Co‐foundress confinement elicits kinship effects in a naturally sub‐social parasitoid

Kinship among interacting individuals is often associated with sociality and also with sex ratio effects. Parasitoids in the bethylid genus Goniozus are sub‐social, with single foundress females exhibiting post‐ovipositional maternal care via short‐term aggressive host and brood defence against conspecific females. Due to local mate competition (LMC) and broods normally being produced by a single foundress, sex ratios are female‐biased. Contests between adult females are, however, not normally fatal, and aggression is reduced when competing females are kin, raising the possibility of multi‐foundress reproduction on some hosts. Here, we screen for further life‐history effects of kinship by varying the numbers and relatedness of foundresses confined together with a host resource and also by varying the size of host. We confined groups of 1–8 Goniozus nephantidis females together with a host for 5+ days. Multi‐foundress groups were either all siblings or all nonsiblings. Our chief expectations included that competition for resources would be more intense among larger foundress groups but diminished by both larger host size and closer foundress relatedness, affecting both foundress mortality and reproductive output. From classical LMC theory, we expected that offspring group sex ratios would be less female‐biased when there were more foundresses, and from extended LMC theory, we expected that sex ratios would be more female‐biased when foundresses were close kin. We found that confinement led to the death of some females (11% overall) but only when host resources were most limiting. Mortality of foundresses was less common when foundresses were siblings. Developmental mortality among offspring was considerably higher in multi‐foundress clutches but was unaffected by foundress relatedness. Groups of sibling foundresses collectively produced similar numbers of offspring to nonsibling groups. There was little advantage for individual females to reproduce in multi‐foundress groups: single foundresses suppressed even the largest hosts presented and had the highest per capita production of adult offspring. Despite single foundress reproduction being the norm, G. nephantidis females in multi‐foundress groups appear to attune sex allocation according to both foundress number and foundress relatedness: broods produced by sibling foundresses had sex ratios similar to broods produced by single foundresses (ca. 11% males), whereas the sex ratios of broods produced by nonsibling females were approximately 20% higher and broadly increased with foundress number. We conclude that relatedness and host size may combine to reduce selection against communal reproduction on hosts and that, unlike other studied parasitoids, G. nephantidis sex ratios conform to predictions of both classical and extended LMC theories.     

Comparative assessments of Gonatocerus ashmeadi and the ‘new association’ parasitoid G. deleoni (Hymenoptera: Mymaridae) as biological control agents of Homalodisca vitripennis (Hemiptera: Cicadellidae)

Egg age preference, competitive ability, and behavior of Gonatocerus deleoni (‘new association’ parasitoid) and G. ashmeadi (the co-evolved dominant parasitoid in California) were investigated in the laboratory to determine whether one species exhibited competitive superiority. When searching concurrently for Homalodisca vitripennis egg masses, G. ashmeadi consistently outperformed G. deleoni by parasitizing 59–89% more eggs under three different experimental systems in the laboratory with varying host densities, egg ages, and exposure times. G. ashmeadi parasitism in control vials containing one parasitoid ranged from 58 to 86% and was up to 28% higher at egg ages 1 and 3 days compared with 5 days. G. deleoni in control vials parasitized on average 7% of H. vitripennis egg masses in 1 h regardless of egg age. G. deleoni failed to parasitize H. vitripennis egg masses in 15 min when caged alone or in competition with G. ashmeadi. In a combined species treatment, parasitism by G. ashmeadi was 11% higher when H. vitripennis eggs were exposed for 5 days compared with 24 h. Conversely parasitism by G. deleoni was 5% lower for this comparison. G. ashmeadi had a significantly female biased sex ratio for all three experimental designs, whereas, G. deleoni offspring sex ratio was not significantly greater than 50%. In comparison to G. ashmeadi, behavioral observations indicated that G. deleoni was absent from host egg infested leaves 53% more frequently and it oviposited 66% less frequently. No incidences of females aggressively chasing competitors off H. vitripennis egg masses were recorded during this study.     

