Oviposition Acceptance Research Articles

Oviposition behaviour in Drosophila melanogaster: Genetic and behavioural decoupling between oviposition acceptance and preference for natural fruits.

In phytophagous insects, oviposition behaviour is an important component of habitat selection and, given the multiplicity of genetic and environmental factors affecting its expression, is defined as a complex character resulting from the sum of interdependent traits. Here, we study two components of egg-laying behaviour: oviposition acceptance (OA) and oviposition preference (OP) in Drosophila melanogaster using three natural fruits as resources (grape, tomato and orange) by means of no-choice and two-choice experiments, respectively. This experimental design allowed us to show that the results obtained in two-choice assays (OP) cannot be accounted for by those resulting from no-choice assays (OA). Since the genomes of all lines used are completely sequenced, we perform a genome-wide association study to identify and characterize the genetic underpinnings of these oviposition behaviour traits. The analyses revealed different candidate genes affecting natural genetic variation of both OA and OP traits. Moreover, our results suggest behavioural and genetic decoupling between OA and OP and that egg-laying behaviour is plastic and context-dependent. Such independence in the genetic architectures of OA and OP variation may influence different aspects of oviposition behaviour, including plasticity, canalization, host shift and maintenance of genetic variability, which contributes to the adoption of adaptive strategies during habitat selection.

Plant Acceptance for Oviposition of Tetranychus urticae on Strawberry Leaves Is Influenced by Aromatic Plants in Laboratory and Greenhouse Intercropping Experiments

The objective was to evaluate aromatic plants’ effects on the acceptance, preference, egg load, and life span of females of the twospotted spider mite (TSSM) in laboratory experiments and TSSM population under aromatic plants’ intercropping in greenhouse experiments. The pseudofruits production was also evaluated. For the laboratory, basil’s, Chinese chives’, chives’, and garlic’s influence on TSSM were tested on strawberry leaves. Four laboratory experiments were conducted: (1) Multiple choice test; (2) T-shaped arena test; (3) host–plant acceptance on aromatic plant or strawberry leaves; and (4) performance of TSSMs on strawberry leaves under aromatic plant influence. For the greenhouse experiments, assessments of the TSSM populations were realized by observing TSSM with a 10× magnifying glass on strawberry leaves in a monocrop or intercropped with Chinese chives, chives, garlic, or onion. Pseudofruit production was evaluated. Our results show that strawberry leaves were strongly preferred by TSSM. The T-shaped arena test revealed that all aromatic plants repel the TSSM. The test with the performance of TSSM females revealed that aromatic plants affected the mite’s biological parameters. Chinese chives reduced the number of eggs laid per day by 33.22%, whereas garlic reduced the number by 17.30% and chives reduced it by 12.46%. The total number of eggs was reduced by 34.79% with Chinese chives and 25.65% with garlic. Greenhouse experiments showed that chives reduced TSSM populations on two cycles and Chinese chives and garlic reduced TSSM populations on the first cycle only. With our findings, we suggest that Chinese chives, chives, and garlic are the primary candidates for intercropping use against TSSM. Chinese chives and garlic reduced the total number of eggs, but only garlic reduced female mite longevity. However, none of the intercropping plants improved strawberry pseudofruit production.

Components of Cowpea Resistance to the Seed Beetle Callosobruchus maculatus (Coleoptera: Chrysomelidae: Bruchinae).

Cowpea, Vigna unguiculata (L.) Walp., serves as a major source of dietary protein in many tropical and subtropical regions around the world. To identify loci associated with agronomically desirable traits, eight elite cowpea cultivars were systematically inter-crossed for eight generations to yield 305 recombinant inbred lines. Here, we investigated whether these founder parents also possess resistance to the seed beetle Callosobruchus maculatus (F.), a highly destructive post-harvest pest. We estimated larval survival in seeds, egg-to-adult development time, adult mass at emergence, and seed acceptance for oviposition. Survival varied significantly among cowpea cultivars, but the pattern was complicated by an unexpected source of mortality; on three cultivars, mature larvae in a substantial fraction of seeds (20-36%) exited seeds prematurely, and consequently failed to molt into viable adults. Even if such seeds were eliminated from the analysis, survival in the remaining seeds varied from 49 to 92% across the eight parents. Development time and body mass also differed among hosts, with particularly slow larval development on three closely related cultivars. Egg-laying females readily accepted all cultivars except one with a moderately rugose seed coat. Overall, suitability ranks of the eight cultivars depended on beetle trait; a cultivar that received the most eggs (IT82E-18) also conferred low survival. However, one cultivar (IT93K-503-1) was a relatively poor host for all traits. Given the magnitude of variation among parental cultivars, future assays of genotyped recombinant progeny can identify genomic regions and candidate genes associated with resistance to seed beetles.

