Adverse effects of the Bordeaux mixture copper-based fungicide on the non-target vineyard pest Lobesia botrana.

BACKGROUND: Bordeaux mixture is a copper-based fungicide commonly used in vineyards to prevent fungal and bacterial infections in grapevines. However, this fungicide may adversely affect the entomological component, including insect pests. Understanding the impacts of Bordeaux mixture on the vineyard pest Lobesia botrana is an increasing concern in the viticultural production. RESULTS: Bordeaux mixture had detrimental effects on the development and reproductive performance of L. botrana. Several physiological traits were adversely affected by copper-based fungicide exposure, including a decrease in larval survival and a delayed larval development to moth emergence, as well as a reduced reproductive performance through a decrease in female fecundity and fertility and male sperm quality. However, we did not detect any effect of Bordeaux mixture on the measured reproductive behaviors (mating success, pre-mating latency and mating duration). CONCLUSION: Ingestion by larvae of food contaminated with Bordeaux mixture had a negative effect on the reproductive performance of the pest L. botrana, which could affect its population dynamics in vineyards. Although this study highlighted collateral damage of Bordeaux mixture on L. botrana, the potential impact of copper-based fungicides on vineyard diversity, including natural predators is discussed and needs to be taken in consideration in integrated pest management. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Sublethal doses of pyriproxyfen stimulate reproduction and aggressive behavior in a non-target parasitoid wasp.

Insecticides are commonly used to control populations of pests and disease vectors. However, they can have multiple unintended effects on non-target species. Assessing their impacts on the physiology and behavior of beneficial insects, such as biological control agents, is thus necessary to gain insight into the diversity and nature of such side effects. Here, we investigated the effect of sublethal doses of the endocrine disrupting insecticide pyriproxyfen, a juvenile hormone agonist, on females of the solitary ectoparasitoid Eupelmus vuilleti (Hymenoptera: Eupelmidae). These parasitoid wasps can be used as biological control agents to control the cowpea weevil, Callosobruchus maculatus (Coleoptera: Bruchidae), that infests cowpea seeds, Vigna unguiculata (Fabacea). To do so, in addition to classical measures on female fecundity and survival, we focused on female behaviors that can have important consequences on female fitness and host exploitation. First, we showed that pyriproxyfen stimulated egg production without affecting female survival. Second, we observed that low doses of this insecticide had no effect on females' exploration and host discrimination ability but stimulated their aggressiveness when fighting for host access. Although a negative impact on other life-history traits cannot be ruled out at this point, these results showed low doses of pyriproxyfen can have unintended positive effects on ectoparasitoid E. vuilleti females, by enhancing at least temporarily their reproduction and host access in a situation of competition. Our work thus highlights the importance of studying the diversity of possible unintended sublethal effects of pesticides on beneficial insects.

Ecdysteroids affect female reproductive status and outcome of contest over hosts in the parasitoid wasp Eupelmus vuilleti.

Ecdysteroids are a family of insect hormones that may play a role in modulating aggressive behavior in reproductive contexts. In Hymenoptera, the few studies investigating the link between ecdysteroid titers, reproduction and aggressiveness during contests concern solely eusocial species. Here, we explored whether ecdysteroid titers influenced female reproductive status as well as aggressiveness and resolution of conflict in a solitary ectoparasitoid, Eupelmus vuilleti (Hymenoptera: Eupelmidae). Eupelmus vuilleti females parasitize and feed upon juvenile stages of Callosobruchus maculatus (Coleoptera: Bruchidae). When two E. vuilleti females are simultaneously present on a patch, they tend to protect the host they exploit by displaying aggressive behaviors towards conspecific competitors. To our knowledge, nothing is known about the association between ecdysteroids and aggressiveness or the outcome of contests for host access in solitary insects. First, we quantified ecdysteroid titers that naturally circulate in females without fighting experience and after a contest over host access. Ecdysteroid titers measured after the contest did not correlate with female aggressiveness during the contest, but winner wasps had higher titers than both losers and females that did not fight. Then, we manipulated hormone titers via injection: ecdysone favored egg maturation (i.e., gonadotropic effect) within 24 h and increased almost immediately the females' probability of winning host access without affecting their aggressiveness. Our results represent an important step in understanding how hormones, such as ecdysteroids, mediate insect behavior during intraspecific competition.

