvae from two populations, one using both P. lanceolata and C. parviflora, the other using only C. parviflora, were not found to differ in relative abilities to grow or survive on P. lanceolata. The potential for E. editha to use P. lanceolata appears in populations that have had no prior exposure to this plant, while oviposition preference for this plant has evolved in the population in which the plant now grows.     

Landscape and oceanic barriers shape dispersal and population structure in the island nematode Pristionchus pacificus

In this study evolutionary host plant patterns at ranks from order to species were analysed using spatial evolutionary and ecological vicariance analysis (SEEVA), based on a multigene phylogeny of 45 ascomycete fungal species. The objective was to understand speciation events and host associations in Ophiognomonia (Gnomoniaceae). Species of this genus are perithecial fungi that occur as endophytes, pathogens, and latent saprobes on plants in the families of Betulaceae, Fagaceae, Juglandaceae, Lauraceae, Malvaceae, Platanaceae, Rosaceae, Salicaceae, and Sapindaceae. A second objective was to determine whether speciation events are influenced by host conservatism, host specialization, or host switching at different taxonomic host ranks. Host differences between sister clades were interpreted using the divergence index (D) from the SEEVA analysis, ranging from 0 for no divergence to 1 for maximum possible divergence. Several fungal subclades showed clear patterns of host order/family conservatism (D = 1.00) for hosts in Betulaceae, Fagaceae, Juglandaceae, and Rosaceae. Clear trends of host specialization at host genus and species ranks (D = 1.00) were suggested within these host families. Independent host jumps were observed for two species at the family rank and three at the order rank. As a result of this study, host specificity and specialization is hypothesized as a mechanism that can strongly contribute to speciation patterns in fungal pathogens. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 1–16.     

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.     

Diet divergence in two sympatric congeneric butterflies: Community or species level phenomenon?

Summary Two species ofEuphydryas butterflies were studied in California, USA, and showed considerable diet overlap at the species level. They utilize many of the same plant genera for oviposition. However,E. editha is less likely to use woody perennials than isE. chalcedona.Both butterfly species are known to specialize on different host plants in different populations, so species level divergence may not be a good predictor of community level divergence. Within five communities,E. editha andE. chalcedona showed no dietary overlap. A major component of the niche ofE. editha in one community was occupied byE. chalcedona in a second community, even though both butterfly species occupied both communities. These resource use patterns indicate that community level interactions may affect diet divergence. The degree to which divergence within communities is greater (or less) than expected from a species level comparison may be used to provide a measure of community organization. Equations are given in the Appendix for calculating overlap probabilities from presence/absence types of data; in this study, presence is oviposition on a particular plant species, absence is no oviposition on that plant species. Given the various assumptions of the model,E. editha andE. chalcedona show significant community level components of their dietary divergence in the areas studied. However, in some other communitiesE. editha andE. chalcedona do share host plant species. Therefore, we could not demonstrate community level divergence conclusively, nor has this been demonstrated for any other pair of insect herbivore species. We do not know whether this is because the phenomenon is truly rare or just very hard to demonstrate.     

Variation among individual butterflies along a generalist–specialist axis: no support for the 'neural constraint' hypothesis

Abstract 1. Degree of host specialisation was a continuous variable in a population of Edith’s checkerspot butterfly (Euphydryas editha). A novel host, Collinsia torreyi, had been added to the diet in response to anthropogenic disturbance, and then abandoned prior to the current study. Butterflies either showed no preference or preferred their traditional host, Pedicularis semibarbata. 2. Strength of preference for Pedicularis over Collinsia was measured in the field and used to estimate host specialisation of individual butterflies. Efficiency was estimated from the times taken by each insect to perform two tasks: (i) identification of a Pedicularis plant as a host, and (ii) successful initiation of oviposition after the decision to do so had been made. 3. There was no clear trend for association between host specialisation and either measure of efficiency. Generalists were not slower than specialists at identifying Pedicularis as a host or at handling it after deciding to oviposit. 4. Prior work indicated that generalists paid no detectable cost in terms of reduced discrimination among individuals of their preferred host species. 5. In contrast to other species, generalist E. editha paid in neither time nor accuracy. Why then does the diet not expand? Behavioural adaptations to the traditional host caused maladaptations to the novel host and generated short‐term constraints to evolutionary expansion of diet breadth. To date, however, no long‐term constraints have been found in this system. In those traits investigated to date, increased adaptation to the novel host has not caused reduced adaptation to the traditional host.     

