Pest control strategies against Helicoverpa armigera (Hübner) using protease inhibitors have relied on the gut protease profile of the later larval stages of the insect, with serine proteases being considered predominant. Little is known about the gut protease profile of early larval instars. Therefore, the aim of the present study was to detect the levels of gut protease activities in the third-, fourth-, fifth- and late fifth-instar larvae of H. armigera reared on an artificial diet using specific substrates and inhibitors. The analysis of the gut protease profiles of different instars revealed different levels of protease activities at different instar stages. Significant variations were also observed in the specific activities of trypsin, chymotrypsin, cysteine protease, carboxypeptidase-A and aminopeptidase-N across the instars. In general, the activities of the proteases increased from the third to the fifth instar and then decreased at the onset of pupation in the late fifth instar. Proteolytic activity was optimal at pH 12 for gut extracts from the third-, fourth- and fifth-instar larvae. Bioassays with phenylmethylsulphonyl fluoride (PMSF), a serine–cysteine protease inhibitor, revealed high mortality, and that with sodium ethylenediaminetetraacetic acid (EDTA-Na), a metalloprotease inhibitor, also showed retarded larval growth. The inhibition induced by 0.05% PMSF and 0.05% EDTA-Na in combination was similar to that induced by 0.1% PMSF alone.

Biological and morphometric studies of the different stages of Lucilia caesar, were carried out using three rearing media prepared from local materials as the test media, and the standard Snyder's medium as control. The materials for the test media were: (i) Garri, soybeans, palmwine and liver (GSPL), (ii) Garri, soybeansand palmwine (GSP) and (iii) Pap, nono, cabbage and liver (PNCL). The Snyder's medium consists of milk, yeast and bacto agar (M Y A). There was no significant difference in the duration of larval instars and adult emergence for the blowflies reared in the standard, PNCLand GSPL media. For blowflies reared in GSP, duration of larval and adult stages was prolonged by about 48 hr and 5 days respectively, when compared with the flies reared from the other three media. The average length and width of each larval stage reared from the four media were not significantly different. Morphometrics of the adults showed that those reared from the GSPL and control media were longer, heavier, and laid significantly more eggs per female than adults reared from PNCL and GSP media. The GSPL medium was considered to be the most suitable alternative to MYA.

Observations on the growth and development of Chilo partellus (Swinhoe) larvae under laboratory and field conditions indicate sexual dimorphism as well as a general developmental polymorphism. Larvae of both sexes went through fifth, sixth or seventh instars before pupation. The mean developmental period, larval head capsule width, and the number of instars before pupation as well as pupal weight were higher in the female compared to the male larvae. These observations suggest differences in the physiological state of fifth-instar larvae in a population; some of them might be in the penultimate, while others might be in the ultimate instar.

Larval instars of Chilo partellus Swinhoe reared on sorghum plants were determined. The larvae were separable into five non-overlapping instars by analysis of variance and Duncan's multiple range test, frequency distribution and scatter diagram of the head capsule widths. Head capsule increment from one instar to the next conformed to Dyar's rule, while at the same time agreeing with Richards' hypothesis. The stadial periods for the five instars were 6, 4, 5, 3 and 7 days, respectively.

Three consecutive generations of Hypsipyla robusta Moore (Lepidoptera: Pyralidae) were reared on the McMorran–Grisdale Diet (MGD) medium. Mortality rates among the older larvae were consistently low (less than 1.0%) but high (up to 50%) in the first instar stage which was due primarily to escapism and non-feeding. Developmental period from egg to adult was not adversely affected by the artificial diet and ranged between 29 and 41 days. However, a comparison of numbers of larval instars and pupal sizes indicated that the nutritional quality of the MGD and natural food sources differed appreciably. A longterm study to evaluate the usefulness of the MGD for planned mass rearing programmes of H. robusta is recommended.

Investigations are reported on oviposition habits, development, and emergence patterns of the pre-adult stages of Aedes (Stegomyia) africanus (Theo.) under laboratory conditions. It was observed that water or at least a wet surface is necessary for oviposition and that the intensity of egg-laying takes place within 2 cm from water surface and is greater in those containers with deeper water levels. Post-oviposition embryonic development lasts an average of 6 days thus conforming with earlier findings (Gillett, 1955). The quantity of water does not affect either the period of post-oviposition embryonic development or the rate of egg hatching. However, an average of 75% of the eggs hatch within the first 13 days after flooding, leaving the rest to hatch in subsequent instalments. At 27°C, the second-instar larvae take the shortest time to develop while the fourth-instar larvae take the longest period. Generally, intra-instar variability in growth rates were observed except in the pupal stage. Emergence of the various pre-imaginal stages and pupation did not appear to have any regular periodicity. Of particular interest was the observation that the number of instars in this species varied from the normal number of four, a finding which is believed not to have been recorded previously in the family Culicidae.