Is there a landscape effect on the abundance of Helicoverpa armigera larvae in cotton fields? A case study in the northern Benin - West Africa
1. Helicoverpa armigera (Hübner) (Lepidoptera, Noctuidae) is a worldwide and polyphagous pest considered to be one of the most important pests threatening several crops, including cotton. In Benin, cotton crop is the most important commercial crop and export product. The aim of this study was to analyse the influence of landscape composition on the abundance of H.armigera adults in cotton fields in northern Benin.
2. The abundance of H. armigera was monitored using light traps for adults and weekly observations of 50 cotton plants for larvae abundance in 20 cotton fields each year during the rainy period from October to November in 2011 and 2012. Cotton fields were selected and studied in relation to circular landscapes with varying compositions in cotton, tomato, maize, and natural vegetation areas, and a radius of 500 metres around the selected cotton field. We analysed the proportion of carbon isotopes in the wing of trapped H. armigera to identify moths which larvae fed on C4 plants.
3. We found that cotton fields that were surrounded by cotton crops (more than 25% of the landscape) were significantly more infested by H. armigeralarvae than the others fields. While for adults, we did not find any landscape composition influence. The trophic origin of adults obtained by analysing the carbon isotopes was not influenced by the landscape composition.
4. This study highlights the importance of considering both landscape variables and agricultural practices to help find an alternative to the use of pesticides. The study shows that landscape ecology studies for H. armigera management should be emphasized on the larval stage. Future studies may be directed to the study of landscapes that favor predators and parasites of H.armigera larvae.
Key words: Helicoverpa armigera – Cotton – Tomato – Maize - Landscape variables – Agricultural practices - Carbon isotope –Biological control