Development of the gregarious ectoparasitoid Nasonia vitripennis using five species of necrophagous flies as hosts and at various developmental temperatures

The utility of five species of necrophagous flies (Diptera) as pupal hosts for Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae) was examined by comparing incidences of parasitism, fecundity, and several features of wasp development at three rearing temperatures. Species differences in host suitability were evident in all life history features examined, with the highest incidences of parasitism, largest clutches and adult body sizes, and shortest periods of development occurring when the sarcophagid Sarcophaga bullata Parker served as hosts, regardless of temperature in which the wasps developed. Puparia of the calliphorids Lucilia illustris Meigen, Phormia regina Meigen, and Protophormia terraenovae Robineau‐Desvoidy were also accepted as hosts by the female parasitoids, albeit not equally so, and each yielded large, female‐biased broods. By contrast, pupae of the calliphorid Chrysomya rufifacies (Macquart) were not well suited to serve as an oviposition site or support the development of N. vitripennis. When successful parasitism did occur on any host species, duration of parasitoid development increased, adult body sizes were truncated, male‐biased sex ratios were produced, and mortality from egg hatch to adult emergence elevated with increasing rearing temperature. Unlike with the four other fly species, C. rufifacies did not yield any adult parasitoids when the rearing temperature was 35 °C. The results argue that developmental data determined for this wasp derived from a single host species is not sufficient for applying to all scenarios in which wasp development is necessary to estimate a postmortem interval or periods of insect activity.     

Opposing effects of mortality factors on progeny operational sex ratio may thwart adaptive manipulation of primary sex ratio

Despite extensive research on mechanisms generating biases in sex ratios, the capacity of natural enemies to shift or further skew operational sex ratios following sex allocation and parental care remains largely unstudied in natural populations. Male cocoons of the sawfly Neodiprion abietis (Hymenoptera: Diprionidae) are consistently smaller than those of females, with very little overlap, and thus, we were able to use cocoon size to sex cocoons. We studied three consecutive cohorts of N. abietis in six forest stands to detect cocoon volume‐associated biases in the attack of predators, pathogens, and parasitoids and examine how the combined effect of natural enemies shapes the realized operational sex ratio. Neodiprion abietis mortality during the cocoon stage was sex‐biased, being 1.6 times greater for males than females. Greater net mortality in males occurred because male‐biased mortality caused by a pteromalid parasitic wasp and a baculovirus was greater and more skewed than female‐biased mortality caused by ichneumonid parasitic wasps. Variation in the susceptibility of each sex to each family of parasitoids was associated with differences in size and life histories of male and female hosts. A simulation based on the data indicated that shifts in the nature of differential mortality have different effects on the sex ratio and fitness of survivors. Because previous work has indicated that reduced host plant foliage quality induces female‐biased mortality in this species, bottom‐up and top‐down factors acting on populations can affect operational sex ratios in similar or opposite ways. Shifts in ecological conditions therefore have the potential to alter progeny fitness and produce extreme sex ratio skews, even in the absence of unbalanced sex allocation. This would limit the capacity of females to anticipate the operational sex ratio and reliably predict the reproductive success of each gender at sex allocation.     

Determination of the optimal parasitoid‐to‐host ratio for efficient mass‐rearing of the parasitoid,Sclerodermus pupariae (Hymenoptera: Bethylidae)

Sclerodermus pupariae Yang et Yao (Hymenoptera: Bethylidae) is used as a potential biocontrol agent for several buprestid and cerambycid larvae. This study aimed to enhance the efficiency of mass‐rearing of this parasitoid by investigating the fitness gain of this bethylid wasp, including the proportion of successful parasitism and development, brood size, sex ratio, proportion of winged female offspring, body size and longevity of female offspring, under eight different maternal parasitoid density treatments using Thyestilla gebleri Faldermann as host in the laboratory. The results indicated that the foundress densities did not affect the parasitism or emergence rate of this parasitoid. Brood size of the parasitoids increased significantly when the number of maternal wasps ranged from one to four. However, further increases in foundress number did not affect the parasitoid brood size. The sex ratios of S. pupariae were always female‐biased. The proportions of male in the progeny colonies were <10% throughout all experimental treatments. The percentage of winged female progeny was not significantly influenced by the density of adult maternal parasitoids. Body sizes of parasitoids significantly declined with increasing maternal parasitoid densities. Although the parasitoid body size reduced when maternal wasp number was higher, it could be compromised by the relatively higher number of female offspring produced. Further, more than 70% of the parasitoids remained alive when they were stored at 12°C for four months throughout the experiments. These findings suggest that exposure of four female wasps to a single host larva would result in the highest fitness of S. pupariae. Our findings might provide a new approach to enhance the efficiency of mass‐rearing of this bethylid wasp.     