Geographic variation of host preference by the invasive tomato leaf miner Tuta absoluta: implications for host range expansion

Host range evolution is a central issue for pest management, particularly for invasive species of agricultural importance. The invasive tomato leaf miner, Tuta absoluta Meyrick (Lepidoptera: Gelechiidae), a key pest of tomato in Europe and recently in sub-Saharan Africa, is a good model organism to better understand underlying processes. We studied oviposition acceptance (proportion of females accepting a given plant as host for laying egg), oviposition preference (number of eggs laid by females on a given host plant) and performance (offspring development estimated as survival from egg to adult) of two T. absoluta populations originating from France (FRA) and Senegal (SEN) on six solanaceous plants (tomato, eggplant, Ethiopian eggplant, potato, sweet pepper and pepper). The ovipositional behavioral pattern differed between the two populations; the SEN population showed higher oviposition acceptance on Ethiopian eggplant and sweet pepper than the FRA population. In addition, SEN population showed higher oviposition preference toward sweet pepper and potato than the FRA population. By contrast, the FRA population showed higher preference toward tomato and eggplant than the SEN population. The two populations of T. absoluta performed best on tomato (the preferred host plant) and showed similar decreasing trend in performance when comparing the two populations on the various other host plants. For both populations, performance on solanaceous plant species was closely related to ovipositional response of females to these plants. The differences observed between the two populations may indicate an ongoing differentiation in the host range of T. absoluta in the two invaded areas, possibly due to the abundance of these alternative host crops in Senegal at a period when tomato crops are scarce.

α-Amylase Mediates Host Acceptance in the Braconid Parasitoid Cotesia flavipes

Foraging parasitoids use chemical signals in host recognition and selection processes. Although, the volatiles play a relevant role in the localization by parasitoids of their hosts feeding on plants, the host identification process for acceptance occurs mainly during contact between the parasitoid and its host where host products related to feeding activities, fecal pellets and oral secretions, play a crucial role. The purpose of this study was to identify the nature of the contact kairomone(s) that mediate the acceptance for oviposition of the parasitoid Cotesia flavipes Cameron (Hymenoptera, Braconidae), which was released in Kenya in 1993 to control the invasive crambid Chilo partellus (Swinhoe). Using host and non-hosts of C. flavipes, we showed that it is mainly the oral secretions of the larvae that harbour the active compound(s) that mediate host acceptance for oviposition by C. flavipes. Using an integration of behavioral observations and biochemical approaches, the active compound of the oral secretions was identified as an α-amylase. Using synthetized α-amylases from Drosophila melanogaster (an insect model for which syntheses of active and inactive α-amylases are available), we observed that the conformation of the enzyme rather than its catalytic site as well as its substrate and its degradation product is responsible for host acceptance and oviposition mediation of C. flavipes females. The results suggest that the α-amylase from oral secretions of the caterpillar host is a good candidate for an evolutionary solution to host acceptance for oviposition in C. flavipes.

Evaluation of nine genotypes of oilseed rape (Brassica napus L.) for larval infestation and performance of rape stem weevil (Ceutorhynchus napi Gyll.).

The rape stem weevil, Ceutorhynchus napi Gyll., is a serious pest of winter oilseed rape (Brassica napus L.) crops in Europe causing severe yield loss. In currently used oilseed rape cultivars no resistance to C. napi has been identified. Resynthesized lines of B. napus have potential to broaden the genetic variability and may improve resistance to insect pests. In this study, the susceptibility to C. napi of three cultivars, one breeding line and five resynthesized lines of oilseed rape was compared in a semi-field plot experiment under multi-choice conditions. Plant acceptance for oviposition was estimated by counting the number of C. napi larvae in stems. The larval instar index and the dry body mass were assessed as indicators of larval performance. The extent of larval feeding within stems was determined by the stem injury coefficient. Morphological stem traits and stem contents of glucosinolates were assessed as potential mediators of resistance. The resynthesized line S30 had significantly fewer larvae than the cultivars Express617 and Visby and the resynthesized lines L122 and L16. The low level of larval infestation in S30 was associated with a low larval instar and stem injury index. Low numbers of larvae were not correlated with the length or diameter of stems, and the level of stem glucosinolates. As indicated by the low larval infestation and slow larval development the resistance of S30 to C. napi is based on both antixenotic and antibiotic properties of the genotypes. The resynthesized line S30 should therefore be introduced into B. napus breeding programs to enhance resistance against C. napi.

