Approaches to vector control: new and trusted. 2. Molecular targets in the insect midgut.

The midgut of blood-feeding insects is an important site for the activity of antibodies and drugs ingested with the blood meal. These agents can be directed at molecular targets in the midgut, and may affect the insect directly by reducing its fitness, or indirectly by blocking transmission of a disease organism to the vector. Both of these result in eventual disease control. Immunization with crude vector or parasite preparations can result in isolation of vaccine candidates which are very effective but often of unknown function. Conversely, by examining carefully the vector's biology and its interactions with the parasite, it is possible to identify various physiological or cellular systems and vector-parasite interactions that can be interfered with. Examples of both approaches are presented in this paper. Anti-vector vaccines offer tremendous potential for disease control, as they can affect the parasite reproductive rate in a number of ways--reducing vector longevity, fecundity or competence. This is most striking if life expectancy of the vector is reduced to a period less than the extrinsic life cycle of the parasite. The rationale often presented for examining molecular systems in vectors is their control potential; it is clearly appropriate to re-examine many of these systems and realistically assess their applicability.