Primary infection of insect tracheae by Autographa californica M nuclear polyhedrosis virus.

Previously we found that Autographa californica M nuclear polyhedrosis virus infections initiated in the midguts of insect hosts are disseminated within the hosts via tracheae, elements composing the insect respiratory system. Herein we report that infection of tracheae also can be initiated directly via the spiracles, exterior openings of the tracheal system to the atmosphere. Infections were initiated both by direct application of viral inoculum to the spiracles and by aerosol. Infections established by both these methods appeared to advance much more rapidly than infections established by the oral route, and a host highly refractory to infection orally was easily susceptible to direct tracheal infection. These findings are important for continuing efforts to improve the use of baculoviruses as pest control agents; they also establish the possibility that direct tracheal infection via aerosol may facilitate horizontal transmission of baculoviruses during natural epizootics.