A Bird in the Hand Versus Two in the Bush? The Specialist Leafhopper Dalbulus maidis (Hemiptera: Cicadellidae) Does Not Discriminate Against Sub-optimal Host Plants (Zea spp.).

The corn leafhopper [Dalbulus maidis (DeLong & Wolcott)] is a specialist on Zea (Poaceae) that coevolved with maize (Zea mays mays) and its teosinte (Zea spp.) relatives. This study tested the hypothesis that host acceptance by females varies among Zea hosts, and is correlated with variation in defensive levels across those hosts. Prior studies revealed differences in plant defenses among Zea hosts and corresponding differences in corn leafhopper performance. Thus, host acceptance was expected to be correlated with defensive levels and offspring performance across Zea hosts, following the hypothesis that offspring performance mediates host preference. In parallel, host acceptance was expected to be correlated with transitions in life history strategy (perennial to annual life cycle), domestication status (wild to domesticated), and breeding intensity (landrace to hybrid variety) in Zea because variation in defensive levels and corn leafhopper performance were shown in prior studies to be correlated with those transitions. The study's hypotheses were tested by comparing, under no-choice conditions, host acceptance by corn leafhopper of a suite of Zea hosts encompassing those transitions: perennial teosinte (Zea diploperennis), Balsas teosinte (Zea mays parviglumis), and landrace and commercial hybrid maize. The results did not show differences in host acceptance for oviposition or feeding among the hosts. Thus, under no-choice conditions, all Zea hosts may be similarly acceptable for feeding and oviposition, despite marked ovipositional preferences under choice conditions and poorer offspring performance on teosintes relative to maize shown previously. The results suggested also that oviposition frequency per plant by females was not correlated with their offspring's performance.

Both Volatiles and Cuticular Plant Compounds Determine Oviposition of the Willow Sawfly Nematus oligospilus on Leaves of Salix spp. (Salicaceae).

Plant volatile organic compounds play a role in selection of host plants by herbivorous insects. Once the insect reaches the plant, contact cues determine host acceptance. Although the willow sawfly Nematus oligospilus (Hymenoptera: Tenthredinidae) can differentiate among willow genotypes, no knowledge is available on the cues used by this insect to seek and accept the host plant. In this study, we recorded behavioral orientation in a Y-tube olfactometer of willow sawfly females to volatiles of the highly preferred genotype Salix nigra and the non-preferred genotype S. viminalis. The volatiles released by undamaged willows of each genotype were analyzed by coupled gas chromatography-mass spectrometry. Contact cues were evaluated first by oviposition preference bioassays after selective leaf wax removal, and then by studying the micromorphology of abaxial and adaxial leaf surfaces and their chemical composition. Willow sawfly females oriented preferentially to S. nigra volatiles, which contained more than 3 times the amount of volatiles than that collected from S. viminalis. Analysis of volatiles showed significant differences in amounts of (Z) and (E)-β-ocimene, undecane, decanal, and β-caryophyllene. The adaxial leaf surface of S. nigra was less preferred after wax removal, suggesting a role of cuticular waxes for oviposition acceptance. No differences were found among the micromorphology of leaf surfaces between preferred and non-preferred genotypes. The chemical analysis of cuticular waxes showed that the abaxial leaf surface of S. viminalis, which is completely avoided for oviposition, possessed 97% of alkanes. The accepted leaf surfaces contained a more diverse wax profile including alcohols, acids, and esters. Thus, non-alkane wax compounds might be related to oviposition. In sum, our study suggests that several cues act in concert to provide oviposition cues for the sawfly N. oligospilus: females are attracted to volatiles from a distance, and once alighting on the plant, they seek specific chemical contact cues in order to lay eggs.

