Immigration, population growth and mortality of insects and mites on cassava in Brazil

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Abstract
A small isolated cassava field in Minas Gerais, Brazil, was readily invaded by species of insects and mites already known as cassava pests. Most immigrants were small (< mm) piercing-rasping feeding types. Three of these (the lace-bug Vatiga illudens (Drake), the thrip Scirtothrips manihoti (Bondar) and the mite Mononychellus tanajoa (Bondar)) showed an exponential population increase in the absence of their natural enemies. The onset of the wet microclimate from dew and rain was a key mortality factor for these three species. Storms resulted in a catastrophic decline of the populations, especially that of M. tanajoa. Predators and interspecific competition from S. manihoti were secondary suppressive factors on the M. tanajoa population. Three other species (the caterpillar of Erinnyis ello (L.) and the mites Tetranychus urticae Koch and T. cinnabarinus (Boisd.)) were completely eliminated in the experimental area by parasites or predators. Other feeders, such as the shoot-inhabiting larva of the flies Neosilba spp. and the fungivorous beetle Psyllobora spp., as well as more minor species, were also studied.

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