Spatial association between Helicoverpa armigera and its predators in smallholder crops in Kenya
- This work is part of a research project on the population dynamics of a polyphagous noctuid pest, Helicoverpa armigera, on crops commonly grown in smallscale agriculture in Kenya. The between-plant and within-plant distributions of H. armigera eggs and larvae are presented for sunflower, maize, sorghum and cotton. The association of H. armigera with its predominant predators, which are anthocorids and ants, was analysed both within plants and between plants to assess the extent to which predators occur on the same plant parts as H. armigera. 2. The distribution of H. armigera eggs between plants was slightly aggregated, but the degree of aggregation tended to decline as H. armigera larvae matured. 3. The distribution of predators was more aggregated than that of H. armigera. Generally, the number of predators per plant was not associated with the number of H. armigera per plant, but associations may have been obscured by the foraging strategy of ants. Only on sunflower were predatory ants associated with H. armigera larvae. 4. Oviposition and larval feeding of H. armigera were concentrated on the flower head of sunflower and the panicle of sorghum. On maize and cotton, however, the majority of eggs were deposited away from the soft plant parts suitable for larval feeding. Implications for survival of hatchlings are discussed. 5. Anthocorids were concentrated in the same types of microhabitat as H. armigera eggs on sorghum, but regression analysis showed that their association within plants was low, mainly because anthocorid populations increased after the H. armigera oviposition had peaked. 6. Ants (Pheidole spp. and Myrmicaria spp. combined) were generally more closely associated with H. armigera stages within plants than were anthocorids.
Van den Berg, H.; Cock, M.J.W. Spatial association between Helicoverpa armigera and its predators in smallholder crops in Kenya. Journal of Applied Ecology (1995) 32: 242-252.