Oviposition acceptance and larval development of Chilo partellus stemborers in drought‐stressed wild and cultivated grasses of East Africa

AbstractMaternal host choices during oviposition by herbivorous insects determine the fitness of their offspring and may be influenced by environmental changes that can alter host‐plant quality. This is of particular relevance to ‘push‐pull’ cropping systems where host preferences are exploited to manage insect pest populations. We tested how drought stress in maize and companion plants that are used in these systems affect oviposition preference, larval feeding, and development of the spotted stemborer, Chilo partellus Swinhoe (Lepidoptera: Crambidae). Five host species were tested (all Poaceae): maize (Zea mays L.), Napier grass (Pennisetum purpureum Schumach), signal grass [Brachiaria brizantha (A. Rich) Stapf], Brachiaria cv. ‘Mulato’, and molasses grass [Melinis minutiflora (Beauv.)]. Under drought stress, maize experienced as much oviposition as control unstressed maize in choice and no‐choice experiments. Similarly, larval leaf damage was not significantly different in drought‐stressed vs. unstressed maize. In contrast, oviposition occurred less on drought‐stressed than on unstressed Napier and signal grass. Oviposition acceptance and leaf damage remained low in both drought‐stressed and unstressed molasses grass and Mulato. Larval survival and development remained high in drought‐stressed maize, but not in Napier, signal, and molasses grass and Mulato, where survival and development were low in both drought‐stressed and unstressed plants. Our results indicate that herbivore responses to drought‐stressed plants depend on the plant species and that drought stress can change host preference and acceptance rankings. In particular, trap‐crops such as Napier grass may not divert oviposition from the main maize crop under drought stress conditions.

What Determines Host Acceptance and Suitability in Tropical AsianDrosophilaparasitoids?

For successful parasitism, parasitoid females must oviposit and the progeny must develop in individual hosts. Here, we investigated the determinants of host acceptance for oviposition and host suitability for larval development of Drosophila parasitoids from Bogor and Kota Kinabalu (≍1,800 km northeast of Bogor), Indonesia, in tropical Asia. Asobara pleuralis (Ashmead) from both localities oviposited frequently (>60%) in all of the drosophilid species tested, except the strain from Kota Kinabalu oviposited rarely (10%) in Drosophila eugracilis Bock & Wheeler. Leptopilina victoriae Nordlander from both localities only oviposited frequently (>77%) in species from the Drosophila melanogaster species group except D. eugracilis (<3.7%), whereas Leptopilina pacifica Novković & Kimura from Bogor oviposited frequently (>85%) only in species from the Drosophila immigrans species group. Thus, host acceptance appeared to be affected by host taxonomy, at least in Leptopilina species. Host suitability varied considerably, even among closely related drosophilid species, which suggests that the host suitability is at least in part independent of host taxonomy and that it has been determined via parasitoid-host coevolutionary interactions (i.e., arms race). Host acceptance did not always coincide with host suitability, i.e., parasitoids sometimes oviposited in unsuitable host species. Geographic origin strongly affected the host acceptance and suitability in the A. pleuralis-D. eugracilis parasitoid-host pair, whereas it only weakly affected the acceptability and suitability in other parasitoid-host combinations.

Host plant choice in the comma butterfly–larval choosiness may ameliorate effects of indiscriminate oviposition

In most phytophagous insects, the larval diet strongly affects future fitness and in species that do not feed on plant parts as adults, larval diet is the main source of nitrogen. In many of these insect-host plant systems, the immature larvae are considered to be fully dependent on the choice of the mothers, who, in turn, possess a highly developed host recognition system. This circumstance allows for a potential mother-offspring conflict, resulting in the female maximizing her fecundity at the expense of larval performance on suboptimal hosts. In two experiments, we aimed to investigate this relationship in the polyphagous comma butterfly, Polygonia c-album, by comparing the relative acceptance of low- and medium-ranked hosts between females and neonate larvae both within individuals between life stages, and between mothers and their offspring. The study shows a variation between females in oviposition acceptance of low-ranked hosts, and that the degree of acceptance in the mothers correlates with the probability of acceptance of the same host in the larvae. We also found a negative relationship between stages within individuals as there was a higher acceptance of lower ranked hosts in females who had abandoned said host as a larva. Notably, however, neonate larvae of the comma butterfly did not unconditionally accept to feed from the least favorable host species even when it was the only food source. Our results suggest the possibility that the disadvantages associated with a generalist oviposition strategy can be decreased by larval participation in host plant choice.

