Seasonal occurrence and interspecific interactions of egg parasitoids of Megacopta cribraria (Heteroptera: Plataspidae) in Japan

Authors: HOSHINO, KEISUKE - UNIVERSITY OF TOKYO; ADATI, TARO - UNIVERSITY OF TOKYO; OLSON, DAWN; TAKASU, KEIJI - KYUSHU UNIVERSITY

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2017
Publication Date: 3/27/2017
Citation: Hoshino, K., Adati, T., Olson, D.M., Takasu, K. 2017. Seasonal occurrence and interspecific interactions of egg parasitoids of Megacopta cribraria (Heteroptera: Plataspidae) in Japan. Environmental Entomology. 46(3):487-493. https://doi.org/10.1093/ee/nvx060.
DOI: https://doi.org/10.1093/ee/nvx060

Interpretive Summary: The kudzu bug has recently invaded the southeastern United States, where it was first found in north Georgia in 2009, and has since spread throughout Georgia, South Carolina, and other southeastern states in the United States. The kudzu bug is a threat to production of soybean in the southeastern United States and insecticide applications is the only current method of control as native enemies are insufficient control agents at present. However, there is a risk of resistance development with chemical control. In addition, the cost of chemical control of kudzu bugs in large areas of kudzu near urban areas and where kudzu bug densities are high would be prohibitive. Therefore, we are investigating the potential of importing and releasing an egg parasitoid, Paratelenomus saccharalis, from Tokyo Japan as a control agent against this invasive pest in the southeastern United States. We found a significant association between parasitism of the same egg mass by P. saccharalis and another egg parasitoid, Ooencyrtus nezarae indicating that egg parasitism by the two species on the same egg mass occurs more often than parasitism by either species alone, regardless of the size of the egg mass. This resulted in lower parasitism rates of both species and the production of more male progeny. The cause of the interaction between the two egg parasitoids is unclear, but O. nezarae out competes P. sacharalis when both parasitize the same egg. This underscores the need to prevent O. nezarae from entering the southeastern US where P. saccharalis may be present. The successful development of P. saccharalis at low temperatures that we found indicate that this P. saccharalis strain could tolerate colder temperatures in the more northern areas of the southeastern US where Kudzu bugs are prevalent, and where we have estimated they could have as many as 8 generations. The parasitoid strain may be a good condidate species for importation and release as they appear to effectively parasitize eggs at high rates and may be better adapted to larger areas of the southeastern United States than is the current P. saccharalis strain recently found in the southeast but where it has established in only southern Georgia and Florida.

Technical Abstract: We conducted a field study to determine seasonal egg parasitism rates of the kudzu bug Megacopta cribraria (Fabricius) on the kudzu plant, Pueraria montana (Lour.) Merr. var. lobata (Willd.) Maesen et Almeida ex Sanjappa and Pradeep in Tokyo, Japan during the period from May 2014 to September 2014. Eggs of M. cribraria were laid on the kudzu plant from May to September. Megacopta cribraria eggs were parasitized by two parasitoid species, Paratelenomus saccharalis (Dodd) and Ooencyrtus nezarae Ishii. Paratelenomus saccharalis first appeared in May and its parasitism rates peaked in July and September. Ooencyrtus nezarae first appeared in June and its parasitism rate peaked in July. More than 30% of parasitized M. cribraria egg masses where at least one egg was parasitized, were concurrently parasitized by both species. Occurrence of parasitism by P. saccharalis and O. nezarae in M. cribraria egg masses was independent at two locations and positively associated at one location, suggesting that the use of host egg masses by P. saccharalis and O. nezarae is not mutually exclusive. Parasitism rates of P. saccharalis or O. nezarae were significantly lower for egg masses parasitized by both species than for those parasitized by a single species. The proportion of males in O. nezarae progeny was significantly higher for egg masses parasitized by O. nezarae together with P. saccharalis than for those parasitized by O. nezarae alone. These results suggest that parasitism of host egg masses by the two species is influenced by their interspecific interactions. Based on developmental times of P. saccharalis under temperatures of 19°C to 31°C, we estimated a lower developmental temperature threshold of 12.5°C. It was estimated that P. saccharalis has at most 8 generations per year in Tokyo, Japan.