Systemic Imidacloprid Affects Intraguild Parasitoids Differently

Parasitism, host feeding, and transgenerational effects of three insecticides on the eulophid parasitoid Tamarixia triozae when exposed in the immature stages

The ectoparasitoid Tamarixia triozae is a promising biological control agent of the tomato psyllid, Bactericera cockerelli, based on its high parasitism rates on different crops. The parasitism, host feeding, and transgenerational effects (in terms of sex ratio) of T. triozae females exposed to three insecticides (soybean oil, imidacloprid, and abamectin) as eggs, larvae, and pupae were evaluated when a mixture of second, third, fourth, and fifth instars of the host B. cockerelli was offered. The concentrations bioassayed of each insecticide corresponded to the minimum field-registered concentration [MiFRC] and one-half the MiFRC. No parasitism of B. cockerelli second instars was recorded when parasitoid's females were exposed in any of the three immature stages to any of the insecticides. In contrast, in some cases, parasitism of T. triozae females treated as eggs, larvae, or pupae with soybean oil and imidacloprid was reduced in third, fourth, or fifth instar. In most cases, the host feeding was reduced in second and third instar of the host B. cockerelli when T. triozae females were treated as eggs, larvae, or pupae. Any insecticide modified the sex ratio in the F2 generation. In conclusion, both parasitism and host feeding were affected by the insecticides depending on the concentration and on the nymphal instar of the host B. cockerelli offered.

Effects of clothianidin-treated seed on the arthropod community in a mid-Atlantic no-till corn agroecosystem

BACKGROUND

Nearly all corn seed in the US is coated with neonicotinoid insecticides to protect against soil and foliar arthropod pests. Exposure in the soil and the systemic activity in the plant can pose non-target risks. We assessed the community-level effects of clothianidin-treated seed on the diversity and abundance of arthropod communities in a no-till corn agroecosystem over a single growing season.

RESULTS

Epigeal and foliage-dwelling communities were disturbed by the clothianidin seed treatment, with significant negative and positive changes in taxa abundances. Clothianidin reduced the abundance of minute pirate bugs by 66.2%, lady beetles by 44.7%, ants by 43.4%, ground beetle adults and larvae by 31.7%, and rove beetles by 44.1% during the early corn growth stages. Herbivores, particularly thrips, were more negatively affected by clothianidin than other trophic groups. In contrast, some groups, such as collembolans and leafhoppers, exhibited significantly higher abundances in the seed treated plots.

CONCLUSION

Clothianidin primarily influenced arthropod communities during the 4 weeks following planting, with disruptions to major natural enemy taxa, but communities showed trends toward recovery at the later corn stages. While the insecticide suppressed multiple herbivores, none were economically damaging to corn; thus, the pest suppression benefits of clothianidin observed in this study did not justify the non-target impacts. © 2018 Society of Chemical Industry.

Imidacloprid Soil Drenches Affect Weight and Functional Response of Spined Soldier Bug (Hemiptera: Pentatomidae)

There are ongoing concerns of potential direct and indirect lethal and sublethal effects of insecticides on nontarget arthropod populations. The risk to natural enemies from systemic insecticides is mainly through exposure to the active ingredient by ingestion, and such risk may be elevated for omnivores that feed on treated plants, as well as herbivores that also feed on those same treated plants. Podisus maculiventris (Say), an important natural enemy in many agricultural systems, can be potentially exposed to the neonicotinoid imidacloprid when ingesting contaminated prey and feeding on plants subjected to soil-drench applications of this compound. In the current study, we examined the potential impact of imidacloprid soil drenches on some functional and morphological endpoints. Cabbage plants were treated with soil drenches of imidacloprid that corresponded to half and full recommended labels rates against whiteflies and aphids. Fourth instar diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae), larvae on plants were used as prey in our experiments; P. xylostella is not a target of imidacloprid applications but may co-occur with other pests in systems where the insecticide is applied. We found that exposure to imidacloprid-treated plants did not cause significant mortality neither to P. maculiventris nor to P. xylostella, but both treatment concentrations impaired the predation, with consequences for predator weight gain during the assessment period. Our results corroborate those from other studies and demonstrate that effects from systemic insecticides can transcend trophic levels to affect natural enemies indirectly, such as through exposure from feeding on pests not targeted by the insecticide.