寄主植物的功能性状对桑寄生寄主专一性的影响初探

为探讨寄主多样性和寄主功能性状对桑寄生植物的寄主专一性的影响,调查了西双版纳热带植物园内桑寄生和寄主植物种类。结果表明,桑寄生植物共有2科5属6种1变种,感染隶属于58科190属286种寄主植物1 323株。桑寄生在不同生境的寄生强度具有极显著差异(P0.01),单一种植园的寄生强度最高,而在森林的分布最少。不同种类桑寄生的寄主范围存在较大差异,专一性程度(H′)为1.92～7.05,多度较高的植物更容易被感染。冗余分析表明,寄主植物的胸径、树皮含水量和树皮粗糙度对不同桑寄生的寄主利用差异有显著影响,而木质密度和树皮pH的影响不显著。因此,不同种类桑寄生在热带植物群落的寄主专一性程度有较大差异,对寄主植物特定功能性状的偏好能解释部分差异。     

Specificity, rank preference, and the colonization of a non-native host plant by the Melissa blue butterfly

Animals often express behavioral preferences for different types of food or other resources, and these preferences can evolve or shift following association with novel food types. Shifts in preference can involve at least two phenomena: a change in rank preference or a change in specificity. The former corresponds to a change in the order in which hosts are preferred, while a shift in specificity can be an increase in the tendency to utilize multiple hosts. These possibilities have been examined in relatively few systems that include extensive population-level replication. The Melissa blue butterfly, Lycaeides melissa, has colonized exotic alfalfa, Medicago sativa, throughout western North America. We assayed the host preferences of 229 females from ten populations associated with novel and native hosts. In four out of five native-associated populations, a native host was preferred over the exotic host, while preference for a native host characterized only two out of five of the alfalfa-associated populations. Across all individuals from alfalfa-associated populations, there appears to have been a decrease in specificity: females from these populations lay fewer eggs on the native host and more eggs on the exotic relative to females from native-host populations. However, females from alfalfa-associated populations did not lay more eggs on a third plant species, which suggests that preferences for specific hosts in this system can potentially be gained and lost independently. Geographic variation in oviposition preference in L. melissa highlights the value of surveying a large number of populations when studying the evolution of a complex behavioral trait.     

Protandry and postandry in two related butterflies: conflicting evidence about sex-specific trade-offs between adult size and emergence time

Natural selection acting on timing of metamorphosis can be sex-specific, resulting in differences in timing between males and females. Insects with discrete generations frequently show protandry: males usually mature before females. Both Euphydryas editha and E. aurinia butterflies followed this trend. The present study was motivated by the unusual observation of consistent postandry in addition to protandry. In a single E. editha population observed over 20 years the emergence period of males was longer than that of females, both the first and last emerging individuals being males. Variance of timing among individual E. editha larvae is imposed by spatial patchiness of the snowmelt that releases them from winter diapause. If individual larvae released late from diapause were to compensate for their lateness by shortening their development times, they would be small at maturity. If such compensation were only partial, they would be both late and small. Size and timing would become associated. If females were more prone to such partial compensation than males, the observations of postandry could be explained and the prediction made that any tendency for late individuals to be small should be stronger in females than in males. This was the case: in 1 year late males were the same size as early males, in a second year they were larger. Late females were significantly smaller than early females in both years. In E. aurinia, results were opposite both to theoretical prediction and to the observations from E. editha: although the male emergence period was longer than that of females exactly as in E. editha, late males were smaller than early ones, while late females were not small. The data from E. editha support the hypothesis of a sex-specific trade-off between size and emergence time, the data from E. aurinia do not.     

