Abai, MR

6th International Congress of DipterologyDifferent directions of displacement in two species ofleafminer fly in different localitiesAbe, Y.Laboratory of Applied Entomology, Graduate School of Agriculture, Kyoto PrefecturalUniversity, Kyoto 606-8522, JapanUntil now, except for two Liriomyza species of leafminer fly (Diptera:Agromyzidae), species displacement has not been known to occur indifferent directions in the same two species under field conditions. Thedisplacement of L. sativae by L. trifolii in the USA in the 1980s can beattributed to the lower insecticide susceptibility of L. trifolii. In Japan, L.trifolii was displaced by L. sativae after 1999. The different directions ofdisplacement indicate that the reason for the displacement of oneLiriomyza species by the other appeared to differ between the USA andJapan. Therefore, differences in the insecticide susceptibility, fecundity,effects of natural enemies, and reproductive interference between L. trifoliiand L. sativae are evaluated as possible causes of the species displacementobserved in Japan. There was no evidence to indicate that L. sativae washighly tolerant than L. trifolii to some of the insecticides, but it is possiblethat the higher fecundity of L. sativae is a key factor involved in thedisplacement. The successful parasitization by a natural enemy Dacnusasibirica (Hymenoptera: Braconidae) on L. trifolii without suchparasitization on L. sativae may have contributed to the displacement of L.trifolii by L. sativae. Under laboratory conditions, L. trifolii and L. sativaecan mate and produce F1 hybrid females, which do not oviposit if backcrossingoccurs. Since courtship and mating discrimination appears to existbetween L. trifolii and L. sativae, interspecific mating between the twospecies is considered to hardly occur under natural conditions.Key Words: species displacement, insecticide susceptibility, fecundity,parasitization, Liriomyza∗∗∗∗∗∗∗∗∗∗4