The challenge hypothesis in insects.

The 'challenge hypothesis' provides a predictive framework for how the social environment influences within-species variation in hormone titers. High testosterone levels are beneficial during reproduction and competition, but they also impose costs because they may suppress traits like parental care and immunity. As a result, the challenge hypothesis predicts that individuals will change their testosterone levels to match the current social environment. Although the vast majority of work on the challenge hypothesis has focused on androgens in vertebrates, there is growing evidence that insect hormones, especially juvenile hormone (JH), may respond to social stimuli in ways that parallel androgens in vertebrates. Many insects rapidly upregulate JH titers during social competition with rivals. Some insects also modulate JH titers based on contest outcomes, with winners upregulating JH and losers downregulating JH. This review will integrate work on social modulation of hormone titers in vertebrates and insects. First, we provide background on insect hormones and describe the functional parallels between androgens and JH. Second, we review evidence that insects rapidly change JH titers in response to social competition. Finally, we highlight opportunities for future work on social modulation of hormones in insects. Overall, the challenge hypothesis provides a useful conceptual framework for hypothesis-driven research in insect endocrinology. Comparing vertebrates and insects provides insight into how selection has shaped patterns of hormone responsiveness as well as the generality of hypotheses originally developed for vertebrates.

Juvenile hormone manipulation affects female reproductive status and aggressiveness in a non-social parasitoid wasp.

In vertebrates, titers of androgens such as testosterone are known to upregulate aggressive behaviors associated with reproduction. In insects, juvenile hormone (JH) is a good candidate for studying the flexibility of insect endocrine responses because it has important effects on both reproductive processes and behavior. JH has a gonadotropic effect across a broad range of insect species, increasing ovarian development in females, and may have a role in the regulation of aggressive behavior during competition. In Hymenoptera, the functions of JH have been studied in facultatively eusocial species such as polistine wasps, bumblebees, ants and bees. Surprisingly, no work has yet focused on the relationship between JH, reproduction and aggressiveness in a non-social Hymenoptera, although it may help to understand how JH actions have evolved across taxa with different degrees of sociality. Here, we explored how JH treatment influenced: i) female reproductive status, and ii) the intensity (aggressiveness) and resolution of conflict, in Eupelmus vuilleti (Hymenoptera: Eupelmidae), a solitary ectoparasitoid wasp in which females fight over hosts. We demonstrated that intra-abdominal injections of JH increased the number of mature eggs in females after 24 h. In addition, the number of aggressive behaviors displayed by females was affected by the interaction between JH treatment and the number of mature eggs in their abdomen, but mature egg load alone predicted the outcome of staged contests. Wasps were more aggressive when they had more ready-to-lay eggs, with this effect being stronger when females were injected with JH. Moreover, females won more frequently when they had higher mature egg load. Our results highlight how JH affects egg maturation and aggressive behaviors in Eupelmus vuilleti females. To our knowledge, this is the first study showing that hormone manipulation can modulate females' reproduction status and behavior during intraspecific competition over hosts in a non-social hymenopteran parasitoid.

Sperm limitation affects sex allocation in a parasitoid wasp Nasonia vitripennis.

Insect reproduction is influenced by various external factors including temperature, a well-studied constraint. We investigated to what extent different levels of sperm limitation of males exposed to different heat stresses (34 and 36 °C) affect females' offspring production and sex allocation in Nasonia vitripennis. In this haplodiploid parasitoid wasp attacking different species of pest flies, we investigated the effect of the quantity of sperm females received and stored in their spermatheca on their sperm use decisions, hence sex allocation, over successive ovipositions. In particular, we compared the sex allocation of females presenting three levels of sperm limitation (i.e., mated with control, 34 °C heat-stressed or 36 °C heat-stressed males) on each host they parasitized. To disentangle the potential reduction of sperm quality after a heat stress exposure from that of sperm quantity, we also explored the clutch size and sex ratio produced by females that were partially sperm limited after copulating with multiply mated males. Independently of their sperm numbers, all types of females produced a similar total number of offspring, but the more limited ones had fewer daughters. Sperm limitation further affected the distribution of daughters' production across time. In addition to constraints acting on female physiology, male fertility should therefore be considered in studies measuring reproductive outputs of insects submitted to heat stresses.

