INFECTION OF ALFALFA WEEVIL HYPERA POSTICA BY FUNGUS BEAUVERIA BASSIANA

The percentage of infection of the alfalfa weevil, Hypera postica, by the fungus Beauveria bassiana was influenced by relative humidity and temperature. A relative humidity of 98% to 100% was required for a high rate of infection to occur as were temperatures above 24°C. Dusting the insects with spores proved to be the most effective means of inoculation. All stages of the weevil were found to be susceptible to the fungus, although spores were not produced from infected larvae as they were from infected adults. The fungus spores entered the tracheal system and penetrated the insect tissues. The first effect of the fungus on the insect was of a chemical nature and affected the fat tissue. The fat body was the first tissue to become permeated with hyphae. Muscle tissue and the Malpighian tubules were the next to be infected, whereas the nerve tissue was the last to become permeated with hyphae. Muscle tissue and the Malpighian tubules were the next to be infected, whereas the nerve tissue was the last to become permeated with the fungus. The fungus was never observed to have penetrated the exoskeleton except through the tracheae. Infection usually began in the anterior regions of the insect and proceeded posteriorly. All tissues may be permeated by the fungus before death occurs. © 1968.