Studies on the biology and ecology of chrysopid predators (Neuroptera; Chrysopidae) of Helicoverpa Armigera (Hubner) (Lepidoptera:Noctuidae) and Aphis Gossypii (Glover) (Homoptera:Aphididae) on cotton, Gossypium Hirsutum (L) in Eastern Tanzania

Studies on the biology and ecology of chrysopid predators of Nelicoverpa armigera (Hubner) and Aphis gossypsi (Glover) were conducted at Ilonga between 1988 and 1990. Surveys conducted on cotton revealed that only rlallada and Chrysoperla sp. indet. showed temporal coincidence with both H. armigera and A.gossypii. H. armigera and chrysopids colonized cotton at the start of flowering. Densities of chrysopids on cotton were 0.8 - 3.0 eggs and 0 - 0.4 larvae per plant. Densities of H. armigera were 0 - 1.1 eggs and 0 - 0.7 larvae per plant. Three parasitoids attacking adults, pupae and larvae of M. were recorded. Total larval, pupal and total developmental periods of reared on eggs of H.armigera were 14.04 ± 0.16, 14.44 ± 0.25 and 28.38 ± 0.26 days, respectively. When reared on first to second instars of A. gossypi, its total larval, pupal and total developmental periods were 14.98±0.19, 14.75 ± 0.25 and 30.50 ± 0.27, days respectively. When Chrysoperla sp. inlet. was reared on eggs of H. armigera, total larval, papal and total developmental periods were 14.75 ± 0.14, 13.80 ± 0.39 and 29.40 ± 0.43 days respectively. When reared on first to second instars of A. gossypii, its total larval, papal and total developmental periods were 13.47 ± 0.23, 12.59 ± 0.29 and 26.35 ± 0.17, days respectively. During its first, second and third stadia and during the total larval period, M. boninensis consumed 23.58 ± 1.07, 40.15 ± 2.20, 127.21 ± 4.57 and 189.00 ± 4.24 aphids respectively. Eggs of H. armigera consumed during the same periods were 14.31 ± 0.74, 29.92 ±1.55, 90.32 ± 2.68 and 135.28 ± 2.66, eggs respectively. During its first, second and third stadia and durign the entire larval period, Chrysoperla sp. indet. consumed 11.25 ± 1.35, 27.57 ± 2.30, 130.70 ± 4.68 and 169.75 ± 4.18 eggs of H. armigera respectively. The numbers of aphids consumed during the same periods were 19.94 ± 1.47, 36.88 ± 2.85, 115.69 ± 4.70 and 171.81 ± 6.04 respectively. Functional response parameters of M. boninensis and Chrysooperla sp.indet. preying on eggs of H. armigera and nymphs of A. gossypii were also estimated. The values on H. armigera for M. boninensis and Chrysoperla sp. indet. wete 0.017 and 0.021 hours respectively. Their attack coefficients were estimated to be 2.245 and 2.600 hrs-1 respectively. The values of M. boninensis and Chrysoperla sp. indet. preying on first to second instars of A. gossypii were 0.0287 and 0.054 hours respectively. Their attack coefficients were estimated to be 1.253 and 3.280 hrs-1 respectively.