Do migrant moth species have adaptations that reduce the cost of long distance flight on future reproduction?

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Studies on several insect species exhibiting wing polymorphism (having both winged and wingless morphs) have shown that the reproductive output of wingless adults is higher than their winged counterparts that migrate out of deteriorating habitats. These results have been interpreted as supporting the idea that flight comes at a cost to reproduction. However, this has not been examined carefully in species where all adults are winged and require flight for the location of food, mates and oviposition sites. Furthermore, it has been hypothesized that migrant species have evolved traits to reduce the cost of maintaining flight apparatus on subsequent reproductive output. In my research group we have been using the true armyworm, P. unipuncta, where all adults have functional wings, as a model system to study pheromone mediated mating and have shown there are marked behavioural and physiological differences between migratory (North America) and non-migratory (Azores) populations. We will use the North American (NA) migrant population, and non migrant populations from the Azores (AZ) and Hawaii (HA), to examine the cost of flight on reproduction in a monomorphic species and to test the hypothesis that migrants have evolved traits to reduce the costs of migration. We will compare NA individuals reared under different controlled conditions in the laboratory and under natural field conditions (insectary) on both artificial diet and natural host plants during the summer (non-migrants) and fall (migrants). We will test for differences in morphology (wing size, thoracic mass) to determine if there is differential allocation to flight machinery (muscle/wings) and examine the effect of flight of different durations on the fecundity of non-migrants and migrants fed different sugar regimes before and after flight. These experiments will allow us to determine if there are reproductive costs associated with migration and whether post-migratory feeding and mating might mitigate them. We will also examine thoracic muscle to determine if there are structural and/or physiology differences between residents and migrants (from natural populations and field rearings) to determine if migrants have modifications that reduce the costs of flight on reproduction. These experiments will be repeated with non migrant individuals from AZ and HA, as AZ adults are smaller and become sexually mature at a younger age, yet have a significantly higher life time reproductive output than those from NA.***Our recent work has shown that the behaviours associated with pheromone mediated mating in three unrelated species changed in response to short term changes in atmospheric pressure (AP). We will now test the hypotheses that flight propensity of adult armyworm moths will be not only be affected by cues associated with seasonal change, but also in response to daily fluctuations in AP that provide reliable indicators of flight conditions.**