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Digitized by Kansas Correctional Industries

Spider mites (Acari: Tetranychidae) are an important agricultural pest of many crops and landscape plants. They can reproduce rapidly and quickly develop resistance to many pesticides, making them difficult to manage. Plant water-stress and high temperatures promote spider mite infestations, while spider mite outbreaks can also result from neonicotinoid insecticide applications. Drought is predicted to increase in the Intermountain West due to increases in temperature and reduced frequency of precipitation events in the region, and neonicotinoids are currently one of the most widely used classes of insecticides in field crops. I studied the interactive effect of these two simultaneously occurring abiotic factors on spider mite outbreaks and plant biosynthesis of herbivore-related defense proteins. I also evaluated ways to alleviate spider mite outbreaks with drought-tolerant corn and the exogenous application of plant phytohormones involved in plant resistance toward biotic stressors. I found that plant water-stress increased spider mites and that neonicotinoids exacerbated the effect of water-stress. Although applications of plant hormones did not reduce the effect of water-stress and neonicotinoids, drought tolerant corn showed promise in reducing the effect of water-stress and spider mite outbreaks.

This thesis reports laboratory and field investigations on the aspects of biology of the Stethorus vagans, an Australian ladybird that feeds on all stages of two-spotted mite, Tetranychus urticae. Aspects of the biology of S. vagans were studied in the laboratory at constant and fluctuating temperatures. They regularly fed on all stages of T. urticae and there was no significant difference in male and female longevity at different temperatures. For field studies potted French bean plants infested with T. urticae were exposed in the field. Adult S. vagans was found to consume a range of alternative prey if the primary host was not available, but only one of the alternative hosts had the potential to support reproduction. Time partitioning behaviour and prey consumption rates were assessed, and how S. vagans located their prey was investigated. S. vagans exhibited many of the attributes of an effective biological control agent such as high reproductive level, location of prey at low levels, reproduction at low densities, and ability to feed on alternative hosts. It is concluded that S. vagans has a number of characteristics likely make them useful as a natural enemy of T. urticae / Doctor of Philosophy (PhD)

Specialist and generalist phytoseiid mites are widely used for biological control of spider mites. Understanding dispersal attributes of these mites is important to implementing more stable, cost-efficient integrated pest management. In this regard, we studied dispersal of phytoseiid mites from a local ambulatory phase of movement within a prey patch to a longer-range phase that includes emigration (aerial take-off and dispersal distance) and immigration to a new plant. Specialist phytoseiids showed higher ambulatory and aerial dispersal than generalist species. Somewhat different dispersal strategies were seen between Neoseiulus fallacis (more specialized predator) and N. calfornicus (more generalized predator): The most important difference was earlier and continuous dispersal of N. californicus from a prey patch. Cues from spider mite infestation suppressed the dispersal rates for specialists, but either increased or did not change the dispersal rates for generalist phytoseiids. Aerodynamic calculations support the hypothesis that Phytoseiulus persimilis may not require a standing take-off behavior to become airborne. However, with less vertical profile, a mite may become airborne more by standing erect (N. fallacis), than a species that does not show standing take-off (N. calfornicus). Jumping behavior by P. persimilis was observed for the first time among Phytoseiidae. Falling speed ranged from 0.4 to 0.73 m/s for 13 phytoseiid species and 0.79 to 0.81 for two-spotted spider mite. These values were quite similar to theoretical estimates for specialist phytoseiids, but less for generalists. From falling speed estimates and other morphological data, it was possible to predict aerial dispersal distance of phytoseiids using analytical models. After landing on bare soil following aerial dispersal, high mortality of N. fallacis was observed in the field during summer. Distance from the landing point to target plants showed negative log linear relationships. Soil surfaces and management actions influenced survival and recovery. Environmental conditions greatly affected survival of the predator. We speculated that phytoseiids that fell on ground were moving to the target plants via both ambulatory and aerial means. / Graduation date: 2001

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Outbreaks of spider mites (Acari: Tetranychidae) in vineyards have been increasing with the expansion of the industry in Virginia. Only three effective acaricides are registered on grapes and as resistance begins to occur, control options are limited. Biological control of spider mites by inoculative or inundative releases of predatory mites has been tried on a wide range of crops including grapes. This project examined the feasibility of using <i>Neoseiulus fallacis</i> (Acari: Phytoseiidae) as a potential large-scale biological control agent in vineyards. Slide dip bioassays were conducted on <i>N. fallacis</i> to determine the toxicity of insecticides, fungicides and herbicides commonly used on grapes in Virginia. In addition to laboratory experiments, commercially obtained <i>N. fallacis</i> were released in vineyards with spider mite infestations. The populations of both mites were then monitored on a regular basis to determine dispersal and distribution patterns. Among the insecticides tested in the laboratory bioassays, carbaryl, azinphos-methyl, phosmet, cyhexatin, and pyridaben all caused significantly higher mortality than the control treatment. Fungicides tested were not toxic to the predator, but three herbicides caused high mortality. Glufosinate caused 100% mortality after 24 hours and both oxyfluorfen and paraquat had adverse effects on <i>N. fallacis</i>. The use of materials that were found to be toxic to the predator would not be compatible with inoculative releases of <i>N. fallacis</i>. Field release results were variable. Three releases were made in 1999 and 2000., Recovery of the predator was low following the releases at two of the sites, probably due to lack of prey. At the third site enough predators were recovered to analyze the spatial distribution of the predator and prey populations. It appears that there is no similar aggregation pattern between the predator and prey at the same point in time although there is an indication of the predator spreading is response to the prey distribution. A more complete season of sampling would give more conclusive evidence of this trend. Although the distribution of the two populations were dissimilar, the predator was present throughout the season and did spread through the entire plot indicating that the predator may be able to colonize the vineyard if it successfully overwinters. / Master of Science