Spatial distribution and host utilization patterns of Cylas formicarius (Coleoptera: Brentidae), Euscepes postfasciatus (Coleoptera: Curculionidae), and Omphisa anastomosalis (Lepidoptera: Crambidae) on the wild host Ipomoea indica (Solanales: Convolvulaceae) in Okinawa, Japan

Abstract

Three major sweet potato pest species, sweet potato weevil Cylas formicarius (Fabricius) (Coleoptera: Brentidae), West Indian sweet potato weevil Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae) and sweet potato vine borer, Omphisa anastomosalis (Guenée) (Lepidoptera: Crambidae), were examined for their utilization patterns and spatial distribution in the wild host plant, blue morning glory, Ipomoea indica ((Burm.) Merr.) (Solanales: Convolvulaceae) in Okinawa, Japan. We investigated 18,720 samples of I. indica and showed that 649 individuals of C. formicarius were found at an infestation rate per 1 m of the vine of 2.44%, which was significantly higher at height levels 0 m than the other levels (0–1 m, 1–2 m and 2–3 m), and tended to be higher at height level >3 m. In the case of E. postfasciatus, 131 individuals were found, and its infestation rate (0.37% on average) was significantly higher at height levels 0–1 m than the other level (2–3 m), and tended to be higher at height level >3 m. In the case of O. anastomosalis, 65 individuals were found and its infestation rate (0.32%) was significantly higher at the 0–3 m height level than at the other level (0 m). The results of analysis of the spatio-temporal dynamics of populations within and across species showed that the pests are randomly distributed across the study area throughout the year. Stochastic simulations showed that E. postfasciatus and the other two species tend to infest the same vines, but C. formicarius and O. anastomosalis tend to infest different vines. We provide valuable information on the distribution patterns of these pests that can their effectively control.