Phenological matching rather than genetic variation in host preference underlies geographical variation in host plants used by orange tip butterflies

An insect species that shows variation in host species association across its geographical range may do so either because of local adaptation in host plant preference of the insect or through environmentally or genetically induced differences in the plants, causing variation in host plant suitability between regions. In the present study, we experimentally investigate the host plant preference of Anthocharis cardamines (orange tip butterfly) in two populations from the UK and two from Sweden. Previous reports indicate that A. cardamines larvae are found on different host plant species in different regions of the UK, and some variation has been reported in Sweden. Host plant choice trials showed that females prefer to oviposit on plants in an earlier phenological stage, as well as on larger plants. When controlling for plant phenological stage and size, the host species had no statistically significant effect on the choice of the females. Moreover, there were no differences in host plant species preference among the four butterfly populations. Based on our experiment, the oviposition choice by A. cardamines mainly depends on the phenological stage and the size of the host plant. This finding supports the idea that the geographical patterns of host–plant association of A. cardamines in the UK and Sweden are consequences of the phenology and availability of the local hosts, rather than regional genetic differences in the host species preference of the butterfly.     

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.     

Natal origin affects host preference and larval performance relationships in a tritrophic system

Many insects face the challenge to select oviposition sites in heterogeneous environments where biotic and abiotic factors can change over time. One way to deal with this complexity is to use sensory experiences made during developmental stages to locate similar habitats or hosts in which larval development can be maximized. While various studies have investigated oviposition preference and larval performance relationships in insects, they have largely overlooked that sensory experiences made during the larval stage can affect such relationships. We addressed this issue by determining the role of natal experience on oviposition preference and larval performance relationships in a tritrophic system consisting of Galerucella sagittariae, feeding on the two host plants Potentilla palustris and Lysimachia thyrsiflora, and its larval parasitoid Asecodes lucens. We firstly determined whether differences in host‐derived olfactory information could lead to divergent host selection, and secondly, whether host preference could result in higher larval performance based on the natal origin of the insects. Our results showed that the natal origin and the quality of the current host are both important aspects in oviposition preference and larval performance relationships. While we found a positive relationship between preference and performance for natal Lysimachia beetles, natal Potentilla larvae showed no such relationship and developed better on L. thyrsiflora. Additionally, the host selection by the parasitoid was mainly affected by the natal origin, while its performance was higher on Lysimachia larvae. With this study, we showed that the relationship between oviposition preference and larval performance depends on the interplay between the natal origin of the female and the quality of the current host. However, without incorporating the full tritrophic context of these interactions, their implication in insect fitness and potential adaptation cannot be fully understood.     

Trichobaris weevils distinguish amongst toxic host plants by sensing volatiles that do not affect larval performance

Herbivorous insects use plant metabolites to inform their host plant selection for oviposition. These host‐selection behaviours are often consistent with the preference–performance hypothesis; females oviposit on hosts that maximize the performance of their offspring. However, the metabolites used for these oviposition choices and those responsible for differences in offspring performance remain unknown for ecologically relevant interactions. Here, we examined the host‐selection behaviours of two sympatric weevils, the Datura (Trichobaris compacta) and tobacco (T. mucorea) weevils in field and glasshouse experiments with transgenic host plants specifically altered in different components of their secondary metabolism. Adult females of both species strongly preferred to feed on D. wrightii rather than on N. attenuata leaves, but T. mucorea preferred to oviposit on N. attenuata, while T. compacta oviposited only on D. wrightii. These oviposition behaviours increased offspring performance: T. compacta larvae only survived in D. wrightii stems and T. mucorea larvae survived better in N. attenuata than in D. wrightii stems. Choice assays with nicotine‐free, JA‐impaired, and sesquiterpene‐over‐produced isogenic N. attenuata plants revealed that although half of the T. compacta larvae survived in nicotine‐free N. attenuata lines, nicotine did not influence the oviposition behaviours of both the nicotine‐adapted and nicotine‐sensitive species. JA‐induced sesquiterpene volatiles are key compounds influencing T. mucorea females’ oviposition choices, but these sesquiterpenes had no effect on larval performance. We conclude that adult females are able to choose the best host plant for their offspring and use chemicals different from those that influence larval performance to inform their oviposition decisions.     

