Diaeretiella rapae (M'cintosh) was the only parasitoid of the cabbage aphid, Brevicoryne brassicae L., during studies reported here.

Percentage parasitism of B. brassicae ranged from 27.1 to 76.1% in studies carried out around Nairobi area during 1978/79. It was highest during the month of September, when the aphid population density had reached maximum, and lowest in May when aphid numbers were low. High parasitism coincided with a decline in aphid population.

Because of these high levels of parasitism and other attributes of the parasitoid, it was concluded that D. rapae played a significant role in suppressing populations of B. brassicae and should be taken into consideration in any control programme aimed at protecting brassica crops against aphid pests in Kenya.

Field studies revealed the nettle caterpillar, Latoia ( = Parasa) viridissima, to be multivoltine with four discrete generations a year. The maximum egg (1800/100 fronds) and larval (1500/100 fronds) densities were attained in April/May 1980. The pupal population was generally low; the highest recorded density of 54/100 fronds was attained in March 1980 during the first generation.

Samples of larvae and pupae from the field were attacked by parasitoids in the families Bombyliidae, Braconidae, Chalcididae, Chrysididae, Eulophidae, Ichneumonidae and Tachinidae. These contributed to mortalities ranging from 6 to 30%, but their combined action with microorganisms (bacteria and fungi) accounted for 28–65% mortality of the insect.