The Present Status of the Established Parasites of Popillia Japonica Newman

Abstract

Of the five established parasites of the Japanese beetle three are true parasites of Popillia Japonica in Japan and two are parasites of allied Popillia occurring in Chosen (Korea). Considering these, Tiphia popilliavora gives much promise as an effective parasite of Popillia in the primary area of heavy beetle infestation, this no doubt being due to proper seasonal adjustment in relation to its host. The Korean Tiphia vernalis also seems to show proper seasonal adjustment, and the growth of the colonies in Pennsylvania and New Jersey indicates that the species may be of much economic value in the future. With the Diptera in all three species there seem to be obstacles in the new or present environment which limit their increase. In Centeter cinerea there seems to be a direct response to climatic conditions which throws it out of alignment with its host. In Prosena siberita the difficulty seems to be with the host, that is, the climatic conditions are such that it has responded with practically a one-year cycle, which is not favorable to the parasite. Also, in the case of Dexia ventralis the lack of a two-year cycle of the host is not favorable and the new habitat does not supply the necessary secondary hosts which might carry the species over the periods when Popillia is in the pupal and adult stages. The only solution for these ill adjustments, as seen by the writer, depends on the use of these parasites in the future when the host has extended its range into new environments, in zones climatically different from. the present center of parasite introduction. Popillia Japonica presents three markedly different conditions in its life cycle in Japan as one progresses northward from Yokohama to Sapporo. This alone is sufficient evidence to indicate that as the species spreads northward in the United States, a two-year cycle will become more and more evident and will undoubtedly parallel the condition as described for Koiwai and Sapporo, Japan. With Centeter cinerea the writer is of the opinion that a more northern climate is necessary to bring about a proper delay in its emergence so that it will appear with its host, and that only under these conditions can the parasite be of any economic value in the control of P. japonica. In the case of Prosena siberita this parasite is likely to be of value in the biological control of P. japonica in regions where a two-year cycle occurs, thus supplying host material more timely and abundantly for the parasite. Dexia ventralis has succeeded in producing two generations per year, apparently without alternate hosts and under adverse conditions. It is believed by the author that this species may be of considerable economic value in controlling P. japonica in regions where this host has an abundant supply of belated two-year larvae in the soil. Native Scarabaeidae if present in sufficient abundance. might also serve as alternate hosts.