Life tables for the diamondback moth (Plutella xylostella) in southeast Brazil indicate ants and spiders as leading mortality factors

Abstract

AbstractThe diamondback moth (DBM), Plutella xylostella (Lep.: Plutellidae), causes significant losses in Brassica crops. Leaf consumption by the larvae reduces plant yield and causes the contamination of heading brassicas. Chemical control usually provides unsatisfactory results due to the quickly developed resistance of DBM populations to insecticides. Thus, natural control by biotic factors (predators, parasitoids, and entomopathogens) is crucial and should be managed upon knowledge of their role as DBM regulators. The leading mortality factors of DBM across the annual seasons in southeast Brazil were investigated by conducting 57 field life tables for 2 years. The highest and lowest total mortalities of DBM occurred in winter (99.7%) and autumn (94%). Predation was the main mortality factor in all seasons. Marginal parasitism rates were higher in spring and lower in autumn, and Oomyzus sokolowskii (Hym.: Eulophidae) accounted for almost 90% of total parasitism. The highest mortalities by rainfall were recorded in spring (44.5%), while physiological death and infection caused low mortalities (≤ 6%) throughout the seasons. In addition, models were built to investigate the main predators acting on the DBM life stages; Araneae, Brachymyrmex bruchi, and Tetramorium simillimum (Hym.: Formicidae) were the predators associated with egg/L1 predation whereas Solenopsis saevissima, T. simillimum and Camponotus spp. (Hym.: Formicidae) were the ones responsible for L4/pupa predation. The L2/L3 stage was the least affected by predation, and the final model for this stage did not include any predator. In light of these findings, habitat manipulation and insecticide selectivity are discussed as measures to preserve the main predators and parasitoid.