The genetic basis of oviposition preference differences between sympatric host races of the brown planthopper (Nilaparvata lugens)

We have previously analysed the genetic architecture of host-associated per formance differences between stocks of the brown planthopper, Nilaparvata l ugens (Homoptera: Delphacidae), derived from two host plants: cultivated ri ce variety TN1 and the semi-aquatic weed Leersia hexandra. It has been esta blished that performance is influenced by a small effective number of loci (1-3), with dominance in the direction of the rice population. The results reported here show that, like performance, oviposition preference has a sim ple genetic basis, but in this case there is no evidence of directional dom inance, sex linkage, non-allelic interaction or genotype-environment intera ction. The simple genetic architecture of host-associated performance and o viposition preference are as expected if there was a sympatric host shift, most probably from Leersia to rice. However, contrary to the theoretical ex pectation from models of sympatric host-race formation, there was no detect able genetic association between the traits. The fact that individual femal es tend to distribute their eggs between plants may have helped to promote a host shift despite this lack of association.