Summary1. Host plant quality affects herbivorous insect performance and consequently their susceptibility to natural enemies. Recently, it has been hypothesized that the immune function of herbivorous insects can be altered by their host plant, thus generating variation in their susceptibility to entomopathogens. Previous studies testing this hypothesis provided contradictory outcomes, mainly as a result of the differences in methodology such as measuring a single-immune parameter rather than considering trade-off-mediated interactions between immune defence systems of the insect. Here, we hypothesized that plant-mediated changes in insect immunity could result from the alteration of physiological immune effectors of the herbivore evident as trade-offs. 2. Larvae of an inbred strain of the European grape berry moth Eupoecilia ambiguella were reared on five artificial diets each based on a different grape variety (Chardonnay, Chasselas, Gewurztraminer, Merlot, Riesling) and tested for changes in the baseline concentration of haemocytes, activities of the prophenoloxidase (PPO) system and of antimicrobial peptides of their haemolymph. Immune responsiveness of larvae across diets was also assessed by measuring changes in haemocyte concentration and activity of the PPO system after a bacterial immune challenge. 3. We found that variation among diets significantly affected immune defences of larvae. The alteration of the E. ambiguella immune system appears plastic and partly mediated by existing physiological trade-offs between immune pathways, at least between induced antibacterial defences and the PPO system. 4. These results clearly show that host plant quality can affect immune defences and potentially disease resistance of E. ambiguella and that these changes in immunity may also result from intrinsic trade-offs between immune defence systems in insects.

Grape is a major crop, covering 7.5 M ha worldwide, that is currently being confronted with three main challenges: intensive pesticide use that must be reduced, invasion by new pests/diseases, and climate change. The biological control of pests and vectors would help address these challenges. Here, we review the scientific literature on the biological control of grape moths by macroorganisms (excluding nematodes). Two components, biological control with an active human role, mainly using biocontrol agents through inundation or inoculation, and conservation biological control, are considered. The major points are the following. (1) Tortricid grape moths seriously damage grapes worldwide, causing yield losses and quality reduction. The more geographically widespread species, Lobesia botrana, continues to extend its range, invading South American and, more recently, North American vineyards. (2) Parasitoids and predators (including arthropods, birds, and bats) that can control grape pests are very diverse. (3) Different methods exist to assess pest control efficiency in the field but some of them remain to be developed. (4) Environmental factors, including host plants, landscape, grass or floral covers, and organic practices, affect the natural control of grape moths. (5) Pest resistance to parasitoids strongly depends on their immune system, which is controlled by the host plant. Future climate changes may modify this tritrophic interaction and thus affect biological control strategies. We conclude that biological control has a great deal of potential in viticulture and that addressing these key factors would improve the efficiency levels of biological control strategies. This would help growers and stakeholders to significantly reduce insecticide use in vineyards.

BackgroundTo optimize their resistance against pathogen infection, individuals are expected to find the right balance between investing into the immune system and other life history traits. In vertebrates, several factors were shown to critically affect the direction of this balance, such as the developmental stage of an individual, its current risk of infection and/or its access to external help such as parental care. However, the independent and/or interactive effects of these factors on immunity remain poorly studied in insects.ResultsHere, we manipulated maternal presence and pathogen exposure in families of the European earwig Forficula auricularia to measure whether and how the survival rate and investment into two key immune parameters changed during offspring development. The pathogen was the entomopathogenic fungus Metarhizium brunneum and the immune parameters were hemocyte concentration and phenol/pro-phenoloxidase enzyme activity (total-PO). Our results surprisingly showed that maternal presence had no effect on offspring immunity, but reduced offspring survival. Pathogen exposure also lowered the survival of offspring during their early development. The concentration of hemocytes and the total-PO activity increased during development, to be eventually higher in adult females compared to adult males. Finally, pathogen exposure overall increased the concentration of hemocytes—but not the total-PO activity—in adults, while it had no effect on these measures in offspring.ConclusionsOur results show that, independent of their infection risk and developmental stage, maternal presence does not shape immune defense in young earwigs. This reveals that pathogen pressure is not a universal evolutionary driver of the emergence and maintenance of post-hatching maternal care in insects.

Investigating the expression of trade-offs between key life-history functions is central to our understanding of how these functions evolved and are maintained. However, detecting trade-offs can be challenging due to variation in resource availability, which masks trade-offs at the population level. Here, we investigated in the European earwig Forficula auricularia whether (1) weapon size trades off with three key immune parameters – hemocyte concentration, phenoloxidase and prophenoloxidase activity - and whether (2) expression and strength of these trade-offs depend on male body condition (body size) and/or change after an immune challenge. Our results partially confirmed condition dependent trade-offs between weapon size and immunity in male earwigs. Specifically, we found that after an immune challenge, weapon size trades off with hemocyte concentrations in low-condition, but not in good-condition males. Contrastingly, weapon size was independent of pre-challenge hemocyte concentration. We also found no trade-off between weapon size and phenoloxidase activity, independent of body condition and immune challenge. Overall, our study reveals that trade-offs with sexual traits may weaken or disappear in good-condition individuals. Given the importance of weapon size for male reproductive success, our results highlight how low-condition individuals may employ alternative life-history investment strategies to cope with resource limitation.