桃红颈天牛成虫的交配行为及对不同寄主植物的栖落和产卵选择性

【目的】桃红颈天牛Aromia bungii是一种钻蛀性害虫,主要以蔷薇科果树和观赏树木为寄主。本研究旨在搞清楚桃红颈天牛成虫的交配产卵行为及其对不同寄主植物的栖落和产卵选择性。【方法】选择苹果Malus pumila、山樱花Prunus serrulata var. spontanea、桃Prunus persica、西府海棠Malus micromalus、毛樱桃Prunus tomentosa、秋子梨Pyrus ussuriensis、杏Prunus armeniaca和红叶李Prunus cerasifera var. atropurea 8种寄主植物木段,构建为成虫的活动场所,观察桃红颈天牛成虫的交配和产卵行为,并测定桃红颈天牛成虫在不同寄主木段上的栖落数量和产卵量。【结果】桃红颈天牛成虫的交配行为分为避让、打斗和交配3种行为。交配过程可分为相遇抱对、插入输精、交配后陪护3个阶段。桃红颈天牛雌虫产卵时无刻槽行为,喜欢将卵产于较为狭窄的缝隙中。雌虫偏好在桃树木段上栖落,雄虫则偏好在毛樱桃木段上栖落。李亚科李属的桃是桃红颈天牛最喜欢的产卵寄主木段,而雌虫在苹果亚科的苹果、海棠和秋子梨木段上产卵极少。相关性分析结果表明雌虫在寄主木段上的栖落数量与产卵量占比间存在正相关性,雄虫在寄主木段上的栖落数量与雌虫在寄主木段上的栖落数量之间也存在正相关性。【结论】桃红颈天牛雌成虫最喜欢桃树木段,雄虫对寄主植物的选择性与雌虫并不完全相同。     

Sex allocation and egg distribution of an autoparasitoid, Encarsia pergandiella (Hymenoptera: Aphelinidae)

Abstract. 1. Encarsia pergandiella Howard females develop as primary parasitoids on immature whiteflies, and males develop as secondary parasitoids on females of their own or a related species. The hypothesis that the sex ratio reflects the relative abundance of the two host types was tested in the laboratory using petri dish arenas with varying proportions of early fourth instar greenhouse whitefly (Trialeurodes vaporariorum (West.)) (primary hosts) and pupal female E.pergandiella (secondary hosts). Egg distribution was analysed with respect to sex ratio, super-parasitism and host discrimination.
2. The proportion of primary and secondary hosts parasitized in each treatment reflected the relative availability of each host type. Thus females presented with 75% primary hosts laid more female eggs than male. However, in all treatments, a greater proportion of secondary hosts were parasitized than would be expected from the proportion of secondary hosts available. This indicates that more male eggs were laid than expected.
3. More secondary hosts than primary hosts were superparasitized.
4. Host discrimination analysis using a new test statistic showed that females generally laid eggs at random with regard to previous parasitism of primary or secondary hosts. However, females in one treatment with 50% of each host type appeared to preferentially oviposit in secondary hosts which did not contain any eggs.     

Potential novel hosts for the lily leaf beetle Lilioceris lilii Scopoli (Coleoptera: Chrysomelidae) in eastern North America

Abstract.  1. Introduced insects often incorporate native plants into their diets and might be expected to show a predilection for novel hosts that are phylogenetically related to their normal hosts. The lily leaf beetle, Lilioceris lilii (Coleoptera: Chrysomelidae), is an introduced pest of cultivated lilies. Oviposition behaviour, larval behaviour, and development of L. lilii was examined on a range of potential host plants, as well as on the normal host, Asiatic hybrid lilies Lilium sp.
2. Neonate larval feeding behaviour was quantified on 15 food plant species: 10 from the Liliales, three from the Asparagales and two eudicots. Larvae fed plants closely related to the genus Lilium were more likely to initiate feeding, less likely to abandon their food leaf, and consumed more leaf area.
3. In no-choice tests, females oviposited on the novel hosts Lilium philadelphicum , Medeola virginiana , Clintonia borealis , Streptopus amplexifolius , and Polygonatum biflorum ; however, all but L. philadelphicum received very few eggs. Non- Lilium novel hosts were not used for oviposition when presented along with Asiatic lilies in choice tests.
4. A single individual was reared to the adult stage on the novel host S. amplexifolius . Several larvae survived to the pupal stage on M. virginiana , although no adults emerged from those pupae. Larvae reared on the native wood lily L. philadelphicum performed equally well or better than on the Asiatic cultivar.
5. Our results indicate that the lily leaf beetle poses a threat to native Liliaceae. Several native Lilium species, including L. philadelphicum , are threatened or endangered in certain jurisdictions throughout their range; these species should be monitored closely for colonisation by the beetle.     

