Assessment of effect of partial sterility on mating performance in sweetpotato weevil (Coleoptera: Curculionidae)

Mate choice errors may contribute to slow spread of an invasive Eurasian longhorn beetle in North America

Tetropium fuscum (Coleoptera: Cerambycidae) is a Eurasian longhorn beetle and forest pest that first became invasive to Nova Scotia, Canada around 1990. In the time since its introduction, T. fuscum has spread only about 150 km from its point of introduction. In its invasive range, T. fuscum co-exists with its congener Tetropium cinnamopterum. Although they are ecologically similar species, T. fuscum tends to infest healthier trees and has a smaller host range than T. cinnamopterum. If they successfully interbreed, this could lead to hybrid individuals that are more problematic than either parent species. On the other hand, if T. fuscum can make mating errors in the field, but is not producing hybrid offspring, then this waste of mating resources could help explain the slow spread of T. fuscum in North America. We conducted no-choice and choice mating experiments between T. fuscum and T. cinnamopterum males and females and determined that both T. fuscum and T. cinnamopterum males make mate-choice errors with heterospecific females in a laboratory setting. Our results suggest that mating errors may play a role in the slow spread of T. fuscum in North America.

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.

Metabolic profiling of somatic tissues from Monochamus alternatus (Coleoptera: Cerambycidae) reveals effects of irradiation on metabolism

A high-level of sexual sterility is of importance for the sterile insect technique (SIT). However, the use of high-dose-intensity gamma radiation to induce sterility has negative impacts not only on reproductive cells but also on somatic cells. In this study, we investigated the metabolite differences in somatic tissues between non-irradiated, 20-Gy-irradiated, and 40-Gy-irradiated male Monochamus alternatus, an important vector of the pathogenic nematode, Bursaphelenchus xylophilus, which kills Asian pines. The results showed that metabolite levels changed moderately in the 20-Gy samples but were markedly altered in the 40-Gy samples compared with the non-irradiated samples. Twenty-six and 53 metabolites were disturbed by 20-Gy and 40-Gy radiation, respectively. Thirty-six metabolites were found to be markedly altered in the 40-Gy samples but were not changed significantly in the 20-Gy samples. The comprehensive metabolomic disorders induced by 40-Gy radiation dysregulated six metabolic pathways involved in the life process. The findings presented in this manuscript will contribute to our knowledge of the characteristic metabolic changes associated with gamma-radiation-induced damage to somatic cells and will allow for better exploration of the SIT for the control of this target pest.