Developmental, morphological, and behavioural plasticity in the reproductive strategies of stink bugs and their egg parasitoids
The environment shapes the physiology, morphology, and behaviour of organisms through complex, multidimensional ecological and evolutionary processes. The reproductive success of individual animals is determined by how well their phenotype is suited to an environment that is constantly changing over single and multi-generational time scales. At the same time, phenotypes are shaped by the environment, which triggers adaptive modifications of animal reproductive strategies while also imposing important constraints. In this thesis, using stink bugs and their parasitoids as model organisms, I considered how several types of plasticity can interact to influence biological fitness, and how plasticity in reproductive strategies responds to several important components of environmental change (host quality, ultraviolet radiation, temperature, biological invasions). Firstly, I compared the response of behavioural and life history traits to body size variation in the parasitoid Telenomus podisi Ashmead (Hymenoptera: Platygastridae), finding that reaction norms of behavioural traits more often had positive slopes than life history traits. Next, I found that the predatory stink bug Podisus maculiventris Say (Hemiptera: Pentatomidae) can selectively control the colouration of its eggs. Egg pigmentation in this species protects embryos against ultraviolet radiation as part of a complex oviposition strategy that evolved in response to a suite of environmental factors. Then, I tested how thermal stress affects the memory dynamics of the parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Platygastridae) learning the reliability of chemical traces left by its host. These experiments revealed that both high and low stressful temperatures prevented forgetting, affecting the time allocation of parasitoids on patches of host chemical traces. I also developed a general framework to classify temperature’s effects on all aspects of ectotherm behaviour, distinguishing constraints from adaptive behavioural adjustments. Finally, I tested the ability of an indigenous parasitoid (T. podisi) to attack the eggs of a new invasive pest of agriculture, Halyomorpha halys Stål (Hemiptera: Pentatomidae). The results showed that T. podisi attacks the eggs of H. halys but cannot develop, demonstrating that the invasive pest is an “evolutionary trap” for indigenous parasitoids, which could indirectly benefit native stink bug species by acting as an egg and time sink for the parasitoid. These findings have important implications for how insects, including those involved in biological control programs, respond to environmental change.
entomologie phenotypic plasticity animal behaviour reproductive biology entomology Pentatomidae Platygastridae