Eizi Yano

A simple model of host-parasitoid interaction with host-feeding

A simple mathematical model of host-parasitoid interaction with host-feeding was presented with special reference to the system of the greenhouse whitefly and the parasitoidEncarsia formosa. In the model, when a parasitoid encounters a host, it has a choice between feeding the host and ovipositing one egg in the host. It was shown that an intermediate value of the feeding ratio of all attacks gives the minimum equilibrium host density and the minimum amplitudes of fluctuation in the densities of the two species. Computer simulations of a modified model with time lags also gave the similar results. The model suggested for natural enemy introduction program that parasitoid species with host-feeding habits are promising agents for effective controls for pest insects and that the timing of introduction is very important. By an evolutionary analysis, it was shown that the feeding ratio evolves to minimize the host density under natural selection among parasitoids.

The Involvement of Volatile Infochemicals from Spider Mites and from Food-Plants in Prey Location of the Generalist Predatory Mite Neoseiulus californicus

We investigated volatile infochemicals possibly involved in location of the generalist predatory mite Neoseiulus californicus to plants infested with spider mites in a Y-tube olfactometer. The predators significantly preferred volatiles from lima bean leaves infested with Tetranychus urticae to uninfested lima bean leaves. Likewise, they were attracted to volatiles from artificially damaged lima bean leaves and those from T. urticae plus their visible products. Significantly more predators chose infested lima bean leaves from which T. urticae plus their visible products had been removed than artificially damaged leaves, T. urticae, and their visible products. These results suggest that N. californicus is capable of exploiting a variety of volatile infochemicals originating from their prey, from the prey-foodplants themselves, and from the complex of the prey and the host plants (e.g., herbivore-induced volatiles). We also investigated predator response to some of the synthetic samples identified as volatile components emitted from T. urticae-infested lima bean leaves and/or artificially damaged lima bean leaves. The predators were attracted to each of the five synthetic volatile components: linalool, methyl salicylate, (Z)-3-hexen-1-ol, (E)-2-hexenal, and (Z)-3-hexenyl acetate. The role of each volatile compound in prey-searching behavior is discussed.

Ecological considerations for biological control of aphids in protected culture

Several braconid and aphelinid parasitoids, midges, lacewings, and ladybird beetles are used to control aphids in greenhouses. Here, I review three topics as ecological bases for the biological control of aphids in a protected culture: the preliminary evaluation of biological control agents, natural enemy release strategies, and the effects of intraguild predation (IGP) on biological control. A comparison of several parasitoid species was conducted to select agents for the biological control of aphids; the intrinsic rate of natural increase was a useful criterion in the preliminary evaluation. To compare predators as biological control agents, the aphid-killing rate must be considered as a critical criterion, rather than reproductive criteria. The banker plant system (open rearing system) is used as a release method for Aphidius colemani and other natural enemies of aphids. Continuous release of parasitoid adults, which is the important characteristic of this method, has a stabilizing effect on population fluctuation in the aphid–parasitoid system. Two species of natural enemies can be used to control aphids in greenhouses. When one parasitoid and one predator are used simultaneously in a greenhouse, IGP of the parasitoid by the predator can occur, but the effect of IGP is less important in greenhouses than in the field.

Olfactory response of the anthocorid predatory bug Orius sauteri to thrips‐infested eggplants

The predator Orius sauteri (Poppius) (Heteroptera: Anthocoridae) is an effective arthropod natural enemy of thrips, especially Thrips palmi Karny (Thysanoptera: Thripidae), a serious pest of vegetables. First, we studied O. sauteris response to the odour from thrips‐infested eggplant [Solamum melongena L. (Solanaceae)] in a laboratory by two‐choice experiments using a Y‐tube olfactometer. When detached eggplant leaves were used as odour sources, O. sauteri preferred the volatiles from uninfested leaves to clean air. Concerning preferences among differently infested leaves, O. sauteri preferred the volatiles from plants infested with 10–100 thrips per leaf to uninfested leaves, but showed no significant preference for artificially damaged leaves over uninfested leaves. Similar results were obtained when complete plants were tested as the odour source. Second, release and recapture experiments in a greenhouse, a more realistic set of conditions, were conducted to confirm whether a significant preference for infested plants occurred at similar infestation levels as in the laboratory. Trends favouring infested plants were detected at densities of five and 500 thrips per plant; however, at the five thrips per plant, this trend was due to the large deviation seen in infested plants in only one replicate. In light of the low tolerable thrips density of eggplant, it is necessary to confirm whether artificial treatments with chemicals induce the emission of herbivore‐induced plant volatiles that can attract O. sauteri and prolong its residence time on the leaf.

Time allocation of Orius sauteri in attacking Thrips palmi on an eggplant leaf

Orius sauteri (Poppius) (Heteroptera: Anthocoridae) is a polyphagous predator used as a biological control agent of palm thrips, Thrips palmi (Karny) (Thysanoptera: Thripidae). We studied O. sauteris searching efficiency, time allocation on a leaf, leaving tendency, and attacking of prey. Approximately 78% of the encountered prey was eaten. Searching for prey was concentrated for 86% of the time on the lower leaf side, where palm thrips are usually found. Patch residence times on empty leaves were different from those on leaves with T. palmi larvae. Walking activity was not affected by the thrips density, and walking took place during 64% of the total search time. The leaving tendency of O. sauteri was affected by the time from patch entry and the presence or absence of palm thrips, but not by the thrips density. If prey were present, the leaving tendency decreased (multiplication factor 0.327), resulting in longer giving‐up times than when no prey was present. The fact that the leaving tendency increases when patch exploitation lasts longer suggests that not much time is wasted on patches where encounters with prey are scarce.

Spatial distribution of greenhouse whitefly (Trialeurodes vaporariorum Westwood) and a suggested sampling plan for estimating its density in greenhouses

Spatial distribution of the greenhouse whitefly population infesting tomato plants in greenhouses was analyzed. A leaf of tomato consists of 7 leaflets, each being used as a basic sampling unit. Distribution patterns between plants, between leaves and between leaflets were analyzed by the analysis of variance and the

A simulation study of population interaction between the greenhouse whitefly,Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae) and the parasitoidEncarsia formosaGahan (Hymenoptera: Aphelinidae) II. Simulation analysis of population dynamics and strategy of biological control

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Behavioral response of mantid Tenodera aridifolia (Mantodea: Mantidae) to windy conditions as a cryptic approach strategy for approaching prey

method. It was found that populations of all the developmental stages were composed of contagiously distributed colonies or individuals between leaves and between leaflets. On the other hand, they showed random distribution of colonies between plants. On leaflets, egg populations were distributed as colonies, each consisting of several eggs, while in larval and adult populations, individuals were distributed rather independently of each other. A three-stage sampling plan was developed to estimate the density at the assigned level of precision.