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.     

Influence of host age and host deprivation on longevity, egg load dynamics and oviposition rate in Microplitis rufiventris

Adult size, longevity, egg load dynamics and oviposition ofMicroplitis rufiventris Kok. which began their development in the first, second, third （preferred hosts） or fourth （non-preferred hosts） instar larvae of Spodoptera littoralis （Boisd.） were studied. The parasitoid size was largely determined by the initial host size at parasitism. Non-ovipositing females derived from older hosts lived for longer periods than those derived from younger ones. However, the ovipositing females, irrespective of their size, lived for almost the same periods. At emergence, the oviducts of adult females contain a significant amount of mature eggs available for oviposition for a few hours on eclosion day. Egg load increases during the early phase of adult life. The amount of additional mature eggs and rate of egg maturation per hour was greater for wasps derived from preferred hosts compared with those in females derived from non-preferred hosts. The pattern of egg production in M. rufiventris females depended on the availability of hosts for parasitization. Host-deprived females depleted the egg complement with aging; the longer the host deprivation, the lower the oviduct egg load. Marked reduction in both realized or potential fecundity of host-deprived females was observed following host availability. Host privation for more than 3 days induced a marked deficit fecundity pattern through the female＇ s life. The realized fecundity was determined by the interaction among host availability, the number of eggs that are matured over the female＇ s life span, oviposition rate and host size from which the female was derived. These results suggest that： （i） M. rufiventris wasp is a weak synovigenic species; （ii） the maturation of additional eggs is inhibited once the maximum oviduct egg load is reached; （iii） the egg load of the newly emerged female is significantly less than the realized fecundity; and （iv） because M. rufiventris females oviposit fewer eggs when they begin depleting their egg supply at 3 days, augmentative releases will require release immediately following emergence to ensure the highest parasitization rate in the field.     

Daily progeny production and thermal influence on development and adult longevity of the leafminer parasitoid, Gronotoma micromorpha (Hym., Eucoilidae)

Abstract:  To evaluate the potential of the parasitoid Gronotoma micromorpha (Perkins) as a biological control agent for the serpentine leafminer Liriomyza trifolii (Burgess) in greenhouses, we determined daily progeny production and thermal influence on both total development (oviposition to adult emergence) and adult longevity of this wasp in the laboratory in the host L. trifolii . The mean total number of progeny produced was 75.6 per female at 25°C under a 15-h light/9-h dark (15L : 9D) photoregime. The developmental rate of G. micromorpha significantly correlated with constant temperature between 18 and 30°C. The lower thermal threshold and thermal constant for total development of this wasp were 11.7°C and 333.3 heat degree-days, respectively. The results indicate that adult female G. micromorpha do not oviposit at 15°C and that the lower threshold for oviposition is approximately 18°C. In heated greenhouses in Japan, leafminers and their parasitoids are exposed to both high temperatures and a short photoregime from late autumn to winter, but these conditions (25°C, 10L : 14D) did not significantly affect the total development of G. micromorpha . When wasps were not exposed to hosts, the mean adult longevity at 15 or 20°C was significantly longer than that at 25°C. When wasps were allowed to oviposit into hosts at 25°C, the mean adult longevity was significantly longer than when wasps were not exposed to hosts. As adult female G. micromorpha do not feed on hosts and are pro-ovigenic, suppression of oviposition probably decreased adult longevity. The biological traits of G. micromorpha elucidated by this and previous studies indicate that this wasp is suitable as a biological control agent for L. trifolii in greenhouses.     

