SPATIAL ASSOCIATION BETWEEN HELICOVERPA-ARMIGERA AND ITS PREDATORS INSMALLHOLDER CROPS IN KENYA

1. This work is part of a research project on the population dynamics of a polyphagous noctuid pest, Helicoverpa armigera, on crops commonly grown in small-scale agriculture in Kenya. The between-plant and with in-plant distributions of H. armigera eggs and larvae are presented fo r sunflower, maize, sorghum and cotton. The association of H. armigera with its predominant predators, which are anthocorids and ants, was a nalysed both within plants and between plants to assess the extent to which predators occur on the same plant parts as H. armigera. 2. The d istribution of H. armigera eggs between plants was slightly aggregated , but the degree of aggregation tended to decline as H. armigera larva e matured. 3. The distribution of predators was more aggregated than t hat of H. armigera. Generally, the number of predators per plant was n ot associated with the number of H. armigera per plant, but associatio ns may have been obscured by the foraging strategy of ants. Only on su nflower were predatory ants associated with H. armigera larvae. 4. Ovi position and larval feeding of H. armigera were concentrated on the fl ower head of sunflower and the panicle of sorghum. On maize and cotton , however, the majority of eggs were deposited away from the soft plan t parts suitable for larval feeding. Implications for survival of hatc hlings are discussed. 5. Anthocorids were concentrated in the same typ es of microhabitat as H. armigera eggs on sorghum, but regression anal ysis showed that their association within plants was low, mainly becau se 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 plant s than were anthocorids.