The effect of infestation of lepidopteran borers on yield of maize was assessed at three locations in the forest and forest/savanna transition zones of Cameroon, during the first and second season of 1992. Maize was treated once or twice with the systemic carbofuran at different developmental stages. The species encountered were the stem-boring noctuids Busseola fusca and Sesamia calamistis, which oviposit on and attack pre-tasseling stages of maize; the stem-boring pyralid Eldana saccharina, which attacks plants at and after tasseling; and two ear borers, namely the pyralid Mussidia nigrivenella and the tortricid Cryptophlebia leucotreta. Generally, carbofuran reduced infestations by B. fusca and S. calamistis but had little or no effect on species attacking the plant's later stages. Thus early treatments with granules into the whorl were more efficient than late treatments as a side dressing, and a second late treatment had little effect. During the first season, late-attacking species were predominant and grain yield losses of 17–44 % were found in one location only. During the second season, species attacking young plants (mainly B. fusca) became predominant in all three locations and yield losses of 30 to 41 % were found in two of the three locations. The percentage of ears with damage was especially high during the second season. As green maize is an important source of cash income in the area and damaged ears cannot be sold, the economic loss was likely considerable.

The phenotypic stability of resistance to the stemborer, Chilo partellus and grain yield in 10 newly developed sorghum hybrids namely HYD-1, HYD-2, HYD-3, HYD-4, HYD-5, HYD-6, HYD-7, HYD-8, HYD-9 and HYD-10, and two local checks, Serena (tolerant) and IS-1044 (resistant), were evaluated for seven seasons at the International Centre of Insect Physiology and Ecology (ICIPE) Mbita Point Field Station and Ungoye Field Site in western Kenya. Two stability parameters were determined: (1) The linear regression (b1) of an entry mean on an environmental index, and (2) the deviation from regression (S2d). The significance found for the linear component of environment implies that the variation over the different environments is adequate to test for cultivar stability. Hybrids HYD-1, HYD-5, HYD-8 and HYD-10 were identified as the most suitable genotypes for future commercial production.

One of the critical factors in assessing maize lines for resistance to Sesamia calamistis is the number of larvae/plant used for infestation. Artificial infestation of maize plants with two and five larvae/plant resulted in 29.1 and 39.5% stand loss (dead hearts and stalk breakage), while 10 and 15 larvae/plant resulted in 52 and 72.9% stand loss, respectively. For a satisfactory artificial infestation in maize screening trials against the maize stem borer in Nigeria, a population level of 10–15 larvae/plant is recommended.

Two indigenous maize cuitivars, Inbred A and Nyamula, were evaluated in a field trial for their susceptibility/resistance to Chilo partellus at the artificial infestation levels of 10 larvae/plant and 20 larvae/plant. Foliar damage was caused predominantly by C. partellus, but stem-tunnelling was caused not only by C. partellus but also by another species of borer, Eldana saccharina, which invaded the crop during the tassel emergence stage and persisted during harvest. In the 10-week old crop, the number of C. partellus recorded on Nyamula was greater than on Inbred A, but the incidence of injury to foliage and stem-tunnelling on the two cuitivars was the same. At harvest the degree of damage to the two cuitivars varied. At the infestation level of 20 larvae/plant, the cuitivars suffered equal stem-tunnelling. There was a significant negative correlation between stem-tunnelling and yield for Inbred A, but the correlation was not significant for Nyamula. At the infestation level of 10 larvae/plant, the correlation between stem-tunnelling and yield was not significant for either of the cuitivars, perhaps, due to excessive activity of E. saccharina in the stalks of Inbred A.