Competition between Two Species of Mites.: II. Factors Influencing Intensity

Abstract

Production of webbing, greater fecundity, faster rate of development, and greater ability to thrive on foliage injured by feeding enabled populations of T. telarius to suppress those of P. ulmi on peach foliage in a greenhouse and insectary. However, these inhibitory factors were non-operative in an orchard environment in southwestern Ontario.The tendency of the two species to populate different levels of a host plant, and of P. ulmi to utilize the upper surfaces of leaves more than T. telarius, each decreased the intensity of competition. The suppression of P. ulmi in an insectary or greenhouse was delayed but not prevented by the above factors.

Amensalism via webs causes unidirectional shifts of dominance in spider mite communities

“…This means that adult female P. ulmi changed their behavior depending upon the densities of T. urticae coexisting on leaves. Despite the disadvantage of the presence of T. urticae webs on lower leaf surfaces (Morimoto et al 2006), juvenile P. ulmi tend to occupy lower leaf surfaces (Foott 1963). These results, i.e., the suppression of populations and niche adjustment of adult female P. ulmi caused by T. urticae, provide evidence that T. urticae exerts amensal eVects on P. ulmi on apple trees in the Weld.…”

“…This implies that T. urticae is a superior competitor, whereas P. ulmi is an inferior competitor. Several authors have therefore speculated that T. urticae suppresses the population growth of P. ulmi as a consequence of interspeciWc competition (Foott 1962(Foott , 1963Slone and Croft 2001; but see Belczewski and Harmsen 1997). However, Weld observations have not been able to elucidate the eVects of interspeciWc competition between them (Foott 1962(Foott , 1963Slone and Croft 2001).…”

“…The seasonal change in the species composition of spider mites, from Panonychus ulmi (Koch) to Tetranychus urticae Koch (Acari: Tetranychidae), has been observed in apple orchards around the world (Lienk and Chapman 1951;Rodriguez 1958;Foott 1962Foott , 1963. P. ulmi is an oligophagous spider mite that uses primarily pomaceous fruit trees as its host plants.…”

The Functional Response to Prey Density in an Acarine System

“…The webbing produced by spider mites may have several functions: 1 facilitation of locomotion and dispersion 2 regulation of the microclimate 3 indication of the state of depletion of the food resources and the conditioning for social interactions (Wynne-Edwards, 1962) 4 exclusion of competing species (Foot, 1963) 5 protection from predation. The protection from predation can be threefold: predators may be barred from webbing covered areas, their activity and speed of locomotion may be reduced, and they may be outrun more easily, promoting the escape of the prey.…”

Consequences of mite feeding injury to beans on the fecundity and survivorship of the two-spotted spider mite (Acari: Tetranychidae)

“…The functional relationship between resistance and intensity of initial injury may be nonlinear such that, at low injury levels resistance increases, but at greater injury levels resistance is lost. The strength of resistance reached an asymptote with increasing mite injury for Panonychus cirri (McGregor) feeding on injured orange leaves (Henderson and Holloway, 1942 ) and P. ulmi (Koch) feeding on injured peach leaves (Foott, 1963 ). In order to examine the relationship between intensity of injury and spidermite performance, we measured daily fecundity and survivorship of adult female T. urticae feeding on upper, undamaged leaves of bean plants (Phaseolus vulgaris L. ) which earlier had been subjected to different levels of spidermite feeding injury to lower leaves.…”