The structure and genetics of a montane population of the checkerspot butterfly,Chlosyne palla

Summary The population structure, genetics and ecology of the checkerspot butterfly, Chlosyne palla, in an area of Gunnison County, Colorado were investigated. The population structure was found to be quite different from that of most butterflies and from all of those aspects known for its thoroughly studied relative, Euphydryas editha. The population unit of Chlosyne palla may cover an area some five to eight times the size of the largest known Euphydryas population and twice the size of an Erebia epipsodea population in the same county of Colorado.Genetic variation at eleven loci of Chlosyne palla was examined by electrophoresis. Three samples of Chlosyne palla separated by 1.6, 4.7, and 12.0 km were not significantly different. Comparison with Euphydryas editha yields a genetic similarity of 0.186, about the same level as found by Ayala (1975) for different genera of Drosophila. Euphydryas editha from the same Colorado location were more similar to California E. editha than to C. palla, showing concordance with the phenetic classification. Decreased heterozygosity was observed for the Colorado E. editha and C. palla compared to California populations of E. editha and E. chalcedona.     

Specialization of rainforest canopy beetles to host trees and microhabitats: not all specialists are leaf‐feeding herbivores

Reliable estimates of host specificity in tropical rainforest beetles are central for an understanding of food web dynamics and biodiversity patterns. However, it is widely assumed that herbivores constitute the majority of host specific species, and that most herbivore species feed on leaves. We tested the generality of this assumption by comparing both plant host‐ and microhabitat‐specificity between beetle communities inhabiting the foliage (flush and mature), flowers, fruit, and suspended dead wood from 23 canopy plant species in a tropical rainforest in north Queensland, Australia. Independent of host tree identity, 76/77 of the most abundant beetle species (N ≥ 12 individuals) were aggregated on a particular microhabitat. Microhabitat specialization (measured by S_m and Lloyd's indices) was very high and did not differ between flower and foliage communities, suggesting that each newly‐sampled microhabitat has a large additive effect on total species richness. In accordance with previous studies, host specificity of foliage‐inhabiting beetles was most pronounced among herbivorous families (Curculionidae, Chrysomelidae). By contrast, host specificity among flower‐visitors was equally high among herbivorous and nonherbivorous families (e.g. Nitidulidae, Staphylinidae, Cleridae). Effective specialization (F_T) measures showed that traditional correction factors used to project total species richness in nonherbivorous groups fail to fully capture diversity in the flower‐visiting beetle fauna. These results demonstrate that host specialization is not concentrated within folivores as previously assumed. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 215–228.     

Experimental evidence of host race formation in Mitoura butterflies (Lepidoptera: Lycaenidae)

A population of herbivorous insects that shifts to a novel host can experience selection pressures that result in adaptation to the new resource. Host race formation, considered an early stage of the speciation process, may result. The current study investigates host shifts and variation in traits potentially involved in the evolution of reproductive isolation among populations of the juniper hairstreak butterfly, Mitoura gryneus. Mitoura are closely associated with their host trees (Cupressaceae) and exhibit host plant fidelity: in addition to larval development and oviposition, host trees support male leks and mating. Female oviposition preference for the natal host, and differential fitness of larvae when reared on natal versus alternate hosts, are indications that specialization and local adaptation to the natal host plant are occurring. Populations with single host plant associations (Juniperus ashei, J. pinchotii and J. virginiana) as well as populations with multiple hosts (both J. ashei and J. pinchotii) were examined. Concordance between female preference and larval performance was found for J. ashei‐associated populations. Population‐level variation in the patterns of female preference and larval performance, both within and among host associations, may reflect differences in the timing and direction of colonization of hosts. For a single nominal species that otherwise exhibits no morphological or phenological differences, the experimental assessment of specialization and host fidelity in M. gryneus provides strong support for the hypothesis of ongoing host race formation in these butterflies.     

