~Effect on beneficial insects.~ Since the more potent of the newer organic insecticides are toxic to many parasitic and predatory insects, all of which help to reduce the populations of injurious species, these insecticides, if used, must be largely relied upon to effect control by themselves. Often no immediate assistance is forthcoming from beneficial insects after these materials have been used.
Nut Insect Investigations
Except for studies on the chestnut weevils, nut insect investigations by the Bureau of Entomology and Plant Quarantine are being conducted primarily on the pecan at southern laboratories. Many of the remarks in this paper are therefore based on information obtained from these laboratories. In view of the short time the new organic insecticides have been available, work to determine their place in nut insect control programs is largely in the experimental stage. Much further work will be necessary before detailed instructions can be given for their general use.
Insects Attacking the Nuts
~The Pecan weevil.~ The adult of the pecan weevil[8] is a snout beetle that attacks not only pecan throughout the South but also hickory in the eastern half of the United States. During mid-season, previous to the formation of the kernel, nuts are frequently punctured for feeding purposes. This results in failure of the nuts to complete their development. The principal injury, however, is caused by grubs that develop from eggs laid in the nuts after the kernels have formed. This is usually during September on pecans in the South. The grubs feed on the kernels and may consume them completely (Fig. 1).
[8] ~Curculio caryae~ (Horn).
Applications of sprays containing 6 pounds of 50 percent DDT wettable powder per 100 gallons of water just previous to and during the oviposition period have proved effective against this pest.
[Illustration: Fig 1.—Nut infested with larvae of the pecan weevil.]
[Illustration: Fig. 2.—Larva of the butternut curculio in Japanese walnut shoot.]
[Illustration: Fig. 3—Adults of the walnut husk maggot on black walnut.
Enlarged.]