The dynamics of the adult population of Heliothis armigera (Hübner) (Lepidoptera: Noctuidae) within the Sudan Gezira in relation to cropping pattern and pest control on cotton

Abstract

AbstractA method is presented for quantifying moth area densities in individual crops and average densities over the total crop area. Mortality within the total Heliothis armigera (Hübner) adult population as a result of insecticide applications against larvae on cotton in the Sudan Gezira was found to be very substantial for males and virgin and inseminated females. The level of adult mortality which was previously unknown, was shown to be an important factor in Heliothis control. The relative importance of alternative host crops as source sites of adults which infest cotton was demonstrated. Initially, larval populations built up in groundnut fields between July and early September. Females emerging from groundnut fields colonized sorghum in late August and early September and cotton slightly later. Larval densities found in groundnut and sorghum fields correlated strongly with the average densities of virgin females found 12 days later. Groundnuts provided the most important source of adults. The virgin female population was in turn highly correlated with the remainder of the adult population (males and inseminated females), demonstrating that H. armigera adults attacking cotton within the Gezira are locally produced. Adults were attracted to sorghum in large numbers for feeding and oviposition, but survival there of older larvae (fourth to sixth instars) to the adult stage was only 25% of that in groundnuts. The implications for pest management are discussed.