Toxicity of selected insecticides to Trichogramma chilonis: Assessing their safety in the rice ecosystem

Abstract

Nine insecticides, namely, imidacloprid, thiamethoxam, chlorantraniliprole, clothianidin, pymetrozine, ethofenprox, BPMC, endosulfan, acephate, and the product Virtako® (Syngenta; chlorantraniliprole 20%+thiamethoxam 20%) were tested to determine their toxicity to the parasitoid Trichogramma chilonis using an insecticide-coated vial (scintillation) residue bioassay. All the insecticides tested showed different degrees of toxicity to the parasitoid. Thiamethoxam showed the highest toxicity to T. chilonis with an LC 50 of 0.0014 mg a.i. l −1 , followed by imidacloprid (0.0027 mg a.i. l −1 ). The LC 50 values of acephate and endosulfan were 4.4703 and 1.8501 mg a.i. l −1 , exhibiting low toxicity when compared with other insecticides tested. Thiamethoxam was found to be 3,195, 1,395 and 1,322 times more toxic than acephate, chlorantraniliprole and endosulfan, respectively, as revealed by the LC 50 values to T. chilonis. Based on risk quotient, which is the ratio between the field-recommended doses and the LC 50 of the beneficial, only chlorantraniliprole was found to be harmless to T. chilonis. The insecticides thiamethoxam, imidacloprid, Virtako®, ethofenprox and BPMC were found to be dangerous to the parasitoid. Since T. chilonis is an important egg parasitoid of leaf folders, reported to reduce the pest population considerably and often released augmentatively in rice IPM programs, the above noted dangerous chemicals should be avoided in the rice ecosystem.

Selectivity of pesticides used in rice crop on Telenomus podisi and Trichogramma pretiosum

“…The harmlessness of chlorantraniliprole was reported for T. pretiosum and other species of parasitoid eggs (Hymenoptera: Trichogrammatidae), such as Trichogramma dendrolimi Matsumura, Trichogramma chilonis Ishii and Trichogramma japonicum Ashmead (Preetha et al 2009, Brugger et al 2010, Uma et al 2014. Similarly, flubendiamide is harmless to non-target organisms, such as predators and parasitoids (Sudhanan et al 2014).…”

“…and Trichogramma spp. (Moura et al 2006, Giolo et al 2007, Stefanello Júnior et al 2008a, Preetha et al 2009, Carmo et al 2010, Koppel et al 2011, Goulart et al 2012, Oliveira et al 2013. As reported by Stefanello Júnior et al (2008a), this toxicity originates from the similarity in the transmission mode of nerve impulses not only between the different orders of insects, but also between the various animal phyla.…”

Sublethal Effects of Virtako™on Life Table Parameters and Wing Formation of the Brown Planthopper (Homoptera: Delphacidae)

“…Pest suppression by predators is often cited as an important ecosystem service provided by natural enemies, but this service is threatened by pesticide use. Several previous studies have shown that thiamethoxam was mildly harmful (20% mortality) to spiders, Coccinella undecimpunctata L. (Coleoptera: Coccinellidae), and Paederus alfierii Koch (Coleoptera: Staphylinidae) in plantations (Al-Kherb 2011;Jiang et al 2011) but highly toxic to C. lividipennis and Trichogramma chilonis Ishii (Hymenoptera: Trichogrammatidae) (Sun et al 2008;Preetha et al 2009). The results of Preetha et al (2009) showed that chlorantraniliprole was highly toxic to T. chilonis in laboratory tests.…”

“…Several previous studies have shown that thiamethoxam was mildly harmful (20% mortality) to spiders, Coccinella undecimpunctata L. (Coleoptera: Coccinellidae), and Paederus alfierii Koch (Coleoptera: Staphylinidae) in plantations (Al-Kherb 2011;Jiang et al 2011) but highly toxic to C. lividipennis and Trichogramma chilonis Ishii (Hymenoptera: Trichogrammatidae) (Sun et al 2008;Preetha et al 2009). The results of Preetha et al (2009) showed that chlorantraniliprole was highly toxic to T. chilonis in laboratory tests. Although chlorantraniliprole did not harm spiders and C. lividipennis (Liu et al 2009;Xu et al 2012) in rice fields, our results indicated that the application of Virtako, regardless of rate, distinctly reduced the total number of predators 7 and 14 d after application (both single and double applications) and affected the diversity indices H′, J, and C. This is likely because Virtako is a combination of the highly toxic thiamethoxam and the less toxic chlorantraniliprole.…”

Control of Bagworms (Lepidoptera: Psychidae) Using Contact and Soil-Applied Systemic Insecticides

“…Insecticides in this class bind to and activate the ryanodine receptors in insect muscle cells, stimulating calcium release from the internal stores and causing impaired regulation, paralysis and death (Lahm et al 2005(Lahm et al 2009Cordova et al 2006Cordova et al , 2007Legocki et al 2008;Wilks et al 2008). Chlorantraniliprole has demonstrated efficacy in the field against biotype B of B. tabaci, especially when applied to the root zone Schuster et al 2008), and has been shown to be safe to non-target arthropods, including pollinators, numerous beneficial insects and predatory mites (Dinter et al 2008;DuPont 2008;Preetha et al 2009;Brugger et al 2010;Shaw & Wallis 2010;Gradish et al 2010Gradish et al , 2011.…”