Insect oviposition preference between Epichloë‐symbiotic and Epichloë‐free grasses does not necessarily reflect larval performance

Variation in plant communities is likely to modulate the feeding and oviposition behavior of herbivorous insects, and plant‐associated microbes are largely ignored in this context. Here, we take into account that insects feeding on grasses commonly encounter systemic and vertically transmitted (via seeds) fungal Epichloë endophytes, which are regarded as defensive grass mutualists. Defensive mutualism is primarily attributable to alkaloids of fungal origin. To study the effects of Epichloë on insect behavior and performance, we selected wild tall fescue (Festuca arundinacea) and red fescue (Festuca rubra) as grass–endophyte models. The plants used either harbored the systemic endophyte (E+) or were endophyte‐free (E?). As a model herbivore, we selected the Coenonympha hero butterfly feeding on grasses as larvae. We examined both oviposition and feeding preferences of the herbivore as well as larval performance in relation to the presence of Epichloë endophytes in the plants. Our findings did not clearly support the female's oviposition preference to reflect the performance of her offspring. First, the preference responses depended greatly on the grass–endophyte symbiotum. In F. arundinacea, C. hero females preferred E+ individuals in oviposition‐choice tests, whereas in F. rubra, the endophytes may decrease exploitation, as both C. hero adults and larvae preferred E? grasses. Second, the endophytes had no effect on larval performance. Overall, F. arundinacea was an inferior host for C. hero larvae. However, the attraction of C. hero females to E+ may not be maladaptive if these plants constitute a favorable oviposition substrate for reasons other than the plants' nutritional quality. For example, rougher surface of E+ plant may physically facilitate the attachment of eggs, or the plants offer greater protection from natural enemies. Our results highlight the importance of considering the preference of herbivorous insects in studies involving the endophyte‐symbiotic grasses as host plants.     

Host plant preference and offspring performance of a leaf‐mining moth,Caloptilia fraxinella,on two Fraxinus species

The preference‐performance or ‘mother‐knows‐best’ hypothesis states that female insects choose to oviposit on a host plant that increases the performance of their offspring. This positive link between host plant choice and larval performance is especially important for leaf miners with non‐motile larvae that are entirely dependent upon the oviposition choice of the female for host plant location. Preference and performance of the ash leaf coneroller, Caloptilia fraxinella (Ely) (Lepidoptera: Gracillariidae), a specialist on ash trees, Fraxinus spp. (Oleaceae), were tested in a series of laboratory and field experiments. Female C. fraxinella were exposed to two closely related hosts, black ash, Fraxinus nigra Marshall, and green ash, Fraxinus pennsylvanica Marshall var. subintegerrima (Vahl), in oviposition choice and wind tunnel flight experiments to determine which host is most attractive for oviposition. Caloptilia fraxinella females were inconsistent in host choice, yet performance of larvae was greater on green than black ash. In preference studies, C. fraxinella preferred to oviposit on black ash when leaflets were removed from the tree, but preferred intact green ash over black ash seedlings for oviposition and host location in a wind tunnel. In the field, however, more C. fraxinella visited black ash var. ‘Fallgold’ at leaf flush than green ash at the same sites. Age of the ash leaflet also influences oviposition in this leaf miner and females preferred new over old leaflets for oviposition. Performance of C. fraxinella larvae was evaluated in field and laboratory experiments and was greater on green ash than on black ash in both experiments based on larval survival and development time parameters. The stronger oviposition and host location preference in the field for black ash were not linked to enhanced performance of offspring, as green ash was the superior host, supporting higher larval survival and faster development. A stronger host location preference in the wind tunnel for green ash over black ash, however, suggests that under certain circumstances with this moth species, ‘mother (may) know best’.     