Reproductive responses to photoperiod and temperature by diapausing and nondiapausing populations of Sesamia nonagrioides Lef. (Lepidoptera − Noctuidae)

Abstract.  The influence of long- and short-day cycles on ovipostion and egg hatch of the corn stalk borer, Sesamia nonagrioides were investigated at a range of temperatures. Oviposition was suppressed when insects are exposed to long days through their immature stages and then transferred to short days after mating. Moreover, mean oviposition and egg hatch increased from 15 to 27.5 °C, whereas oviposition declined significantly at 30 °C at both photoperiodic regimes. Females derived from a diapausing population exposed to long days after mating showed a significantly higher egg production compared to females derived from a nondiapausing population. However, when females from a diapausing population were left to oviposit under short days, fewer eggs were produced compared to those exposed to long days after mating. Thus, photoperiod appears to affect reproductive traits of this species in a quantitative manner. Larval diapause duration is positively correlated with fecundity of the adults. There is also a positive correlation between pupal weight of individuals derived from a diapausing population and the postdiapause fecundity of adults.     

Mating prior to overwintering in the imported willow leaf beetle, Plagiodera versicolora (Coleoptera: Chrysomelidae)

Abstract. 1. We report on the mating status of overwintering adults of the imported leaf beetle, Plagiodera versicolora Laicharting. This species overwinters as adults, under the bark of willow trees.
2. Individuals were collected both in the autumn, just after initiation of diapause, and in the spring, just before natural termination of diapause. From the autumn sample, we discovered that diapause can be terminated by husbanding the adults at 4°C for 4 weeks.
3. Most females lay fertile eggs upon the termination of diapause; however, a significant number of females lay non-fertile eggs after overwintering in the field.
4. Many females mate with more than one male before entering diapause. Progeny analysis using allozyme genetic markers shows that, on average, females who are fertile upon termination of diapause utilize sperm from 1.2 males to fertilize their eggs.     

Parasitoid size as a function of host sex: potential for different sex allocation strategies

Parasitoid females are known to preferentially allocate female eggs to hosts with the higher resource value, usually leading to oviposition of female eggs in larger hosts and male eggs in smaller hosts. For koinobiont parasitoids, if male and female hosts are of equal size at time of oviposition, but differ in size in later developmental stages, the sex of the host could be used to indicate future resource value. Using parasitoids of the braconid genus Asobara, which are larval parasitoids of Drosophila, it is shown that parasitoids emerging from female hosts are larger than those from male hosts. Given this difference in resource value, ovipositing females should preferentially allocate female eggs to female hosts. An alternative strategy would be to decrease the difference in resource value between male and female hosts by castrating male hosts. The primary sex ratio of A. tabida in their two main host species does not differ between male and female hosts. In contrast to A. tabida, A. citri is known to partially castrate male hosts, but this does not decrease the size difference between male and female hosts. As in A. tabida, there is no difference in sex allocation to male and female hosts in A. citri. Despite the clear difference between the resource value of male and female hosts, these parasitoid species do not seem to make optimal use of this difference. They may not be able to discriminate between host sexes or, alternatively, there is a presently unknown fitness disadvantage to ovipositing in female hosts.     

A comparison of the host preference of monarch butterflies (Danaus plexippus) for milkweed (Asclepias syriaca) over dog-strangler vine (Vincetoxicum rossicum)

Observations in the field indicate that monarch butterflies will oviposit on dog‐strangler vine, an invasive introduced species in the same family as milkweed (Asclepias spp.), the principal larval host of monarchs. The potential impact of this behaviour depends on the strength of the preference of monarch adults to oviposit on these two hosts and the relative ability of larvae to survive on each. We determined the preference for milkweed vs. dog‐strangler vine of ovipositing adults and first instar larvae in choice and no‐choice tests. We also compared the ability of larvae to consume, develop, and survive on either host. In the presence of both hosts, adults exhibited a strong preference to oviposit on milkweed over dog‐strangler vine (mean 80.7 eggs compared to 0.4 eggs over 48 h, respectively). In the absence of milkweed, adults ceased oviposition (mean 0.9 eggs in 48 h), but resumed oviposition when the dog‐strangler vine was replaced with milkweed (mean 99.1 eggs in 48 h). Given a choice between hosts over 24 h, 92% of larvae moved to milkweed leaves and consumed 3.94 cm² of milkweed leaves compared to 2% of larvae that moved to dog‐strangler vine and consumed negligible amounts of leaf material (0.01 cm²). Without a choice, larvae on dog‐strangler vine never consumed more than mean 0.02 cm² larva^?1 in a 24‐h period, did not develop beyond the first instar, and died within 96 h. We obtained no data in support of an effect of the presence of dog‐strangler vine on monarch butterfly populations.     

