TRANSMISSION OF BURSAPHELENCHUS LIGNICOLUS (NEMATODA: APHELENCHOIDIDAE) BY MONOCHAMUS ALTERNATUS (COLEOPTERA: CERAMBYCIDAE)

BY

YASUHARU MAMIYA AND NOBUO ENDA Government Forest Experiment Station, Meguro, Tokyo, Japan A total of 21 species, all of which were associated with deteriorated trees, were examined for the presence of Bursaphelenchus lignicolus. Dauerlarvae of this nematode were recovered from adults of four species of the Cerambycidae;Monochamus alternatus, griseus, Arhopalus rusticus, and Corymbia succedanea. Between 75%-100% of the field population of M. alternatus in the diseased pine forests was contaminated, carrying an average number of 15,000 living nematodes per . Dauerlarvae were transmitted to pine tissues via feeding site of the insect on living branches. It appears that M. alternatus plays an important role in the spread of the nematode and on associated wilt disease in pine forests.

Bursaphelenchus lignicolus Mamiya & Kiyohara was found in wood in associa- tion with the wilting disease in pine trees (Pinus densiflora Sieb. et Zucc.. and P. thunbergii Parl) (Tokushige & Kiyohara, 1969). The wilting disease occurred in epidemic proportions in pine forests throughout central to southwestern Japan. Kiyohara & Tokushige (1971) first suggested that B. lignicolus might be one of the causative organisms of the disease. Bursaphelenchus spp. are usually associated with and apparently are distributed by them (Ruhm, 1956). The investigations were undertaken to reveal the relationships of B. lignicolus and some which were found associated with weakened or dead pine trees, and to find which species of insect played an important role in the dissemination of the nematode.

MATERIALSAND METHODS Beetles of the various genera in the Cerambycidae, the Curculionidae, and the Scolytidae were collected during the spring and the summer of 1971 in pine forests located in Kanto district and were examined for the presence of B. ligni- colus. Adult beetles were collected from the stems, branches and roots of dete- riorated and of dead trees, and from cut-logs of pine trees prepared for insect feeding and reproduction in the previous season. Nematodes were extracted by placing crushed beetles on tissue paper in water for one day using the Baermann technique. B. lignicolus was found on the body of adult Monochamus alternatus Hops., and the number of nematodes present was estimated. Adults of M. alter- natus were collected as they emerged from dead trees and also about a month later on the stems of weakened trees where they had been attracted for egg laying. M. alternatus adults contaminated with B. lignicolus were caged onto the fresh, 160 live, 20 cm long twigs of pine trees. These cut-twigs were examined for nematodes in the xylem 3 weeks later by the Baermann funnel technique. RESULTS More than 4,000 adults of 21 species of beetles were examined (Table I). B. lignicolus was found associated with four species of the Cerambycidae, M. alter- natns, Acanthocinus griseus Fabricius, Arhopalris rusticus Linn6, and Corymbia .ruccedanea Lewis. Dauerlarvae of B. lignicolus were recovered from adults of the above-mentioned beetles and they occurred most frequently and greatest numbers in M. alternatu.r. TABLE I

The recovery of B. lignicolus from beetles

About 300 M. alternatus adults collected from the stems of dead pine that had been attacked the previous summer were examined and of these, 73% to 100% were contaminated with B. lignicolus. An average of 15,000 Dauerlarvae per insect were recovered and the maximum was 175,000. The number of Dauer- larvae recovered from mature adult beetles which were collected at the time of beetle egg laying markedly decreased (Table II). M. alternatus were collected also in pine forests in which there were few deteriorated trees, and in which B. lignicolus had not been detected from dead trees. None of the 200 adult insects examined carried B. /??r<9/?.