On the Biology and Control of the North American Chestnut Weevils
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Curculio auriger (Casey) and Curculio proboscideus Fab. are indigenous North American nut weevils and attack only the fruits of chestnut and chinquapin. Their natural distribution occurs over the same geographical areas that the American chestnut was found. Since the destruction of most of the native chestnut trees by chestnut blight, Endothia parasitica (Murr.), the weevils have been able to survive on scattered plantings of oriental chestnuts which are resistant to blight, from a few native chestnut trees partially resistant and from the coppice growth of old chestnut stumps. Rearing of both species in the field was accomplished by the use of soil cages set into the ground to a depth of 12 inches. Adult behavior was studied in large cages that completely covered the tree. Chestnut weevils lay their eggs in the kernel. The eggs of C. auriger hatch in about eight days and those of C. proboscideus hatch in about 10 days under the conditions in central Maryland. There are four larval instars in each species and these are described and illustrated. Head characters were found that will separate the species and the instars. C. auriger completes its larval development in 21 days while it takes 30 days for Q. proboscideus. The pupae of both species are of' the exerate type and may be separated by the presence of two small bristles on the beak, near the insertion of the antennae, of C. auriger. These bristles are lacking in C. proboscideus. The usual life cycle of C. auriger is two years. The life cycle of C. proboscideus is usually one year. A few individuals of each species require an additional year to complete their cycle. The adult C. auriger issues from the ground in May and feeds on the chestnut catkins. After the catkins wither they disperse and are not seen again until the chestnuts are nearing maturity. C. proboscideus issues from the ground late in July and may be seen in the trees a few days after emergence. The male genitalia were studied for taxonomic characters. These characters are sufficiently clear so that the two chestnut weevils may be identified thereby. Two species of internal insect parasites were found. Myiophasia nigrifrons Tns., a tachinid fly, was reared from the larvae of both species of' chestnut weevils and was observed in its larval stage within the body cavity of the chestnut weevil larva. Urosigalphus armatus Ashm. is a braconid parasite and was found only in the larvae of Q. prohoscideus. Chemical control studies have shown that the adult stage is the most susceptible to insecticides. Preliminary tests with heptachlor, applied at the rate of six to eight pounds of the chemical per acre, as a spray or dust to the ground cover under the trees, have given excellent results for the control of chestnut weevils.