The influence of demography and local mating environment on sex ratios in a wind‐pollinated dioecious plant

Negative frequency‐dependent selection should result in equal sex ratios in large populations of dioecious flowering plants, but deviations from equality are commonly reported. A variety of ecological and genetic factors can explain biased sex ratios, although the mechanisms involved are not well understood. Most dioecious species are long‐lived and/or clonal complicating efforts to identify stages during the life cycle when biases develop. We investigated the demographic correlates of sex‐ratio variation in two chromosome races of Rumex hastatulus, an annual, wind‐pollinated colonizer of open habitats from the southern USA. We examined sex ratios in 46 populations and evaluated the hypothesis that the proximity of males in the local mating environment, through its influence on gametophytic selection, is the primary cause of female‐biased sex ratios. Female‐biased sex ratios characterized most populations of R.  hastatulus (mean sex ratio = 0.62), with significant female bias in 89% of populations. Large, high‐density populations had the highest proportion of females, whereas smaller, low‐density populations had sex ratios closer to equality. Progeny sex ratios were more female biased when males were in closer proximity to females, a result consistent with the gametophytic selection hypothesis. Our results suggest that interactions between demographic and genetic factors are probably the main cause of female‐biased sex ratios in R. hastatulus. The annual life cycle of this species may limit the scope for selection against males and may account for the weaker degree of bias in comparison with perennial Rumex species.     

Increasing host age does not have the expected negative effects on the fitness parameters of an egg parasitoid

Host age is an important determinant of host acceptance and suitability for egg parasitoids. As host embryonic development advances, the quality of resources available to the parasitoid offspring typically declines, usually resulting in reduced acceptance levels by foraging females and lower offspring fitness. We examined the ability of the parasitoid Telenomus podisi Ashmead (Hymenoptera: Scelionidae) to parasitize and develop in Podisus maculiventris (Say) (Hemiptera: Pentatomidae) eggs of different ages. In laboratory experiments, we measured the effect of host age (6, 24, 48, 72, 96, or 120 h old) on parasitism rate and offspring fitness parameters such as survival, development time, sex ratio, and size. Contrary to our expectations, parasitism rate did not differ between host age treatments, nor did sex ratio allocation, offspring size, or the fecundity of newly emerged female offspring. However, parasitoid offspring had a longer development time with increasing host age. This trend was stronger for males than for females, which we suggest could reduce the degree of protandry among offspring emerging from older host eggs, thus increasing the rate of virginity upon leaving the emergence patch and resulting in more frequent off‐patch mating by female offspring in nature. Overall, our results suggest that all stages of P. maculiventris embryonic development are suitable for acceptance and development of T. podisi. Unlike most species of egg parasitoids, T. podisi has evolved mechanisms to utilize host resources, regardless of host developmental stage, with relatively minor fitness consequences.     

Brood parasitism causes female‐biased host nestling mortality regardless of parasite species

Inequality in male and female numbers may affect population dynamics and extinction probabilities and so has significant conservation implications. We previously demonstrated that Brown‐headed Cowbird Molothrus ater brood parasitism of Song Sparrows Melospiza melodia results in a 50% reduction in the proportion of female host offspring by day 6 post‐hatch and at fledging, which modelling demonstrated is as significant as nest predation in affecting demography. Many avian brood parasites possess special adaptations to parasitize specific hosts so this sex‐ratio effect could be specific to the interaction between these two species. Alternatively, perturbations associated with brood parasitism per se (e.g. the addition of an extra, larger, unrelated nestling), rather than a Cowbird nestling specifically, may be responsible. We experimentally eliminated the effects of Cowbird‐specific traits by parasitizing nests with a conspecific nestling rather than a Cowbird, while otherwise emulating the circumstances of Cowbird parasitism by adding an extra, larger (2‐day‐older), unrelated Song Sparrow nestling to Song Sparrow nests. Our parasitism treatment led to few host offspring deaths and no evidence of male‐biased sex ratios by day 6 post‐hatch. However, after day 6, female nestling mortality rates increased significantly in experimentally parasitized nests, resulting in a 60% reduction in the proportion of females fledging. Cowbird‐specific traits are thus not necessary to cause female‐biased host nestling mortality and far more general features associated with Cowbird parasitism instead appear responsible. Our results suggest, however, that Cowbird‐specific traits may help accelerate the pace of female host deaths. The conservation implications of our results could be wide reaching. Cowbirds are unrelated to all their hosts, are larger than the great majority, and a Cowbird nestling's presence can mean there is an extra mouth to feed. Thus, sex‐biased mortality in parasitized nests could be occurring across a range of host species.     

