The citrus rust mite (CRM), Phyllocoptruta oleivora (Acari: Eriophyidae) is a cosmopolitan key pest of citrus, inflicting severe economic damage if not controlled. In Israel, CRM damages all citrus cultivars. International regulation and increasing control failures of CRM led growers to seek sustainable biological control solutions such as acarine biological control agents. Laboratory studies conducted in Israel have indicated that the indigenous predator species Amblyseius swirskii, Iphiseius degenerans, Typhlodromus athiasae and Euseius scutalis (all Acari: Phytoseiidae) can potentially control CRM. Our general objective in the present study was to bridge the gap of knowledge between laboratory studies and the lack of control efficacy of these species in commercial orchards. Predator augmentation in the field showed that although predator populations increased immediately following releases they later decreased and did not affect CRM populations. When A. swirskii augmentation was combined with a series of maize pollen applications, A. swirskii populations were enhanced substantially and continuously but again CRM populations were not affected. Growth chamber studies with CRM-infested seedlings, with or without a maize pollen supplement, indicated that pollen provisioning led to population increase of E. scutalis and A. swirskii but only E. scutalis significantly lowered CRM populations. Control with E. scutalis was confirmed in the field on CRM infested seedlings with pollen provisioned by adjacent flowering Rhodes grass. While experiments in mature citrus orchard showed that pollen supplement usually increased predator populations they also indicated that other factors such as intraguild interactions and pesticide treatments should be taken into account when devising CRM biological control programs.
Summary• The relationship between floral morphology and electrostatic pollination was studied here. To test the effects of floral morphology on pollen deposition on the stigma and other floral parts by means of electrostatic forces, metal replicas of almond ( Amygdalus communis ) flowers were constructed and then dusted with electrostatically charged and uncharged almond pollen. The pollen was applied to the flowers with a specially designed electrostatic powder-coating device.• Pollen deposition on the flower was found to be higher when the pollen was electrostatically charged than when it was not. Most of the charged pollen grains were deposited on the corolla extremities and on the stigma, whereas uncharged pollen grains were evenly distributed on the entire flower.• Stigma exsertion was the most important morphological feature of the flower promoting pollen deposition on the stigma when electrostatic charge was used. Large flowers with corollas showed higher electrodeposition on the corolla than smaller, narrower ones.• These results collectively imply that morphological features of a plant might be adaptations to take advantage of electrostatic forces. This provided us with a very important tool for future research on floral morphology and pollination biology.
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