Lethal and behavioral effects of synthetic and organic insecticides Spodoptera exigua and its predator Podisus maculiventris

Authors: DE CASTRO, ANCIDERITON - Universidade Federal De Vicosa; Legaspi, Jesusa; TAVARES, WAGNER - Universidade Federal De Vicosa; Meagher, Robert - Rob; Miller, Neil; KANGA, LAMBERT - Florida A & M University; HASEEB, MUHAMMAD - Florida A & M University; SERRAO, JOSE - Universidade Federal De Vicosa; WILCKEP, CARLOS - Universidade Estadual Paulista (UNESP); ZANUNCIO, JOSE - Universidade Federal De Vicosa

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2018
Publication Date: 11/8/2018
Citation: De Castro, A.A., Legaspi, J.C., Tavares, W.S., Meagher Jr, R.L., Miller, N.W., Kanga, L., Haseeb, M., Serrao, J.E., Wilckep, C.F., Zanuncio, J.C. 2018. Lethal and behavioral effects of synthetic and organic insecticides Spodoptera exigua and its predator Podisus maculiventris. PLoS One. 13(11):e0206789. https://doi.org/10.1371/journal.pone.0206789.
DOI: https://doi.org/10.1371/journal.pone.0206789

Interpretive Summary: The beet armyworm is a major insect pest of vegetables worldwide, and is resistant to various classes of chemical insecticides. Integrated pest management (IPM) of the armyworm includes the use of selective chemical insectcides, as well as promising biological control agents such as predatory stinkbugs. To test the compatibility of these control tactics, the toxicity of selective and botanical insecticides were evaluated in the laboratory against beet armyworm, and the spined soldier bug. Botanical insecticides are natural chemicals derived from plants and approved by the Organic Materials Review Institute (OMRI). Insecticides evaluated were Azera® (from chrysanthemum and neem plants), PyGanic® (from chrysanthemum), Entrust® (from bacteria) and one non-OMRI-listed formulation, Coragen® (a novel insecticide). The toxicity of Entrust® and Coragen® was higher against the pest than the predator. However, PyGanic® and Azera® showed higher toxicity against the predator than the beet armyworm in glass-vial bioassays. Coragen® also had the highest toxicity to the armyworm in diet incorporation bioassays, followed by Entrust®, PyGanic® and Azera®. Oral toxicity bioassays showed that Entrust® had the highest toxicity against the spined soldier bug, followed by PyGanic®, Azera® and Coragen®. This study provides evidence against the widely held belief that natural compounds are safer to non-target and beneficial insects than synthetic chemicals. The synthetic insecticide Coragen® was less toxic than the natural insecticides PyGanic®, Azera® and Entrust®. Therefore, naturally-derived bioinsecticides should not be exempted from risk assessment studies, and non-target sub-lethal effects should not be ignored for insecticide use in IPM programs.

Technical Abstract: The beet armyworm, Spodoptera exigua (Hübner) is one of the major insect pests of vegetables around the world, and resistant to various classes of chemical insecticide. Selective insecticides are required to control S. exigua in integrated pest management (IPM) programs. In addition, biological control of this pest using predatory stinkbugs is a promising control tactic. Toxicity of botanical insecticides approved by the Organic Materials Review Institute (OMRI) was evaluated under laboratory conditions for S. exigua and P. maculiventris. Insecticides evaluated were Azera® (pyrethrin and azadirachtin), PyGanic® (pyrethrin), Entrust® (spinosad) and one non-OMRI-listed formulation, chlorantraniliprole Coragen® (diamine). The toxicity of Entrust® and Coragen® was higher to the pest compared to the predator and PyGanic® and Azera® showed higher toxicity to the predator compared to the pest using glass-vials bioassays. Coragen® also had the highest toxicity to S. exigua using diet incorporation bioassays, followed by Entrust®, PyGanic® and Azera®. The oral toxicity bioassays showed that Entrust® had the highest toxicity against P. maculiventris followed by PyGanic®, Azera® and Coragen®. The notion that natural compounds are safer than synthetic compounds to non-target species is refuted, because the synthetic insecticide Coragen® was less toxic than the natural insecticides PyGanic®, Azera® and Entrust®. Therefore, bioinsecticides should not be exempted from risk assessment schemes, and non-target sub-lethal effects should not be forgotten for insecticide use in integrated pest management programs.