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Haïfa University (2014)

Plant feeding by predatory mites : from mechanism to implications

Adar, Einat

Titre : Plant feeding by predatory mites : from mechanism to implications

Auteur : Adar, Einat

Etablissement de soutenance : Haïfa University

Grade : Doctor of Philosophy (PhD) 2014

Résumé partiel
Omnivorous predators that feed on plant-provided food may enhance plant defense against pests. They sustain on the plant longer when prey is scarce and therefore prevent pest outbreaks. In biologically controlled agricultural systems, several methods are used to increase the populations of generalist omnivores on crops, providing them with alternative food and domatia. My first major aim was to develop and evaluate a new method, combining food, shelter and oviposition sites for promoting predacious mites of the family Phytoseiidae (important biological control agents) on protected crops. Some species of this predacious family also feed on plant sap, a characteristic that may be problematic among biological control agents. They may be exposed to systemic insecticides, they may directly damage the plant and may be more host (plant) specific. Nevertheless, either the mechanism of plant-sap feeding, nor its affect on the plant were never examined in phytoseiids. Therefore, the other major aims of this work were to describe the plant sap feeding mechanism of phytoseiids, and its effects on the host plant. First I developed and evaluated a novel method for increasing and preserving predator populations on protected crops. Applying ‘pollen on-twine’ on the plant may provide suitable conditions for the predators by combining alternative food, shelter and oviposition sites. The effect of two twine types and two pollen species on the establishment of Euseius scutalis (Athias-Henriot) and Amblyseius swirskii AthiasHenriot (important predatory phytoseiids) was evaluated on pepper plants in a growth chamber. I found that rayon jute was more beneficial than polypropylene twine for both predators, and that there were no differences in the effect of corn and oak pollen. The populations of both predators were best promoted when given clean twine and pollen was applied on the leaves. However, E. scutalis population increased by more than tenfold and A. swirskii doubled when plants were applied with pollen on-twine. I propose that after further refining, pollen on-twine can serve as a feasible solution for the establishment of predatory mites on protected crops. Next, I documented E. scutalis while plant sap feeding using a high resolution stereomicroscope. Additionally I examined the ability of the plant sap feeder E. scutalis and the non-plant sap feeder A. swirskii to penetrate an artificial membrane and feed on green dyed water. As expected, I found that E. scutalis pierced the membrane and fed whereas A. swirskii did not. Based on these observations, I suggested that plant tissue penetration mechanism by E. scutalis is as follows : the movable digit penetrates the epidermis and the fixed digit presses down on the leaf surface from above. To evaluate whether these penetration abilities has a morphological correlatives among related species, the chelicerae of 13 phytoseiid species (females), including plant sap and non-plant sap feeders, were measured and compared under a scanning electron microscope (SEM). The results indicate that plant sap feeders had shorter and less curved movable digits than non-plant sap feeders. I suggest that this morphological difference facilitates the penetration of plant tissue and make plant sap feeding possible in this group.


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