PROF. KHAMALA CANUTE P M

In field trials with (a) determinate and (b) indeterminate pigeon pea cv., pod damage by Heliothis armigera, Pardasena virgulana and Melanagromyza obtusa and seed yield losses ranged from 37% and 23% in an early-flowering cv. of (b) to 64% and 52% in a late-flowering cv. of (b), resp

The population dynamics of Pineus pini (Gmel.) was examined in two locations in the Kenya Highlands where the mean annual precipitation ranges from 620 to 1400 mm. Variations in population densities were related to rainfall. Generally, there was a marked decrease in population during the three months of heavy rainfall in March to May and a significant increase during dry weather from August to October. This was followed by a slight decrease in the rate of population build-up, until the long rains in April again resulted in another population collapse. Nine species of predatory insects were identified, and population fluctuations of the most common of these, Exochomus spp., was studied. Predators seemed to remove about 12% of the aphid population. Other mortality factors included heat and crawler dispersion. The greatest mortality occurred early in the life-cycle and was mainly due to eggs and crawlers being washed off the host-tree by rain.

Sequential survey procedures are described from Kenya for classifying the damage caused by the aphid Pineus pini (Gmel.) to Pinus patula. The criteria used are the degree of needle stunting caused by a given number of aphids per centimetre of shoot length, the percentage of twigs on individual trees with mats of aphid wool, and the amount of tree surface covered with aphid wool. Field procedures for making measurements are given, and the survey procedures are presented.

It is reported in this further paper on the damage caused by Pineus pini (Gmel.) to Pinus patula in Kenya [see preceding abstract] that reduction in the elongation of the needles and stems occurs only after crown damage and aphid infestation become extreme. Lighter infestations are reflected in slight reductions of needle length. Damage to the trees and consequent losses of wood volume are most severe under warm dry conditions. Severely stunted needles caused by aphid feeding result in loss of half the tree yield. Infested stands may incur up to 5% economic loss in wood volume. These relations are, however, affected by site factors such as rainfall and altitude. With stands of P. patula at suitable sites. Pineus pini need not pose an important threat to plantations in Kenya.

Three insecticides were tested in sprays in the field in Kenya in 1976 for the control of podboring insects, especially the noctuids Pardasena virgulana (Mab.) and Heliothis armigera (Hb.) and the agromyzid Melanagromyza obtusa (Mall.), on pigeon pea (Cajanus cajan). DDT was applied twice at a concentration of 25% diluted to 180 ml/10 litres water, 40% dimethoate was applied at 30 ml/18 litres, and 35% endosulfan at 102 ml/18 litres water; these quantities were applied to 450 m2. The percentage pod damage and (in brackets) percentage seed damage totalled 30.4 (18.3) for DDT, 24.7 (13.5) for dimethoate, and 32.4 (17.3) for endosulfan, as compared with 47.9 (24.4) for no treatment.