Larval and/or Adult Exposure to Intraguild Predator Harmonia axyridis Alters Reproductive Allocation Decisions and Offspring Growth in Menochilus sexmaculatus

Simple Summary Predation has significant impacts on a prey’s ecology and evolution. In many species, maternal effects can improve offspring survival in response to predation by altering resource allocation to young and reproducing larger offspring. While the perception of predation risk can vary according to a prey’s life stage, whether maternally experienced intraguild predation (IGP) risk during different life stages affects the maternal effects of predatory insects remains unknown. This study examined the influence of exposure to intraguild predators (Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae)) during the larval and/or adult stages on reproductive decisions and offspring growth in Menochilus sexmaculatus (Fabricius). Although the exposure of M. sexmaculatus larvae and/or adults to IGP risk did not influence egg size, it increased offspring body size in IGP environments; however, their exposure to IGP risk increased trophic egg production. Because IGP is commonly observed in M. sexmaculatus and favours relatively larger protagonists, the IGP risk perceived by different stages of M. sexmaculatus induces maternal effects; this can be an adaptive survival strategy to defend against H. axyridis. This study is an essential step towards understanding the role of maternal effects on the survival of M. sexmaculatus in IGP scenarios and furthers our understanding of M. sexmaculatus population dynamics in the field. Abstract Maternal effects can reduce offspring susceptibility to predators by altering resource allocation to young and reproducing larger offspring. While the perception of predation risk can vary according to a prey’s life stage, it is unclear whether maternally experienced intraguild predation (IGP) risk during different life stages influences the maternal effects of predatory insects. We investigated the influence of exposure to intraguild predators (Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae)) during the larval and/or adult stages on reproductive decisions and offspring growth in Menochilus sexmaculatus (Fabricius). Independent of the life stage, when M. sexmaculatus females experienced IGP risk, their body weight and fecundity decreased, but the proportion of trophic eggs produced increased. However, egg mass, egg clutch number, and egg clutch size were not influenced by the treatment. Next, when offspring encountered H. axyridis, mothers experiencing IGP risk during the larval and/or adult stages could increase their offspring’s weight. Moreover, offspring in IGP environments reached a similar size as those with no-IGP environments when mothers experienced IGP risk during the larval and/or adult stages. Overall, M. sexmaculatus larval and/or adult exposure to IGP risk had no influence on egg size, but increased offspring body size when faced with H. axyridis. Additionally, mothers experiencing IGP risk during different life stages showed increased production of trophic eggs. Because IGP is frequently observed on M. sexmaculatus and favours relatively larger individuals, different stages of M. sexmaculatus express threat-sensitively to IGP risk; inducing maternal effects can be an adaptive survival strategy to defend against H. axyridis.