MIGRATION IN INSECTS - COST AND STRATEGIES

1. An optimal energy partitioning model is used to predict the optimum adult sizes of the soma, gonads and flight apparatus in insects. A comparison of the investment in gonads and lipoidal reserves in winged and unwinged individuals in species from three families of aphids is used to test the predictions and define the cost of developing a flight apparatus. 2. In accordance with theoretical predictions winged aphids had smaller gonads than wingless aphids and there appeared to be a trade-off between the investment in gonads and lipoidal reserves in both morphs. 3. Developing a flight apparatus prolongs development and resulted in a 20% reduction in gonad size. 4. The length of time for which aphids survived starvation was positively correlated with the relative size of their lipoidal reserves. 5. The relative size of the lipoidal reserves appeared to be negatively correlated with habitat quality and positively correlated with habitat fragmentation. 6. In accordance with theoretical predictions autolysis of wing muscles was correlated with a great increase in the size of the gonads and occurred in aphids that live in fragmented habitats. 7. The ecological significance of these findings are discussed in the context of the way in which phytophagous insects, and aphids in particular, might perceive their environment.