Effect of host plant on bionomic and life history parameters of Anagyrus pseudococci (Hymenoptera: Encyrtidae), a parasitoid of the mango mealybug Rastrococcus iceryoides (Homoptera: Pseudococcidae)

Anagyrus pseudococci Girault is a solitary koinobiont endoparasitoid of several mealybug species. The effect of five host plants (Mangifera indica L., Cucurbita moschata Duchesne, Parkinsonia aculeata L., Cajanus cajan L. and Ficus benjamina Roxb.) on host acceptability for oviposition and suitability for immature development of this parasitoid in the invasive mango mealybug Rastrococcus iceryoides Green were investigated. Effect of host plant on fitness traits (parasitoid size, egg load and longevity) and life table parameters were also assessed. Although A. pseudococci accepted the mealybug regardless of the host plant, the level of acceptability varied significantly. Percentage of parasitized nymphs was higher on C. moschata, followed by P. aculeata and M. indica, while it was lowest on F. benjamina. Host suitability was also strongly affected by the host plant and largely mirrored host acceptability for all the parameters evaluated. Female wasps reared on mealybugs maintained on C. moschata and P. aculeata were bigger and more fecund, while those reared from mealybugs maintained on F. benjamina were of inferior quality with regard to all fitness parameters evaluated. A. pseudococci achieved a greater intrinsic rate of natural increase (rm), net reproductive rate (Ro) and finite rate of increase (λ) on mealybugs maintained on C. moschata and P. aculeata. In addition, the wasp had a shorter mean generation time (G) and population doubling time (Td) on mealybugs maintained on C. moschata. The reverse was true for those maintained on F. benjamina. The findings are discussed in view of improvement of laboratory mass rearing, as well as field enhancement of the parasitoid performance.

Influence of different tropical fruits on biological and behavioral aspects of the Mediterranean fruit fly Ceratitis capitata (Wiedemann) (Diptera, Tephritidae)

Influence of different tropical fruits on biological and behavioral aspects of the Mediterranean fruit fly Ceratitis capitata (Wiedemann) (Diptera, Tephritidae). Studies on Ceratitis capitata, a world fruit pest, can aid the implementation of control programs by determining the plants with higher vulnerability to attacks and plants able to sustain their population in areas of fly distribution. The objective of the present study was to evaluate the influence of eight tropical fruits on the following biological and behavioral parameters of C. capitata: emergence percentage, life cycle duration, adult size, egg production, longevity, fecundity, egg viability, and oviposition acceptance. The fruits tested were: acerola (Malpighia glabra L.), cashew (Anacardium occidentale L.), star fruit (Averrhoa carambola L.), guava (Psidium guajava L.), soursop (Annona muricata L.), yellow mombin (Spondias mombin L.), Malay apple (Syzygium malaccense L.), and umbu (Spondias tuberosa L.). The biological parameters were obtained by rearing the recently hatched larvae on each of the fruit kinds. Acceptance of fruits for oviposition experiment was assessed using no-choice tests, as couples were exposed to two pieces of the same fruit. The best performances were obtained with guava, soursop, and star fruit. Larvae reared on cashew and acerola fruits had regular performances. No adults emerged from yellow mombin, Malay apple, or umbu. Fruit species did not affect adult longevity, female fecundity, or egg viability. Guava, soursop, and acerola were preferred for oviposition, followed by star fruit, Malay apple, cashew, and yellow mombin. Oviposition did not occur on umbu. In general, fruits with better larval development were also more accepted for oviposition.

Oviposition of diamondback moth in the presence and absence of a novel host plant.

The diamondback moth (DBM, Plutella xylostella L. (Lepidoptera: Plutellidae)) consumes a wide variety of brassicaceous host plants and is a common pest of crucifer crops worldwide. A highly unusual infestation of a sugar pea crop was recorded in Kenya in 1999, which persisted for two consecutive years. A strain (DBM-P) from this population was established in the laboratory and is the only one of several strains tested that can complete larval development on sugar peas. The oviposition acceptance and preference of the DBM-P strain was assessed in the presence of cabbage plants, sugar pea plants or both, in comparison to another strain (DBM-Cj) that was collected from cabbage and is unable to grow on pea plants. As expected, DBM-Cj females preferred to oviposit on cabbage plants. Surprisingly, DBM-P females also laid most eggs on cabbage and very few on peas. However, they laid significantly more eggs on the cabbage plant when pea plants were present. Our findings suggest that DBM-P manifested the initial stages of an evolutionary host range expansion, which is incomplete due to lack of oviposition fidelity on pea plants.

