Amblyseius

Abstract: The searching behaviour of individual predators of four phytoseiid species ( Phytoseiulus persimilis , Amblyseius p o tentillae , Amblyseius bibens , Metaseiulus occidentalis ) is investigated in relation to the two-spotted spider mite ( Tetranychus urticae ), which infests greenhouse roses. Especially the role of spider- mite webbing in the predator-prey relation is studied. Webbing interferes with searching, decreasing the rate of encounter per unit prey density. Low walking speeds and activity in webbing ensure that the predator is rarely disturbed after contact with other mites. Webbing also positively influences searching, as spider mites aggregate within the webbed area: prey density, defined here as the number of prey per square centimetre of webbed leaf area, is high, as is the rate of encounter with prey. The ability to capture a prey after tarsal contact depends on the food content of the gut, the prey-stage and, in two specific cases, the webbing; the success ratio of P. persimilis increased on a webbed substrate, that of A. potentillae decreased. Models to simulate rate of predation on the basis of the dynamics of the motivational state and the state dependent rate of successful encounter are proposed. The food content of the gut is chosen as an indicator of the motivational state. A stochastic queueing model simulates predation as accurately as a Monte Carlo model or a compound simulation model. The queueing model is preferred because of its economic use of computer time and the relatively few variables used. The model was validated in predation experiments. Systems analysis showed that the effect of temperature on the rate of predation is largely determined by its relation with the relative rate of food conversion into egg biomass and not by behavioural changes related to temperature. Also, it was shown that webbing has an important influence on the predation rate. A new model for the analysis of prey-stage preference is proposed. Predators invade the webbed leaf area after contact with the silk strands, irrespective of the presence of prey. The residence time in the prey colony is determined by prey density. Simulation of experimentally defined walking behaviour shows that predators remain in profitable prey patches by turning at the edge of the webbed leaf area. However, when predator density increases, the tendency to leave the prey colony also increases, even at high prey densities. Only A. potentillae avoided the webbed leaf area, preferring the thickest parts of the leaf ribs or other protected places on the plant. A survey of references on life history data is presented; emphasis is given to the role of food, temperature and relative humidity. Experiments by the author show that oviposition history of predatory females is a major factor in determining the actual rate of food conversion into egg biomass; and that the egg stage of the predators is very vulnerable to relative humidities below 70%, though the evapotranspiration of the plant and the hygroscopic properties of the webbing buffer this to some extent. As the juvenile mortality of the phytoseiids increases above 30°C, and that of the two-spotted spider mites above 35°C, spider-mite control at temperatures above 30°C is not effective. The four phytoseiid species are ranked on their capacities for numerical increase and predation: P. persimilis , A. bibens , M. occidentalis and A. potentillae . On capacity to survive on alternative foods they are ranked: A. potentillae , A. bibens , M. occidentalis and P. persimilis . Some trials with alternative food supply did not improve survival rates established for prevailing greenhouse conditions. The rate of increase of the webbed area per individual spider mite is quantified by experiment. This knowledge will enable continuous monitoring of the prey density during simulations of the predator-prey interactions on the population level.

Abstract: The searching behaviour of individual predators of four phytoseiid species ( Phytoseiulus persimilis , Amblyseius p o tentillae , Amblyseius bibens , Metaseiulus occidentalis ) is investigated in relation to the two-spotted spider mite ( Tetranychus urticae ), which infests greenhouse roses. Especially the role of spider- mite webbing in the predator-prey relation is studied. Webbing interferes with searching, decreasing the rate of encounter per unit prey density. Low walking speeds and activity in webbing ensure that the predator is rarely disturbed after contact with other mites. Webbing also positively influences searching, as spider mites aggregate within the webbed area: prey density, defined here as the number of prey per square centimetre of webbed leaf area, is high, as is the rate of encounter with prey. The ability to capture a prey after tarsal contact depends on the food content of the gut, the prey-stage and, in two specific cases, the webbing; the success ratio of P. persimilis increased on a webbed substrate, that of A. potentillae decreased.Models to simulate rate of predation on the basis of the dynamics of the motivational state and the state dependent rate of successful encounter are proposed. The food content of the gut is chosen as an indicator of the motivational state. A stochastic queueing model simulates predation as accurately as a Monte Carlo model or a compound simulation model. The queueing model is preferred because of its economic use of computer time and the relatively few variables used. The model was validated in predation experiments.Systems analysis showed that the effect of temperature on the rate of predation is largely determined by its relation with the relative rate of food conversion into egg biomass and not by behavioural changes related to temperature. Also, it was shown that webbing has an important influence on the predation rate. A new model for the analysis of prey-stage preference is proposed.Predators invade the webbed leaf area after contact with the silk strands, irrespective of the presence of prey. The residence time in the prey colony is determined by prey density. Simulation of experimentally defined walking behaviour shows that predators remain in profitable prey patches by turning at the edge of the webbed leaf area. However, when predator density increases, the tendency to leave the prey colony also increases, even at high prey densities. Only A. potentillae avoided the webbed leaf area, preferring the thickest parts of the leaf ribs or other protected places on the plant.A survey of references on life history data is presented; emphasis is given to the role of food, temperature and relative humidity. Experiments by the author show that oviposition history of predatory females is a major factor in determining the actual rate of food conversion into egg biomass; and that the egg stage of the predators is very vulnerable to relative humidities below 70%, though the evapotranspiration of the plant and the hygroscopic properties of the webbing buffer this to some extent. As the juvenile mortality of the phytoseiids increases above 30°C, and that of the two-spotted spider mites above 35°C, spider-mite control at temperatures above 30°C is not effective.The four phytoseiid species are ranked on their capacities for numerical increase and predation: P. persimilis , A. bibens , M. occidentalis and A. potentillae . On capacity to survive on alternative foods they are ranked: A. potentillae , A. bibens , M. occidentalis and P. persimilis . Some trials with alternative food supply did not improve survival rates established for prevailing greenhouse conditions.The rate of increase of the webbed area per individual spider mite is quantified by experiment. This knowledge will enable continuous monitoring of the prey density during simulations of the predator-prey interactions on the population level.