Effect of temperature on immature development and longevity of two introduced opiine parasitoids on Bactrocera invadens

Temperature‐dependent development, parasitism and longevity of the braconid parasitoids, Fopius arisanus Sonan and Diachasmimorpha longicaudata Ashmed on Bactorcera invadens Drew Tsuruta & White, was evaluated across five constant temperatures (15, 20, 25, 30 and 35°C). Developmental rate decreased linearly with increasing temperature for both the parasitoid species. Linear and Brière‐2 nonlinear models were used to determine the lower temperature threshold at which the developmental rate (1/D) approached zero. For F. arisanus, lower thresholds to complete development estimated with the linear and nonlinear models were 10.1 and 6.9°C, respectively. The total degree‐days (DD) required to complete the development estimated by the linear model for F. arisanus was 360. In D. longicaudata, the linear and nonlinear models estimated lower thresholds of 10.4 and 7.3°C, respectively, and the total DD estimated was 282. In F. arisanus, percentage parasitism differed significantly across all temperatures tested and was highest at 25°C (71.1 ± 2.5) and lowest at 15°C (46.4 ± 1.4). Parasitoid progeny sex ratio was female biased at all temperatures except at 20°C. In D. longicaudata, percentage parasitism was highest at 20°C (52.2 ± 4.0) and lowest at 15°C (27.7 ± 2.5). Parasitoid progeny sex ratio was female biased and similar for all temperatures. Adult longevity of both parasitoids was shortest at 35°C and longest at 15°C, and females lived significantly longer than males at all temperatures tested. Our findings provide some guidance for future mass rearing and field releases of the two parasitoids for the management of B. invadens in Africa.     

Determination of Homalodisca coagulata (Hemiptera: Cicadellidae) egg ages suitable for oviposition by Gonatocerus ashmeadi, Gonatocerus triguttatus, and Gonatocerus fasciatus (Hymenoptera: Mymaridae)

Homalodisca coagulata (Say) (Hemiptera: Cicadellidae) eggs 1–10 days of age were exposed to Gonatocerus ashmeadi Girault, Gonatocerus triguttatus Girault, and Gonatocerus fasciatus Girault (all Hymenoptera: Mymaridae) in no choice laboratory trials to investigate egg age utilization and to determine which egg ages are vulnerable to attack by these three parasitoids. The H. coagulata egg ages that were most suitable for oviposition by G. ashmeadi, G. triguttatus, and G. fasciatus were eggs 3, 4, and 2 days of age, respectively. Egg ages least suitable for parasitoid development were 6–10 days for G. ashmeadi (resulting in <50% parasitism), 1–2 and 7–10 days for G. triguttatus (resulting in <25% parasitism), and 3–10 days for G. fasciatus (resulting in <11% parasitism). Pooling parasitism data across all egg ages showed that parasitism by G. ashmeadi was 12.9 and 28.5% higher compared with G. triguttatus and G. fasciatus, respectively, and G. triguttatus resulted in 15.6% higher percentage parasitism compared with G. fasciatus. Egg age had a significant effect on the percentage of female G. ashmeadi offspring produced, but this was not significant for G. triguttatus, and low G. fasciatus parasitism prevented statistical analyses for comparisons. Results from tests where females were offered a choice for oviposition between eggs 1, 3, and 5 days of age demonstrated that G. ashmeadi and G. triguttatus showed no significant oviposition preference, while percentage parasitism by G. fasciatus was 29.4 and 7.4% higher when females were presented eggs 1 and 3 days of age, respectively, compared with eggs 5 days of age. Choice tests indicated that an overlap in egg age suitability for oviposition exists between G. ashmeadi, G. triguttatus, and G. fasciatus, and that interspecific competition for eggs 1, 2, and 3 days of age may occur in the field environment.     

