Appl. Entomol. Zool. 45 (4): 587–592 (2010) http://odokon.org/ Determination of major host plants and seasonal changes in infestation frequency of the sweetpotato vine borer, Omphisa anastomosalis (Lepidoptera: Crambidae), on Kume Island, Okinawa Suguru OHNO,1,* Dai HARAGUCHI2 and Tsuguo KOHAMA1 1 Okinawa Prefectural Agricultural Research Center; Itoman, Okinawa 901–0336, Japan 2 Okinawa Prefectural Plant Protection Center; Naha, Okinawa 902–0072, Japan (Received 16 April 2010; Accepted 29 June 2010) Abstract The host plants and seasonal occurrence of larvae and pupae of Omphisa anastomosalis were examined on Kume Is- land through the extensive collection of convolvulaceous host candidates from 2001 to 2010. The frequency of infes- tation was highest on Ipomoea indica (5.8 insects per 100 m of vine) followed by sweet potato (2.1 insects). Other Ipomoea spp. were infested rarely or not at all (Ͻ0.6 insects). On I. indica, infestation frequency was negatively corre- lated with air temperature, with a large peak from January to February. The pupal ratio among the total population showed two clear peaks in June and October, and was zero or nearly zero in August and from December to April. These results suppose that at least two generations occur within a year, and may suggest a delay of larval development due to low temperatures in winter and the inhibition of pupation by high temperatures or other unknown factor(s) in summer. Further, the infestation frequency of I. indica decreased from April to July, while it increased or did not change in the sweetpotato field during this period. Key words: Convolvulaceae; Pyraustinae; quarantine pest; seasonal occurrence; wild host plant and Euscepes postfasciatus (Fairmaire) (Coleo- INTRODUCTION ptera: Curculionidae), O. anastomosalis is speci- The sweetpotato vine borer, Omphisa anasto- fied as a quarantine pest under the Plant Protection mosalis (Guenée) (Lepidoptera: Crambidae), is a Law, which prohibits the movement of host plants pest of the sweet potato (Ipomoea batatas (L.) of these species from a pest-infested region (i.e., Lam.; Convolvulaceae) that significantly reduces Ryukyus) to non-infested regions (i.e., main is- yields of sweetpotato roots (Sakae, 1968; Talekar lands of Japan). Knowledge in relation to the host and Cheng, 1987). The larvae of this moth bore plants and the seasonal occurrence of O. anasto- into and feed inside the main vine of the sweet po- mosalis in the field is therefore essential for its tato, often leading to the death of aerial parts of the control. Although brief investigations have been plant (Talekar and Pollard, 1991). The species is conducted on some Ipomoea host plants of this widespread in tropical to subtropical Asia-Pacific pest (Sakae, 1968; Tobaru et al., 1999; Yoshimura regions and infests only plants belonging to Con- and Yoneda, 1999), the relative importance of Ipo- volvulaceae (Talekar and Pollard, 1991). It was first moea plants as source hosts, as well as whether recorded in Japan in the southernmost part of the other convolvulaceous species are utilized as hosts, Ryukyu archipelago in the early 1940s (Takara, has remained unclear. Information on the seasonal 1954), expanding its range northward to the north- occurrence of O. anastomosalis is of significance ern part of the central Ryukyus (Amami-ôshima for determining the optimal timing of its control. Island) by the early 1960s (Sakae, 1968). In Japan, Monitoring O. anastomosalis populations is diffi- along with two invasive sweetpotato pests, Cylas cult because no effective attractant for the species, formicarius (Fabricius) (Coleoptera: Brentidae) such as a sex pheromone, has yet been identified * To whom correspondence should be addressed at: E-mail: [email protected] DOI: 10.1303/aez.2010.587 587 588 S. OHNO et al. (Talekar et al., 1992). mined by visual inspection) were collected. For Since the Okinawa Prefectural Government is other convolvulaceous plants whose vines rarely currently going ahead with an eradication project lignify, samples were collected regardless of thick- targeting C. formicarius and E. postfasciatus on ness. The lengths of vines in all samples were Kume Island using sterile insect releases, we have measured and the vines were carefully dissected at monitored infestation rates on vines of convolvula- Okinawa Prefectural Plant Protection Center ceous plants to evaluate the effectiveness of re- (OPPPC; former Fruit Fly Eradication Project Of- leases (Kohama et al., 2006; Ohno et al., 2006). fice), Naha City within three days of collection. Because both larvae and pupae of O. anastomosalis From May 2005, the vines were also weighed be- were found during this survey, we accumulated fore dissection. All insects recognizable by the much information on the host plants and the sea- naked eye were recovered from