Effect of maize variety and storage form on the development of the maize weevil, Sitophilus zeamais Motschulsky

The effects of maize variety and storage form on development of the maize weevil, Sitophilus zeamais Motschulsky, were studied under artificial infestation at 25 ± 2 °C and 70 ± 5% r.h. in the laboratory. Three improved West African maize varieties, Abeleehi, EV8725-SR, Pop63-SR and the local variety, Volta Local, stored shelled and as cobs without husks (=unshelled) were used. Dissections of infested grain were used to monitor insect development at regular intervals. Maize variety and storage form had a significant effect (P < 0.05) on the mean duration of most developmental stages. Across varieties, the mean total duration of larval stages (first to fourth) was 25.2 d on unshelled grain vs 22.8 d on shelled grain. By day 30, 76% of third instar larvae in shelled kernels had tunnelled to the germ and fed on the radicle and scutellum portions compared to 44% of the larvae in unshelled grain. The pre-emerged adult spent 5.3 d longer in unshelled than in shelled maize. The mean weights of the developing insect (across varieties) were not significantly influenced by storage form, except for the first and third instar larvae, which gave higher mean weights on shelled than unshelled grain. Both maize variety and storage form influenced the site of weevil emergence from the kernel

Intraspecific competition in larvae of the larger grain borer, Prostephanus truncatus (Horn) with maize grains

The effects of egg clutch size on development and survivorship of the larger grain borer, Prostephanus truncatus (Horn) (Col.: Bostrichidae) on maize were measured in the laboratory using single grains of the white maize variety, TZSR-W, at 30 ± 2°C and 70 ± 5% RH. Varying numbers of P. truncatus eggs (1, 2, 4, 8, or 16) were introduced into a hole drilled into a single maize grain. Destructive sampling was used at regular intervals to obtain data on immature developmental parameters, the location of immatures within the grain and the weight and sex of any emerged adults. First instars fed mainly on the floury endosperm tissue whereas the second and third instars preferred the germ tissue. Mortality due to competition was highest in first instars. At high initial densities (> 4 per kernel), some P. truncatus larvae reduced competition by moving out of the grain. A maximum of 6 adults emerged from a single grain. The mean number of adults that emerged per grain for initial egg densities of 8 and 16 were 3.3 and 3.5, respectively. Prostephanus truncatus adult weight at emergence was not significantly influenced by initial egg density except in the case of clutch size 16. The sex ratio of emerged adults was also unaffected by competition, and was always 1:1. Complete developmental period within grains ranged between 28 and 32 days

Distribution and sampling of Prostephanus truncatus (Coleoptera: Bostrichidae) and Sitophilus zeamais (Coleoptera: Curculionidae) in maize stores in Benin

The distribution among and within grain stores of 2 grain store pests, Prostephanus Truncatus (Horn) and Sitophilus zeamais Motschulsky were examined over time using different maize cultivars. Incidence in stores was variable between seasons for both species. The b coefficient of Taylor's power law did not differ among maize cultivars. Within-store distribution among cobs could be approximated by the negative binomial and an overall k parameter was estimated for both species. These data were used to develop sampling plans to estimate sample size needed to determine insect density for both pest species over different densities given a desired precision. Sequential sampling stop lines were calculated to determine pest status given action and no-action threshold densities. The possibility of applying the sampling plans as an integrated pest management tool is discussed