Spatial analysis of Listronotus maculicollis immature stages demonstrates strong associations with conspecifics and turfgrass damage but not with optimal hosts on golf course fairways

For insects that develop on few hosts and/or have immobile immature stages, optimal oviposition theory suggests that females should seek high‐quality hosts that maximize larval development and reduce competition from conspecifics. However, there is a growing amount of evidence that suggests female choice may often be at odds with their offspring's development. Listronotus maculicollis (Kirby) (Coleoptera: Curculionidae) is a serious pest of golf course turfgrass in eastern North America. The weevil develops on few hosts and demonstrates improved fitness traits when developing on Poa annua L. (Poaceae). However, previous population studies observed either weak or no correlations between the spatial dispersion of larval populations and P. annua in the field. In this study, populations on three golf course fairways were monitored over a 4‐year period (2009–2012) to determine whether the lack of spatial associations between preferred hosts and immatures was a result of spatial scale or the density and distribution of conspecifics. Spatial Analysis by Distance IndicEs (SADIE) was used to characterize the spatial dispersion of populations of individual stages (larvae and pupae), P. annua, and turfgrass damage. Life stages were aggregated in each observation, independent of population density or the spatial dispersion of hosts. The distribution of consecutive and non‐consecutive immature stages was found to be correlated in all years, suggesting that females do not avoid patches already occupied by conspecific eggs. Surprisingly, significant spatial associations were not found between larvae and P. annua when the host plant was relatively abundant. Hence, multiple mechanisms may drive L. maculicollis oviposition site‐selection behavior, and a flexible strategy may allow the weevil to persist in areas where P. annua is not the dominant species. Future studies are required to determine what other factors (e.g., natural enemy‐free space, egg or time limitations) influence oviposition behavior.     

Sex‐biased oviposition by a nursery pollinator on a gynodioecious host plant: Implications for breeding system evolution and evolution of mutualism

Dioecy, a breeding system where individual plants are exclusively male or female, has evolved repeatedly. Extensive theory describes when dioecy should arise from hermaphroditism, frequently through gynodioecy, where females and hermaphrodites coexist, and when gynodioecy should be stable. Both pollinators and herbivores often prefer the pollen‐bearing sex, with sex‐specific fitness effects that can affect breeding system evolution. Nursery pollination, where adult insects pollinate flowers but their larvae feed on plant reproductive tissues, is a model for understanding mutualism evolution but could also yield insights into plant breeding system evolution. We studied a recently established nursery pollination interaction between native Hadena ectypa moths and introduced gynodioecious Silene vulgaris plants in North America to assess whether oviposition was biased toward females or hermaphrodites, which traits were associated with oviposition, and the effect of oviposition on host plant fitness. Oviposition was hermaphrodite‐biased and associated with deeper flowers and more stems. Sexual dimorphism in flower depth, a trait also associated with oviposition on the native host plant (Silene stellata), explained the hermaphrodite bias. Egg‐receiving plants experienced more fruit predation than plants that received no eggs, but relatively few fruits were lost, and egg receipt did not significantly alter total fruit production at the plant level. Oviposition did not enhance pollination; egg‐receiving flowers usually failed to expand and produce seeds. Together, our results suggest that H. ectypa oviposition does not exert a large fitness cost on host plants, sex‐biased interactions can emerge from preferences developed on a hermaphroditic host species, and new nursery pollination interactions can arise as negative or neutral rather than as mutualistic for the plant.     

