Biology of Bracon mellitor, a Parasite of the Boll Weevil123

Abstract

Under optimum conditions in the laboratory, using 3rd stage larvae of the boll weevil, Anthonomus grandis Boheman, for hosts, minimum life cycle averaged 11 days, average longevity of females was almost 22 days, and that of males was 10 days. The species was satisfactorily reared in the laboratory in the range of 21-29°C and 40-70% RH. Adult mortality rates increased sharply at lower levels of relative humidity. Females mated almost immediately after emergence. The egg was greatly contorted during oviposition and required 23-25 hours to hatch at 27-29°C. In a laboratory test females deposited an average of 7.75 eggs per day or an average total of 164 eggs per female. They readily paralyzed and laid eggs on older boll weevil larvae; they rarely attacked pupae. Newly hatched larvae of the parasites were cannibalistic, limiting production per host material. Diapause and over wintering occurred in the prepupal stage. The over wintered generation was characterized by denser cocoons and black markings on the emerging adults. In the laboratory, relative humidity below 35% tended to induce diapause, and diapausing prepupae conditioned at 2-6°C for 2 weeks pupated and emerged as adults more promptly than when they were not thus cold treated. The release of adults at the rate of more than 800 females per acre of cotton per week in I field test increased parasitism from 0 to more than 50% in naturally falling boll-weevil-infested squares and to more than 80% in squares tied to the plants. This effect contrasts with the 25 and 35% maximum parasitism, respectively, observed in natural populations. Mass releases made periodically might produce effective control of boll weevils. However, mass rearing has not been perfected.