Evaluation of the Efficacy of Insecticides in the Control of the Larger Borer (Prostephanus truncatus) on Maize (zea mays L.) in Zimbabwe

Abstract

The Larger Grain Borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) is an important storage pest of maize which causes substantial damage on stored maize thus affecting quantity and quality of maize in the smallholder and commercial sector. A study was conducted to determine the impact of P. truncatus on maize varieties and the efficacy of insecticides and cultural methods used by farmers in Zimbabwe. The objectives were; to identify larger grain borer tolerant maize varieties that can be grown in LGB infested areas, to evaluate the effectiveness of the insecticides used by seed companies in Zimbabwe and to evaluate the effectiveness of registered insecticides and wood-ash on reducing damage caused by P. truncatus on stored maize. Two laboratory experiments were conducted on the efficacy of dust insecticide protectants used by farmers and using Msasa wood-ash on the white maize variety SC403 and the yellow maize variety PHB30D50. A third laboratory experiment was a bioassay on grain protectants used by seed companies namely; Apron star (Prime Seeds) and Superguard 50EC used by ARDA, Pioneer and Pannar. A fourth laboratory experiment was a bioassay on the Manyika landrace using Actelic Gold Chirindamatura Dust grain protectant. Data on grain weight loss (g); frass weight (g); LGB mortality (%) and LGB population counts was recorded. Grain weight and frass weight was subjected to analysis of variance and comparisons between treated and untreated samples were calculated using the t-test statistic. MINITAB version 13 and GENSTAT version 14.1 statistical packages were used. Results for experiments one and two showed that Actelic Gold Chirindamatura Dust, Shumba Super Dust Grain Protectant, Chikwapuro Grain Protectant and Superguard Dust Insecticide were effective against LGB. The differences among all four insecticides were not significant (p>0.05) at 28, 56 and 84 days for both yellow and white maize. Wood ash was not effective as an abrasive to control P. truncatus. For experiment three, Apron star and Superguard 50EC were effective insecticides in controlling and managing LGB, although Superguard 50EC in PAN 53 was not effective at all three dates. Farmers are encouraged to use Actelic Gold Chirindamatura Dust, Superguard Dust Insecticide, Chikwapuro Grain Protectant and Shumba Super Dust Grain Protectant combined with other IPM measures such as early harvesting and storage hygiene to manage the larger grain borer pest. Seed companies need to treat the seed using effective grain protectants such as Actelic Gold Chirindamatura Dust and Apron star and implement IPM measures to reduce LGB infestation of seed in storage.