Insect migration and dispersal with emphasis on Mediterranean ecosystems

Abstract

Insects migrate in many different scales ranging from a few metres to many hundreds of kilometres. The holistic conceptual model hosts a suite of widely accepted definition of insect migration. The predisposition of some insects for migration is called migratory syndrome and involves the condition of the flight muscles, the oviposition period and timing, the fecundity, the energy uptake and wing polymorphism. Pheromones are another useful trait of migratory insects since they are used to gather the scattered migrants in a restricted space. The cost of a migration event was compared to the cost of other solutions to the problems of overcrowding or habitat destruction. In many cases migration is the less costly solution apart from other benefits that may incur to the insect such as natural selection, since migration is a safe estimator of the abilities of the insect and its health status. To estimate the cost of insect migration several authors have proposed formulas with hardly estimable parameters. Moreover, it is very difficult for the insect to manipulate parameters such as the migration time and the available energy for migration. It is speculated that in evolutionary time, the manipulation in evolutionary time of some parameters is not possible in the physiological context of an insect, and for this, a migration event may last more than two or three generations. The migration of insects is now studied using, apart from biological methods, new approaches such as specifically constructed entomological radars. Climate change in general and global warming in particular affect insect migration in several ways. It causes phenological shifts to the host plants, destruction of habitat, extensive fragmentation of landscapes, marine incursions and faunal reshuffling. Also, many insects and host plants are responding in different ways to global warming and greenhouse gases. In Mediterranean insects such as Euplagia quadripunctaria there is a short scale migration primarily caused by searching for ideal climatic conditions.