Short-distance dispersal behavior and establishment of the parasitoid Gonatocerus ashmeadi (Hymenoptera: Mymaridae) in Tahiti: Implications for its use as a biological control agent against Homalodisca vitripennis (Hemiptera: Cicadellidae)

The egg parasitoid Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae), was introduced into French Polynesia as a biological control agent to control the invasive plant feeding pest Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae). The short-distance dispersal of G. ashmeadi was monitored as part of the biological control program. G. ashmeadi showed exponential dispersal capacity with 47 m/day being a minimum estimate of its natural rate of spread at high host densities (>150 nymphs per minute of sweep net sampling) in urbanized areas at sea level, which were characterized by a high diversity of exotic ornamental plants. This rate of spread contrasted starkly with almost nonexistent establishment and dispersal where host densities were very low (<2 nymphs per minute of sweep net sampling) at high elevation (800 m) with relatively undisturbed native vegetation. Survey results across different altitudes revealed an effect of vegetative diversity and host density on the measurable mobility and establishment of G. ashmeadi. In contrast, no significant influence of wind direction was found on G. ashmeadi dispersal rate or direction. Survey results for G. ashmeadi from French Polynesia suggest that the best release establishment strategies for classical biological control of H. vitripennis are: (1) many small releases where host density is high, or (2) larger and fewer releases where host densities are low.     

Artificial selection on ant female caste ratio uncovers a link between female‐biased sex ratios and infection by Wolbachia endosymbionts

Social insect sex and caste ratios are well‐studied targets of evolutionary conflicts, but the heritable factors affecting these traits remain unknown. To elucidate these factors, we carried out a short‐term artificial selection study on female caste ratio in the ant Monomorium pharaonis. Across three generations of bidirectional selection, we observed no response for caste ratio, but sex ratios rapidly became more female‐biased in the two replicate high selection lines and less female‐biased in the two replicate low selection lines. We hypothesized that this rapid divergence for sex ratio was caused by changes in the frequency of infection by the heritable bacterial endosymbiont Wolbachia, because the initial breeding stock varied for Wolbachia infection, and Wolbachia is known to cause female‐biased sex ratios in other insects. Consistent with this hypothesis, the proportions of Wolbachia‐infected colonies in the selection lines changed rapidly, mirroring the sex ratio changes. Moreover, the estimated effect of Wolbachia on sex ratio (~13% female bias) was similar in colonies before and during artificial selection, indicating that this Wolbachia effect is likely independent of the effects of artificial selection on other heritable factors. Our study provides evidence for the first case of endosymbiont sex ratio manipulation in a social insect.     

Maximum realised lifetime parasitism and occurrence of time limitation in Gonatocerus ashmeadi (Hymenoptera: Mymaridae) foraging in citrus orchards

The relationship between body size (hind tibia length), <12 h egg load, wing wear and parasitoid age was used to estimate realised lifetime parasitism of recently dead Gonatocerus ashmeadi collected in a citrus orchard. Under prevailing field conditions and methodology assumptions, it was estimated that female G. ashmeadi lived on average for 183 ± 17 degree-days, parasitised a total of 87 ± 9 Homalodisca vitripennis eggs, and died with 34 ± 5 eggs remaining in the ovaries. Only 17% of dead G. ashmeadi died with no mature eggs suggesting that 83% of G. ashmeadi were not egg limited at time of death. Estimates of realised lifetime parasitism for female G. ashmeadi under prevailing field conditions in July and August in a southern California citrus orchard indicated that time of year had a significant effect on reproductive output. Additionally, live G. ashmeadi captured daily during June through August 2006 had body size, egg load and wing wear recorded to detect possible monthly changes in parasitoid age and egg load. Foraging G. ashmeadi captured alive in June were older and oviposited more eggs in the field compared with August. Only 0.5% of live G. ashmeadi were captured with no mature eggs in their ovaries indicating that the vast majority of live G. ashmeadi were not egg limited.     

