INSECT HERBIVORE ABUNDANCE IN TROPICAL MONOCULTURES AND POLYCULTURES: AN EXPERIMENTAL TEST OF TWO HYPOTHESES'

摘要: The population dynamics of six beetle pests (Chrysomelidae: Galerucinae) were studied for three seasons in monocultures and polycultures the corn—bean—squash agroecosystem Costa Rica. study was designed to determine if abundance differed among these treatments, so, whether differences caused primarily by predators parasites (Enemies Hypothesis) or movement patterns adult beetles (Resource Concentration Hypothesis). In containing at least one nonhost plant, numbers per unit host plant (squash bean) significantly lower relative on plants monocultures. This pattern generally observed each species between 40 60 d after planting continued until end season. When a given fed both crop diculture (i.e., squash—bean diculture), general polyculture effect reversed: greater respective These effects apparently changes richness plots se rather than density total plot. There no rates parasitism predation polycultures. Neither there significant emergence treatments that could account Instead, several lines evidence show different responsible distribution. Direct measurements movements field showed tended emigrate more from included Field observations experiments this due factors: (1) avoided shaded corn; (2) cornstalks interfered some way with flight beetles; (3) as moved through they remained less time their overall rate higher. data suggest Resource Hypothesis Enemies can implication finding predicting herbivore yet untried agreocosystems are discussed. It is suggested it not sufficient merely recognize herbivores common particular Practical issues design theoretical questions plant—herbivore coevolution depend knowing exactly what ecological processes create reduced loads