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Host Plant-induced Susceptibility of Two-spotted Spider Mite Tetranychus Urticae (acari: Tetranychidae) to Some Reduced-risk Acaricides

Tarikul Islam
Department of Entomology, Bangladesh Agricultural University, Mymensingh, Bangladesh

Abstract/ Executive Summary:

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.

Keywords: Host Plants, Toxicity, Bioassay, Tetranychus urticae, Acaricides

Location:

Start Date:

End Date:

Program Area: Pest Management

Commodity: Spider, Mite

Objectives:

The present study was planned to find out the toxicity of five reduced-risk acaricides viz. azadirachtin, abamectin, spinosad, hexythiazox and emamectin benzoate on the Tetranychus urticae population reared on three different susceptible host plants namely country bean (Phaseolus vulgaris L), Jute (Corchorus olitorius L) and papaya (Carica papaya L).

Methodology:

Rearing of Two-Spotted Spider Mites The spider mites were collected from the research fields of Bangladesh Agricultural University, Mymensingh and were reared continuously on leaf discs (ca. 16 cm² ) of country bean, jute and papaya. Leaf discs of bean, jute and papaya were kept on water-saturated polyurethane mats in plastic Petri dishes (90 mm diameter, 20 mm depth). To eliminate the effect of any previous pesticide exposure, the fifth generation adult female spider mites were used in the bioassay. For obtaining fixed-age females, same aged eggs were separated from the mite culture and transferred on fresh leaf discs of the same plant. Rearing trays were always kept under controlled conditions at 25±1°C temperature, 75±5% RH and 16L: 8Dh photoperiod. After every four days, withered leaves were replaced with new fresh leaves of the same plant. Tested Reduced Risk Acaricides Five reduced risk acaricides were selected for the bioassay. There was a botanical called azadirachtin marketed as Bioneem plus 1 EC by Ispahani Biotech Ltd., Bangladesh and a mite growth regulator named hexythiazox marketed as Mite scavenger 10 EC by Eminence Chemical Industries Ltd. Other three pesticides were bacterial fermented derivatives namely spinosad marketed by Asia Trade International as Libsen 45SC, abamectin marketed by Haychem Bangladesh Ltd. as Ambush 1.8 EC and emamectin benzoate marketed by Haychem Bangladesh Ltd. as Suspend 5 SG. All the selected pesticides were collected from the local markets of Mymensingh, Bangladesh. Bioassay Procedures The toxicity of five reduced-risk pesticides against two-spotted spider mite, T. urticae was evaluated by leaf disc bioassay method on three different host leaves under laboratory conditions. In brief, leaf discs (ca. 16 cm² ) using leaves of common bean, jute and papaya were prepared and placed on wet cotton pads in Petri dishes (90 mm diameter). Four to five-day-old mated females of T. urticae were placed on a new leaf disc (ca. 4×4 cm2 ) and incubated for 24 h. The acaricide solutions were prepared by diluting in water and five concentrations were used for each acaricide to determine the LC50 values. All the concentrations were selected based on preliminary concentration versus mortality experiments using a wide range of doses to find out the appropriate concentration range for the final bioassay (data not shown). One ml solution of each concentration of selected pesticides was applied directly to individual mite-infested leaf discs of bean, jute and papaya by using a hand operated micro-applicator sprayer (Burkard Scientific, UK). The control group was treated with distilled water only. There were three replicates for each treatment and 20 adult female mites were used in each replicate. After air drying, the mite-infested discs were kept at 25±2°C temperature, 80±5% RH and 16L: 8D photoperiod in an incubator. Mortality was recorded daily until the death of all the tested organisms. Statistical Analyses The mortality percentage of spider mites was corrected using Abbott’s (1925) formula. The median lethal values (LC50) were determined by probit analysis using ‘Ldp line’ software (http://www.ehabsoft.com/ldpline/). Statistical differences between LC50 estimates were determined by using a 95% CI for the ratio of two estimates (Robertson et al., 2007).

Source of Information: American Journal of Agricultural and Biological Sciences 2019, Volume 14: 11.15

Article Link (Online Journal): DOI: 10.3844/ajabssp.2019.11.15

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Based on our experimental results, it might be concluded that feeding on diverse hosts significantly alters the susceptibility of Tetranychus urticae to different pesticides which need to be addressed for the effective management of spider mites. Moreover, abamectin could be used successfully for controlling Tetranychus urticae population irrespective of their host plants.

Knowledge Management: Journal