Insecticidal properties of Bacillus thuringiensis var. Israelensis. I. The activity spectrum of a larvicidal preparation based on industrial strain 7-1/23a

Blood-sucking mosquitoes and blackflies belonging to the order Diptera cause sanitary-epidemiological and veterinary-epizootological damages in humans and animals and serve as the carriers of various dangerous transmissible diseases. The productivity and milk yield of livestock as well as egg production in poultry birds are significantly affected by harmful Diptera species. The problem of bioprotection from harmful insects is extremely relevant in crop production, including the cultivation of seeded fodder crops. Currently, the spore-forming bacterium Bacillus thuringiensis Berliner (Bt) represents the most common agent for biological control of the number of insect species and is considered as the basis for the production of insecticides. Biological preparations are of particular importance due to their significant advantages over chemical pesticides and are considered in modern agricultural systems as environmentally and socially beneficial alternatives to agrochemicals. A liquid form of larvicidal preparation against blood-sucking and herbivorous mosquitoes based on the original strain Bacillus thuringiensis var. israelensis 7-1/23А was developed at the ARRIAM. Under registration number RCAM 00626 (RF patent 2539732 dated 12/09/2014), the strain was deposited in the ARRIAM Collection of beneficial agricultural microorganisms (RCAM). The composition of the liquid form of the biopreparation includes a spore-crystalline complex, 5 % sodium chloride, 2 % coniferous extract (as a preservative and perfume, respectively), and the remains of a nutrient medium. The titer was 4.25½109 CFU/ml. Larvicidal activity expressed in LC50 for Aedes aegypti IV instar larvae was 0.11½10-3 % (biotest proposed by the World Health Organization). The strain was previously isolated from an anophelogenic reservoir in the Leningrad region, studied for physiological and cultural features, and characterized according to Н. De Barjac's and А. Bonnefoi's classification. In this work, for the first time, a comprehensive analysis of a larvicidal preparation based on BtH14 7-1/23A was performed, including the molecular characterization of the strain, determination of its larvicidal activity against a number of harmful dipterans, and an assessment of its effects on the growth and development of non-target objects (oyster mushroom mycelium and champignon). Sequencing of the gene encoding B subunit of the DNA gyrase (GyrB) confirmed that the isolated strain belongs to B. thuringiensis var. israelensis. The presence of the cry4 and cry11 genes encoding protein insecticidal toxins was detected by PCR analysis. We also studied the spectrum of action of the larvicidal biopreparation against the blood-sucking mosquitoes of the genera Aedes , Anopheles , Culex , and harmful herbivorous dipterans: rice ( Сricotopus sylvestris Fabr.) and mushroom ( Lycoriella fucorum Frey) flies. The analysis was carried out in laboratory and field conditions (2014-2016, Leningrad and Moscow regions, Krasnodar Territory, aedogenic, anofelogenic ponds, raw basement rooms, rice checks) and also included an assessment of the effect of the preparation on the growth of mycelium of oyster mushrooms ( Pleurotus ostreatus ) and champignon ( Agaricus campestris ) as bio-eco indicators. LC50 values in laboratory tests were 0.11×10-3 and 0.12×10-3 % for Culex and Аеdes , respectively, and 0.29×10-3 % for Anopheles maculipennis Meigen. Field tests in water reservoirs against malarial ( Anopheles maculipennis ) and non-malarial mosquitoes of the genus Aedes - communis , dorsalis , punctor , caspius , and flavescens ; in moist basement rooms ( Culex pipiens Linnaeus f. molestus Forskål), rice fields ( Сricotopus sylvestris Fabr.) showed 90.2-100 % mortality of larvae. The effect of the biological preparation on the growth of mycelium of oyster mushrooms and champignon w