The developmental potential of the palm aphid Cerataphis palmae Ghesquière (Homoptera: Pemphigidae) on three dwarf coconut varieties—Malayan dwarf red (Mdr), Malayan dwarf green (Mdg) and Malayan dwarf yellow (Mdy)—was studied in a screenhouse using leaf clip-on cages. Under similar temperature (30°C ± 1.13) and relative humidity (69.8% ± 1.63) conditions, the aphid expressed significant differences in fecundity, longevity and developmental period on the coconut varieties. The total developmental period on Mdr lasted 12.17 ± 0.76 days while on Mdg and Mdy it was 14.84 ± 0.63 and 13.83 ± 1.05 days, respectively. Thus the aphid population increased on the dwarf red variety over a significantly shorter period than it did on the other two varieties. Furthermore, fecundity and longevity of C. palmae on Mdr were significantly higher than on the Mdg and Mdy varieties (P < 0.01). These results indicate that Mdr supports C. palmae development better than the other two palm varieties.

Some aspects of the biology of Callosobruchus maculatus (F.) on three varieties of bambara groundnut, Voandzeia subterranea (L.) Thou and a local brown cowpea variety, Vigna unguiculata (L.) Walp were studied under ambient laboratory conditions. Egg hatchability of C. maculatus was above 90% on all the legume varieties. The mean developmental period of C. maculatus ranged from 23.7 days on cowpea to 28.5 days on the Piele kargu variety of groundnut. The percent emergence of C. maculatus ranged from 61.1% on var. Piele kargu to 89.5% on var. Piele balgu. There was a significant difference (P < 0.05) between the damage caused to the brown cowpea and the bambara groundnut varieties. However, there were no significant differences (P > 0.05) in damage among the three groundnut varieties. In experiments to assess the insecticidal potential of three plant materials against C. maculatus, Azadirachta indica (neem) seed powder showed a higher efficacy than both Citrus sinensis peel powder and the powder of Chromolaena odorata leaves. At 1.0 g per 40 g of legume seed, it was twice as effective as Ci. sinensis and Ch. odorata over a period of 40 days.

The length of the reproduction cycle of Lasioderma serricorne (F.) under ambient laboratory conditions (temperature range 28.0–32°C and 72.5–80.5% r.h.)was shown to depend on the identity and state of division of various cereal grains, cowpeas, groundnuts and dried root crops. Cut dried yams allowed the shortest cycle andwholericethelongest.The rate of population increase by L. serricorne was also assessed and this was maximal when cut wheat and minimal when whole rice was provided. Fecundity was highest with sorghum and lowest with rice as food source. Females of the species lived longer than males.

The life cycle of Cathartus quadricollis (Guerin-Meneville) was studied under ambient laboratory condition on maize, sorghum, wheat, cowpea and melon. Egg hatchability was found to be 95.5% with an incubation period of 3–7 days. Five larval instars were recorded based on head-capsule width measurements. The growth ratio of the head-capsule width ranged from 1.05–1.20 with a grand mean of 1.12. This range falls within the acceptable range in Dyar's rule. The mean growth rate of C. quadricollis after 2 weeks of rearing on maize, sorghum, melon, wheat and cowpea, ranged from 22.4 to 1.6. While the mean developmental periods of C. quadricollis on the selected food media ranged from 18.80 days on cut maize to 30.70 days on cut cowpea.

The life cycles of two phycitid moths, Plodia interpunctella (Hubn.) and Ephestia cautella (Wik.) were studied under ambient laboratory conditions on groundnut, maize, sorghum, wheat and standard medium (maize/wheat/glycerol, 8:8:1, w/w). Egg hatchabilities were found to be 98.6 and 91.6% for P. interpunctella and E. cautella respectively. Five larval instars were recorded for each species based on head-capsule width measurements. The growth ratios of the larval head-capsule width ranged from 1.08–1.72 in P. interpunctella: and 1.33–1.57 in E. cautella. These ranges fall within the acceptable range in Dyar's rule. Mean fecundities ranged from 96.83 ± 0.31 on wheat to 190.87 ± 0.47 on standard medium for P. interpunctella; and 96.83 ± 0.31 on groundnut to 192 ± 1.33 on standard medium for E. cautella. Mean developmental periods of the two moths on the selected food media ranged from 25.65 days on standard medium to 46.11 days in broken wheat for P. interpunctella; and 26.95 days in broken sorghum to 40.14 days in ground maize for E. cautella.

Studies on larval movement, feeding and development of Chilo partellus Swinhoe were carried out at Mbita, Western Kenya. Larval movement away from the plant was observed during the first and third instars. Plants inoculated at the stems recorded greater larval migration compared to those inoculated at the leaf whorls. Larval feeding was greater on IS 18363 than on IS 2146, but growth rate, weight gain and efficiency of conversion into body substances were greater in IS 2146. Thus it seems that varietal susceptibility to damage by C. partellus is different from varietal suitability for growth of the larvae.

Microscopic examination of stem tissues damaged during larval feeding revealed that feeding was mainly restricted to the pith and that the vascular bundles were hardly affected.

A study on the biology of the sorghum midge, Contarinia sorghicola Coq., and the damage and crop loss it causes was carried out under field conditions during the main planting season at Mbita, in Western Kenya. The developmental period from egg to adult ranged from 17 to 34 days with a mean of 23 days. On average, 3.2 adult midges emerged from each damaged spikelet. Adult emergence was bimodal, with a major morning peak and minor late afternoon peak. A predator, Diaperasticus erythrocephala Olivier (Dermaptera: Forficulidae), was found preying on newly emerged adults. The level of damage varied among 38 sorghum lines tested, with the size of the panicle (r = 0.73; P < 0.05) and the number of days to 50% flowering (r = 0.49; P < 0.001) influencing the level. The level of damage for the sorghum variety Serena ranged from 1.8 to 97.7% and grain yield from 22.3 to 0.9 kg/50 m2, respectively for plantings during the months of March–June. The relationship between damage and crop loss was almost perfect (r = 0.998; P < 0.001).