Insect predators for controlling aphids on potatoes. 7. A pilot test of spraying eggs of predators on potatoes in plots separated by bare fallow land.

Abstract

Evaluations were made of the effectiveness of applying eggs of Coccinella septempunctata L. or C. transversoguttata Faldermann for controlling aphids on ‘Katahdin’ potatoes in field plots, 34×16 ft, separated by strips of bare fallow land 15 ft wide. The treatments with each species consisted of applying, with compressed-air machines, the eggs in spray mixtures containing water and 0.25% agar. The 3 treatments included 4 early-season, weekly applications for estimated totals of about 25,000 batching larvae per acre, 3 early-season, semiweekly applications for totals of about 14,500 hatching larvae, and 4 late-season, semiweekly applications for about 25.000. None of the treatments gave satisfactory control of the aphids; however, the early-season applications were best. The early-season treatment consisting of 3 semiweekly applications of C. septempunctata eggs gave about 40% greater reduction of the apterous aphids than did the late-season treatment consisting of 4 semiweekly applications. The 3rd treatment, consisting of 4 weekly applications of eggs, gave 25–30% reduction. The degree of control from C. transversoguttata was not markedly different from that of C. septempunctata but there was a reversal in order of effectiveness of the 2 most-effective treatments; the 4 weekly applications gave 31–46% greater reduction than the 4 semiweekly late-season applications, while the 3 semiweekly, early season applications gave only 14–28% greater reduction on the same basis. The larvae of Coccinella spp. were more abundant in plots where eggs of C. septempunctata were applied than in untreated plots, but the adults were less abundant in plots having the semiweekly applications than in untreated plots or in those having the weekly applications in early season. In C. transversoguttata there were lesser degrees of positive association among treatments.