Distribution and sampling of Chilo partellus (Lepidoptera: Pyralidae) in maize and sorghum on the Kenya coast

Abstract

The seasonal occurrence and spatial distribution of the crambine stem borer, Chilo partellus (Swinhoe) were investigated in maize, Zea mays, and sorghum, Sorghum bicolor, fields at the Kenya coast. During the vegetative growth stage, small-sized larvae were typically found behind leaf sheaths and in whorls in maize and sorghum. In reproductive and senescent maize, small-sized larvae were also found feeding in ears. Later immature life stages were located predominantly in stems in sorghum, and in the stems and ears in maize. Density and variance estimates of small, medium-, and large-sized larvae and pupae in maize and sorghum were fitted to Taylor's power law which provided significant regressions in all cases. The between-plant distribution was aggregated in all life stages. In maize, the distribution remained aggregated through the larval and pupal life stages, but in sorghum the distribution became progressively less aggregated as insects aged. The relationship of C. partellus density to the proportion of plants infested also suggested aggregation. Optimal sample sizes were determined for both binomial and enumerative sampling plans at two levels of precision, and a discussion is included on the relationship of optimal sample sizes to economic injury levels. Additionally, a presence/absence sequential sampling plan is proposed.

Distribution and relative importance of cereal stem borers and their natural enemies in the semi-arid and cool-wet ecozones of the Amhara State of Ethiopia

“…Similar fi ndings were reported from C. partellus (Overholt et al 1994b), on B. fusca (Chabi-Olaye et al 2005b) and on S. calamistis (Schulthess et al 1991). Th e distributions become progressively less aggregated as insects aged (Overholt et al 1994b;Ndemah et al 2001b).…”

Assessment of the impact of natural enemies on stemborer infestations and yield loss in maize using selected insecticides in Mozambique

“…Previous work indicated that despite the large numbers of parasitoids and relatively high parasitism levels by indigenous parasitoids of maize stemborers (Berger 1981;Gonçalves 1970;Kfi r 1995), the parasitoids are not able to prevent economic damage and/or reduce pest populations to below economic threshold levels (Kfi r 1997;2000;Overholt 1998;Overholt et al 1994). Th e present work, however, suggests that their impact on pest infestations and maize yield can be considerable.…”

Cotesia flavipes Cameron and Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) do not exhibit complementary sex determination: Evidence from field populations

“…Data for the short rains of 1996 was unavailable. The sampling methodology was described in Overholt et al (1994b). Plants were sampled starting at plant emergence up to senescence by excising and dissecting randomly selected plants from the field.…”