Attempts to increase percent parasitism of three hymenopterous species on the eggs of two soybean [Glycine max] stink bugs by host eggs aded artificially in an open field
1995
Kikuchi, A. (Agricultural Research Center, Tsukuba, Ibaraki (Japan)) | Naito, A. | Matsuura, H.
Stink bugs which occur widely and frequently are serious pests of soybean in Japan. Especially two species; Piezodorus hybneri and Riptortus clavatus, are very important in the Kanto district or the central part of Honsyu Island. More than 60% of the eggs of stink bugs are occasionally destroyed by egg parasitoids, and Telenomus triptus Nixon mainly on P. hybneri, Grion japonicum on R. clavatus. The present experiment was conducted to develop a method for maintaining high percentages of parasitism by egg parasitoids on the two stink bugs in an open field at the National Agriculture Research Center, in Tsukuba in the year of 1985. One egg mass of P. hybneri and 10 eggs of R. clavatus were additionally placed at 16 sites/replication in the treated plots every 2-5 days from early August (onset of pod formation) through the end of September (beginning of bean maturity) in 1985. Such eggs were collected every 2-5 days after placement and the percentage of parasitism was determined. After the observation, the parasitized eggs were returned to the plots, whereas unparasitized eggs were removed. Comparison of the percentage of parasitism between the treated plots and the untreated control plots was conducted once on September 10. 1) In P. hybneri, more than 80% parasitism was observed for the eggs additionally placed during most of the season, and the hatching ratio of the host eggs ranged from 0 to 2.3%. 2) In R. clavatus, about 70% parasitism was observed for the eggs placed during most of the season, and the hatching ratio of the host eggs exceeded 14.3%. 3) In P. hybneri, the percentage of parasitism was significantly higher in the treated plots than in the untreated ones. In R. clavatus, however, there was no significant difference in the percentage of parasitism between the treated plots and the untreated ones
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