Seasonal variation of natural mortality factors of the guava psyllid Triozoida limbata.

It is important to understand how components of the agroecosystem interfere with the attack of a pest species and their seasonality in order to use these components in IPM programs. This study focused on the evaluation of the seasonality of natural control factors associated with the guava psyllid Triozoida limbata (Enderlein) in Brazil. Life-table data were collected from an experimental guava orchard during four periods that roughly represented four seasons. Natural mortality was monitored daily through the immature stages, and the relative importance of each natural mortality factor and its seasonality was determined. Significant statistical differences were observed in the mortality during the four periods (P < 0.05). Several factors contributed to the mortality of T. limbata, including rainfall, physiological disturbance, the parasitoid Psyllaephagus sp. (Hymenoptera: Encyrtidae) and specific predators: syrphids, predatory wasps and other generalist predators. Depending on the location of nymphs (exposed or inside galls), the relative importance of the different natural mortality factors changed. The principal component analysis (PCA) showed some trends in the relationship of natural control agents and weather conditions. For example, the occurrence of predatory wasps was positively correlated with temperature and occurrence of winds; the occurrence of syrphids and Psyllaephagus sp. were negatively correlated with temperature and winds; and the occurrence of other generalist predators were negatively correlated with the occurrence of rainfall and photoperiod. The results showed the importance of natural mortality factors for the management of T. limbata and their changes through the different seasons which should be considered when implementing IPM programs in guava orchards.