Rainfall and the interaction of microclimate with larval resources in the population dynamics of checkerspot butterflies (Euphydryas editha) inhabiting serpentine grassland

Summary The interaction of host plant phenology and microclimatic heterogeneity was examined to determine its role in the population dynamics of checkerspot butterflies, Euphydryas editha, inhabiting serpentine grassland in California's outer Coast Range.Within the 2–3 hectares inhabited by a population of E. editha (Jasper Ridge Area H), microclimatic differences resulting from topographic heterogeneity largely determine the temporal and spatial pattern of senescence of the larval host plants, Plantago erecta and Orthocarpus densiflorus. Survival of larvae from hatching to diapause is extremely low as a result of unpredictable variation in the timing of larval development relative to the timing of host plant senescence, both of which are mediated by microclimatic patterns. During this study, population H declined to near extinction as a result of two consecutive years of record rainfall that apparently disrupted the tenuous temporal relationship between larval development and plant senescence. Retarded development of post-diapause larvae led to a late and extended flight season and delayed egg production; this in turn resulted in massive mortality of pre-diapause larvae due to starvation because host plant senescence occurred before larvae became large enough to enter diapause. Adult population size the following spring was the smallest in 25 years of study. This work emphasizes the importance of microclimatic heterogeneity for understanding population-level processes in small ectothermic animals and underlines the potential importance of such heterogeneity in the establishment of reserves designed to protect such animals     

Geographic host use variability and host range evolutionary dynamics in the phytophagous insect <Emphasis Type="Italic">Apagomerella versicolor</Emphasis> (Cerambycidae)

The high diversity of phytophagous insects has been explained by the tendency of the group towards specialization; however, generalism may be advantageous in some environments. The cerambycid Apagomerella versicolor exhibits intraspecific geographical variation in host use. In northern Argentina it is highly specialized on the herb Pluchea sagittalis (Asteraceae), while in central and southern areas it uses seven Asteraceae species. To study host species geographical variation from ecological and evolutionary perspectives, we investigated field host availability and use across a wide latitudinal range, and performed laboratory studies on insect oviposition preference and larval performance and mitochondrial DNA (mtDNA) variation in a phylogeographical framework. Geographic variation in host use was unrelated to host availability but was highly associated with laboratory oviposition preference, larval performance, and mtDNA variation. Genetic studies revealed three geographic races of A. versicolor with gene flow restriction and recent geographic expansion. Trophic generalism and oligophagy within A. versicolor seem to have evolved as adaptations to seasonal and spatial unavailability of the preferred host P. sagittalis in cooler areas of the species’ geographic range. No single genotype is successful in all environments; specialization may be advantageous in environments with uniform temporal and spatial host availability, while being a trophic generalist may provide an adaptive advantage in host-constrained environments.     

Contribution of oribatid and mesostigmatid soil mites in ecologically based estimates of global species richness

Erwin’s method for estimating total global species richness assumes some host‐specificity among the canopy arthropods. This study examined possible host habitat specialization in two major groups of soil arthropods, the oribatid and mesostigmatid mites, by sampling beneath three tree species: Eucalyptus pilularis Smith, Eucalyptus propinqua Deane and Maiden and Allocasuarina torulosa (Aiton) L. Johnson. The sample sites were in the Lansdowne State Forest, New South Wales, Australia and the three tree species were selected on the basis of their known differential effects on soil. Sampling was conducted over three seasons, and 79 oribatid and 34 mesostigmatid species were identified from 25 196 and 3634 individuals, respectively. Tree species had little effect on mite species composition with only three oribatid species and no mesostigmatid species identified as host‐habitat specialists using a niche breadth measure. Of mite species found under E. pilularis, E. propinqua and A. torulosa trees, 2%, 1% and 0% were defined as host‐habitat specialists, respectively. In contrast, tree species had significant and consistent effects on mite community structure, which differed in relative abundance of the oribatid species, their size class distributions and species rankings. In the mesostigmatid communities, there was a difference in the ranking of the mite species among tree species. Although it was demonstrated that tree species have an impact on the soil environment, the differences between tree species were insufficient to change species composition. The low degree of host‐habitat specialization suggested that other factors were more important for determining mite species composition at a site, and soil mite host‐habitat specialization may not make a large contribution to estimates of total global species richness using methods such as those proposed by Erwin (1982) .     

