Formulation of Bacteria, Viruses and Protozoa to Control Insects

Three major groups of insect pathogens - bacteria, viruses and Protozoa - have one feature in common: they normally infect or poison the insects perorally when they contaminate insect food. Thus to control an insect infestation they must usually be eaten, and need to be spread evenly over the food environment and be hardy enough to stay alive whilst waiting for the insect to eat them. Formulation is vital to ensure the efficiency of these processes. The first task is to make the pathogen-treated food palatable and able to cover the food evenly. On ingestion, the pathogens invade the haemolymph and target tissues, grow within and kill the insects; then in nature survival stages of the pathogen are protected inside the cadavers, which eventually disintegrate. In con-trast, survival stages of pathogens produced for insect control have to be applied as sprays or solids spread thinly over the surface of the insects’ food, and so are more exposed to the environment. Thus, formulation must replace the natural protection afforded by insect cadavers. The chosen pathogens need to be highly virulent to kill by the smallest possible dosages, a requirement also facilitated by formulation. The modes of action and the main features of the three peroral groups of pathogens are summarized in Table 3.1