Within-Vine Distribution and Damage of Sweetpotato Weevil, Cylas formicarius elegantulus (Coleoptera: Curculionidae), on Four Cultivars of Sweet Potato in Southern Florida

Abstract

The sweetpotato weevil (SPW), Cylas formicarius elegantulus (Summers) is the most economically important insect pest of sweet potato, Ipomoea batatas (L.) Lam., worldwide. Low level infestations reduce quality and marketable yield (Proshold 1983). Terpenoids that are produced by sweet potato in response to SPW feeding may make even slightly damaged roots unfit for human consumption (Uritani et al. 1975, Akazawa et al. 1960). Yield losses of up to 60-80% have been attributed to SPW (Hua 1970, Subramaniam et al. 1977, Mullen 1984). Economically effective control measures for SPW in regions with large resident populations are lacking. There are no insecticides that will adequately control weevils in an infested field (Stall et al. 1984) because SPW immature stages are spent within vines and/or roots. For this reason, other SPW management approaches, such as host plant resistance, have been explored (Waddill & Conover 1978, Mullen et al. 1980a,b, 1981, 1982, 1985). With one exception (Waddill & Conover 1978), resistant cultivars have not been field tested in regions with high SPW population pressure. The present study was conducted to evaluate SPW resistance in four sweet potato cultivars in southern Florida, a region with a dense SPW population. Also, we determined the -impact of a mechanical barrier (polyethylene mulch) on field plant protection from SPW. Lastly, we compiled preliminary data on the within-vine distribution of SPW in sweet potato. The experiment was conducted in 1986 at the Tropical Research and Education Center in Homestead, Florida. Four sweet potato cultivars, I. batatas cv. Resisto, Regal, Sumor, and NC1135, were planted in a split-plot design with three replications. Plastic polyethylene mulch (white/black, 38 microns thick covering a 0.9-m bed width) was the whole-plot factor and cultivar was the split-plot factor. Cultivars were handplanted on 22 April in raised beds with 1.8 m centers. Slips (0.3-m long) of each cultivar were planted 0.3 m apart in one row per bed. Replicate plots consisted of 40 slips