Influence of Conspecific Presence, Experience, and Host Quality on Oviposition Behavior and Clutch Size Determination in Anastrepha ludens (Diptera: Tephritidae)

Females of some insect species adjust the number of ovipositions and clutch size adaptively depending on conspecific density and probably experience. In a series of three experiments, we examined the effect of the presence of conspecifics, host quality, and oviposition experience on oviposition behavior and clutch size determination by females of the polyphagous fruit fly Anastrepha ludens (Diptera: Tephritidae). In the first experiment, we determined that grouped (eight females per cage) A. ludens females tended to visit and oviposit in more hosts than did solitary females probably as a result of stimulation by the presence of conspecifics. We also determined that females with previous oviposition experience visited and oviposited in more hosts than inexperienced ones. Importantly, when females were grouped, we observed significantly more landings on unoccupied hosts (i.e., devoid of flies) than on occupied ones (i.e., with at least one fly on it). However, oviposition experience, and not female density, was the most important factor affecting clutch size. Naive females deposited larger egg clutches than experienced ones. In the second experiment, we found that oviposition experience and host quality (i.e., clean fruit or fruit covered with a host marking pheromone [HMP] extract), influenced clutch size and the decision of females to defend or not defend the host. Clutch size and number of fights were greater on clean than on HMP-marked hosts. In the third experiment, we observed that host quality (i.e., size) played a significant role with regard to the number of female fights, host marking behavior, and clutch size. Specifically, females fought and dragged their aculeus longer on small- and medium-sized hosts than on large ones. But this behavior varied according to whether females were kept alone or grouped. Clutch size was greatest in the largest hosts. Considering all the above, we believe that the observed increase in ovipositional activity by grouped A. ludens females can be attributed to competition through mutual interference and not social facilitation as has been reported in other tephritid species.     

Host-marking behaviour as a quantitative signal of competition in the walnut fly Rhagoletis juglandis

Abstract.  1. Walnut-infesting flies in the Rhagoletis suavis species group actively re-use hosts for oviposition despite engaging in a genus-typical host-marking behaviour which, in other Rhagoletis groups, deters oviposition. In a study of the walnut fly, R. juglandis (Cresson), alternative hypotheses for the putative marking behaviour were evaluated.
2. The oviposition site attraction hypothesis proposes that the host mark guides females to oviposition sites on occupied fruit. The competition intensity signal hypothesis proposes that the host mark is an indicator of the level of competition to be incurred if fruit are re-used.
3. In a field cage, females were presented simultaneously with fruit previously exposed to 25 females that were also allowed to oviposit and engage in the putative marking behaviour, and control fruit on which females were allowed only to oviposit. The occurrence of host marking reduced a female's propensity to oviposit from 46% to just over 10%, consistent with the competition intensity signal hypothesis only.
4. In a laboratory assay, the duration of host marking was correlated positively with the size of a female's clutch. This result, also consistent with the competition intensity signal hypothesis, suggests that the amount of marking pheromone on a fruit is a reliable indicator of the number of eggs already deposited within.
5. In a second field-cage experiment, females were allowed to mark on fruit for 0, 10, 20, or 30 min and fruit were presented to test females. Whether or not females alighted on a particular host was not affected by the duration of marking; however, the frequency of both ovipositor probing and egg deposition decreased with increasing duration of marking. Consistent with the competition intensity signal hypothesis, this result suggests that the host mark permits females to assess the level of competition that a clutch will incur within re-used fruit.     

Oviposition and host-feeding patterns in Aphelinus asychis (Hymenoptera: Aphelinidae) at different aphid densities

Abstract. 1. The patterns of host-feeding and oviposition were examined in Aphelinus asychis Walker, which had been provided with second-instar pea aphids as hosts.
2. Female wasps responded to increasing host density (between one and forty aphids for 24 h) with an increasing tendency to oviposit rather than to feed. Superparasitism occurred at all aphid densities, even when unparasitized aphids were available.
3. Aphids intended for feeding were paralysed and died. Wasps did not feed on and oviposit in the same aphid.
4. Feeding to satiation lasted between 4 min and 42 min. Females that had starved for ≰18 h generally deposited one or more eggs before feeding again, while the reverse was true in wasps that had starved for 21 h.
5. The host-feeding behaviour of A. asychis is determined by a female's nutritional status. At low rates of host encounter, the anhydropic eggs may be resorbed. This reproductive strategy conforms to the destructive non-concurrent type among the Hymenoptera.     

