Investigations On The Susceptibility Of Common Cereal Grains In Kenya To The Angoumois Grain Moth, Sitotroga Cerealella Olivier (Lepidoptera: Gelechiidae) And Some Aspects Of Its Ecology

Abstract

The susceptibility of 10 varieties of wheat, 16 varieties of maize and 12 varieties of sorghum cultivated in Kenya to the Angoumois Grain Moth, Sitotroga cerealella Olivier was investigated. The depth of infestation by the moth into layers of grain in bulk storage was also studied. Lastly, the moth was studied in relation to its pteromalid parasite Habrocytus cerealellae Ashmead in a cage ecosystem. All varieties of the three types of grain were found to be susceptible to ~. cerealella but to varying extents. Hybrid 622 of the maize varieties appeared to possess some resistance to the moth attack. Mealy sorghum varieties were found to be more susceptible than the vitreous ones. Hardness appeared to have some bearing to resistance against moth attack in sorghum in that harder varieties were less susceptible. Superficial layers of grain in a grain bulk were found to suffer considerably greater damage than deeper layers of grain. Beyond 2 cm depth in wheat, 8 cm. depth in maize and 2 cm. depth in sorghum, there was very little dam 4]e by this moth. No infestation was observed at depths greater than 4 cm. depth in wheat, 12 cm. in maize and 6 cm. in sorghum. The cage ecosystem experiment showed that the parasite H. cerealellae was ineffective in regulating the numbers of the host moth, H. cerealella. The effect of parasitism on 4th instar larval density was only mildly delayed density dependent. The key factor responsible for fluctuations in the populations of S. cerealella through 9 generations was found to be the mortality occurring between the egg stage and late first instar larva when the latter establishes itself in the grain kernel.