Factors involved in the success and establishment of the field bindweed gall mite Aceria malherbae Nuzzaci (Acari: eriophyidae)
Konigsberg, Evelyn Rivka
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Despite years of study and management, field bindweed (Convolvulus arvensis L., Fam.: Convolvulaceae) remains a problematic invasive species across the United States and is in need of better management options. Studies were conducted to determine factors affecting the establishment and performance of the biological control agent Aceria malherbae Nuzzaci. To determine the effects of sub-lethal herbicide applications on gall induction and development of A. malherbae, a bioassay was conducted with four herbicides, each having different modes of action. Atrazine, glyphosate, imazapic, and picloram were applied at 25% of their recommended dosages on plants infested and not infested with A. malherbae. Sub-lethal herbicide applications had an adverse effect on plant stem height, total stem length, numbers of leaves or branches, or on above-ground or below-ground biomass; whereas A. malherbae did not. Synergistic impacts of herbicide applications and A. malherbae on growth parameters of field bindweed were not observed. Pre- and post-spray gall counts were not significantly different, indicating that gall induction and development was not altered by these sub-lethal dosages. The establishment and effectiveness of A. malherbae has been reported to vary across western North America, with genetic variation of field bindweed as a possible contributing factor. Four field bindweed populations, collected from Montana, California, Oregon, and New Mexico, were exposed to A. malherbae to determine if growth parameters conducive or detrimental to the development of the mite vary among plant populations. When grown in a common environment, plant height, stem length, and number of branches and leaves significantly varied among populations although biomass did not differ. Galling by A. malherbae did not impact field bindweed growth, except for slight reduction in root biomass of infested plants. Gall induction was lower on plants from New Mexico than Oregon. Field studies assessed the relationship between habitat characteristics and plant cover and the presence and abundance of the mite. Multidimensional scaling of site characteristics indicated a spatial relationship, though no habitat relationship, among established A. malherbae populations. In within-field studies, a significant positive relationship was observed between percent grass cover and mite abundance and a negative relationship between field bindweed and mite abundance.