Dynamics of Natural Mortality Factors of Immature Diatraea saccharalis (Fabricius) (Lepidoptera: Crambidae) in Sugarcane Adjacent to Forest Fragments

Abstract

Pest regulation may be favoured in crop fields adjacent to semi-natural vegetation such as fragments of the Atlantic Forest in Southeastern Brazil. Therefore, the objective of this study was to analyse the dynamics of mortality factors for eggs and larvae of Diatraea saccharalis (Lepidoptera: Crambidae) in sugarcane adjacent to two types of forest fragments (Plateau and Gallery) at two distances from these fragments during two growing seasons. In each area (seven sugarcane plots), two 50 m long transects were established, parallel and spaced at 5 and 100 m from the field edge, and cohorts of the insect at each stage of development were monitored. The collected data were used to construct an ecological life table and determine the main mortality factors. Natural mortality factors that could not be characterised were grouped as unknown. In both seasons and stages of development observed, there was no difference in mortality between the two types of forest fragments (Plateau and Gallery) or between the two distances from the forest. For the egg stage, the mortality factors were classified as inviable due to infertility, predation, parasitism, desiccation and dislodgement. In both seasons, there was a significant difference in the natural mortality factors of D. saccharalis, with predation distinct from the others. Ants (Hymenoptera: Formicidae) and green lacewings (Neuroptera: Chrysopidae) were the most frequent predatory agents and occurred at both distances and types of forest fragments. For the larval stage, the mortality factors were classified as predation, parasitism, drowning and unknown, with the unknown group differing from the others. Unknown factors might have included predation, larval movement towards other plants and displacement caused by wind after hatching. Overall, predation is a key mortality component of D. saccharalis suppression. Therefore, agricultural practices focused on the conservation of natural enemies such as predators may provide more sustainable management.