Soil nutrient effects on oviposition preference,larval performance,and chemical defense of a specialist insect herbivore

This study examined the effects of increased leaf nitrogen in natural host-plants (Plantago spp.) on female oviposition preference, larval performance, and larval chemical defense of the butterfly Junonia coenia. Increased availability of soil nutrients caused the host-plant’s foliar nitrogen to increase and its chemical defense to decrease. Larval performance did not correlate with increases in foliar nitrogen. Larval growth rate and survival were equivalent across host-plant treatments. However, larvae raised on fertilized host-plants showed concomitant decreases in chemical defense as compared to larvae reared on unfertilized host-plants. Since most butterfly larvae cannot move long distances during their first few instars and are forced to feed upon the plant on which they hatched, J. coenia larval chemical defense is determined, in large part, by female oviposition choice. Female butterflies preferred host-plants with high nitrogen over host-plants with low nitrogen; however, this preference was also mediated by plant chemical defense. Female butterflies preferred more chemically defended host-plants when foliar nitrogen was equivalent between host-plants. J. coenia larvae experience intense predation in the field, especially when larvae are not chemically well defended. Any qualitative or quantitative variation in plant allelochemical defense has fitness consequences on these larvae. Thus, these results indicate that females may be making sub-optimal oviposition decisions under a nutrient-enriched regime, when predators are present. Given the recent increase in fertilizer application and nitrogen deposition on the terrestrial landscape, these interactions between female preference, larval performance, and larval chemical defense may result in long-term changes in population dynamics and persistence of specialist insects.     

Timing of flowering and intensity of attack by a butterfly herbivore in a polyploid herb

Timing of plant development both determines the abiotic conditions that the plant experiences and strongly influences the intensity of interactions with other organisms. Plants and herbivores differ in their response to environmental cues, and spatial and temporal variation in environmental conditions might influence the synchrony between host plants and herbivores, and the intensity of their interactions. We investigated whether differences in first day of flowering among and within 21 populations of the polyploid herb Cardamine pratensis influenced the frequency of oviposition by the butterfly Anthocharis cardamines during four study years. The proportion of plants that became oviposited upon differed among populations, but these differences were not related to mean flowering phenology within the population in any of the four study years. Attack rates in the field were also not correlated with resistance to oviposition estimated under controlled conditions. Within populations, the frequency of butterfly attack was higher in early‐flowering individuals in two of the four study years, while there was no significant relationship in the other 2 years. Larger plants were more likely to become oviposited upon in all 4 years. The effects of first flowering day and size on the frequency of butterfly attack did not differ among populations. The results suggest that differences in attack intensities among populations are driven mainly by differences in the environmental context of populations while mean differences in plant traits play a minor role. The fact that within populations timing of flowering influenced the frequency of herbivore attack only in some years and suggests that herbivore‐mediated selection on plant phenology differs among years, possibly because plants and herbivores respond differently to environmental cues.     

Innate preference hierarchies coupled with adult experience,rather than larval imprinting or transgenerational acclimation,determine host plant use in Pieris rapae

The evolution of host range drives diversification in phytophagous insects, and understanding the female oviposition choices is pivotal for understanding host specialization. One controversial mechanism for female host choice is Hopkins’ host selection principle, where females are predicted to increase their preference for the host species they were feeding upon as larvae. A recent hypothesis posits that such larval imprinting is especially adaptive in combination with anticipatory transgenerational acclimation, so that females both allocate and adapt their offspring to their future host. We study the butterfly Pieris rapae, for which previous evidence suggests that females prefer to oviposit on host individuals of similar nitrogen content as the plant they were feeding upon as larvae, and where the offspring show higher performance on the mother's host type. We test the hypothesis that larval experience and anticipatory transgenerational effects influence female host plant acceptance (no‐choice) and preference (choice) of two host plant species (Barbarea vulgaris and Berteroa incana) of varying nitrogen content. We then test the offspring performance on these hosts. We found no evidence of larval imprinting affecting female decision‐making during oviposition, but that an adult female experience of egg laying in no‐choice trials on the less‐preferred host Be. incana slightly increased the P. rapae propensity to oviposit on Be. incana in subsequent choice trials. We found no transgenerational effects on female host acceptance or preference, but negative transgenerational effects on larval performance, because the offspring of P. rapae females that had developed on Be. incana as larvae grew slower on both hosts, and especially on Be. incana. Our results suggest that among host species, preferences are guided by hard‐wired preference hierarchies linked to species‐specific host traits and less affected by larval experience or transgenerational effects, which may be more important for females evaluating different host individuals of the same species.     

