Studies on Pests and Their Predators at Two Groves of "Kuroshima-mikan", a Native Citrus on Nagashima, Kagoshima Pref.

Abstract

Investigation was made at two groves (Kasedo and Kawatoko) of "Kuroshima-mikan", a native citrus on Nagashima, Kagoshima Prefecture, in order to determine the most desirable relation between the pests and their predators in citrus groves.Of the predators, Saula japonica feeding on the arrowhead scale, citrus red mite, etc. was the largest in number and Pseudoscymnus hareja feeding on the arrowhead scale, aphids, etc.was next. These two species amounted to about 60% of the total. Of the pests, the arrowhead scale was dominant and there were many species, but none whose population was noticeably high. The population of citrus red mite was far below the control threshold.The population of Saula japonica was very high and that of Unaspis yanonensis was somewhat higher at Kasedo where the grove was darker, not windy, and humid. But the populations of some predators were higher at Kawatoko which was lighter, windy, and dry. Thus both the pest and predator seem to choose a habitat condition.The population of the arrowhead scale was higher at the grove of "Kuroshima-mikan"than at the orchard of natsudaidai cultivated and sprayed in Hagi; that of citrus red mite was far below the control threshold. The predator fauna was moer rich both in species and individual numbers at the grove of "Kuroshima-mikan"than at the orchard cultivated but unsprayed in Nago. The abundance of fauna seems to contribute to control the population of arrowhead scale below a certain point and to keep the citrus red mite at an extremely low density.