The Effect of Chemical Information on the Spatial Distribution of Fruit Flies: I Model Results

Animal aggregation is a general phenomenon in ecological systems. Aggregations are generally considered as an evolutionary advantageous state in which members derive the benefits of protection and mate choice, balanced by the costs of limiting resources and competition. In insects, chemical information conveyance plays an important role in finding conspecifics and forming aggregations. In this study, we describe a spatio-temporal simulation model designed to explore and quantify the effects of these infochemicals, i.e., food odors and an aggregation pheromone, on the spatial distribution of a fruit fly (Drosophila melanogaster) population, where the lower and upper limit of local population size are controlled by an Allee effect and competition. We found that during the spatial expansion and strong growth of the population, the use of infochemicals had a positive effect on population size. The positive effects of reduced mortality at low population numbers outweighed the negative effects of increased mortality due to competition. At low resource densities, attraction toward infochemicals also had a positive effect on population size during recolonization of an area after a local population crash, by decreasing the mortality due to the Allee effect. However, when the whole area was colonized and the population was large, the negative effects of competition on population size were larger than the positive effects of the reduction in mortality due to the Allee effect. The use of infochemicals thus has mainly positive effects on population size and population persistence when the population is small and during the colonization of an area

Control of moth pests by mating disruption: Successes and constraints

Male moths generally find their mates by following the females' pheromone plume to its source. A formulated copy of this message is used to regulate mating of many important pests, including pink bollworm Pectinophora gossypiella, oriental fruit moth Grapholita molesta and tomato pinworm Keiferia lycopersicella. How synthetic disruptant interrupts normal orientation is uncertain, but the most probable mechanisms invoke adaptation and habituation, competition between point sources of formulation and females, and a camouflage of a female's pheromone plume by the formulation. The efficacy of this technology is related principally to the motility of mated females into the area to be managed, the initial population levels of the pest, and the release characteristics of the formulation. In most cases, implementation of this technology necessitates a sophisticated monitoring and management program. Area-wide management schemes are ideal vehicles for using disruptants. -from Author

Structure of host-odour plumes influences catch of Anopheles gambiae s.s. and Aedes aegypti in a dual-choice olfactometer

The effects of structure, concentration and composition of host-odour plumes on catch of female Anopheles gambiae Giles sensu stricto and Aedes aegypti (L.) (Diptera: Culicidae) were investigated in a dual-choice olfactometer. We demonstrate that the fine-scale structure of host-odour plumes modulates capture of An. gambiae and Ae. aegypti. In both species homogeneous skin-odour plumes result in trap entry, whereas homogeneous CO2 plumes reduce trap catch. Reduced trap catch also result from combining skin odour with a homogeneous CO2 plume. Trap capture rates in homogeneous CO2 plumes were concentration-dependent and differed between the two species. Electric nets placed in front of the trap entrances intercepted mosquitoes before they could enter the traps. This showed that An. gambiae flew along CO2 plumes, but did not enter the traps. Survivorship analysis of the trap-entry times of Ae. aegypti indicated interactions between the time until capture and treatment. The assay's duration therefore can alter the distribution in a dual-choice olfactometer

Host recognition by Pimpla instigator F. (Hymenoptera: Ichneumonidae): preferences and learned responses

This study identifies some previously unreported tactile and visual cues used by the pupal parasitoid Pimpla instigatorF. (Ichneumonidae) to recognize potential hosts. Paper cylinders were presented to the wasps as simple models of lepidopteran pupae. Acceptance of these models was evaluated by determining the frequency with which the wasps punctured the cylinders with their ovipositors. The length of the cylinders did not influence acceptance of the models; however, both surface texture and structural modifications to the ends of the cylinder did affect the frequency of punctures. Smooth cylinders were punctured more often than roughened cylinders, and cylinders with closed ends were frequently punctured, whereas open-ended cylinders were consistently rejected. The wasps also discriminated between blue and yellow cylinders and could be trained to associate blue or yellow with the presence of hosts. Preferences were established during a single 90- min training period and persisted for at least 4 days following training.