First case of successful eradication of the sweet potato weevil, Cylas formicarius (Fabricius), using the sterile insect technique.

This paper presents the first case of the successful eradication of a Coleoptera pest species over a wide area using a combination of male annihilation technique (MAT) and sterile insect technique (SIT) application. The sweet potato weevil, Cylas formicarius, is one of the most destructive and widely distributed pests of sweet potato, Ipomoea batatas. A project to eradicate it was launched in 1994 on Kume Island, Okinawa Prefecture, Japan. The MAT application was first used from November 1994 to January 1999 to reduce the density of wild populations. The distribution and densities of weevils were assessed by trapping them and surveying infestation rates in wild hosts and sweet potatoes in the field. The C. formicarius populations were suppressed by approximately 90% and plant infestations were reduced from 9.5% to less than 0.1% by using the MAT. Then, hundreds of thousands to millions of sterile weevils were released each week (ca. 460 million in total from 1999 to 2012). As a result, based on an analysis of 12748 stems and 48749 tubers, no weevil infections were detected in the stems or tubers of sweet potato since 1997. Since 2009, almost no wild weevils were captured in traps, and in wild host and sweet potato surveys no weevils have been found in any of the 580 locations and 8833 samples since October 2011. As of 28 December, 2012, C. formicarius is considered to have been eradicated from Kume Island. This paper describes the process of eradicating C. formicarius using SIT application integrated with MAT application for the first time and discusses some of the main challenges associated with the weevil eradication campaignl.

Synthesis and activity of 3-oxo-α-ionone analogs as male attractants for the solanaceous fruit fly, Bactrocera latifrons (Diptera: Tephritidae).

A series of 3-oxygenated α-ionone analogs have been developed as highly specific male lures for the solanaceous fruit fly Bactrocera latifrons, a pest of solanaceous fruits. We compared the attractant and phagostimulant activities of analogs with or without (i) unsaturations at the 4,5- and/or 7,8-positions and (ii) oxygen moieties at the 3- and/or 9-positions of the ionone molecule. Since naturally occurring vomifoliol (V2) was found to induce a highly potent phagostimulant activity in B. latifrons males, related analogs including dehydrovomifoliol (V1), 6-hydroxy-α-ionone (U1), and 6-hydroxy-α-ionol (U2) were synthesized to evaluate their attractant and phagostimulant activities. Synthetic V1, V2, U1, and U2 exhibited low attractant activity, but their phagostimulant activity was relatively high. Optical isomers of 3-oxo-7,8-dihydro-α-ionone (P3) and V1 were prepared to examine the stereochemical specificity of attractants. (+)-(6R)-P3 and (+)-(6S)-V1 exhibited the corresponding activities, while their respective antipodal enantiomers were found entirely inactive.

Effects of Irradiation Dose on Sperm Production, Insemination, and Male Mating Possible Period in the Sweetpotato Weevil (Coleoptera: Brentidae).

The sterile insect technique (SIT) has been used for the control or eradication of target insect pests. To successfully apply SIT, it is very important to clarify the effect of irradiation on male reproduction in the target pest, because their mating and spermiogenesis abilities affect the success of eradication program. The sweetpotato weevil, Cylas formicarius (Fabricius) (Coleoptera: Brentidae) is a notorious and worldwide pest of sweet potato. We investigated the effect of irradiation at five doses ranging from 0 (control) to 150 Gy on 9-d-old males. Survival rate of the control (no treatment) remained high from day 10 to 20 of adult life, whereas higher doses of irradiation reduced it, maximally by approximately 70%. Mating rates showed a similar tendency. Radiation dose neither affected sperm production nor sperm transfer at any dose, although spermiogenesis is active during the adult stage. However, radiation dose affected the lifetime total of ejaculated sperm number, likely because of fewer matings by irradiated males. These results suggest that use of a dose of 150 Gy or higher is appropriate for the final step of eradication of this weevil. At least, lower dose of irradiation may arise the inadequate sterilization, resulting in a failure of eradication program. We conclude that weekly release of sweetpotato weevil sterilized with high dose, achieving complete sterilization, could be useful for eradication program after reducing the population by male annihilation method.

The neogregarine protozoan Farinocystis sp. reduces longevity and fecundity in the West Indian sweet potato weevil, Euscepes postfasciatus (Fairmaire).

The number of West Indian sweet potato weevils, Euscepes postfasciatus, being mass-reared in a facility for use in sterile insect technique (SIT) eradication programs has undergone a drastic reduction. A neogregarine protozoan pathogen Farinocystis sp. (an undescribed species) was detected in vivo in the mass-reared E. postfasciatus. We investigated the effects of this disease on the longevity and fecundity of host weevils and the incubation time of the disease in the host body under mass-rearing conditions. Our results demonstrated that infection by this Farinocystis sp. decreased both longevity and fecundity in E. postfasciatus. In particular, the pathogen severely limited the production of progeny by infected females compared to healthy females. Therefore, we consider this protozoan infection to be the major cause of the decreased E. postfasciatus production in the mass-rearing facility.

Sperm storage and viability within females of Euscepes postfasciatus: effect of irradiation on sperm abundance and viability within female.

Irradiation has been widely used in suppression or eradication programs that use the sterile insect technique (SIT) or in studying sperm competition. Although it is well known that irradiation has negative impacts on reproductive (sperm) cells, previous studies have assumed that sperm from irradiated males behave identically to normal sperm in the female reproductive tract after mating. In this study, we used the West Indian sweetpotato weevil Euscepes postfasciatus to investigate the effect of irradiation on the abundance and viability of sperm in female spermatheca for 14 days after copulation. The abundance of sperm in females did not change throughout the experimental period, and sperm viability gradually decreased regardless of irradiation. In this weevil, irradiated sperm appear to behave identically to normal sperm in females for 14 days following irradiation/copulation. Therefore, the effect of irradiation on sperm viability within the female spermatheca is considered to be insignificant.

Effect of irradiation on dispersal ability of male sweetpotato weevils (Coleoptera: Brentidae) in the field.

We used the mark-and-recapture method in the field to test the effect of gamma radiation on the dispersal ability of the male sweetpotato weevil, Cylas formicarius elegantulus (Summers) (Coleoptera: Brentidae), a serious sweetpotato pest in Japan. To evaluate the dispersal ability of male sweetpotato weevil, we released 27,218 males (13,302 males irradiated with a dose of 200 Gy and 13,916 nonirradiated males) in two replications (September and October 2005). Each replication lasted 5 d from the release of weevils to the removal of traps, and male weevils were released twice (1 and 3 d before trap setting). Forty pheromone traps were placed in lines corresponding to eight compass directions and five distance classes (20, 50,100, 200, and 500 m) in each replication. We captured 2,263 irradiated males (17.0%) and 2,007 nonirradiated males (14.4%) in the two replications. Six irradiated and eight nonirradiated males were captured in the traps 500 m far from the release point. All parameters to evaluate the dispersal ability of irradiated male sweetpotato weevil (recapture rate, dispersal distance, and dispersal direction) were similar to nonirradiated males in three of the four trials. However, parameters were different between irradiated males and nonirradiated males in one trial. Because the majority of parameters consistently show that the similarity of the dispersal ability, we considered that male sweetpotato weevil irradiated with a dose of 200 Gy possessed equal dispersal ability to that of nonirradiated males in the field.