The nutritional suitability of prey is an important determinant of predator fitness that can have a cascade of effects on life history. We manipulated the quality of cucumber plants by fertilizing them with three rates of nitrogen, 110, 160 and 210 ppm N, representing low, medium and high levels of N fertilization, respectively. Colonies of Aphis gossypii Glover were reared on these plants and used as prey for Hippodamia variegata (Goeze) in experiments that measured the predator's development, reproduction, and predation rate. Biological parameters were calculated and an age-stage, two-sex life table was constructed. Larval development was extended and aphid consumption increased at the low level of N fertilization, likely due to the reduced N content of the aphids. However, female longevity was greatest in this treatment, likely because of a reduced reproductive rate, and there was no compensatory consumption of aphids by adults, as observed in larval stages, possibly due to carry-over effects of poor larval nutrition. Despite feeding on aphids with the highest N content, the high N treatment did not yield the highest intrinsic rate of increase (r). Rather, the medium N treatment (160 ppm N) yielded the highest aphid consumption rate and r value, and the highest efficiency of conversion of aphids into eggs.

Keywords