Abundance and diversity of predatory insects in cotton agroecosystems under malathion ULV application

Abstract

Background: Cotton is one of the main industrial crops worldwide and a key raw material for the textile industry, generating thousands of jobs along its value chain. In Mexico, the main producing states are Chihuahua, Coahuila, Durango, and Tamaulipas. The cotton boll weevil is the most important pest of the crop, and its control relies on aerial applications of malathion ULV, a widely used organophosphate insecticide. However, its use may cause adverse effects on predatory insects within the agroecosystem, which play a key role in the natural regulation of secondary pests. Objective: To identify the diversity and abundance of predatory insects associated with cotton agroecosystems in relation to the number of malathion ULV applications. Methodology: Three fields were selected in the states of Chihuahua, Coahuila, Durango, and Tamaulipas, with a range of 0 to 30 aerial applications of malathion ULV. Sampling consisted of 20 net sweeps strokes at five sites per field, for a total of 100 sweeps per field. Predatory insects collected were identified and counted in the laboratory. The evaluated variable was the number of insects per 100 net sweeps for each species or taxonomic group. Abundance data were transformed using the natural logarithm (x + 1). Statistical analysis was performed using LSD tests at a 5% significance level for mean comparisons. Results: Thirteen species of predatory insects were identified. In 2023, Chrysoperla sp. and Hippodamia convergens showed higher abundance in Coahuila and Durango. In Tamaulipas, Coleomegilla maculata and Geocoris punctipes were predominant, whereas arachnids were dominant in Chihuahua. In 2024, H. convergens and Orius tristicolor were mainly abundant in Durango, while Zelus sp., G. punctipes, and arachnids were more representative in Chihuahua. Implications: These results highlight the importance of implementing selective pest management strategies that minimize negative effects on beneficial fauna within cotton agroecosystems. Conclusion: Orius tristicolor was the most abundant predatory species across the evaluated cotton agroecosystems in Mexico. The observed variation among densities and taxonomic groups of predatory insects may be associated with differences in exposure and application conditions of malathion ULV, rather than with a uniform direct toxic effect on the entire beneficial fauna.