the vines, sorted sonal occurrence of this moth during its immature and counted. We could identify the larvae and stages. In the present paper, we have summarized pupae of O. anastomosalis without difficulty be- the data on the infestation by O. anastomosalis of cause no other morphologically similar lepidopter- convolvulaceous plants obtained from 2001 to ans were found on the vines. Several individuals 2010 on Kume Island to determine the major hosts were reared to adulthood by keeping them at room and the pattern of seasonal occurrence of this temperature (Ϸ26°C), pinned and dried, and pre- species in the field. served in OPPPC as voucher specimens. The total length and weight of vines dissected and the total number of O. anastomosalis found were calculated MATERIALS AND METHODS for each of the Ipomoea species collected. Infesta- The study site, Kume Island (ca. 6,000 ha), is lo- tion frequencies of O. anastomosalis were ex- cated about 90 km west of Naha City, Okinawa Is- pressed as the number of individuals (larvae land in the central Ryukyus. All convolvulaceous ϩpupae) per 100 m of vine or per kilogram of vine species which we could find on this island and on and compared among the plant species. Since the Ou Island (a small neighboring island connected to early instar larvae of O. anastomosalis bore into Kume Island by a bridge) were included in this leaf veins and petioles of the host plants (Sakae, study. From January 2001 to January 2010, vines 1968; Kamikado, 1989), data from vines do not were collected extensively in all areas of the is- represent the total number of larvae infesting the lands (excluding sweetpotato fields) at least once a entire plant body. The number of pupae found on month. Collections were made at 25 sites or more vines should reflect the occurrence of pupae on the (at least nine sites for Ipomoea indica (Burm.) whole plant body because O. anastomosalis pu- Merr.) per month. From June 2002 to October pates usually in the vine and rarely in the other 2009, samples were also collected from sweet- parts of the plant (Sakae, 1968; Talekar and Pol- potato fields where no control measures for O. lard, 1991; authors, personal observations). anastomosalis have been applied. This survey was To describe the pattern of the seasonal occur- conducted in 20 randomly chosen fields at one rence of O. anastomosalis, we used the data on I. time, usually four times per year at approximately indica and sweet potato because these plants were three-month intervals. In Okinawa, sweet potato is collected throughout the study period and were fre- generally planted from March to October and har- quently infested by O. anastomosalis (see Results). vested five to seven months after planting; there- The numbers of O. anastomosalis pupae and larvae fore, we could find sweetpotato plants all year per 100 m of vine and per kilogram of vine were round in the fields in Okinawa, including Kume Is- calculated for each month by pooling data from land. Although pesticide application targeting other different collection sites. The monthly number of pests in each of the surveyed sweetpotato fields insects per kilogram of vines was regressed to that was unclear, the major tactic, if used, was mainly per 100 m of vine for each plant species to test the granule application for soil insect pests at the time validity of using the latter variable as an indicator of planting. For the sweet potato, I. cairica (L.) of infestation. Data on monthly mean temperature Sweet, I. indica and I. pes-caprae (L.) Sweet, ligni- were obtained from the webpage of the Japan Me- fied vines thicker than 5 mm in diameter (deter- teorological Agency (http://www.data.jma.go.jp/ Wild Host Plants of the Sweetpotato Vine Borer 589 Table 1. Data of Ipomoea plants and Omphisa anastomosalis larvae and pupae collected on Kume Island from January 2001 to January 2010 Total No. Weight No. Cumulative Plant species length of Total No. insects per per 100 m insects per No. collection (common name, if any) vines insects 100 m of of vine kilogram sites (m) vine (kg)a of vinea I. aquatica (water spinach) 13 521 3 0.58 3.3 0.00 I. batatas (sweet potato) 751 7,564 159 2.10 2.7 0.30 I. biflora 5 147 0 0.00 2.1 0.00 I. cairica (Cairo morning glory) 46 8,374 15 0.18 3.0 0.07 I. indica (blue morning glory) 4,397 857,341 49,809 5.81 3.5 1.69 I. littoralis (whiteflower beach morning glory) 9 133 0 0.00 1.5 0.00 I. pes-caprae (beach morning glory) 1,184 104,854 85 0.08 5.1 0.00 I. triloba (three-lobed morning glory) 1 51 0 0.00 No data — Total 6,406 978,985 50,071 — — — a Calculated for the data from May 2005 to January 2010. obd/stats/etrn/index.php). When the monthly infes- tation frequency of one plant species was corre- lated to that of another plant species or the other variable, Spearman’s rank correlation (rs) was used.