Oviposition site preference and developmental performance of a gall‐inducing leafhopper on galled and non‐galled host plants

Oviposition preferences of herbivorous insects affect offspring performance. Both positive and negative links between oviposition preference and offspring performance have been reported for many species. A gall‐inducing leafhopper, Cicadulina bipunctata Melichar (Hemiptera: Cicadellidae), feeds on various Poaceae plants and induces galls of enhanced nutritional value for their offspring. Although gall induction by C. bipunctata improves nymphal performance, the oviposition preference of females between galled and non‐galled host plants is still unclear. In this paper, the nymphal performance and oviposition and feeding‐site preference of C. bipunctata were investigated using galled wheat, Triticum aestivum L., and non‐galled barley, Hordeum vulgare L., as host plants. The survival rate of C. bipunctata on wheat was significantly higher than on barley. In the choice test, significantly more eggs were laid into barley, whereas the number of eggs deposited on both hosts was not significantly different in the no‐choice test. The number of settling individuals per leaf area was not significantly different between wheat and barley, suggesting no clear preference for oviposition between these plants. Experience as a nymph with a growing host did not affect oviposition preference as adult female. The inconsistent correspondence between offspring performance and oviposition preference of C. bipunctata may reflect the high mobility of nymphs and/or differences in leaf area between host plants. The results indicate that the previous finding that oviposition preference and offspring performance are not always positively correlated in herbivorous insects is applicable to gall‐inducing insects.     

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.     

Maintenance of body‐size variation and host range in the orange‐tip butterfly: evidence for a trade‐off between adult life‐history traits

1. The evolution of host range and preference in phytophagous insects is driven by a female's oviposition choice impacting her offspring's fitness. Analysis of the fitness of progeny on different host plants has commonly been restricted to the performance of immature stages. However, since host use can affect adult size, it is important to measure the ongoing effects of host choice on the resulting imagines. 2. The orange‐tip butterfly, Anthocharis cardamines, shows a strong preference for two host plants in Britain, Alliaria petiolata and Cardamine pratensis, which affect body size. Whilst females exhibit a strong positive size–fecundity relation, the impact of body‐size alteration is unknown in males. In this study, fitness effects of host plant choice for male A. cardamines were examined. 3. Males reared on C. pratensis were smaller and emerged earlier than those reared on A. petiolata, and early‐season males were smaller than late‐season ones in the field. Interestingly, regression analysis indicated that the earlier emergence of small males was a host‐mediated rather than a size‐mediated effect. Small size was associated with reduced male dispersal in a semi‐isolated wild population over a 3‐year period. 4. It is proposed that the earlier emergence associated with C. pratensis has evolved in response to depressed dispersal in isolated/semi‐isolated populations associated with this patchily distributed host. We suggest that adult life‐history traits are important for the maintenance of host range in this species, and offer a critique of Courtney's earlier hypothesis that host range is maintained by time‐limited oviposition behaviour.     

Host plant conspicuousness and the distribution of eggs and larvae in the butterfly,Anthocharis scolymus (Lepidoptera: Pieridae)

We investigated how the distribution pattern of eggs and larval on the host plant, Turritus glabra, was influenced by the oviposition behavior of the pierid butterfly Anthocharis scolymus. Females searched for the host plants visually and they frequently approached taller host plants with sparse surrounding vegetation. After encountering host plants, oviposition behavior of females was independent of host plant characteristics such as height, density, and type of surrounding vegetation. A female laid eggs singly on a host plants. Most females appeared to lay their eggs regardless of the presense of eggs on the host plant. Consequently egg and larva tended to be abundant on conspicuous host plants as measured by height or relative isolation from other plants. However, overcrowding of eggs on an individual host decreased the survival rate of larvae.     