Do males choose their mates in the lekking moth Achroia grisella? Influence of female body mass and male reproductive status on male mate choice.

Lekking males aggregate to attract females and contribute solely to egg fertilization, without any further parental care. Evolutionary theory therefore predicts them to be nonchoosy toward their mates, because any lost mating opportunities would outweigh the benefits associated with such preferences. Nevertheless, due to time costs, the production of energetically costly sexual displays, and potential sperm limitation, the mating effort of lekking males is often considerable. These factors, combined with the fact that many females of varying quality are likely to visit leks, could favor the evolution of male mate preferences. Here, we show that males of the lekking lesser wax moth, Achroia grisella, were indeed more likely to mate with heavier females in choice experiments, even at their virgin mating (i.e., when their reproductive resources have not yet been depleted by previous matings). This differential female mating success could not be attributed to female behavior as heavy and light females showed similar motivation to mate (i.e., latency to approach the males) and time to copulate. Males seem to benefit from mating with heavier females, as fecundity positively correlated with female mass. This new empirical evidence shows that male mate choice may have been underestimated in lekking species.

The metabolic costs of fighting and host exploitation in a seed-drilling parasitic wasp.

Oviposition sites may be challenging and energetically costly to access for females in the presence of competitors contesting that resource. Additionally, oviposition sites may be difficult to reach, and penetrating a hard substrate can raise energy costs. In the seed-drilling parasitic wasp Eupelmus vuilleti, females actively fight with conspecific competitors over access to hosts. They are often observed laying eggs on already parasitized hosts (superparasitism) living inside cowpea seeds despite the resulting larval competition. Using flow-through respirometry, we quantified the metabolic costs of fighting and of drilling through the seed to access the host, to understand the wasp's fighting strategies and the occurrence of superparasitism. Agonistic interactions such as kicks or pushes generated very small instantaneous costs, but the females that won their contests had higher pre-contest metabolic rates, suggesting a potential long-term cost associated with dominance. We also found that drilling holes through the seed accounted for approximately 15% of a wasp's estimated daily energy budget, and that females can reduce these drilling costs by reusing existing holes. Because exploiting new seeds incurs both drilling costs and the risk of fights, it appears cost effective in some situations for females to avoid confrontations and lay eggs in existing holes, on already parasitized hosts. Our study helps explain the evolution of superparasitism in this system.

Volatile Chemical Emission as a Weapon of Rearguard Action: A Game-Theoretic Model of Contest Behavior.

We use a game-theoretic model to explore whether volatile chemical (spiroacetal) emissions can serve as a weapon of rearguard action. Our basic model explores whether such emissions serve as a means of temporary withdrawal, preventing the winner of the current round of a contest from translating its victory into permanent possession of a contested resource. A variant of this model explores an alternative possibility, namely, that such emissions serve as a means of permanent retreat, attempting to prevent a winner from inflicting costs on a fleeing loser. Our results confirm that the underlying logic of either interpretation of weapons of rearguard action is sound; however, empirical observations on parasitoid wasp contests suggest that the more likely function of chemical weapons is to serve as a means of temporary withdrawal. While our work is centered around the particular biology of contest behavior in parasitoid wasps, it also provides the first contest model to explicitly consider self-inflicted damage costs and thus responds to a recent call by empiricists for theory in this area.

Modeling the evolution of winner and loser effects: A survey and prospectus.

The evolution of winner or loser effects-higher probabilities of winning after winning or of losing after losing-has received remarkably little attention from theoreticians, even though such effects are widespread across the animal kingdom. We review game-theoretic models that regard such winner and loser effects as outcomes of a strategic response. We show that these models have been well supported by the empirical literature in the past, but are not designed to address some recent observations. In the light of this recent progress on the empirical front, we identify factors that newer theory must be developed to explore.

Amino acid composition of the bushcricket spermatophore and the function of courtship feeding: Variable composition suggests a dynamic role of the nuptial gift.

