Spatial distribution of Diuraphis noxia and one of its parasitoids, Diaeretiella rapae

Spatial distribution or how abundances vary through space is an important trait of insect populations. Knowledge of the spatial distribution provides a basis for understanding various aspects of population biology including resource exploitation, intraspecific competition or the dynamics of predators and parasitoids. For insect pests, information on the spatial structure of populations may help in developing rational chemical control and release strategies for natural enemies. For parasitoids, spatial density dependence (a correlation between parasitism rate and host density) may stabilize otherwise unstable population models (Hassel & May 1973) and maximize parasitoid oviposition rate, at least in theory (Charnov 1976, Cook & Hubbard 1977). However in nature, density-dependence occurs in about only half of the species studied (Walde & Murdoch 1988). Here, we have analyzed spatial distribution and abundance of the Russian wheat aphid (RWA) Diuraphis noxia (Hemiptera: Aphididae) and one of its parasitoids, Diaeretiella rapae (Hymenoptera: Braconidae). Two questions are addressed: (1) How are RW A and D. rapae distributed in space? (2) Does parasitism of RW A by D. rapae depend on RW A density?