Postharvest Azadirachta indica (A. Juss) biofumigant for Trichoplusia ni (Hübner) larvae control

Trichoplusia ni is a widely distributed pest that affects many cole crops, including broccoli,

Brussels sprouts, cabbage, cauliflower, collards, kale, and kohlrabi. Chemical insecticides are the first choice for its control. Nevertheless, during cole crops postharvest, lepidoptera neonates may damage the vegetable and reduce its profitability.  The Neem tree is known to act as a repellent, anti-food and growth regulator in many insect species, and possesses antibiotic effect against many microorganisms. On the other hand, changes in gut microbiota of several lepidoptera larvae have been linked to an increased susceptibility of Bacillus thuringiensis products as well as immune response markers, but insect metabolic changes after neem volatiles exposure is unknown. This study was undertaken to evaluate the potential of volatile compounds from neem tree leaves as biofumigant to control T. ni larvae during postharvest. Results showed that neonates exposure to neem resulted in 79% mortality, and weight reduction in surviving larvae. Midgut analysis revealed that microbiota was decreased when the expression of Enterobacteriaceae group 16S ribosomal group gene was compared with unexposed larvae. In addition, RT-PCR semi-quantitative analysis revealed an increased expression of a gene associated with detoxification of chemical insecticides (C-P₄₅₀) and two antimicrobial peptide genes involved in humoral immunity (lysozyme), the expression of attacin, defensin, galleriomycin, gloverin, lebocin, PGRP and phenoloxidase genes was not altered, and cecropin was not expressed. The relevance of using neem leaves as biofumigant to control cabbage looper during postharvest is discussed.