Abstract
The two-spotted spider mite Tetranychus urticae (Acari: Tetranychidae) is a cosmopolitan pest of a large number of host plants having extensive damage potential and the terrific ability of pesticide resistance. In the present study, spider mite population were reared continuously on the leaves of three susceptible host plants namely country bean (Phaseolus vulgaris L), papaya (Carica papaya L) and jute (Corchorus olitorius L) and their susceptibility to some reduced-risk acaricides were determined by leaf disc bioassay method. Abamectin was found to be the most toxic acaricide (LC50 values were 0.432, 0.342 and 0.324 mg L-1 on the country bean, papaya and jute leaf discs respectively at 24 h after treatment application) which was followed by azadirachtin, emamectin benzoate, spinosad and hexythiazox respectively. For all the tested acaricides, toxicity increased proportionately with increasing time duration after treatment application. Moreover, spider mites reared on country bean leaves were comparatively less susceptible to all acaricides followed by mites reared on papaya and jute leaves respectively. Based on the present study, it might be inferred that host plants play a considerable role in the susceptibility of spider mites to acaricides and abamectin could be used as a puissant chemical for controlling spider mites.
Highlights
The two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) is a ubiquitous phytophagous pest that causes severe damage in a large number of crop plants, including fruits, vegetables and ornamentals (Stumpf et al, 2001; Migeon and Dorkeld, 2007)
Among the selected reduced-risk pesticides, abamectin showed the highest toxicity against Tetranychus urticae (LC50 values were 0.432, 0.234 and 0.162 mg L−1 on country bean leaf; 0.342, 0.216 and 0.144 mg L−1 on papaya leaf; 0.324, 0.198 and 0.126 mg L−1 on jute leaf at 24, 48 and 72 h after treatment application (HAT) respectively) which was followed by azadirachtin, emamectin benzoate, spinosad and hexythiazox respectively (Table 1)
We evaluated five reduced risk acaricides against two-spotted spider mites on the leaf discs of country bean, papaya and jute plants and determined the median lethal concentrations
Summary
The two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) is a ubiquitous phytophagous pest that causes severe damage in a large number of crop plants, including fruits, vegetables and ornamentals (Stumpf et al, 2001; Migeon and Dorkeld, 2007). Spider mites feed by inserting their needle-like piercing-sucking mouthparts inside the plant tissue and they prefer to feed on the lower leaf surface (Attia et al, 2013) They inject phytotoxic substances which lead to the destruction of chloroplast and produce necrotic spots on the leaf surface (Attia et al, 2013). The excess use of acaricides against this pest in combination with its high reproductive potential, short life cycle and arrhenotokous mating system inevitably led to the development of resistance (Van Leeuwen et al, 2009) It is considered as the most resistant species among the arthropods based on the total number of pesticides to which it has developed resistance (Van Leeuwen et al, 2009)
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