Diversity of storage Insect Pests in Maize and susceptibility of Maize varieties to Maize weevil (Sitophilus zeamais)
Maize is the major source of food in Kenya grown both as a subsistence and commercial crop. Storage insect pests attacking maize continue to pose a major problem to small scale farmers in Africa where subsistence grain production supports the livelihood of majority of the population threatening the family food security. The damage affects the quality and quantity of the stored produce. The objective of this study was to determine the occurrence and the diversity of post harvest insect pests and susceptibility of maize varieties to maize weevils. A survey was conducted between November 2008- May 2009 in different agro-ecological zones of Eastern and North Rift regions of Kenya. Whole and semi processed maize grain samples were randomly collected from farmers, traders and the National Cereals and Produce Board. Sub samples of each grain sample were incubated for 42 days and the emerging storage pests were identified to species level. Susceptibility of sixteen maize varieties to the maize weevil for laboratory and field infestation was determined. Field trials were conducted in Mwea and Waruhiu and after harvest grain samples were incubated and the insects that emerged were counted and identified to species level. Insect free grain samples of the sixteen maize varieties were inoculated with unsexed maize weevils and incubated for three months to determine percentage grain damage, seed weight loss and Fl progeny. The main insect pests infesting maize grain samples from farmers and traders were larger grain borer (Prostephanus truncates Horn); maize weevil (Sitophilus zeamais Motsch), angoumois grain moth (Sitotroga cerealella Olivier) and red flour beetle (Tribolium spp). Maize weevil had the highest prevalence of up to 100% in all the agio-ecological zones. Whole grain maize samples from traders had high infestation of the maize weevils of 19 insects per 100 grams compared to those from the farmers. Maize grain samples from farmers stores had high infestation of larger grain borer of three insects per 100 grams than those from traders. Samples from Ishiara National Cereals and Produce Board store had the highest infestation of 46 and seven storage insect pests per 100 grams of maize weevil and larger grain borer respectively. High levels of infestation with storage pests were recorded in Eastern province for all the major storage pests compared to the North rift region. Varieties Panner 67 and DK 8031 had the highest maize weevil infestation while varieties H614D and KCB had the highest levels of the Angoumois grain moth. Maize weevil and angoumois grain moth infestation in Mwea was high compared to Waruhiu. Inbred line CKPH080020 had the lowest index of susceptibility of 2.3 and therefore it was considered to be a resistant variety. Variety DK 8031 had the shortest median development time of 17.5 days and also had a high number of F1 progeny of 126 insects' counts after three months and the highest index of susceptibility of 8.5 thus was considered to be the most susceptible variety. Resistant varieties showed low numbers of F1 progeny, had a high median developmental time and a low percentage of seed damage and seed weight loss. The study showed that the grain from the Eastern region had higher levels of storage insect pest infestation which can be attributed to the favourable temperatures. The maize varieties differed in the level of susceptibility to storage insect pests with inbred line CKPH080020 showing high level of resistance. Farmers should be encouraged to grow less susceptible varieties as this will reduce post harvest loss and also reduce the possibility of grains being infested with the mycotoxin producing fungi. More studies could be conducted to incorporate the resistance from CKPH080020 into other local popular susceptible maize varieties.