No abstract

Sampling plans are an essential part of integrated pest management programs. Sequential sampling plans enable rapid and low-cost assessment of pest densities. Thrips are emerging pests in soybean crops, and the main method used in pest control is chemical. In soybean crops, insecticides are applied mainly using tractors or airplanes. Thus, this work aimed to determine sequential sampling plans for thrips in soybean crops with insecticide applications using a tractor or airplane. Data were collected in 56 soybean fields, and each field was 20 ha. Sampling plans were determined and validated. The lower (m0) and upper (m1) limits of the sequential sampling plans were: m0 = 1.72 and m1 = 3.43 (by tractor applications) and, m0 = 2.27 and m1 = 4.53 thrips. sample−1 (by airplane applications). The slope (S) and the lower (h0) and upper (h1) intercepts of the sequential sampling plans were: S = 2.42, h0 = −5.79, and h1 = 5.79 (by tractor applications) and, S = 3.19, h0 = −6.83, and h1 = 6.83 (by airplane applications). Sequential sampling plans allowed for correct decisions to be made in all situations using a maximum of 10 samples. The sequential plan reduced the sampling effort by over 87% compared to conventional sampling plans. Therefore, these control decision-making systems have proven feasible and advantageous for implementing integrated pest management programs for controlling thrips species in soybean crops.

We evaluated the efficacy and residual toxicity of nine commercial insecticides on Plutella xylostella and their selectivity to the predator ant Solenopsis saevissima under laboratory and field conditions. First, to test the insecticides’ effectiveness and selectivity, we conducted concentration-response bioassays on both species and the mortalities were recorded 48 h after exposure. Next, rapeseed plants were sprayed following label rate recommendations in the field. Finally, insecticide-treated leaves were removed from the field up to 20 days after application and both organisms were exposed to them as in the first experiment. Our concentration-response bioassay indicated that seven insecticides caused mortality ≥80% of P. xylostella: bifenthrin, chlorfenapyr, chlorantraniliprole, cyantraniliprole, indoxacarb, spinetoram, and spinosad. However, only chlorantraniliprole and cyantraniliprole caused mortality ≤30% of S. saevissima. The residual bioassay indicated that four insecticides had a long-lasting effect, causing mortality of 100% to P. xylostella 20 days after application: chlorantraniliprole, cyantraniliprole, spinetoram, and spinosad. For S. saevissima, bifenthrin caused mortality of 100% during the evaluated period. Additionally, mortality rates below 30% occurred four days after the application of spinetoram and spinosad. Thus, chlorantraniliprole and cyantraniliprole are safe options for P. xylostella management since their efficacy favor S. saevissima.

There has been an excitement toward novel eco-friendly alternatives to pest management, particularly formulations based on essential oils (EOs). Here, the biological activity of an EO-based emulsion derived from patchouli, Pogostemon cablin, was assessed against Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), a devastating and invasive pest in tomato crops worldwide. Laboratory bioassays were carried out to determine and compare lethal doses, lethal times, oviposition of treated individuals, and oviposition of T. absoluta on treated leaves of tomato to pure patchouli essential oil or its emulsion containing 18% of oil. The LD50 were 10.06 and 2.57 µg of patchouli per mg of insect for the EO and emulsion, respectively. Oviposition was reduced in adults derived from the second instar treated with LD10 by 78.5% (EO) and 85.4% (emulsion). The EO and its emulsion conferred similar avoidance to adults when sprayed on tomato leaves. Therefore, both formulations present similar lethal and sublethal effects against T. absoluta. This study demonstrated a remarkable potential of an emulsion containing 18% of P. cablin oil to be employed for T. absoluta management on tomato crops. Further studies are needed to assess and guarantee open field applications.