Matheus Rakes

Toxicity of Pesticide Tank Mixtures from Rice Crops Against Telenomus podisi Ashmead (Hymenoptera: Platygastridae)

The use of insecticides, herbicides, and fungicides commonly occurs in mixtures in tanks in order to control phytosanitary problems in crops. However, there is no information regarding the effects of these mixtures on non-target organisms associated to the rice agroecosystem. The aim of this study was to know the toxicity of pesticide tank mixtures from rice crops against Telenomus podisi Ashmead (Hymenoptera: Platygastridae). Based on the methods adapted from the International Organisation for Biological and Integrated Control of Noxious Animals and Plants (IOBC), adults of T. podisi were exposed to residues of insecticides, herbicides, and fungicides, individually or in mixture commonly used by growers, in laboratory and on rice plants in a greenhouse. The mixture between fungicides tebuconazole, triclyclazole, and azoxystrobin and the mixture between herbicides cyhalofop-butyl, imazethapyr, imazapyr/imazapic, and penoxsulam are harmless to T. podisi and can be used in irrigated rice crops without harming the natural biological control. The insecticides cypermethin, thiamethoxam, and bifenthrin/carbosulfan increase the toxicity of the mixtures in tank with herbicides and fungicides, being more toxic to T. podisi and less preferred for use in phytosanitary treatments in the rice crop protection.

Side-effects of pesticides used in irrigated rice areas on Telenomus podisi Ashmead (Hymenoptera: Platygastridae)

Telenomus podisi Ashmead (Hymenoptera: Platygastridae) is an important agent for the biological control of stink bug eggs in irrigated rice areas and the best strategy for its preservation is the use of selective pesticides. The aim of this study was to know the side-effects of pesticides used in Brazilian irrigated rice areas on egg parasitoid T. podisi. We evaluated, under laboratory conditions, 13 insecticides, 11 fungicides, 11 herbicides, and a control (distilled water) in choice and no-choice tests. In the no-choice tests, the pesticides were sprayed at pre and post-parasitism stages (egg and larval stages of T. podisi). In the choice tests, sprays were conducted only at pre-parasitism stages. For all tests, we prepared cards with 25 eggs of the alternative host Euschistus heros (Fabricius) (Hemiptera: Pentatomidae) non-parasitized (pre-parasitism) and parasitized (post-parasitism), which were subjected to pesticide sprays. The parasitism and emergence rates of T. podisi were determined classifying the pesticides in terms of the reduction of parasitism or emergence rates compared to the control. The neurotoxic insecticide cypermethrin, lambda-cyhalothrin, zeta-cypermethrin, etofenprox, thiamethoxam, thiamethoxam + lambda-cyhalothrin, acetamiprid + alpha-cypermethrin, and bifenthrin + alpha-cypermethrin + carbosulfan were more harmful to T. podisi and, therefore, are less suitable for the integrated management of insect pests in irrigated rice areas.

Toxicity of soybean-registered agrochemicals to Telenomus podisi and Trissolcus basalis immature stages

Biological control of phytophagous bugs in soybean crops is efficiently performed by egg parasitoids, such as Telenomus podisi and Trissolcus basalis. Based on this, the use of agrochemicals in these crops must be managed consciously, making use of pesticides that are selective to the egg of these parasitoids, in order to ensure a balanced ecosystem. The aim of this study was to assess the selectivity of 15 registered pesticides to the immature stages (pre and post-parasitism) of T. podisi and T. basalis, following the method proposed by the “International Organization for Biological and Integrated Control” (IOBC). Pesticides were classified as class 1 – harmless (RP < 30%); class 2 – slightly harmful (30% ≤ RP ≤ 79%); class 3 – moderately harmful (80% ≤ RP ≤ 99%); and class 4 – harmful (RP > 99%). During pre-parasitism, the insecticides imidacloprid+beta-cyfluthrin, deltamethrin, lambda-cyhalothrin+thiamethoxam, acephate, and fenitrothion reduced parasitism of both parasitoids. The others: flubendiamide, diflubenzuron, Bacillus thuringiensis, lufenuron, and the herbicide isopropylamine were selective, i.e. harmless (class 1), to both parasitoids, except for pyraclostrobin+metconazole, which significantly reduced T. basalis parasitism, being considered slightly harmful (class 2). In post parasitism, all the aforementioned pesticides were harmless to T. podisi and T. basalis. Moreover, in pre-parasitism, T. basalis was found to be more sensitive to the tested pesticides when compared to T. podisi. Still, more studies must be conducted to provide a better understanding of the impact of agrochemicals on these parasitoid species in semi-field conditions.