Seasonal occurrence of specialist and generalist insect predators of spider mites and their response to volatiles from spider-mite-infested plants inJapanese pear orchards

In two adjacent Japanese pear orchards (orchards 1 and 2), we studied the s easonal occurrence of the Kanzawa spider mite, Tetranychus kanzawai, and it s predators. Also the response of these predators to the volatiles from kid ney bean plants infested with T. kanzawai was investigated using trap boxes in orchard 1. The mite density in orchard 1 was unimodal, with one peak at the end of August. In this orchard, population development of the speciali st insect predators, Scolothrips takahashii, Oligota kashmirica benefica an d Stethorus japonicus, was almost synchronized with that of the spider mite s. These predators disappeared when the density of their prey became very l ow in mid-September. Both S. takahashii and O. kashmirica benefica abruptly increased in number in orchard 2 when the spider mite population in orchar d 1 decreased. These results suggested that some of the predators migrated from orchard 1 to orchard 2. In this period, predator-traps with T. kanzawa i-infested bean plants attracted significantly more S. takahashii than trap s with uninfested plants. Very few individuals of S. japonicus and O. kashi mirica benefica were found in the traps, despite their abundance in orchard 1. The generalist insect predator, Orius sp., was attracted to the traps t hroughout the experimental period irrespective of the density of spider mit es, although this predator was never observed inside the orchards.