Bioecology of Alabama argillacea II. Thermal requirements and number of generations in the state of São Paulo, Brazil

Abstract

The cotton leafworm (Alabama argillacea Hübner (1818) has, each year, a constant period of occurence during the cotton growing season, in the State of São Paulo, Brazil. Surveys with light traps in six localities of the State (Assis, Campinas, Mococa, Piracicaba, Ribeirão Preto and Valinhos) were made in order to find out those periods. With its thermal requirements it was possible to know the number of its generations all through the year in order to provide basic data concerning this pest, as a prediction of its outbreak, and for improving control procedures in the crop. The thermal requirements of the cotton leafworm were determined based on the biological results obtained in climatic chambers set at 20, 25, 30 and 35°C (60 ± 10% relative humidity and a 14-hour photoperiod) with IAC-17 cultivar leaves. The threshold of development for the egg, larval, pre-pupal and pupal phases was calculated by the coefficient of variation method; values of 12.6; 9.3; 14.9 and 13.5°C, respectively, were found. The formula for obtaining those thermal requirement data was: K = y (t - a). Values of 37.20, 195.97, 10.10 and 110.35 degree-days for the phases of egg, larva, pre-pupa and pupa, respectively, were obtained. Basing on the total sum of degree-days per "péntada" for the six localities, two to seven generations per year may occur.