Rice Planthoppers in Tropics and Temperate East Asia: Difference in Their Biology

Abstract

Differences in population growth and physiological characters of Nilaparvata lugens between the populations of the tropics and of temperate East Asia are discussed. Fundamental differences in population dynamics seem to be related to the origin of initial immigrants and activity of natural enemies. In tropical fields, initial immigrants originate from nearby paddy fields, resulting usually in high immigrant densities. On the other hand, few immigrants after seasonal long-distance migration initiate population in temperate paddy fields. In the tropics, N. lugens exhibit various population growth patterns depending on the interaction with the natural enemies. While in the temperate areas, populations tend to increase gradually due to paucity of natural enemies probably due to collapse of natural enemies during cold winter. N. lugens in subtropical and temperate East Asia, compared to tropical Asia, produce more macropters, and have longer pre-ovipositional period and more starvation tolerance. Thus, the East Asian population of N. lugens is more adapted to migration, while tropical populations in southeast Asia are adapted to multiplication. Biotype compositions and insecticide resistance in N. lugens populations in time and space are quite similar within East Asia (subtropical and temperate areas), while they tended to slightly differ depending on locations in the tropics. It is considered that these characters in East Asian N. lugens population are genetically maintained by a migration system mediated by seasonal monsoon wind. Strong population suppression by natural enemies in the tropics implies the possibility that escape from natural enemies was a driving force for evolution of migration in N. lugens.