2012 Annual Report
1a.Objectives (from AD-416):
The whitefly Bemisia tabaci is one of the most important pests of agricultural and ornamental crops worldwide, causing direct feeding damage, negatively affecting post-harvest of numerous crops, and transmitting devastating plant viral diseases. B. tabaci feeds exclusively on plant sap, and therefore has evolved a unique digestive system that handles excess dietary fluid and maintains osmotic pressure. Previously, we characterized an aquaporin protein from B. tabaci (BtAQP1) that functions as a water channel protein to transport water through the specialized digestive tract. The objective of the proposed cooperative research is to test novel antagonists specifically developed to target aquaporins and ascertain if these agents interfere with water permeability of the BtAQP1 and thus negatively impact B. tabaci. Compounds optimized for efficacy and specificity against insect aquaporin targets represent a novel insecticidal approach for insect pest control.
1b.Approach (from AD-416):
We propose to first evaluate agents that are fast unidirectional blockers of water flux as well as slower bidirectional blockers against BtAQP1 produced using a frog oocyte expression system. Any compounds found to be effective on the BtAQP1 in the oocyte expression system, would then be tested on the developing and adult whiteflies. Compounds will be tested against B. tabaci by direct application and through oral feeding, using both plants and artificial feeding systems. For promising compounds, we will develop a chemical library of analogs around the active structure, and improve potency for selective channel block and whitefly efficacy.
This Non Funded Cooperative Agreement directly addresses Objective 1 – Develop knowledge and control tactics based on the physiology, biochemistry, genetics and vector-pathogen interactions of insect pests, Subobjective 1.3 – Characterization of gene-silencing of a functional aquaporin water transport protein from B. tabaci, of the approved parent project. The whitefly, Bemisia (B.) tabaci, is one of the most important pests of agricultural and ornamental crops worldwide. This pest directly injures crop plants by sucking sap, and produces indirect damage by exuding a sticky honeydew that promotes fungal growth and reduces crop quality. In addition, the whitefly transmits a cadre of viruses that can produce devastating diseases. Another sucking insect, the western tarnished plant bug, Lygus hesperus, is a serious pest of numerous field, fruit, and vegetable crops in the western United States. Although the feeding habits and injury caused by these two pests differ, both species ingest a liquid diet that requires specific adaptations of the digestive tract in order to regulate water balance. One such adaptation involves the efficient processing of water through the digestive tract. Insects, like other animals and plants, use a class of water channel proteins, known as aquaporins, that serve as channels to facilitate movement of water through tissues with high water permeability. By characterizing pest insect aquaporins, compounds can be identified that moderate these channel proteins, thereby disrupting water balance leading to reduced insect growth, reproduction, or survival. We previously characterized an aquaporin protein (designated BtAQP1) from B. tabaci and showed that it functions as a water channel protein. Additional genes that appear to correspond to aquaporins were identified in B. tabaci and Lartodectus (L.) hesperus. Five aquaporins from L. hesperus (designated LhAQP1 through LhAQP5) were partially characterized. LhAQP1, which closely resembles the functional aquaporin from B. tabaci (BtAQP1), was shown to be a functional water channel protein. This aquaporin from L. hesperus (LhAQP1) was exposed in the laboratory to leaf extracts of marigold, Tagetes patula, which is thought to harbor insecticidal compounds that may interfere with aquaporin function. Different extracts of marigold either inhibited or increased water transport by the aquaporin, thereby demonstrating that the marigold produces natural compounds that influence the activity of pest insect water channels. Additional extracts and compounds will now be tested for activity against additional B. tabaci and L. hesperus aquaporins, as well as for insecticidal properties by feeding them to the pest insects in laboratory assays.