Comparison of larval performance and oviposition preference of Spodoptera frugiperda among three host plants: Potential risks to potato and tobacco crops

Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is a major polyphagous pest with the potential to seriously damage various crops. A better understanding of FAW's performance on different hosts may help to predict which plants will be attacked when the preferred host is absent, and facilitate the development of effective pest management practices. We compared the larval performance of FAW fed on maize with that of FAW fed on potato and tobacco, which are important crops in China, using an age-stage two-sex life table and adult female oviposition preference experiments. In cage experiments with potato, tobacco, or maize as the host, FAW reared on maize exhibited the strongest performance with shorter developmental time in the larval stage, longer longevity, and a higher reproductive rate in adults. Females oviposited on maize in preference to potato or tobacco. Compared with larvae fed on maize, those fed on potato and tobacco exhibited significantly lower survival, with only 31.61% and 8.13% developing to the adult stage, respectively. Several life table parameters, including the mean generation time (T), net reproductive rate (R₀), finite rate of increase (λ), and intrinsic rate of natural increase (r) were negatively affected in FAW fed on potato and tobacco. Our results support the preference–performance hypothesis, that is, that herbivore females maximize fitness by choosing host plants associated with strong larval performance. Although larvae and adults performed poorly on potato and tobacco, their offspring will be capable of establishing populations on them, posing a potential threat to these crops in China.     

Escaping an evolutionary trap: preference and performance of a native insect on an exotic invasive host

Exotic plants may act as population sinks or evolutionary traps for native herbivores. The native butterfly Pieris oleracea lays eggs on garlic mustard, Alliaria petiolata, but larvae develop very poorly on this exotic invasive plant. We examined oviposition preference of individual females and larval performance of their offspring for individuals from one area where garlic mustard is well established and one where it is absent. These data were used to assess whether garlic mustard is being incorporated into or excluded from the diet. Females from the area without garlic mustard showed a wide range of preference, families had low larval survival on garlic mustard, and larval survivorship showed no correlation with mothers’ preferences. Females from the area with garlic mustard preferred it to the native host, and larval survivorship on garlic mustard was positively correlated with the mother’s preference. Individuals surviving on garlic mustard took longer to pupate and weighed >30% less compared to pupae reared on normal hosts. Our results suggest that where garlic mustard is well established P. oleracea may be adapting to this plant by both improved larval performance and increased adult female oviposition preference for it.     

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.     

Trade-offs of host use between generalist and specialist <Emphasis Type="Italic">Helicoverpa</Emphasis> sibling species: adult oviposition and larval performance

Much attention has been paid to the question of the relative importance of female behaviour versus larval feeding capacities in determining the host range of herbivorous insects. Host-use trade-offs displayed by generalist and specialist sister species of the genus Helicoverpa were evaluated to examine the relationship between maternal choice and offspring performance. The prediction of optimal oviposition theory, that females will choose to lay eggs on plants on which their offspring perform best as larvae, was tested by measuring oviposition preference and larval performance of Helicoverpa armigera and H. assulta on tobacco, sunflower, and hot pepper. These two measures were more highly correlated in the specialist H. assulta. Both species exhibited the same oviposition preference ranking: tobacco > sunflower > hot pepper. H. armigera larvae preferred sunflower, followed by tobacco and hot pepper; while H. assulta larvae preferred tobacco to sunflower and hot pepper, consistent with their mothers’ oviposition preference. Duration of the total period from egg to adult emergence for each species was significantly shorter on the host plant preferred by the larvae. H. assulta had shorter larval duration and higher relative growth rate than H. armigera on tobacco and hot pepper, and vice versa for sunflower, indicating species differences in host utilization. Thus, while only the specialist H. assulta displayed the predicted optimal oviposition pattern, females of both species show the least preference for the plant on which their offspring perform worst. Selection for optimal oviposition may be stronger on the specialist, which has fewer choices and lower lifetime fecundity than the generalist.