Direct and Indirect Competition Between Spider Mites Feeding on Grapes

Abstract

Agents for biological control of arthropod pests have generally come from the trophic level above the pest (predators, parasites, diseases) rather than from the same trophic level (competitors). The rationale behind this approach is twofold. First, interspecific competition among herbivorous arthropods is thought to be weak; populations are kept at low levels through the action of natural enemies. Second, the potential benefits of an herbivorous biological control agent must be weighed against the damage it causes to the host plant through its feeding. In the field we have been successful at using less economically important Willamette mites to control economically important Pacific mites. In greenhouse and field experiments reported here, we examined both direct and indirect mechanisms (via the host plant or a shared predator) to explain this negative interaction. In our first greenhouse experiment we injured leaves on single canes of young Zinfandel grapevines with Willamette mites at four density levels, removed theses mites and then measured consequences of this past injury on Pacific mites placed on newly produced leaves. Pacific mite populations were reduced significantly by previous Willamette mite injury, suggesting a systemic induced response. In our second greenhouse experiment we measured the relative importance of interspecific interactions between concurrent populations of Willamette and Pacific mites, direct predation by a phytoseiid predator, and interactions between predation and competition (apparent competition). Predators and prey were confined to single canes and, at this small scale, direct predation was of overriding importance while interspecific competition and apparent competition were not significant in determining Pacific mite populations. We examined the relative importance of an early season release of Willamette mites, predaceous mites, or both in a large field experiment conducted in a commercial Zinfandel vineyard. Pacific mite populations were most strongly reduced by the early release of Willamette mites and by midseason abundance of predaceous mites. Our ANOVA results did not detect a significant interaction between the early season release of Williamette mites and predaceous mites. The presence of Willamette mites did not make releases of predators more effective at controlling Pacific mites. Grape yield and berry sugar concentration were unaffected by either Willamette mite or predaceous mite treatments in the year of the mite releases nor in the following season. Path analysis showed that Willamette mite density was never strongly negatively correlated with Pacific mite density in the subsequent time period (2-wk intervals between sampling dates), despite the strong negative effect that the early-season release of Willamette mites had on Pacific mite densities later in the season. This suggests that Willamette mites affected Pacific mites indirectly.

Negative effects of habitat drying and prior exploitation on the detritus resource in an ephemeral aquatic habitat

“…Such resource-based interactions among non-overlapping asynchronous cohorts in these systems are probably underappreciated. Inter-and intraspeci®c amensalism aecting later cohorts and caused by changes in resource quality also occur in terrestrial plant-herbivore systems in which herbivory of a seasonal host plant results in induced resistance to herbivores, which negatively aects the performance of herbivorous insects developing later in the season (Haukioja and NiemalaÈ 1979;English-Loeb et al 1993;Brown and Weis 1995).…”

Metabolomic analysis of the interaction between plants and herbivores

“…As induced responses may also be present for long periods of time they may affect not only current, but also successive herbivores and herbivores feeding on plant parts that were not damaged before (Bodnaryk 1994;Broeckling et al 2005). Induced plant responses thus may mediate interactions between herbivores that feed temporally or spatially separated on the same plant (Englishloeb et al 1993;Viswanathan et al 2005).…”

Characteristics of Hydroxamic Acid Induction in Wheat Triggered by Aphid Infestation

“…Outstanding exceptions to this generalization come from the works on IR of wild tobacco alkaloids (Baldwin, 1989;Baldwin et al, 1990) and wild parsnip furanocoumarins (Zangerl, 1990;Zangerl and Berenbaum, 1995). Although work on IR has mainly addressed questions regarding theoretical issues such as optimal patterns of defense allocation (Ohnmeiss and Baldwin, 1994), patterns of insect grazing (Gibberd et al, 1988), and plant competition (Edwards et al, 1992), it recently has included applied approaches stressing the usefulness of induced resistance as a tool in pest management programs (English-Loeb et al, 1993). In order to achieve their goals, both major foci of IR studies require a thorough knowledge of the already mentioned characteristics of IR.…”