Chemical insecticides are widely used to control soil pests but not always effective. Entomopathogenic nematodes (NEPs) are found in the soil and depend on host insects to complete their life cycle, and therefore have the potential to control soil pests. Thus, we aimed to investigate the possible joint use of these control methods by assessing the compatibility of two nematodes (Heterorhabditis amazonensis GL and Heterorhabditis amazonensis MC01) with five crop protection products used for maize seed treatment (Maxim®, Cruiser 350 FS®, Fortenza 600 FS®, Avicta 500 FS®, and Amulet®), as well as one neem-based product (NeenMax®). The experimental design was completely randomized with five replicates, six treatments, and one control, in which only distilled water was added to nematode suspension. Each replicate consisted of a test tube containing 1 mL suspension with 2,000 infective juveniles (IJs) and 1 mL of diluted product, following the manufacturer's recommendation. The evaluated parameters were viability, infectivity on Tenebrio molitor larvae and IJs production after exposure to products. Both nematodes were compatible with NeenMax® and Fortenza 600 FS® since they did not differ from the control and were classified as innocuous. Cruiser 350 FS ® was also compatible with the nematodes since the effect value of the product was lower than 30%. Amulet® was classified as slightly noxious, reducing H. amazonensis MC01 and H. amazonensis GL infectivity by 17.5% and 28.5%, and production by 18.2% and 22.3%, respectively. Despite not having reduced viability, Avicta 500 FS® and Maxim® were considered harmful. This is because Avicta 500 FS® and Maxim® reduced productivity by 70.0% and 72.5% and production by 66.1% and 65.4% for H. amazonensis MC01, respectively. For H. amazonensis MC01, both Avicta 500 FS® and Maxim® reduced infectivity by 76.19%, and production by 63.7% and 62.3%, respectively.
Virulence and concentration of entomopathogenic nematodes (NEPs)in Elasmopalpus lignosellus pupae were evaluated. In the laboratory, the virulence of the isolates Heterorhabditis amazonensis MC01, H. amazonensis JPM3, H. amazonensis GL, Steinernema carpocapsae All and Heterorhabditis sp. Nepet 11 was evaluated and, subsequently, H. amazonensis GL was applied at concentrations of 8; 16; 24 and 32 IJ cm-2. The EPNs were applied to Petri dishes containing ten pupae with five replications. Mortality was assessed every 24 hours for three days. In a greenhouse, H. amazonensis GL was tested at concentrations 24, 25, 26 and 27 IJ cm-2. The IJs were applied in pots containing a 20-cm high ‘BM 3061’ maize plant, besides six pupae with four replications. Knowing that the efficiency of EPNss is directly related to the ability to search and penetrate the host, it was found that H. amazonensis GL is highly virulent to E. lignosellus, presenting an LC50 of 6.49 IJ cm-2 after 48 hours, 5.61 IJ cm-2 in 72 hours and LC90 of 39.70 IJ cm-2 in 48 and 27.73 IJ cm-2 in 72 hours under laboratory conditions. In the soil, pupal mortality was lower and a concentration of 25 IJ cm-2 was responsible for the death of 50% of the population, since environmental variability influences the dynamics of IJ infection and insect defense.
The cornstalk borer, Elasmopalpus lignosellus (Zeller) (Lepidoptera: Pyralidae), is one of the pests responsible for the decrease of the productive potential of the corn, because it forms gallery on the stem, causing the tillering or death of the plant. Despite being considered a difficult-to-manage pest, it is currently used chemical control, via seed treatment and insecticide applications. However, the use of this method has presented low efficiency, besides generating problems due to incorrect use, insect resistance, population outbreaks, rise of secondary pests, increased production costs and increased human and environmental contamination. Initially, the virulence of the isolates, Heterorhabditis amazonensis MC01, H. amazonensis JPM3, H. amazonensis GL, Steinernema carpocapsae All and Heterorhabditis sp. Nepet 11 was tested on E. lignosellus pupae and caterpillars in the laboratory. The avarages were compared by the Scott-Knott test (p ≤ 0.05). Subsequently, the concentrations of 50, 100, 150 and 200 JI insect-1 of H. amazonensis GL for pupae and of H. amazonensis MC01 for caterpillars were tested in a completely randomized design with five replicates. Data were submitted to regression analysis. In greenhouse the concentrations of the isolates were again tested in vase containing corn. For caterpillars the concentrations of 190, 210, 230 and 250 JI larve-1 of H. amazonensis MC01 were tested following the completely randomized design with five replicates. For the pupae the concentrations 3380, 3500, 3620, 3740 JI vase-1 of H. amazonensis GL were tested following the same design with four replicates. Finally, the compatibility of phytosanitary products used in the treatment of corn seeds with H. amazonensis MC01 and H. amazonensis GL nematodes was tested. The isolate selection test for caterpillars showed that after 72 hours the nematodes H. amazonensis MC01 and S. carpocapse All were equally virulent differing from the others, reducing the caterpillar population by more than 90%. The isolate H. amazonensis GL stood out from the others, causing a mortality of 94% of pupae after 48 h. The concentration of H. amazonensis MC01 that caused the highest mortality of caterpillars in the laboratory was approximately 190 JI larve-1 , and the concentration of H. amazonensis GL was 157 JI pupa-1. In greenhouse the concentrations of H. amazonensis MC01 tested did not differ among themselves. In the pupae assay the concentration that caused the highest mortality was 3500 JI vase-1. The compatibility test showed that the nematodes were compatible with NeemMax®, Fortenza 600 FS® and Cruiser 350 FS® products.
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