Ecological studies on the tropical warehouse moth Ephestia Cautella (walker) (Lepidoptera : Pyralidae) and its predator mite Blattisocius Tarsalis (berlese) (Acari : Ascidae) in relation to effective warehouse integrated pest management programmes

Abstract

The abundance and economic importance 01 the moth Ephestia cautella (Walker) on maize grain was established through field surveys in central storage depots and detailed evaluations carried out in selected warehouses. Through regular grain sampling on maize stacks, it was found that moth population and damage were well correlated and that damage reached 15.26 percent after 8 months of storage. It was found too that this pest is common throughout the country wherever maize is stored and that control was a problem even with sustained use of chemicals. Population studies were carried out both in the 1ield and in the laboratory on the moth and its mite predator Blattisocius tarsalis (Berlese) in a continuous interaction for 33 weeks. Through life-table analysis, mortality factors regulating the moth's population were identified where density dependence was demonstrated on some especially in the first larval instar. Despite this marked effect of the mite on the moth's population, and particularly demonstrated density dependence, mite predator alone was determined to be of limited value in the control of E. cautella. This was considered to be partly due to the continuous availability of alternative hosts especially Tribolium castaneum, Corcyra cephalonica and Plodia interpunctella which occurred simultane'6usly and in abundant numbers in the storage 1acilities studied and partly due to other unknown factors including the architectural design of the facilities which exposed maize to the environment. This encouraged re-infestation by the moth and thus interrupted ongoing regulatory effect of the mite. The alternative hosts also comprised storage pests themselves whose thresholds could not be ignored if economic damage was to be avoided. Negative effects of these alternative hosts otherwise negated their advantage of providing sustenance to the mite when the moth's eggs were in low numbers. Similarly, through 1ield surveys and laboratory screening, it was found that control with insecticides such as malathion, pirimiphos-methyl and fenitrothion or with recently introduced ones like pyrethroids; permethrin and deltamethrin, rarely eliminated the moth. The use of some chemicals such as malathion, led to increased populations of the moth after 3 months of application. The combined use of selected pesticides and mite control yielded positive results by significantly suppressing the moth population below economic threshold level. This was demonstrated in the laboratory cage systems and in normally operating maize storage warehouses where moth population was monitored for 8 months with selected insecticide application. This revealed that integrated control was the most suitable strategy available to achieve effective pest management of E. cautella and other associated pests in warehouse storage systems for maize in Kenya.