Influência da estrutura populacional e do estádio de desenvolvimento no controle biológico de Mononychellus tanajoa (Bondar) por ácaros predadores (Acari: Tetranychidae, Phytoseiidae)

Abstract

The attack of the cassava green mite Mononychellus tanajoa is the leading cause of cassava yield reduction in the state of Maranhão, Brazil. Predatory mites of the family Phytoseiidae are the most important natural enemies of pest mites. We determined the abundance of the developmental stages of M. tanajoa and E. ho during the cultivation cycle of cassava. Additionally, we evaluated the effectiveness of active stages (nymph and female) of the predatory mite Euseius concordis, found in cassava fields, on the stages of egg, immature and female of the cassava green mite by predation, oviposition and population growth bioassays. The larva stage of the cassava green mite M. tanajoa had lower population densities compared with the other developmental stages from the beginning of the dry season onwards. There was a tendency for higher egg densities of M. tanajoa followed by the stages of adult and nymph. There was no difference in the abundance of different developmental stages of the predatory mite E. ho throughout the cultivation cycle of cassava. Densities of all developmental stages of M. tanajoa were negatively correlated with precipitation. The stages of egg, nymph and adult of M. tanajoa were positively correlated with temperature while the stage of larva was negatively correlated. Furthermore, the developmental stages of M. tanajoa were not correlated with the relative humidity. Densities of all developmental stages of the predatory mite E. ho were not correlated with any environmental variable. Egg and immature stages of M. tanajoa were the most preyed on by females and nymphs of E. concordis. There was a trend towards greater consumption of eggs of the green spider mite by both females and nymphs of the predatory mite E. concordis. Additionally, the oviposition rates and population growth rates of E. concordis were higher when fed on eggs and immatures of M. tanajoa in comparison to females. We conclude that it is important to consider the population structure in studies of population dynamics of arthropods as each developmental stage experiences and responds uniquely to the local environment over time. Additionally, the potential for biological control of E. concordis depends on its active phase of development (nymph, female) as well as the stage of development (egg, immature, female) of the cassava green mite.