Finding Hosts Indirectly

Habitat location appears to be the first step for a number of species, although it is difficult to prove in practice. For example, grass-feeding grasshoppers are attracted to open habitats where grasses are generally abundant, but there are likely to be other reasons for this behavior. The pierid butterfly Euchloe belemia, however, is attracted to patches of thorn plants where, typically, its small host plants grow most densely.

Some small insects that find their hosts within fairly short distances may simply rely on increases in activity and turning behavior when they detect the appropriate odor, so that they are more likely to encounter their hosts. Among chrysomelid beetles, some engage in random movements that show little change with level of host odor; crucifer flea beetles in the genus Phyllotreta, for example, move randomly within and between host patches. It has been shown mathematically that random activity is important in overall efficiency of search strategies because, under many circumstances and especially when host signals are weak and plant suitability variable, exploratory search enhances the likelihood that an individual will contact the better plants.

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