Effect of exposure time on mass‐rearing production of the olive fruit fly parasitoid,Psyttalia lounsburyi (Hymenoptera: Braconidae)

Classical biological control programmes rely on mass production of high‐quality beneficial insects for subsequent releases into the field. Psyttalia lounsburyi (Silvestri) (Hymenoptera: Braconidae) is a koinobiont larval–pupal endoparasitoid of tephritid flies that is being reared to support a classical biological control programme for olive fruit fly in California. The mass‐rearing system for a P. lounsburyi colony, initiated with insects originally collected in Kenya, was evaluated with the goal of increasing production, while at the same time reducing time requirements for rearing in a quarantine facility. We tested the effect of exposure time of a factitious host Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), on parasitization, adult production, superparasitism, and sex ratio of P. lounsburyi and survival of the host. Parasitization rates were highest (31%) at 3‐ and 4‐hr exposure times, while adult production (i.e., emergence of wasp progeny) was highest (16%) at the 2‐hr exposure time. Superparasitism over the course of the study was 1.5% and did not appear to be a factor affecting parasitoid production. The sex ratio of wasp progeny was male‐biased and did not vary significantly over different exposure times. The rate of stings on host larvae increased with exposure time and was consistent with decreases in pupal eclosion from larvae and emergence rate of adult flies. When compared to current rearing procedures, the 2‐hr exposure time resulted in an overall 2.8‐fold increase in P. lounsburyi production when standardized for time.     

Cold storage effects on maternal and progeny quality of Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae)

This study determined the effects of cold storage on the survival, development and reproduction of the mymarid wasp, Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae). Following storage of the immature parasitoids within host eggs of the glassy-winged sharpshooter, Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae) under a daily fluctuating temperature for up to 50 d, the quality of the parental and F₁ generations was assessed by examining several reproductive and developmental parameters indicating fitness. Immature wasps were stored for 20 d within the host without reducing their subsequent survival, development or progeny fitness parameters. After 30 d of storage, survival declined, post-storage developmental time was extended, and the fecundity of the adult females decreased. Storage for 40 d severely damaged G. ashmeadi, because it not only yielded a 12% survival rate, 44% female sterility and increased the proportion of progeny males by 155%, but it also reduced parasitism and fecundity by 70% and 73%, respectively. No wasps emerged after 50 d of storage. Cold storage affected the emergence pattern of the parental but not the F₁ and F₂ generations. Parental emergence was extended and the pattern displayed two additional peaks after the initial onset. Analysis of several demographic parameters for the parental and F₁ generations further confirmed that the quality of the adult parents declined after they had been stored as immatures for 30 d. The detrimental effects caused by cold storage of the parental generation do not extend to the F₁ generation. Our results indicate that short-term cold storage of G. ashmeadi within its host could be used for maintaining and accumulating these parasitoids during mass propagation for release in a control program.     

Sex ratio rather than population size affects genetic diversity in Antennaria dioica

• Habitat fragmentation and small population size can lead to genetic erosion in threatened plant populations. Classical theory implies that dioecy can counteract genetic erosion as it decreases the magnitude of inbreeding and genetic drift due to obligate outcrossing. However, in small populations, sex ratios may be strongly male‐ or female‐biased, leading to substantial reductions in effective population size. This may theoretically result in a unimodal relationship between sex ratios and genetic diversity; yet, empirical studies on this relationship are scarce.
• Using AFLP markers, we studied genetic diversity, structure and differentiation in 14 highly fragmented Antennaria dioica populations from the Central European lowlands. Our analyses focused on the relationship between sex ratio, population size and genetic diversity.
• Although most populations were small (mean: 35.5 patches), genetic diversity was moderately high. We found evidence for isolation‐by‐distance, but overall differentiation of the populations was rather weak. Females dominated 11 populations, which overall resulted in a slightly female‐biased sex ratio (61.5%). There was no significant relationship between population size and genetic diversity. The proportion of females was not unimodally but positively linearly related to genetic diversity.
• The high genetic diversity and low genetic differentiation suggest that A. dioica has been widely distributed in the Central European lowlands in the past, while fragmentation occurred only in the last decades. Sex ratio has more immediate consequences on genetic diversity than population size. An increasing proportion of females can increase genetic diversity in dioecious plants, probably due to a higher amount of sexual reproduction.