Nuptial gifts are packages of non-gametic material transferred by males to females at mating. These gifts are common in bushcrickets, where males produce a complex spermatophore consisting in a sperm-containing ampulla and an edible sperm-free spermatophylax. Two non-mutually exclusive hypotheses have been suggested to explain the function of the spermatophylax: the paternal investment hypothesis proposes that it represents a male nutritional investment in offspring; the mating effort hypothesis proposes that the spermatophylax maximizes the male's sperm transfer. Because gift production may represent significant energy expenditure, males are expected to adjust their investment relative to the perceived quality of the female. In this study, we first examined the free amino acid composition and protein-bound amino acid composition of the nuptial gift in the bushcricket, Ephippiger diurnus (Orthoptera: Tettigoniidae). Second, we investigated whether this composition was altered according to female age and body weight. Our study represents the first investigation of both free and protein-bound amino acid fractions of a bushcricket spermatophylax. We found that composition of the nuptial gift varied both qualitatively and quantitatively with respect to traits of the receiving female: older females received larger amounts of protein-bound amino acids (both essential and non-essential), less water and less free glycine. This result suggests that gift composition is highly labile in E. diurnus, and we propose that gift allocation might represent a form of cryptic male mate choice, allowing males to maximize their chances of paternity according to the risk of sperm competition that is associated with mate quality.

A combined approach to heat stress effect on male fertility in Nasonia vitripennis: from the physiological consequences on spermatogenesis to the reproductive adjustment of females mated with stressed males.

In recent years, several studies have shown a decline in reproductive success in males in both humans and wildlife. Research on male fertility has largely focused on vertebrates, although invertebrates constitute the vast majority of terrestrial biodiversity. The reduction of their reproductive capacities due to environmental stresses can have strong negative ecological impacts, and also dramatic consequences on world food production if it affects the reproductive success of biological control agents, such as parasitic wasps used to control crop pests. Here Nasonia vitripennis, a parasitic wasp of various fly species, was studied to test the effects of 24h-heat stress applied during the first pupal stage on male fertility. Results showed that only primary spermatocytes were present at the first pupal stage in all cysts of the testes. Heat stress caused a delay in spermatogenesis during development and a significant decrease in sperm stock at emergence. Females mated with these heat-stressed males showed a reduce sperm count stored in their spermatheca. Females did not appear to distinguish heat-stressed from control males and did not remate more frequently to compensate for the lack of sperm transferred. As a result, females mated with heat-stressed males produced a suboptimal lifetime offspring sex ratio compared to those mated with control males. This could further impact the population dynamics of this species. N. vitripennis appears to be an interesting biological model to study the mechanisms of subfertility and its consequence on female reproductive strategies and provides new research perspectives in both invertebrates and vertebrates.

The effect of direct interspecific competition on patch exploitation strategies in parasitoid wasps.

The presence of competitors may affect the pay-off of individuals' foraging strategies. They should therefore modify their resource exploitation decisions accordingly. In such a direct competition situation, theory predicts that individuals should stay longer on a resource patch than when foraging alone. However, models predicting patch residence time focus on intraspecific competition without agonistic interactions. Here, we investigate the patch use strategies of females of two parasitoid species, Eupelmus vuilleti and Dinarmus basalis, attacking the same host, Callosobruchus maculatus, knowing that D. basalis is more aggressive and can exclude E. vuilleti during pairwise contests for single hosts. Our results showed that time allocation and oviposition strategies differed in relation to the species and type of competition (i.e., presence/absence of competitor, simultaneous/sequential female introduction or resident/intruder female). Eupelmus vuilleti females tended to wait in the patch surroundings for D. basalis females' departure to return and exploit hosts parasitized by the opponent (after destruction of her eggs). In contrast, D. basalis females tended to self-superparasitize and stay motionless near the hosts. After detecting an E. vuilleti female entering the patch, they attacked and chased her permanently from the patch. Females of both species spent less time in the patch when faced with a competitor than when alone. This study is the first to test the influence of direct interspecific competition and arrival order on patch exploitation strategies in parasitoid species, and highlights the necessity to include agonistic behaviors in theoretical models predicting optimal patch residence time in competitive situations.

Previous experience and contest outcome: winner effects persist in absence of evident loser effects in a parasitoid wasp.

