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Studies on Insecticide Resistance of the Brown Planthopper (Nilaparvata lugens) on Rice in the Mekong Delta, Vietnam
Dissertation Abstract:
The brown planthopper (BPH), Nilaparvata lugens, is a serious pest affecting rice crops in East Asian countries including Vietnam. To deal with this pest problem, farmers have mainly relied on chemical pesticides. This study aimed to (1) understand the status of pesticide use for controlling the BPH by farmers from the main rice producing areas of the Mekong Delta through direct interview, (2) evaluate the bio- efficacy of some commonly used insecticides by farmers for controlling the BPH under field conditions, and (3) determine the current status of insecticide resistance to the active ingredients of insecticides from different classes or with different modes of action in three BPH populations collected from the three major rice producing provinces of Tien Giang, Can Tho, and An Giang in the Mekong Delta.
This study found that (1) a majority of respondent farmers improperly used and managed pesticides—that a high proportion of farmers were found to be spraying insecticides many times per rice season and to use higher doses than recommended on the labels; (2) most of the insecticides tested were minimally effective at controlling the BPH and that the decline in insecticide efficacy identified in this study may be due to overuse of these insecticides for long periods of time, leading to the development of insecticide resistance; and (3) that BPH populations from the study sites were highly resistant to fenobucarb, imidacloprid, profenofos, nitenpyram, and were beginning to show resistance to dinotefuran and sulfoxaflor at the time tested.
The study concludes that the incidence of chemical resistance in the region could be due to a number of reasons, such as the high selection pressure of inexpensive insecticides, traditional calendar spraying, willing acceptance of recommendations by local pesticide distributors, and copying the chemical used by neighboring farmers. The present study demonstrates that the BPH did not appear to show cross- resistance between imidacloprid and dinotefuran at the time of study (2015–2016). This suggests that neonicotinoid substitutes could be compatible for controlling the BPH. The low efficacy of the newly released active ingredient sulfoxaflor could be due to a similar chemical structure and mode of action as imidacloprid, potentially leading to cross-resistance between the two active ingredients.