Temporary host paralysis and avoidance of self-superparasitism in the solitary endoparasitoid Meteorus pulchricornis

We suggest a new mechanism for the avoidance of self-superparasitism by a solitary endoparasitoid of free-living hosts. Meteorus pulchricornis (Wesmael) (Hymenoptera: Braconidae) is a solitary larval endoparasitoid of a wide range of Lepidoptera. First, we tested the tendency to avoid multiple oviposition on Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) larvae, examining the distribution pattern of eggs deposited in 20 hosts in 24 h. The standardized Morisita index of dispersion (Ip) for the number of eggs in a host larva was almost always below zero, and the 95% confidence limits of the means were lower than zero for both experienced and inexperienced females, indicating that parasitoids tend to avoid multiple oviposition, although not completely. Second, we observed changes in host movements (head shaking and forward movement) after oviposition and the occurrence of additional ovipositions in pre-oviposited hosts, because a recent study indicated the necessity of visual cues provided by host movements for oviposition by this species. The incidence of host movements decreased markedly after oviposition and remained at a low level for approximately 1 h, during which time additional ovipositions were rarely observed. Temporary host paralysis after oviposition would be a new mechanism for the avoidance of self-superparasitism in a solitary endoparasitoid using visual cues from moving hosts for oviposition.     

Differences in host plant selection among three Athalia sawflies feeding on crucifers in Japan

Abstract 1. The ways of using host plants were compared among the three Athalia sawflies [ A. japonica (Klug), A. rosae ruficornis Jakovlev, and A. infumata (Marlatt)] feeding on crucifers in Japan to determine whether host specialisation can explain the difference in their life-history traits. The occurrence of their larvae was examined on each crucifer species in the field, and the suitability of each crucifer species for the three successive steps of host use by the sawflies was evaluated: microhabitat selection by adult females, female oviposition, and larval growth.
2. There were 11 species of crucifer in the study area, and A. japonica , A. rosae , and A. infumata used nine, seven, and eight species respectively. Thus, sawfly host ranges overlapped.
3. Adult females of A. japonica , A. rosae , and A. infumata preferred shady clumps of crucifers, sunny clumps of crucifers, and disturbed areas respectively.
4. Unsuitable hosts for larval performance such as Brassica oleracea and Arabis plants were eliminated from the host ranges of the three sawflies.
5. Once they chose microhabitats, the suitability of each host plant for female oviposition and larval growth was similar.
6. Because of the divergent preferences for microhabitats, the host plants that were suitable for all the three steps were restricted to different sets of plants among the sawflies: Cardamine for A. japonica , cultivated crucifers ( Raphanus and Brassica ) for A. rosae , and Rorippa for A. infumata . These plants could be recognised as the respective primary host plants.
7. The spatio-temporal distributions of primary hosts were consistent with and explained the pattern of diapause and migration of each sawfly, suggesting that host specialisation caused their life-history traits to differentiate.     

Clutch size in frugivorous insects as a function of host firmness: the case of the tephritid fly Anastrepha ludens

