An experiment was carried out to evaluate the bioefficacy of some microbial pesticides (entomopathogens) viz., Beauveria bassiana, Metarhizium anisopliae, Streptomyces avermitilis, Paecilomyces fumosoroseus, Verticillium lecanii, and Pseudomonas fluorescens against red spider mite, Oligonychus coffeae infesting tea under both in the Entomology Laboratory and main farm of Bangladesh Tea Research Institute (BTRI), Srimangal, Moulvibazar during the period from March 2013 to December 2014. The Red spider mite was collected from different sections of BTRI main farm and reared in the Entomology Laboratory, BTRI, at 27-30°C temperature and 70- 80% relative humidity on a susceptible tea clone, BT2 by following detached leaf culture method of Helle and Sabelis (1985) with slight modifications. The mite pests were reared on tea leaves in rectangular jars (9.5 cm x 7.5 cm x 20 cm).
The test materials Formulations of six commercial microbial pesticides (entomopathogens) i.e. Beauveria bassiana, Metarhizium anisopliae, Streptomyces avermitilis, Paecilomyces fumosoroseus, Pseudomonas fluorescens Verticillium lecanii were collected from different multinational companies.
Beauveria bassiana Beauveria bassiana is an insect pathogenic fungus that grows naturally in soils throughout the world. When spore of this fungus come in contact with the cuticle (skin) of susceptible insects, they germinate and grow directly through the cuticle to the inner body of their host eventually killing it. It is being used as a biological insecticide to control a number of pests such as termites, thrips, whiteflies, aphids, different beetles and mites. The product contains WP 2 x 108 CFU/gm spores. It is target specific and do not destroy beneficial organisms. It does not leave any harmful residues in the finished products.
Metarhizium anisopliae Metarhizium anisopliae, formerly known as Entomophthora anisopliae, is a fungus that grows naturally in soil throughout the world. The fungus was first isolated by a Russian scientist Ilya I. Mechnikov from the diseased beetle Anisoplia austriaca in 1878. The formulation of M. anisopliae is highly effective and naturally parasitizes several insect pests such as aphids, jassids, termites, white grubs and mites of different agricultural crops. When sprayed on the plants it generally enters into the insects through spiracles and pores in the sense organs and kills the insect. The product contains WP 2 x 108 CFU/gm spores.
Field evaluation of entomopathogens against red spider mite A field trial was conducted to evaluate the bioefficacy of different entomopathogens (biopesticides) against red spider mite in tea fields at BTRI main farm. The treatments were Beauveria bassiana @ 5.0 kg/ha, Metarhizium anisopliae @ 5.0 kg/ha, Streptomyces avermitilis @ 2.0 L/ha, Paecilomyces fumosoroseus @ 5.0 kg/ha, Pseudomonas fluorescens @ 5.0 kg/ha and Verticillium lecanii @ 4.0 kg/ha and untreated control. The experiment was set up in randomized complete block design (RCBD) with three replications. After selection of the plots, pre-treatment count was taken in the respective plots and two rounds of spray were given at an interval of two weeks with hand operated knapsack sprayer with water volume of 1000 L/ha. Mite populations were assessed at weekly interval by collecting 10 mature leaves at random from each block and from each leaf; mites were counted using mite brushing machine (ModelLeedom Engineering, USA) and a compound microscope. Field performance of selected biopesticides against red spider mites in tea was calculated by using Henderson & Tilton (1955) formula.
Effect of entomopathogens on Stethorus gilviforns and Oxyopes sp. Entomopathogens was also tested for its effect on the mortality of two important predators of red spider mite i.e. Stethorus gilviforns and Oxyopes sp. Approved concentrations of biopesticides were sprayed directly onto adults of Stethorus gilviforns and Oxyopes sp. Spraying was performed as described for the laboratory bioassay and observed everyday for mortality.
Statistical analysis: The experimental data were statistically analyzed by Completely Randomized Design (factorial CRD) and Randomized Complete Block Design (RCBD) using MSTAT statistical software in a microcomputer. The results are expressed as Mean ± SE and data were statistically analyzed by one-way ANOVA, with the level of significance set at p<0.05. The mean values adjusted by Duncan’s Multiple Range Test (DMRT).