Contact toxicity of a new acaricide, SYP-9625, to the natural predator, Chrysopa pallens

Highlights

• We first evaluated the contact toxicity of an acaricide, SYP-9625, on C. pallens.

• SYP-9625 only had mild detrimental impacts on insect growth and metamorphosis.

• SYP-9625 had significant adverse effects on adult survival and Vg expression.

• The paper will strengthen the compatibility of acaricide and natural predators.

Abstract

SYP-9625 is a novel acaricide synthesized by using cyenopyrafen as lead compound. It is characterized by high acaricidal activity and low toxicity to mammals and has been widely used in Chinese farming areas. However, to date, the toxicity of SYP-9625 to natural enemy insects remained unclear. Here, we evaluated the effects of SYP-9625 on survival, growth, metamorphosis and reproduction of a common natural predator, Chrysopa pallens. Contact toxicity bioassay revealed that SYP-9625 had no significant detrimental impacts on egg hatchability, larval survival and duration, pupation rate, pupal mass, emergence rate, digestive enzyme activity, reproductive output and offspring quality, but drastically reduced adult survival rate, adult lifespan, secondary follicle size and vitellogenin (Vg) transcripts by 27.8%, 15.4%, 33.4% and 59.4%, respectively, suggesting a low contact toxicity of SYP-9625 to C. pallens. This study will strengthen the compatibility of chemical acaricide and natural enemy insects in integrated pest management.

Introduction

Pesticides, such as insecticide and acaricide, are mainly applied to manage arthropod pest population in agricultural and horticultural crop planting systems. Nevertheless, excessive reliance on pesticides may lead to various ecological problems including pest resurgence, secondary pest outbreaks and detrimental effects on non-target arthropods (Hardin et al., 1995, Ruberson et al., 1998, Fernandes et al., 2010). Integrated pest management (IPM) programs attach importance to the combination of different strategies, such as chemical and biological control, to keep pest populations below economic thresholds (Roubos et al., 2014). IPM advocates usage of molecules reasonably compatible to the natural enemies (Gonzalez-Zamora et al., 2013). For this, pesticide selectivity must be taken into consideration during the progress of poison free management of insect pests (Sparks, 2013).

Cyenopyrafen is a relative novel acaricide developed by Otsuka AgriTechno Co, Ltd, (Riga et al., 2015). It is the first commercialized acrylonitrile derivative with important acaricidal activity against spider mites (Tetranychus cinnabarinus). Cyenopyrafen belongs to a mitochondrial electron transport inhibitor and has been globally registered now. It significantly improved efficiency in control of spider mites and phytophagous mites in citrus and other crops (Yu et al., 2012, Srivastava et al., 2017, Tan et al., 2018, Chen et al., 2019).

In 2008, a highly efficient acaricide, SYP-9625 (CAS number: 1253429–01-4), was synthesized in Shenyang Sinochem Agrochemicals R&D Co., Ltd (Ouyang et al., 2018). SYP-9625 was synthesized using 2-(4-(tert-butyl) phenyl) acetonitrile as starting material via condensation and acylation (Yu et al., 2016). Its name is (Z)-2-(4-(tert-Butyl)phenyl)-2-cyano-1-(1-ethyl-3-methyl-1H-pyrazol-5-yl)vinyl pivalate (Molecular formula: C₂₄H₃₁N₃O₂). SYP-9625 has been officially registered in China in 2015 and available in market in 2017 (Li et al., 2016). It is characterized by low toxicity to mammals and high levels of acaricidal activity on spider mites, showing attractive application potential (Li et al., 2016). As a complex II inhibitor, the acaricide SYP-9625 is commonly used to control two-spotted spider mite (TSSM) and Tetranychus urticae Koch (Chen et al., 2019).

Currently, many novel pesticides of low-toxicity are applied as potential alternatives to replace highly toxic ones. Except for evaluation of toxicological impacts on target pests, assessment of adverse effects on natural enemies is also indispensable for these pesticides. In 2018, SYP-9625 was tested for impacts on a predatory mite, Neoseiulus californicus (McGregor) (Ouyang et al., 2018). However, its effects on natural enemy insects have so far not been determined yet.

The green lacewing Chrysopa pallens is a very excellent entomophagous predator and can be found in most agricultural regions of the world (Tauber et al., 2000). Both larvae and adult C. pallens are predators. C. pallens larvae have a wide spectrum of prey, including aphids, caterpillars, and other insect larvae and eggs (Brooks and Barnard, 1990, Boo et al., 2003, Zhang et al., 2004, Bezerra et al., 2012).

In this paper, impacts of spraying SYP-9625 on survival, growth and reproduction of C. pallens were examined. The goal of the study is to provide knowledge on the compatibility of SYP-9625 and natural enemy insects. The results can be useful for farmers and consultants to make decisions on acaricide selection and application timing in IPM implementation when natural enemy insects are present at field and landscape scales.