Exposure to males reduces the benefit gained from multiple mating in female Galerucella birmanica Jacoby (Coleoptera: Chrysomelidae)

Polyandry contributes to Gonipterus platensis (Coleoptera: Curculionidae) rearing

Background

Gonipterus platensis Marelli, 1926 (Coleoptera: Curculionidae) is one of the main defoliating beetles in Eucalyptus plantations. Biological control with egg parasitoids is one of the main control strategies for this pest and a constant supply of fresh host eggs is required to rear the parasitoids. Polyandry can influence Gonipterus oviposition by increasing female fecundity and fertility; however, the high density of individuals in laboratory colonies can lead to male harassment, resulting in lower reproduction rate. The aim of this study was to measure the effects of monoandry and polyandry on the reproduction of G. platensis and the effects of male harassment on laboratory rearing conditions.

Methods

Reproductive parameters were compared between three treatments: monoandry, where the female was allowed to mate daily with the same male; no choice polyandry, where the female was allowed to mate daily with a different male; and polyandry with choice, where the female was allowed to mate daily, but with a choice between five different males. Another experiment varying the density of males was conducted to evaluate the effect of male harassment.

Results

Polyandry with choice resulted in the longest period of oviposition, highest fecundity and highest number of eggs per egg capsules when compared to monoandrous females. No negative effect related to male harassment in the laboratory, such as decreased fertility, fecundity, or number of eggs per egg capsule, was detected.

Conclusion

Polyandry contributes to mass rearing as it increases fecundity and oviposition period on females and there is no evidence of male harassment on G. platensis.

Males, but not females, perform strategic mate searching movements between host plants in a leaf beetle with scramble competition polygyny

Mate searching is assumed to be performed mostly by males, but when females benefit from multiple mating or are under risk of failing to mate, they may also perform mate searching. This is especially important in scramble competition polygynies, in which mate searching is the main mechanism of mate competition. Typically, more mobile individuals are expected to achieve higher mating success because mobility increases their probability of finding mates. If we assume individual movements are mainly explained by mate searching in scramble competition polygynies, we can investigate searching strategies by asking when individuals should leave their location and where they should go. We hypothesize that individuals will leave their locations when mating opportunities are scarce and will seek spatially close sites with better mating opportunities. We tested these hypotheses for males and females of Leptinotarsa undecimlineata, a leaf beetle with scramble competition polygyny in which both sexes are promiscuous. Individuals mate and feed exclusively on Solanum plants, and thus, individual movements can be described as switches between plants. Females were less likely than males to leave isolated plants, and both males and females moved preferentially to neighboring plants. Males were more likely to leave when the local number of females was low, and the number of males was high. They moved to plants with more females, a behavior consistent with a mate searching strategy. Females were more likely to move to plants with fewer males and many females, a behavior consistent with male harassment avoidance. Strategic movement is widely considered in foraging context, but seldom in a mate searching context. Considering that selection to minimize searching costs, maximize mating success, and minimize harassment may be ubiquitous in nature, we argue that strategic movements by mate searching individuals are likely to occur in many species.

Genetic Structure of Water Chestnut Beetle: Providing Evidence for Origin of Water Chestnut

Water chestnut beetle (Galerucella birmanica Jacoby) is a pest of the water chestnut (Trapa natans L.). To analyze the phylogeny and biogeography of the beetle and provide evidence for the origin of T. natans in China, we conducted this by using three mitochondrial genes (COI, COII and Cytb) and nuclear ITS2 ribosomal DNA of G. birmanica. As for mtDNA genes, the beetle could be subdivided into three groups: northeastern China (NEC), central-northern-southern China (CC-NC-SC) and southwestern China (SWC) based on SAMOVA, phylogenetic analyses and haplotype networks. But for ITS2, no obvious lineages were obtained but individuals which were from NEC region clustered into one clade, which might be due to sequence conservation of ITS2. Significant genetic variation was observed among the three groups with infrequent gene flow between groups, which may have been restricted due to natural barriers and events in the Late Pleistocene. Based on our analyses of genetic variation in the CC-NC-SC geographical region, the star-like haplotype networks, approximate Bayesian computation, niche modelling and phylogeographic variation of the beetle, we concluded that the beetle population has been lasting in the lower, central reaches of the Yangtze River Basin with its host plant, water chestnut, which is consistent with archaeological records. Moreover, we speculate that the CC-NC-SC population of G. birmanica may have undergone a period of expansion coincident with domestication of the water chestnut approximately 113,900-126,500 years ago.