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

Investigations 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.     

Oviposition specificity and behavior of the watermilfoil specialist Euhrychiopsis lecontei

Eurasian watermilfoil (Myriophyllum spicatum L.) is a nuisance aquatic weed, exotic to North America. The freshwater weevil Euhrychiopsis lecontei (Dietz) is a potential control agent of Eurasian watermilfoil and is a fully submersed aquatic specialist herbivore. Its presumed original host is the native northern watermilfoil (Myriophyllum sibiricum Komarov). We conducted a set of oviposition experiments to reveal first and second oviposition preference of Euhrychiopsis lecontei when presented with seven macrophytes. We tested differences between source (lake) populations of weevils, differences in behavior between weevils reared on the exotic Eurasian watermilfoil and the native northern watermilfoil and between weevils in the presence and absence of their preferred hostplant. Oviposition assays confirmed that E. lecontei is a watermilfoil specialist. Out of the 207 females that laid eggs, only three oviposited on a non-watermilfoil plant, Megalodonta beckii. The weevils' degree of specificity was influenced by the watermilfoil species on which they were reared. Weevils reared on Eurasian watermilfoil tended to oviposit on Eurasian watermilfoil, spent more time on Eurasian watermilfoil than on other plants, and spent more time off plants and took longer to oviposit when Eurasian watermilfoil was removed. Weevils reared on northern watermilfoil did not exhibit a preference for either watermilfoil species in oviposition or in time allocation, although they oviposited on and spent significantly more time on watermilfoils than on other species. Rearing of the two populations on their complementary watermilfoil hostplant resulted in responses typical of the rearing plant, not the original host. These results show that although both weevil populations are watermilfoil specialists, Eurasian-reared weevils prefer Eurasian watermilfoil in general host attraction and oviposition, whereas northern-reared weevils do not. The results support the contention that E. lecontei may be a good biocontrol agent for Eurasian watermilfoil because of its high specificity. The results also suggest that the current host range expansion of the weevil to Eurasian watermilfoil has the potential to become a host shift due to the increased specificity. Herbivory in freshwater systems is not well studied, and the E. lecontei-M. spicatum relationship is a rare example of submersed freshwater specialist herbivore-host-plant interactions.     

Specialized host-plant performance of the cotton aphid is altered by experience

Although distinct host specialization is observed for the cotton-melon aphid (Aphis gossypii Glover) on cotton and cucurbit plants, it is still ambiguous whether the specialization is altered by experience on a novel host plant. Here the performance of cotton and cucurbit-specialized aphids, A. gossypii on novel host plants was studied by a host-selection test and by the life-table method. The two host-specialized aphids cannot survive and establish populations after reciprocal host transfers. They have ability to recognize the host plants on which they were reared, and escape behavior from novel hosts was observed. Interestingly, the cotton and cucurbit-specialized aphids survive and reproduce normally on hibiscus (Hibiscus syriacus), a main overwintering host plant, and host-fidelity of A. gossypii to cucurbit plants is altered by feeding and living experience on hibiscus, which confers the same capacity to use cotton and cucumber on to the cucurbit-specialized population, but host-fidelity to cotton is not altered and the fitness of the cotton specialized population to cucumber is still poorer. A. gossypii from hibiscus has a significant preference for cotton to cucumber in the host-selection process, and none stays on cucumber more than 20 h after transfer. The results presented imply that cucurbit-specialized aphids might not return to an overwintering host plant (hibiscus) in wild fields, so host conservatism to cucurbit plants is maintained. The potential of cucurbit-specialized aphids of A. gossypii to use cotton plants, intermediated by experience on hibiscus, suggests that the specialized host-plant performance of phytophagous insects is not wholly conservative.