Abstract

RAMIREZ, Lorena et al. Standardising a bioassay for the preliminary evaluation of three commercial Bacillus thuringiensis formulations against Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae). Rev. colomb. biotecnol [online]. 2010, vol.12, n.1, pp.12-21. ISSN 0123-3475.

The tomato moth (Tuta absoluta Meyrick; Lepidoptera: Gelechiidae) is one of the most devastating tomato pests in Colombia and South-American countries, producing losses of up to 100% in unprotected crops. T. absoluta was detected in Spain, Portugal and Mediterranean countries in 2009, as well as England, Bulgaria and Germany. Chemical insecticides are used for controlling it; however, they produce resistance and an environmental and human health impact. Finding an alternative to using biopesticides against this pest is becoming increasingly important. This study evaluated five bioassay methods measuring three commercial products’ toxicity on T. absoluta larvae: Dipel, XenTary and Turilav Bacillus thuringiensis (Bt) -based formulations. The leaf dipping bioassay method caused 100% larvae mortality with Dipel, the control group having 95% survival rate. The other products showed significant differences on the 2nd (F=0.025, p>0.05) and 4th (F=0.0018, p>0.05) days after application (DAA). The leaf spray airbrush method produced 100% larvae mortality with Dipel on the 2nd DAA, having significant differences from the other products tested on 2nd (DAA F=7.94 x 10^-10, p>0.05 ), 4th (F=3.45x10^-6, p>0.05 ) and 8th (F=1.07x10^-5, p>0.05 ) DAA. Submerged leaflet and culture medium methods caused high mortality in controls and were thus rejected. A variation of the leaflet immersion method was standardised. The three commercial products produced high mortality in Lab conditions regarding T. absolute larvae control at 1.25 g/L concentration, thereby corroborating the biological activity of B. thuringiensis against this insect pest

Keywords : Tuta absoluta; Bacillus thuringiensis; Dipel; XenTary; Turilav (the last 3 being commercial insecticide brand names).

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