Journal of Insect Science (2008) 8 (4), 4-5
Judit Arnó, J. Roig and R. Gabarra (2008)
Activity of some biorational and conventional insecticides against Bemisia tabaci and their compatibility with whitefly parasitoids
Journal of Insect Science 8 (4), 4-5
in P. A. Stansly and C.L. McKenzie, organizers: Fourth International Bemisia Workshop - International Whitefly Genomics Workshop, December 3-8, 2006, Duck Key, Florida, USA
Abstract: We have evaluated the efficacy of several compounds with insecticidal activity against Bemisia tabaci nymphs and adults and their compatibility with whitefly parasitoids. The trials were conducted in 2004 and 2005 in exclusion cages inside an experimental greenhouse of poinsettia. The plants were colonized with natural populations of B. tabaci (biotype Q) and the parasitoids Eretmocerus mundus, Encarsia pergandiella and En. formosa. Seven different commercial products were tested, including two potassium soaps (Tec Bom™ and Soapline 60™), one mineral oil (Sunspray Ultrafine™), neem (Iber-Neem™), algae extracts (Agri Sea-Green™) and two conventional insecticides: thiamethoxam (Actara™) and thiacloprid (Calypso™). Water was used as a control. To test the efficacy of the products to control B. tabaci nymphs and their effect on parasitoid emergence, all the compounds, except Actara™, were sprayed on poinsettia plants until run-off. Actara™ was applied by irrigation at two doses, the maximum labeled rate and a 2.5 times higher rate. To evaluate nymphal mortality, 2 days after the treatment, plants were taken to the laboratory where samples (1.5 cm diameter disks) were cut and stored in a climatic chamber at 25ºC. Seven days after the treatment, the number of dead and live B. tabaci nymphs was evaluated. To estimate the impact on B. tabaci parasitoids, 2 days after the treatment 100 parasitized pupae were isolated and held for at least two weeks. Number of emerged adult parasitoids was recorded. In another experiment, the efficacy of the products to control B. tabaci adults was tested. The same compounds mentioned above were applied on poinsettia plants naturally infested with whitefly adults and their survivorship was evaluated 72 hours after the treatment. Efficacy to control B. tabaci nymphs was very limited for all the tested products. The mineral oil Sunspray Ultrafine was the product that killed most nymphs (58%). A second group of compounds, including Tec-Bom, Agri Sea-Green and Calypso, produced mortalities between 30 and 49%, while, Actara, at both doses, and Iber-neem killed less than 20% of whitefly nymphs. Regarding toxicity on B. tabaci adults, the two conventional insecticides Actara (at labeled dose) and Calypso produced the highest mortalities (70 and 88%, respectively). Less effective were the soaps (Tec-Bom and Soapline 60) and the mineral oil Sunspray Ultrafine that produced mortalities ranging from 35 to 40%. The least effective among the tested compounds, were Agri Sea-Green and Iber-neem (causing mortalities around 20%). None of the insecticides evaluated caused mortality to Er. mundus significantly different than the control. On the other hand, emergence of En. formosa adults from pupae treated with Soapline 60 was significantly greater than emergence from pupae treated with Tec-Bom, Sunspray Ultrafine and Agri Sea-Green. En. pergandiella proved very sensitive to all the tested products and significantly fewer parasitoids emerged from pupae treated with all the formulations when compared with the control. To control B. tabaci nymphs, our results demonstrate than some of the called 'biorational' insecticides (e.g. potassium soaps or mineral oil) are as effective as conventional insecticides, or even better. In contrast, to control B. tabaci adults, the most effective products were the two conventional insecticides tested (Actara and Calypso). Therefore, since B. tabaci is difficult to control, it could be useful to integrate biological control with safe insecticides to natural enemies. To do so, our results indicate that the impact on biological control of some of the termed 'biorational' insecticides should not be neglected and, the integration of both control methods will depend on the parasitoid species used.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Database assignments for author(s): Judit Arnó, Rosa Gabarra
Research topic(s) for pests/diseases/weeds:
control - general
health/environmental effects of pesticides
Research topic(s) for beneficials or antagonists:
resistance to pesticides
