Abstract
Euschistus heros (Fabricius) (Hemiptera: Pentatomidae) primarily attack the pods and seeds of soybean plants, causing severe economic losses in Neotropical Region, and chemical control is essential to avoid these losses. Thus, insecticides more effective against this pest and less toxic to Telenomus podisi Ashmead (Hymenoptera: Platygastridae) - the main biological control agent of E. heros - should be used. In this report, we studied the differential acute impacts of pesticides used in Brazilian soybean against E. heros and T. podisi and evaluated their sublethal effects on the parasitoid to identify effective pesticides towards the pest with less harmful effect to the natural enemy. The LC50 of the insecticides to E. heros ranged from 1.20 to 533.74 ng a.i./cm2; the order of toxicity was thiamethoxam + lambda-cyhalothrin > acetamiprid + fenpropathrin > zeta-cypermethrin > acephate > imidacloprid. All pesticides were classified as slightly to moderately toxic to T. podisi based on the risk quotient. The exposure of T. podisi females to imidacloprid and the insecticide pre-formulated mixtures reduced the emergence of the offspring parasitoids by up to 40% whereas zeta-cypermethrin and the insecticides pre-formulated mixtures reduced offspring survival. The preferred order of choice of insecticides for the management of E. heros according to agronomic, toxicological, and environmental feasibility was the following: thiamethoxam + lambda-cyhalothrin > zeta-cypermethrin > acetamiprid + fenpropathrin > acephate > imidacloprid. Our study provides important and pioneer information to select insecticides for effective control of E. heros with lower impacts on T. podisi.
Highlights
Soybean (Glycine max L.) (Fabaceae: Phaseoleae) is one of the most economically important leguminous crops worldwide
The median lethal concentration (LC50) values for acephate, imidacloprid, zeta-cypermethrin, acetamiprid + fenpropathrin, and thiamethoxam + lambda-cyhalothrin after exposure in glass vials were significantly different between E. heros and T. podisi (Table 1)
The LC50 values for T. podisi ranged from 0.69 to 57.43 ng of a.i. per cm[2], and the order of acute toxicity was thiamethoxam + lambda-cyhalothrin > imidacloprid > acetamiprid + fenpropathrin > zeta-cypermethrin > acephate (LC50 values with overlaps in the 95% confidence intervals were classified as having the same level of toxicity) (Table 1)
Summary
Soybean (Glycine max L.) (Fabaceae: Phaseoleae) is one of the most economically important leguminous crops worldwide. Insect populations are managed by frequent spraying of insecticides, and in many situations, the chemical control is the only method capable of effectively avoid economic losses[4]. The egg parasitoids of the Platygastridae family are considered the main natural enemies of stink bugs pests (Hemiptera: Pentatomidae) in different crops[12,13,14,15,16]. Parasitoids of stink bugs eggs have been used in 0.03 million hectares of soybean crops in South America in augmentative biological control programs[17]. Telenomus podisi Ashmead (Hymenoptera: Platygastridae) is the most efficient parasitoid of E. heros and Piezodorus guildinii (Westwood) (Hemiptera: Pentatomidae) eggs[18], insects which cause the highest economic losses to soybean crops in Brazil[19]. In Brazil, T. podisi is found from the Midwest[20] to the extreme South Regions[21]
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