Abstract. 1. Optimal clutch size theory predicts that individuals will oviposit the number of eggs that increases their fitness. In Anastrepha ludens Loew (Diptera: Tephritidae), females oviposit larger clutches in unripe (firm) fruits than in ripe (soft) fruits. The following hypotheses were tested: (1) Using fruit firmness as an indicator of fruit quality, A. ludens females vary the number of eggs per clutch every time they reach an oviposition decision. (2) Maximising offspring survival with respect to either unripe or ripe fruit requires placing large clutches in firm fruit and smaller clutches in soft fruit. 2. Agar spheres were used as artificial hosts. Three agar concentrations resulted in three degrees of firmness. Mango fruits Mangifera indica L. served as natural hosts. Ripe and unripe fruits were used to test soft and firm host conditions respectively. Females laid significantly larger clutches in the firmer artificial hosts than in the softer hosts. They also laid significantly more eggs in artificial hosts without sugar than in hosts with sugar. Firm (unripe) mangoes also received significantly larger clutches than soft (ripe) mangoes. 3. When an individual female was first presented with a firm artificial host, it laid a large clutch. If subsequently offered a soft host, the female laid a significantly smaller clutch. Finally, if again offered a firm host, clutch size was increased significantly. 4. Possible trade‐offs in offspring fitness were explored in ripe and unripe mangoes by measuring offspring egg‐to‐adult survival, pupal weight, mean adult longevity, and fecundity. Despite the fact that larval survival was greater in soft fruit than in firm fruit, parameters such as pupal weight, mean longevity, and fecundity of adults stemming from both fruit types did not differ significantly. 5. A probable trade‐off between high offspring mortality caused by host unsuitability and low offspring and adult mortality caused by parasitism and predation is discussed as the reason for the exploitation of sub‐optimal hosts.     

Host discrimination modulates brood guarding behaviour and the adaptive superparasitism in the parasitoid wasp Trissolcus semistriatus (Hymenoptera: Scelionidae)

Because hosts utilized by parasitoids are vulnerable to further oviposition by conspecifics, host guarding benefits female wasps. The present study aims to test whether female adults regulate brood guarding behaviour by host discrimination in a solitary parasitoid Trissolcus semistriatus by presenting an intact or parasitized host egg mass to a female adult. Virgin females without oviposition experience have host discrimination ability, which enables them to adjust the number of eggs laid in the hosts. Mating experience increases superparasitism by female adults, whereas mated females achieve a higher discrimination ability as a result of oviposition experience and show a lower superparasitism rate. As expected, females exhibit brood guard after parasitizing an intact host egg mass, whereas those females visiting a previously parasitized host egg mass, do not. Because the survival of eggs in superparasitized hosts is relatively low, regulating brood guarding behaviour by host discrimination is adaptive for female wasps.     

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

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

Putting more eggs in the best basket: clutch-size regulation in the comma butterfly

Abstract.  1. Many studies have identified different factors influencing clutch-size regulation, primarily within various groups of insects. One prediction is that ovipositing females should increase clutch size with host quality. However, in many studies it is not clear whether ovipositing females are responding to host quality or quantity.
2. Females of the polyphagous comma butterfly, Polygonia c-album (L.), were allowed to oviposit on two hosts differing greatly in quality: the preferred host, stinging nettle ( Urtica dioica L.), and the low-ranked host, birch ( Betula pubescens Ehrh). Ovipositing females were observed visually and clutch sizes were recorded. The experiment was repeated in three different years; in total, 938 observations of oviposition events were made.
3. In all three years, females ovipositing on U. dioica laid larger clutches (median 1.6–1.85) compared with females ovipositing on B. pubescens (median 1.0–1.3) . The difference was significant in two out of three years and when all three years were pooled.
4. Thus, P. c-album females exhibit clutch-size regulation, with larger clutches on better hosts. It is suggested that the proximate mechanism is likely to be a response to the same stimuli used for female ranking of host plants in the preference hierarchy.     

Comparison of oviposition behavior of a solitary and a gregarious parasitoid (Hymenoptera: Mymaridae)

Anaphes victus Huber andAnaphes listronoti Huber (Hymenoptera: Mymaridae) are respectively solitary and gregarious egg parasitoids of the carrot weevil,Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae). We made detailed ethograms of the oviposition behavior on unparasitized and parasitized hosts for the two species. We then compared the behavior of virgin and mated females for the oviposition of male and female progenies. The two species did not always oviposit after insertion of the ovipositor, but these punctures without oviposition could be readily differentiated from oviposition.A. victus oviposited only once by puncture, whileA. listronoti deposited one to three eggs during the same sequence. The variability of the duration of the various components was generally lower for a given female than between females. Two components, the abdominal vibrations and the pause, were significantly shorter in ovipositions that resulted in male progency for the two species. However, an important overlap in duration prevents using these differences to sex the progeny at oviposition. Virgin females of both species, although capable of producing only males, exhibited both behaviors. Parasitized hosts were recognized through internal and external markings that were used in host discrimination.