Whiteflies of the Mediterranean chaparral: A case of mutual manipulation

The life cycles of two plant species in the Mediterranean chaparral, the evergreen Arbutus andrachne and the deciduous Rhamnus lycioides, were studied, as were the cycles of two stenophagous whitefly species that live on them, Trialeurodes lauri and Dialeurolobus rhamni, respectively. Trialeurodes lauri is univoltine, diapausing from June to March corresponding to the plant’s leaf dormancy. The diapause is related to the plant’s leaf dormancy, and removal of branches infested with diapausing whiteflies between July and February causes a break in the diapause. Dialeurolobus rhamni has two generations a year. Eggs are laid in March with adults resulting in May and June. These lay again and their immatures overwinter till the next spring. By examining the leaves on the plants and those shed to the ground, it was shown that the overwintering mode of D. rhamni on the deciduous R. lycioides is mainly achieved by remaining on non-shed leaves until the next springtime. This is enabled through the delay of leaf shed and adherence of infested leaves to the plant significantly longer than uninfested leaves. In addition, some adults will emerge from infested leaves shed to the ground, with their diapause apparently independent of the status of the leaf they are on. Thus, although the two systems reflect plant–insect adaptations to the Mediterranean conditions, they differ markedly in the details of the interaction, each reflecting both the cycle of the plant and the adaptations of the insect.