Old and new host-parasitoid associations: parasitism of the invasive fruit fly Bactrocera invadens (Diptera: Tephritidae) and five African fruit fly species by Fopius arisanus, an Asian opiine parasitoid

Fopius arisanus (Sonan), a solitary koinobiont endoparasitoid of fruit flies, was introduced for testing and final release against the recently discovered species Bactrocera invadens Drew, Tsuruta and White in Africa. Laboratory experiments were conducted to assess host preference, host acceptability for oviposition, and physiological suitability of B. invadens and five other indigenous tephritid fruit fly species, namely, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), C. cosyra (Walker), C. rosa Karsch, C. fasciventris (Bezzi), and C. anonae Graham. Females of F. arisanus visited all host egg patches, but showed a stronger preference to eggs of B. invadens, which was also most accepted for oviposition. Successful development of parasitoid progenies varied greatly across hosts, with B. invadens yielding the highest parasitoid progeny and C. fasciventris yielding no F. arisanus progeny. Most of the parasitoid eggs laid in C. rosa and C. fasciventris were encapsulated. Sex ratio was not influenced by host species and it was female biased in all hosts that produced parasitoid progeny. Fopius arisanus was able to establish a new association with C. capitata, C. cosyra and to a lesser extent C. anonae. The results are discussed in the light of the potential use of F. arisanus as a biological control agent of B. invadens.

Evaluation of the impact of Diachasmimorpha longicaudata on Bactrocera invadens and five African fruit fly species

Abstract Diachasmimorpha longicaudata (Ashmead), a solitary koinobiont larval–prepupal endoparasitoid of fruit flies, was introduced into Kenya for testing and final release against the recently discovered invasive species, Bactrocera invadens Drew, Tsuruta and White in Africa. Laboratory experiments were conducted to determine host preference, host acceptability for oviposition and physiological suitability of B. invadens and five other indigenous tephritid fruit fly species –Ceratitis capitata (Wiedemann), Ceratitis cosyra (Walker), Ceratitis rosa Karsch, Ceratitis fasciventris (Bezzi) and Ceratitis anonae Graham – for the development of D. longicaudata. Females of D. longicaudata visited all host‐larval patches, and were also attracted to these hosts at comparable levels. Acceptability, successful development of parasitoid progenies and their sex ratio varied widely across hosts. C. capitata yielded the highest parasitoid numbers whereas B. invadens was the only host that yielded a female‐biased sex ratio. Larvae of B. invadens, C. rosa, C. fasciventris and C. anonae mounted differential immune reaction towards D. longicaudata eggs. Although, the parasitoid performed poorly on the target host B. invadens, it was able to form new association with C. cosyra and C. capitata. The prospect of using this parasitoid in biological control of African indigenous fruit flies is discussed.

Performance of Host-Races of the Fruit Fly,Tephritis conuraon a Derived Host Plant, the Cabbage ThistleCirsium oleraceum: Implications for the Original Host Shift

The thistle-infesting fruit fly Tephritis conura Loew (Diptera: Tephritidae) forms host races on the melancholy thistle, Cirsium hetewphyllum (L.) Hill (Asterales: Asteraceae) and the cabbage thistle, Cirsium olemceum (L.). Scop. Previous research indicates that the host shift occurred from C. hetewphyllum to C. oleraceum. In this paper we address whether the host shift involved physiological adaptations by studying oviposition acceptance and survival of the two host races on the derived host C. oleraceum. Performance differed significantly between host races. T. conura originating from C. oleraceum produced adults in 75% of all egg-laying trials in contrast to only 6.6% in T. conura originating from C. hetewphyllum. Population fitness components measured as a function of life-stage was linear decreasing for T. conura on C. oleraceum but stepwise for T. conura on C. heterophyllum. Low performance of T. conura on C. hetewphyllum was determined by low plant acceptance and high mortality during the larval stage, whereas hatching (at least one larva per batch) and pupae survival were not affected.

