Prospects of integrated microbial and radiation control of harmful insects

Abstract

This paper is a “theoretical insect pathology” consideration of the prospects of integrated microbial and radiation control of harmful insects. While considering this topic our attention is directed first to the possible applications of the radiation sterilizing method of population suppression. The exploratory investigations of this subject have shown that ionizing radiation will induce sterility but there is considerable variation in the amounts needed. The research also suggests that radiation damage may in some cases prevent application of the method to some insects. In nature some insects appear to be so abundant that the use of the sterile-male technique may not be feasible without first processing the geographically isolated and nonisolated infested area with other control measures to bring wild populations “within reach”. Such a situation can be approached from two angles. The population may be controlled by means of well-tried microbial pathogens. Also, the release of sterile male insects carrying parasites or pathogens has control possibilities. In such a situation an intensified search has to be made for those pathogens that are nonvirulent when present in or on the adult, but are highly virulent to the larvae. Coelomomyces and Thelohania are probably of this category. The increased susceptibility of irradiated insects to pathogens is opening a new field of investigation. The life span of Tribolium castaneum and Tribolium confusum beetles was shortened considerably when the test insects received Bacillus thuringiensis immediately and after an interval of 24 and 144 hours following exposure to X-rays. The life span of the irradiated beetles was somewhat shortened by the presence of Farinocystis tribolii, Nosema whitei, and Adelina tribolii, protozoan parasites in the fat body of the test insects. There are promising prospects of evolving, through irradiation, new strains of pathogens of high virulence. Already strains of increased virulence of Beauveria bassiana and Aspergillus flavus have been evolved by means of ionizing radiation. There is economic feasibility in using gamma radiation from cobalt-60 in the control of diseases of the honey bee, and in the sterilization of honey. The use of radiation as an insect repellent and the behavioral aspects of radiation on insects is a fascinating field of future investigation. Examples of this phenomenon are cited.