Banca de QUALIFICAÇÃO: AMÉRICO DE CASTRO MONTEIRO SOBRINHO

Evaluation of the effectiveness of entomopathogenic nematodes subjected to different pressures on larvae of Stomoxys calcitrans (Linnaeus, 1758) (Diptera:Muscidae) in by-products of the sugar and alcohol industry.

Pressures, vinasse fly, biological control, sugar cane, fertigation

Stomoxys calcitrans is a hematophagous dipteran known as the “stable fly”. The present study aimed to determine under what pressures entomopathogenic nematodes (NEPs) maintain their viability and ability to infect and kill S. calcitrans larvae in by-products of the sugar and alcohol industry.

To obtain the desired pressures, a hydraulic pump with a pressure controller and a sprinkler nozzle were used to reproduce the pressures used in fertigation of sugarcane fields. Groups of 10 third-instar fly larvae were deposited in plastic containers containing two sheets of filter paper and different sugarcane by-products (according to each group). Infectious Juveniles (JIs) of Heterorhabditis bacteriophora HP88, H. baujardi LPP7 and H. indica LPP30 were used, already subjected to pressures of 60, 70 and 80 psi. The total volume was four mL of distilled water per treatment (in bioassays with water) and four mL of 50% vinasse (in bioassays with vinasse), the concentration of NEPs used in all bioassays was 200 JIs/fly larva. The control group had the same concentration of JIs, but without having passed through the pressure system.

There was also a control group without the presence of NEPs. Larval mortality was observed daily. The bioassays were maintained at 27±1° C and 70±10% RH, with six replications. The data were subjected to the Shapiro-Wilk normality and Bartlett homoscedasticity tests. When the assumptions were observed, analysis of variance was applied, followed by the Tukey test (p<0.05) to compare means. It was identified that regardless of the substrate used, nematodes, whether or not subjected to different pressures, impacted S. calcitrans larval mortality. In the bioassay in distilled water without the presence of sugarcane by-products, the species H. bacteriophora HP88 and H. indica LPP30 were the most virulent to S. calcitrans larvae, with mortality rates exceeding 85%. Pressure apparently did not affect the virulence of NEPs, as mortality in groups treated with pressure was higher than in the control group. In filter cake, the species H. bacteriophora HP88 and H. indica LPP30 did not have their virulence affected by the pressures used, whereas H. baujardi LPP7 showed a drop in efficiency after being subjected to 60, 70 and 80 psi. In sugarcane bagasse, only the mortality rates caused by NEPs were variants, with H. bacteriophora HP88 (81.7%) being the most virulent. It was identified that the pressures evaluated did not reduce the virulence of the NEPs, which, after being subjected to 60, 70 and 80 psi, maintained their harmful effect on fly larvae, with an average mortality rate exceeding 70%. In sugarcane straw, H. bacteriophora HP88 had a slight reduction in its virulence when subjected to 80 psi, causing S. calcitrans larval mortality of 72%, however, up to 70 psi, this species promoted mortality of fly larvae in levels above 85%. In the species H. indica LPP30 and H. baujardi LPP7, the application of pressures (60,70 and 80 psi) promoted a reduction in larval mortality by approximately 19% and 17%, respectively, even though the final values were significantly higher. compared to the mortality observed in the control group (4.1%). In vinasse, it was observed that all treatments had mortality averages higher than the control group without NEPs, but equal to each other.