Suppression of Colorado Potato Beetle, Leptinotarsa decemlineata (Say), (Coleoptera: Chrysomelidae) Populations with Antifeedant Fungicides

Laboratory, small-field plot, and commercial-scale experiments were completed, using Connecticut, Rhode Island, and New York Colorado potato beetle, (CPB) Leptinotarsa decemlineata (Say), populations to determine if "antifeedant fungicides" might reduce the suitability of potato for CPB while simultaneously protecting potato from early and late blight. In the laboratory. fungicides formulated from triphenyltin hydroxide (TPTH) or Cu(OH), reduced CPB feeding 95 and 61%. In small-field plots, CPB larval densities were significantly reduced where TPTH and Cu(OH), were used regularly. In commercial-scale experiments, L. decemlineata populations were significantly reduced and required fewer insecticide applications for acceptable control where TPTH was used regularly. The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), is a destructive pest of potato in most of North America and Europe. Populations are capable of completely defoliating plants and causing substantial yield reduction (Hare 1980a). To manage pest populations, growers may apply up to nine insecticide applications per season at a materials cost of up to $60/ha per application (Wright et aL 1983). Managing southern New England CPB populations with pesticides is hindered by the relatively low toxicity of most registered insecticides (Hare I980b). Potato is also susceptible to early blight, Alternaria solani, and late blight, Phytophthora infestans. Growers customarily make up to I3 applications of protectant fungicides at intervals of 5 to 14 days, depending on disease incidence and weather conditions (Wright et al. 1983). CPB feeding behavior can be altered by a number of organic and inorganic compounds synonymously known as "feeding deterrents" or "antifeedants" (Schoonhoven 1982). Known antifeedants include glycoalkaloids (Hsiao 1974), various phytochemicals from nonhost species (Jermy et al. 1981), and several inorganic and organometallic compounds (Jermy 1961, Chapman 1974). Some of the latter are also the active ingredients in registered fungicides effective for potato disease protection. We performed several laboratory and field experiments with Connecticut, Long Island, N.Y., and Rhode Island CPB populations to determine if "antifeedant" fungicides significantly inhibited CPB feeding, reproduction, growth, or survival. With the cooperation of three Connecticut commercial potato growers, we also determined if one antifeedant fungicide formulated from triphenyltin hydroxide (TPTH) was compatible with other potato cultural practices and sufficiently effective as a feeding deterrent to reduce the frequency of insecticide applications necessary for acceptable CPB control. IReceived for publication 23 February 1983; accepted 12 May 1983. 'Dept. of Plant Pathology & Entomology. University of Rhode Island. Kingston. RI 02881. 'Dept. of Entomology, Cornell University, Long Island Horticultural Research Laboratory. 39 Sound Ave .. Riverhead. NY 11901. Materials and Methods Laboratory Experiments Formulations of TPTH (Duter, 47.5% WP), Cu(OH), (Kocide 101, 83% WP), maneb (Dithane M-22, 80% WP) mancozeb (Dithane M-45, 80% WP), and chiorothalonil (Bravo 500 F) were mixed with distilled water at concentrations equivalent to those used for disease protection in the field (0.20% AI for maneb and mancozeb, 0.125% Al for chlorothalonil, 0.10 and 0.20% AI for Cu(OH)" and 0.02% Al for TPTH). The control solution for all experiments was distilled water. CPB adults used in these experiments were the firstgeneration progeny reared on 'Katahdin' potato foliage in the laboratory (24°C 40 to 60% relative humidity [RHJ, photoperiod LD 16:8) from adults collected from the Lockwood Farm, Mt. Carmel, Conn. Within 24 h after emergence, experimental adults were sexed and confined as pairs in 500-ml unwaxed paper containers with transparent lids. Mature leaves were excised from 'Katahdin' potato plants in the greenhouse. Overlapping leaflets were removed, and the area of the remaining leaflets was determined photoelectrically. Each leaf was dipped in one of the test solutions and allowed to dry. The leaf was then inserted into a water reservoir and placed in the container with the adult pair. Leaves were measured and replaced every 24 h, consumption being calculated by subtraction. Any eggs were counted and removed. Consumption was monitored for the first 14 days for 10 pairs per treatment. Egg production was monitored for the first 28 days for 20 pairs per treatment, except for TPTH, where only 10 pairs were monitored. Another oviposition experiment was completed using potato leaves taken from untreated plants in the field or from plants sprayed weekly with Cu(OH), (1.86 kg of AIIha), mancozeb (1.80 kg of AIIha), or TPTH + mancozeb (0.17 + 0.90 kg of AIIha). Newly emerged summer adults were sexed and confined as pairs as described above. Insects were maintained in an outdoor insectary so that they were exposed to ambient temperatures and photoperiods, but were shaded from direct sunlight. Leaves were replaced every 24 to 36 h, and eggs were