Abstract: Amblyseius (Neoseiulus) californicus is an indigenous mite in Japan that feeds on many spider mite species. We evaluated the development, survivorship and life-history parameters of A. californicus on a diet of eggs of Tetranychus urticae (red form). More than 97.3% of A. californicus eggs hatched and more than 81.6% of newly hatched larvae attained maturity at temperatures between 15 and 35 °C. Females oviposited at 37.5 °C, but no eggs hatched. At 40 °C, no females laid eggs. The lower threshold temperature from egg to oviposition was 10.3 °C and the thermal constant was 86.2 degree-days. Based on these data, the maximum number of generations that could complete development in a year under field conditions in Ibaraki, central Japan, would be between 21 and 28. At 25 °C, females laid a mean of 41.6 eggs during a mean oviposition period of 19.4 days. The intrinsic rates of natural increase (r m ) were 0.173 at 20 °C, 0.274 at 25 °C and 0.340 at 30 °C.

Abstract: Part 1 Life-history strategies: the life strategies of mites life-history evolution of spider mites life-cycle strategies in unpredictably varying environments - genetic adaptations in a colonizing mite the evolutionary transformation of osmotic regulation in the life cycle of freshwater mites (Hydrachnidia) development and life-history strategies in mussel mites (Hydrachnellae - Unionicolidae). Part 2 Reproduction: spermatology in the Acari - systematic and functional implications the distribution, mechanisms and evolutionary significance of parthenogenesis in oribatid mites indirect sperm transfer in prostigmatic from a phylogenetic viewpoint spermatophore deposition in relation to atmospheric humidity among terrestrial Parasitengonae (Prostigmata) the role of Alderocystis sp. in the reproduction of argasid ticks a scanning electron-microscopy study of spermatogenesis in Pergamasus barbarus Berl. (Gamasida) precise sex-ratio control in the pseudo-arrhenotokous pytoseiid mite, Typhlodromus occidentalis Nesbitt sex ratio, fitness and capacity for population increase in Pyemotes tritici (pyemotidae) preliminary observations of ovoviviparity in the gall-forming mite, Aceria caulobius laboratory observations of copulation and egg production of three phytoseiid species fed on pollen precopulatory mate guarding in the spider mite, Tetranychus cinnabarinus. Part 3 Diapause, development and trophic relations: physiological aspects of diapause in plant-inhabiting mites repeated induction and termination of diapause in the predacious mite, Amblyseius potentillae inheritance of the photoperiodic responses controlling diapause in the two-spotted spider mite, Tetranychus urticae some observations on diapause in the winter eggs of Panonychus ulmi reporduction, embryonic and postembryonic development of Trichouropoda obscurasimilis Hirschmann & Zirngiebl-Nicol 1961 resource allocation and utilization contrasts in Hypoaspis aculeifer and Alliphis halleri with emphasis on food source the influence of different host plants on the reproductive potential of Tyrophagus putrescentiae and Tyrophagus neiswanderi Johnston & Bruce the relationship between house-dust mites and fungi How plants maintain body-guards - plant exudate as a food source for phytoseiid mites. Part 4 Systematics, morphology, physiology and behaviour: distribution of characters and phylogenetic age - systematic problems in the higher taxa of the Oribatida a new approach to the systematics of the genus Stegnacarus the morphology of the immature stages of Phthiracaroidea a new interpretation of the epimeral theory of Grandjean a comparison of the aclerotized parts of the reproductive organs of house-dust mites of the genus Dermatophagoides using scanning electron microscopy. (Part contents).