     

Monitoring oriental fruit moth and codling moth (Lepidoptera: Tortricidae) with combinations of pheromones and kairomones

Experiments were conducted in North and South America during 2012–2013 to evaluate the use of lure combinations of sex pheromones (PH), host plant volatiles (HPVs) and food baits in traps to capture the oriental fruit moth, Grapholita molesta (Busck), and codling moth, Cydia pomonella (L.), in pome and stone fruit orchards treated with sex pheromones. The combination of the sex pheromone of both species (PH combo lure) significantly increased G. molesta and marginally decreased C. pomonella captures as compared with captures of each species with either of their sex pheromones alone. The addition of a HPV combination lure [(E,Z)‐2,4‐ethyl decadienoate plus (E)‐β‐ocimene] or acetic acid used alone or together did not significantly increase the catch of either species in traps with the PH combo lure. The Ajar trap baited with terpinyl acetate and brown sugar (TAS bait) caught significantly more G. molesta than the delta trap baited with PH combo plus acetic acid in California during 2012. The addition of a PH combo lure to an Ajar trap significantly increased catches of G. molesta compared to the use of the TAS bait or PH combo lure alone in 2013. Female G. molesta were caught in TAS‐baited Ajar traps at similar levels with or without the use of additional lures. Ajar traps baited with the TAS bait alone or with (E)‐β‐ocimene and/or PH combo lures caught significantly fewer C. pomonella than delta traps with sex pheromone alone. Ajar traps with 6.4‐mm screened flaps caught similar numbers of total and female G. molesta as similarly baited open Ajar traps, and with a significant reduction in the catch of non‐targets. Broader testing of HPV and PH combo lures for G. molesta in either delta or screened or open Ajar traps is warranted.     

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.     

Variability in the efficacy of sex pheromone lures for monitoring oriental fruit moth (Lepidoptera: Tortricidae)

Studies were conducted in Chile and the United States to compare the attractiveness of various commercial sex pheromone lures and two experimental lures for oriental fruit moth, Grapholita molesta (Busck), in peach orchards treated with or without sex pheromone dispensers. The experimental lures contained the three‐component sex pheromone blend of G. molesta: Z‐8‐dodecenyl acetate, E‐8‐dodecenyl acetate and Z‐8‐dodecenol (Z8‐12:OH), and the sex pheromone of codling moth, Cydia pomonella (L.), (E,E)‐8,10‐dodecadien‐1‐ol, (codlemone). Commercial lures varied in their substrate, initial loading and blend ratio of components. Significant differences in male catches were found among commercial lures in orchards treated with or without sex pheromone dispensers. Experimental lures with the addition of codlemone significantly increased the catches of G. molesta using lures loaded with 0%, 1% or 5% Z8‐12:OH in the G. molesta blend compared with the same ratio of components in just the G. molesta blend. The experimental lures were significantly more attractive than all commercial lures in the untreated orchard. However, moth catch with the experimental lures in the sex pheromone‐treated orchard was only intermediate among all of the lures tested. These findings highlight the need to develop more effective and standardized lures that can be used in trap‐based monitoring programme for this important pest.     

The potential for arms race and Red Queen coevolution in a protist host–parasite system

The dynamics and consequences of host–parasite coevolution depend on the nature of host genotype‐by‐parasite genotype interactions (G × G) for host and parasite fitness. G × G with crossing reaction norms can yield cyclic dynamics of allele frequencies (“Red Queen” dynamics) while G × G where the variance among host genotypes differs between parasite genotypes results in selective sweeps (“arms race” dynamics). Here, we investigate the relative potential for arms race and Red Queen coevolution in a protist host–parasite system, the dinoflagellate Alexandrium minutum and its parasite Parvilucifera sinerae. We challenged nine different clones of A. minutum with 10 clones of P. sinerae in a fully factorial design and measured infection success and host and parasite fitness. Each host genotype was successfully infected by four to ten of the parasite genotypes. There were strong G × Gs for infection success, as well as both host and parasite fitness. About three quarters of the G × G variance components for host and parasite fitness were due to crossing reaction norms. There were no general costs of resistance or infectivity. We conclude that there is high potential for Red Queen dynamics in this host–parasite system.