The experience of a previous conflict can affect animals' performance during a later contest: a victory usually increases and a defeat usually decreases the probability of winning a subsequent conflict. These winner and loser effects could result from a reassessment by contestants of their perceived fighting abilities. Game-theoretic models based on this assumption predict that a loser effect can exist alone or in the presence of a winner effect, but a winner effect cannot persist alone, at least when contestants are young and without experience of contest. Moreover, when both effects coexist, the loser effect is expected to be of a greater magnitude and last longer than the winner effect. To date, these predictions have been supported by empirical evidence. Here we show for the first time that a winner effect can exist in the absence of any evident loser effect in a parasitoid wasp, Eupelmus vuilleti, when fighting for hosts. This finding consequently raises questions about the possible mechanisms involved and challenges the main assumption of previous theoretical models. We suggest an alternative explanation for the evolution of only winner effects that is based on the modification of contestants' subjective value of the resource rather than on a reestimation of their fighting abilities.

Abdominal sensory equipment involved in external host discrimination in a solitary parasitoid wasp.

Already parasitized hosts are often of poorer quality than healthy hosts. It is therefore usually advantageous for parasitoid females to recognize and reject them. Parasitized hosts can be identified on the basis of various physical or chemical marks present on the surface or inside the hosts or their surroundings in the case of concealed host. Here we studied host discrimination behaviors of females of a certain population of Pachycrepoideus vindemmiae, a solitary ectoparasitoid, which are known to reject large-sized parasitized hosts after an abdominal examination of their surface. We first investigated females' recognition behaviors of host parasitism status when confronted to small-sized hosts (Drosophila melanogaster pupae) as host size may influence the use of different cues for host selection. We showed that, in such a situation, females also discriminate parasitized hosts after an external host exploration with the tip of their ovipositor sheath (third valvulae). We then described the sense organs present on the different parts of the ovipositor by means of scanning and transmission electron microscopy analysis. As the extremity of the third valvulae bears only one type of sensilla that appears to be chemoreceptors, we considered these sensilla as highly likely to be involved in host discrimination in P. vindemmiae. To our knowledge, this is the first time that receptors located on the ovipositor sheath are described as implicated in host discrimination in parasitoid wasps. We discuss potential chemical markers that might be detected by these receptors.

Encountering competitors reduces clutch size and increases offspring size in a parasitoid with female-female fighting.

Understanding the size of clutches produced by only one parent may require a game-theoretic approach: clutch size may affect offspring fitness in terms of future competitive ability. If larger clutches generate smaller offspring and larger adults are more successful in acquiring and retaining resources, clutch size optima should be reduced when the probability of future competitive encounters is higher. We test this using Goniozus nephantidis, a gregarious parasitoid wasp in which the assumption of size-dependent resource acquisition is met via female-female contests for hosts. As predicted, smaller clutches are produced by mothers experiencing competition, due to fewer eggs being matured and to a reduced proportion of matured eggs being laid. As assumed, smaller clutches generate fewer but larger offspring. We believe this is the first direct evidence for pre-ovipositional and game-theoretic clutch size adjustment in response to an intergenerational fitness effect when clutches are produced by a single individual.

Volatile emission by contest losers revealed by real-time chemical analysis.

Animal interactions often involve chemical exchange but simultaneous evaluation of chemistry and behaviour has been problematical. Here we report findings from a novel method, atmospheric pressure chemical ionization-mass spectrometry (APCI-MS) coupled with manipulation of molecular-mass achieved by rearing organisms on deuterium-enhanced nutrients. This allows real-time monitoring of the occurrence and quantity of volatile chemicals released by each of two interacting individuals, in tandem with behavioural observations. We apply these methods to female-female contests in the parasitoid wasp Goniozus legneri. We show that this species emits the spiroacetal 2-methyl-1,7-dioxaspiro[5.5]undecane. Chemical release is most common in more behaviourally aggressive contests, which occur when prior resource owners successfully resist take-over by similar-sized intruder females. Volatiles released during contests are always emitted by the loser. Aggression in contests is reduced after spiroacetal release. We suggest that the spiroacetal functions as a weapon of rearguard action. We anticipate that APCI-MS, which is rapid, non-intrusive and relatively inexpensive to operate, will be widely applied in studies linking chemistry and behaviour.