Inhibition of premature leaf abscission by a leafminer and its adaptive significance

We tested the possibility that a lepidopteran leafminer, Coptotriche japoniella Puplesis and Diskus, inhibits the host plant Eurya japonica Thunberg from abscising mined leaves prematurely to increase its survivorship in immature stage. We monitored abscission patterns of mined leaves with sacrificed larvae, mined leaves with living larvae, and unmined leaves from April to July 2004 and 2005 until leafminers emerged as adults. Unmined leaves rarely abscised before July. Mined leaves with sacrificed larvae fell at a constant rate after May, abscising significantly more than unmined leaves. In contrast, mined leaves with living larvae rarely fell before adult emergence; afterward they abscised rapidly. We also examined larval/pupal survivorship and mortality sources on the ground and trees after leafminers completed larval development. Leafminers on the ground suffered a higher mortality from predation than those on trees, and thus they emerged as adults on the ground less successfully. These findings suggest that the leafminer C. japoniella prevents the host plant from abscising mined leaves prematurely until adult emergence, thereby increasing their survivorship.