Lethal and Sublethal Effects of Conventional and Organic Insecticides on the Parasitoid Trissolcus japonicus, a Biological Control Agent for Halyomorpha halys

Abstract

The egg parasitoid Trissolcus japonicus is a natural enemy of Halyomorpha halys, a polyphagous invasive pest in Europe and North and South America. Integration of chemical and biological control tactics could facilitate effective and sustainable integrated pest management programs. This study was conducted to assess (i) the lethal effects of field rates, (ii) the sublethal effects of maximum and half field rates, and (iii) the lethal effects of different routes of exposure of three organic and two conventional insecticides against T. japonicus. Maximum field rates of spinosad and sulfoxaflor resulted in acute lethal toxicity to adult T. japonicus 1 week after residual contact exposure. Maximum and half field rates of pyrethrins, the mixture of azadirachtin and pyrethrins, and clothianidin caused sublethal effects to female wasps through residual contact exposure. Furthermore, all insecticides caused acute lethal effects 1 week after ingestion by unmated female wasps. Taken together, these results suggest that careful planning is necessary to ensure compatibility between biological and chemical control for H. halys. The insecticides evaluated in this study varied in toxicity to T. japonicus and should be used with caution to conserve this natural enemy for biological control of H. halys.

Keywords: brown marmorated stink bug; exposure routes; fecundity; fertility; longevity; samurai wasp; sex.

Figure 1

Mean proportional survival (± SEM) of T. japonicus 7 days after residual contact exposure to the maximum recommended field rates of five insecticides and an untreated control (i.e., distilled water). Different letters above bars indicate differences among treatments according to the Tukey's test (P < 0.05). Con, control; Pyr, pyrethrins; Aza + pyr, azadirachtin + pyrethrins; Clo, clothianidin; Sul, sulfoxaflor; Spi, spinosad.

Figure 2

Longevity (Kaplan-Meier survival probability curves) of T. japonicus unmated females with residual contact exposure to 100 and 50% of the maximum field rates of three insecticides and an untreated control (distilled water). Different letters in parentheses in the legend indicate differences among survival curves according to the Log-Rank test adjusted with the Benjamini-Hochberg method (P < 0.05). Con, control; Pyr, pyrethrins; Aza + pyr, azadirachtin + pyrethrins; Clo, clothianidin.

Figure 3

Kaplan-Meier survival probability curves of mated females (A), and proportion of emerged females per egg mass (B), mean cumulative parasitism (fertility) (C), and mean cumulative number of offspring (fecundity) (D) per mated female of T. japonicus after residual contact exposure to 100 and 50% of the maximum recommended field rates of three insecticides and an untreated control (distilled water). Different letters in parentheses in the legend indicate differences among treatments (P < 0.05) according to: (A) the Log-Rank test adjusted with the Benjamini-Hochberg method; (C,D) the Tukey's test. Note that the survival probability curve of Pyganic 50% is completely overlapped by the control. Con, control; Pyr, pyrethrins; Aza + pyr, azadirachtin + pyrethrins; Clo, clothianidin.

Figure 4

Kaplan-Meier survival probability curves of T. japonicus unmated females exposed to the maximum recommended field rates of pyrethrins (A), azadirachtin + pyrethrins (B), clothianidin (C), sulfoxaflor (D), and spinosad (E) through residual contact (paper: treated filter paper), oral (sucrose: treated sucrose solution), combined residual contact and oral exposure routes (both), and an untreated control with no insecticide (none). Different letters in parentheses in the legends indicate differences among survival curves according to the Log-Rank test adjusted with the Benjamini-Hochberg method (P < 0.05).

Figure 5

Kaplan-Meier survival probability curves of T. japonicus unmated females exposed to the maximum recommended field rates of five insecticides through residual contact (treated filter paper) (A), oral (treated sucrose solution) (B), combined residual contact and oral exposure routes (C), and an untreated control with no insecticide. Different letters in parentheses in the legends indicate differences among survival curves according to the Log-Rank test adjusted with the Benjamini-Hochberg method (P < 0.05). Con, control; Pyr, pyrethrins; Aza + pyr, azadirachtin + pyrethrins; Clo, clothianidin; Sul, sulfoxaflor; Spi, spinosad.