SOME DYNAMIC ASPECTS OF FIELD POPULATIONS OF THE CABBAGE ARMYWORM, MAMESTRA BRASSICAE LINNE, IN TOHOKU DISTRICT : II. MORTALITIES DURING THE PROGRESS AND BREAKDOWN OF AN OUTBREAK ON THE SUGAR BEET

概要

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During four generations of the cabbage armyworm, Mamestra brassicae Linne, from late autumn of 1964 to early summer of 1966, population fluctuation and mortalities have been investigated in a sugar beet field at Morioka. In two generations of 1965, there were found two age intervals with remarkably high mortality, the first and last larval instars. Major mortality factors in the first instar could not be clarified, and those in the last instar appeared to be predation by birds and diseases, Spicaria pracina, etc. Egg and larval parasites (Telenomus sp., Trichogramma spp., Microplitis medianus, Euplectrus sp., and Exorista japonica), several arthropod predators and pupal diseases caused lower mortalities. Some eggs were lost by dislodgement from the host leaf and by feeding by older armyworm larvae on the oviposited leaf. It seemed also that operation of a beet harvester and autumn plowing provided remarkable reduction of overwintering pupal population. In the experimental field, cabbage armyworm population grew progressively up to the overwintering generation of 1965 and then suddenly diminished before the advent of the succeeding generation. This rapid breakdown of outbreak may be caused mainly by the autumn plowing just after the peak of outbreak.
日本昆虫学会の論文
1973-09-25