TRANSMISSION OF PLODIA-INTERPUNCTELLA GRANULOSIS-VIRUS DOES NOT CONFORM TO THE MASS-ACTION MODEL

1. Transmission of insect pathogens is traditionally described by a te rm which states that transmission is proportional to the densities of the susceptible hosts and the infectious units, multiplied by a consta nt, the transmission coefficient. Theoretical studies suggest chat dev iations from this can be important in host-pathogen population dynamic s, but little is known of how commonly pathogen transmission conforms to the conventional model. 2. We describe a test of the traditional as sumption for the Indian meal moth, Plodia interpunctella (Lepidoptera: Pyralidae) (Hubner) and its granulosis virus using a modification of the previous methods, which allows for unpredictable declines in the a mount of infectious material present. 3. The estimated transmission co efficient increased with the density of susceptible hosts and showed a marked decline with density of infectious cadavers. This suggests tha t the usual assumption does not adequately describe transmission in th is system. 4. The reasons for this deviation from the usual assumption are likely to be a combination of behavioural and physiological chang es at high host density, and differential susceptibility to the pathog en leading to an effect analogous to pseudo-interference in parasitoid s.