Influence of fruit traits on the infestation of Dacus persicus in two fruit morphs of Calotropis procera

The larvae of Dacus (Leptoxyda) persicus (aak fruit fly) are key predispersal seed predators in Calotropis procera (Asclepiadaceae). Based on fruit characteristics, two morphs are distinguishable in C. procera viz., the soft-fruited morph (SF morph) and the hard-fruited morph (HF morph). The work reported here examined whether the fruit characteristics influenced the infestation by the aak fruit fly and, if so, what mechanism(s) were operative. Fruits in the SF morph were significantly more acceptable to the aak fruit fly than those of the HF morph irrespective of their size class and availability or fly population density. A general ranking of fruit acceptability for oviposition by the aak fruit fly within the fruit size class was: size class III ≥ size class II > size class I and IV. The negative relationship between fruit infestation and pericarp toughness, which is suggestive of trade-offs between the fly’s oviposition obligation and energy/time (predation risk) constraint, was found to correlate with the requirement of greater force to puncture the pericarp in the hard fruits. Lower penetrability of the pericarp in the hard fruits appeared to be primarily due to the thickness of pericarp and secondarily on account of the thickened walls of endocarpic–mesocarpic cells in the inner pericarpic layer. The present data point to the existence of two fruit morphs in C. procera differing in the acceptability of fruits for oviposition by the aak fruit fly primarily on account of toughness and internal structure of the pericarp.

Importance of plant physical cues in host acceptance for oviposition by Busseola fusca

AbstractPlant and surrogate stems exhibiting specific combinations of physical cues were used to determine which plant‐related stimuli influence the oviposition of Busseola fusca (Fuller) (Lepidoptera: Noctuidae). The number of eggs and egg batches laid per female increased with an increase in diameter of both natural and artificial stems. Direct observations of the oviposition behaviour (walking, antennating, and sweeping with the ovipositor) indicated that the female moths preferred oviposition supports with a large diameter and non‐pubescent or smooth surfaces over pubescent or rough ones. Pubescence and rough surfaces significantly affected the behavioural steps leading to oviposition by interfering with the ovipositor sweep process necessary to find a suitable oviposition site. Furthermore, more eggs and egg batches were laid on soft than rigid supports. The rigidity of the support affected the proper insertion of the ovipositor for egg deposition. Our results underline the importance of physical stimuli in B. fusca's choice of an oviposition site, which may facilitate the identification of potential host plants or preferred oviposition sites on a plant for this species.

Diversification of host use in two polyphagous butterflies: differences in oviposition specificity or host rank hierarchy?

AbstractNovel host usage may represent an initial step towards diversification or radiation onto novel hosts within an evolutionary lineage, particularly if a shift in host plant preference ranking takes place. Polyphagous stages of evolutionary lineages may represent transitional states in which novel host associations are more likely to develop, but may be more difficult to detect experimentally. The polyphagous sister species Papilio glaucus L. and Papilio canadensis (Lepidoptera: Papilionidae; these Papilio = Pterourus) are known to exhibit differences in host‐plant use, despite significant overlap in host‐use abilities, providing an opportunity to examine how host shifts in polyphagous species may occur and what the implications for future divergence may be. In particular, we were interested in (i) determining whether differences in oviposition behavior of these species were due to changes in specificity or shifts in host‐plant hierarchy, (ii) whether the varying preference for primary hosts also affected the preference for secondary hosts, and (iii) what the oviposition preferences of a new hybrid swarm population are. We examined more than 40 000 oviposition bouts from more than 400 P. glaucus, P. canadensis, and hybrid females placed in seven‐, three‐, or two‐choice assays. In each of the choice assays, leaves from plants in different plant families of varying suitability for P. glaucus and P. canadensis larvae were used. We found the primary difference between P. glaucus and P. canadensis to be limited to a Z‐linked shift in host rank hierarchy due to an acceptance of Populus tremuloides Michx. (Salicaceae) and reduced specificity for Liriodendron tulipifera L. (Magnoliaceae) in P. canadensis. In addition, we found the absence of the Z‐linked oviposition acceptance of P. tremuloides in a recently formed allochronically separated hybrid swarm population found in P. canadensis territory at the northern border of the P. glaucus and P. canadensis hybrid zone.