Protection of stored potatoes from infestation with the potato tuber moth, Phthorimaea operculella (Zeller)(Lepidoptera: Gelechiidae) using plant powders

Abstract

BackgroundThe potato tuber moth (PTM), Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is an important storage pest of potato (Solanum tuberosum L.) in Saudi Arabia and Egypt. Infestation in the store starts mostly through freshly harvested infested tubers or through moths entering the storage facilities. Larvae mine in tubers making them unsuitable for sale and consumption. Damage increases rapidly when several generations develop during the storage period. Larvae are capable of causing damage to the crop either in the field or in the store. Biopesticides are certain types of pesticides derived from animals, plants, bacteria, and certain minerals. During the course of evolution, plants have developed, as part of their defensive mechanism, various chemical molecules, which proved a protection against insect pests, since the overall pressure of insect on plant is much more than any other herbivore. Biopesticides prepared from plants are reported to have the ability to kill or keep away the pests. They are eco-friendly. The plant products have additional advantage over synthetic insecticides, as they are biodegradable, safe to non-target organisms, leave no residues, and decrease the buildup of resistance strains of insects. Present research is conducted to evaluate the capacity of certain natural local alternative plant powders against PTM under storage conditions as attempts to providing alternative and novel strategies that can be used by both the commercial and/or small-scale potato farmers to control the pest in the store.MethodsTwelve different plants (Zygophyllum, Solanum, Coriander, Arnoglosse, Jasmine, Senna, Colocynth, Camomile, Harmel, Geranium, Basil, and Mint) locally available in the fields of the Eastern Province of the Saudi Arabian kingdom were air-dried under a shad at ambient tropical condition. The air dried materials were grinded into fine powders and kept in tight containers until using. Potato tubers were shacked with the plant powders for a good mixing, until tubers were uniformly covered and the powders stick well to the tuber surfaces. Different dried leaves or fruits of the 12 tested plants were powdered to be used at rate of 25 g plant powder per 1 Kg tubers. The experiments were distributed in a randomized complete block design. Different biological aspects of the treatments were calculated; damage index to tubers and persistence of protection to the tubers during different intervals of storage were recorded.ResultsAll plant powders had a reduction effect on the deposited eggs laid on the treated tubers with different degrees. The dried powders of Coriander, Clocynth, and Zygophyllum reduced egg deposition on the treated tubers than the control, followed by Jassmin, Senna, Cammomil, and Harmel. The powders of Basil and Solanum also recorded a moderate reduction in egg deposition. Zygophyllum and Coriander could protect the tubers for more than 8 weeks. All other treatments greatly minimized the number of emerged moths from the treated tubers (F1), as follows: Coriander = Zygophyllum (0) > Basil (17.39) > Geranium (17.85) > Cammomil (18.75) > Arnoglosse (19.32) > Jasmine (21.62) > Mint (21.69) > Harmel (52.77) > Senna and Colocynth (72.72) > Solanum (100) compared with untreated tubers (95.17). All treatments had no effects on the tuber germination.ConclusionThe study showed that all the tested plant powders, at the rate of 25 g plant powder per 1 Kg potato tubers, could protect the tubers for more than 8 weeks from PTM infestation during storage. The most potent powders were Coriander and Zygophyllum. All other powders decreased the number of the emerged adults from the treated tubers, with variable degrees, and decreased the percentage of tubers’ damage index recorded. Besides, all the tested plant powders had no effects on the tubers’ germination.