Preference-performance Linkage in the Willow Twig-galling Agromyzid Fly, Hexomyza simplicoides (Diptera : Agromyzidae) on the Willow Salix chaenomeloides

Bionomics of Hexomyza simplicoides was surveyed in Kyoto, central Japan. Adults emerged and oviposited in spring. Knot-like galls containing one larva were formed on the twigs of spring shoots of Salix chaenomeloides (Salicaceae) in autumn. On attacked shoots, shoot length and the number of galls were positively correlated. Long shoots (≧150mm long) of the host plant harbored galls more frequently than short shoots (<150mm), although long shoots were smaller in number. Adult emergence rate in longer shoots was higher than that in shorter shoots. The field census and laboratory experiment indicate that the preference of ovipositing females for longer shoots is correlated with high larval performance.