Successful development of a biological pesticide requires attention not only to the biological agent, but also to formulation, application, and the biology of the pest–pathogen interaction in the field. Emphasis in our review is given to fungi, Metarhizium spp. and Beauveria bassiana (Balsamo) Vuillemin, as the most suitable agents, and oil-based ULV formulations or baits as the most promising application techniques for use with locusts and grasshoppers. The efficacy of the pathogen isolate must be maximized; selection is aimed at those that are suitably virulent, specific, and well adapted to the relevant environmental conditions. Opportunities exist for manipulation of the characteristics of the isolate by genetic means and by developments in culturing techniques. Formulation requirements are stability during storage and the ability to carry the active ingredient successfully to the target insect at application. Likely storage methods for fungi would be as dry conidia, perhaps with clay diluents, or in oils; the characteristics of both are briefly discussed. At application, efficacy of dose transfer and protection of the biological agent against environmental constraints such as UV radiation are needed. Baits have advantages in terms of dose transfer but logistical problems associated with the bulkiness of the carrier remain. Technological advances, including those that offer the prospect of carrier production in situ from dense precursors, and better knowledge of feeding behaviour have improved the prospects for baits. Multi-disciplinary research reducing dependency on the biological agent and exploiting formulation chemistry and application technology is required in developing biological pesticides.