Assesment of bacteria to control the two-spotted spider mite Tetranychus urticae (ACARI: TETRANYCHIDAE)

Abstract

The two-spotted spider mite Tetranychus urticae is an agricultural pest of worldwide relevance. Being a polyphagous, cosmopolitan organism with high reproductive rates, it is capable of affecting 1100 plant species and about 150 crops. Their infestations reduce the productivity of the field and can cause the death of plants. The main technique used for its control is the application of chemical pesticides that in many cases are not efficient and lead to the selection of resistant populations. As an alternative to the use of pesticides, biological control has been highlighted, where species of bacteria are capable of producing secondary metabolites with insecticidal action, showing potential as biological control agents. Thus, this work aimed to assess bacterial strains for the control of T. urticae. A screening was performed with previously selected 104 strains from the Collection of Microorganisms of the Laboratory of Biological Control, in the Advanced Centre of Research on Plant Protection and Animal Health (CAPSA). After the screening, the three strains that caused the highest mortality percentages were selected for a multiple rates test by dilution of the bacterial cultures to 2%, 5%, 10%, 20% and 40%. The three most effective strains (365, 268 and 321b) were molecularly identified as Serratia sp 365, Bacillus sp 268 and Heyndrickxia sp 321b. The bacteria with the highest performance, Serratia sp 365, was selected for a test on macaúba (Acromia aculeata) seedlings production. The experiment consisted of 6 treatments represented by the bacterial culture diluted at rates of 5%, 10%, 20% and 40%, and by the two controls water and liquid culture. For the rate test, the three best strains Serratia sp 365, Bacillus sp 268 and Heyndrickxia 321b showed LC50 of 38.67%; 57.32% and 150.65%, respectively. For the test with Serratia sp 365 on macaúba, the highest rates (40% and 20%) suppressed the mite population and the egg density after a single application of the bacterium. The two lowest rates (5% and 10%) suppressed the population and eggs only after two applications.