Steven L. Peck

The Effect of Economic Thresholds and Life-History Parameters on the Evolution of Pesticide Resistance in a Regional Setting

We explore the dynamics of alleles conferring insecticide resistance in agroecosystems in which economic thresholds are used to manage insect pest populations. The dynamics of economic thresholds on resistance evolution are first explored in a single-field model. A two-dimensional cellular automata model is then used to examine the effects of migration, refuges, and crop rotation in a large region of fields under different management strategies. The single-field model indicates that economic thresholds may have important implications for pesticide management strategies, because resistance evolution is no longer independent of the growth process. In the regional model, the growth rate of the population, the selection pressure on the resistant allele, and migration all affect the time to resistance. Rotation is most beneficial when migration rates are either very high or very low and has little effect at intermediate migration rates. Resistance develops in large patches, so the level of resistance in a given field may be only weakly related to the history of pesticide treatment in that field. This finding may explain the high regional variability found in field studies of resistance in pests such as Colorado potato beetle.

Enhancement of Attraction of Alpha-Ionol to Male Bactrocera latifrons (Diptera: Tephritidae) by Addition of a Synergist, Cade Oil

Abstract Male lures are known for many tephritid fruit fly species and are often preferred over food bait based traps for detection trapping because of their high specificity and ability to attract flies over a wide area. Alpha-ionol has been identified as a male lure for the tephritid fruit fly Bactrocera latifrons (Hendel). The attraction of this compound to male B. latifrons individuals, however, is not as strong as is the attraction of other tephritid fruit fly species to their respective male lures. Cade oil, an essential oil produced by destructive distillation of juniper (Juniperus oxycedrus L.) twigs, synergizes the attraction of α-ionol to male B. latifrons. Catches of male B. latifrons at traps baited with a mixture of α-ionol and cade oil were more than three times greater than at traps baited with α-ionol alone. Substitution of α-ionol + cade oil for α-ionol alone in detection programs could considerably improve the chance of detecting invading or incipient populations of B. latifrons. However, detection programs should not rely solely on this lure but also make use of protein baited traps as well as fruit collections. Further work with fractions of cade oil may help to identify the active ingredient(s), which could help to further improve this male lure for B. latifrons.

A SPATIALLY EXPLICIT STOCHASTIC MODEL DEMONSTRATES THE FEASIBILITY OF WRIGHT'S SHIFTING BALANCE THEORY

Recently there has been a resurgence of theoretical papers exploring Wrights Shifting Balance Theory (SBT) of evolution. The SBT explains how traits which must pass through an adaptive valley may evolve in substructured populations. It has been suggested that Phase III of the SBT (the spread of new advantageous traits through the populations) proceeds only under a very restricted set of conditions. We show that Phase III can proceed under a much broader set of conditions in models that properly incorporate a key feature of Wrights theory: local, random migration of discrete individuals.

Comparative Evaluation of Spinosad and Phloxine B as Toxicants in Protein Baits for Suppression of Three Fruit Fly (Diptera: Tephritidae) Species

Abstract Spinosad and phloxine B are two more environmentally friendly alternative toxicants to malathion for use in bait sprays for tephritid fruit fly suppression or eradication programs. Laboratory tests were conducted to assess the relative toxicity of these two toxicants for melon fly, Bactrocera cucurbitae Coquillett; oriental fruit fly, Bactrocera dorsalis Hendel; and Mediterranean fruit fly, Ceratitis capitata (Wiedemann) females. Field tests also were conducted with all three species to compare these toxicants outdoors under higher light and temperature conditions. In laboratory tests, spinosad was effective at much lower concentrations with LC50 values at 5 h of 9.16, 9.03, and 4.30 compared with 250.0, 562.1, and 658.9 for phloxine B (27, 62, and 153 times higher) for these three species, respectively. At 16 ppm spinosad, LT50 values were lower for all three species (significantly lower for C. capitata and B. dorsalis) than 630 ppm phloxine B LT50 values. At 6.3 ppm spinosad, the LT50 value for C. capitata (3.94) was still significantly less than the 630 ppm phloxine B LT50 value (6.33). For all species, the 100 ppm spinosad concentrations gave LT50 values of <2 h. In comparison among species, C. capitata was significantly more sensitive to spinosad than were B. cucurbitae or B. dorsalis, whereas B. cucurbitae was significantly more sensitive to phloxine B than were C. capitata or B. dorsalis. LC50 values were reduced for both toxicants in outdoor tests, with greater reductions for phloxine B than for spinosad for B. dorsalis and B. cucurbitae. Fly behavior, though, is likely to keep flies from being exposed to maximum possible outdoor light intensities. Comparable levels of population suppression for any of the three species tested here will require a much higher concentration of phloxine B than spinosad in the bait.

VARYING MIGRATION AND DEME SIZE AND THE FEASIBILITY OF THE SHIFTING BALANCE

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Indicators of the Ecological Status of Agroecosystems

Agroecosystems can be viewed as production systems that provide food and fiber products essential for the health and well-being of humankind. This view is not incorrect, but it is incomplete. Agricultural commodities such as crops and livestock are one of several agroecosystem components (Fig. 35.1). Agroecosystems include land used for crops, pasture and livestock; the adjacent uncultivated land that supports other vegetation (hedgerows, woodlots, etc.) and wildlife; the underlying soils and groundwater; and the associated drainage networks. Inputs to the agroecosystem are both natural and anthropogenic, and outputs include both desirable and undesirable quantities. By design, agroecosystems are among the most intensively managed ecosystems in the world. A challenge of a program designed to monitor and assess the health of agroecosystems is to ensure a balanced assessment of the productivity and the ecological well-being of the system.

An educational test of health behavior models in relation to emergency helping.

This study used a true experimental design to evaluate the quality and occurrence of emergency helping behavior among university first-aid students in response to a supplemental educational unit designed to improve bystander helping. The educational unit addressed the inhibitors of emergency helping behavior within the framework of bystander behavior models and was delivered using several behavior modification strategies. Using chi-square analysis, it was found that the 43 treatment students exposed to the supplemental unit responded appropriately to a simulated emergency more often than 41 similar control students not exposed to the unit (32.6% vs. 7.3%, p = .004) and that the effect was confined primarily to women (p = .001). Future emergency care education incorporating similar theory-based educational strategies might improve trained bystander responsiveness and thus enhance the efficiency of prehospital care. Theoretical and future research implications are discussed.