Direct and Indirect Effects of Ivermectin on Phytophagous, Frugivorous and Parasitoid Insects

TL;DR

This study shows that ivermectin, a common dewormer, harms various insects, including herbivores and parasitoids, even at low doses, affecting ecosystems.

Contribution

The study reveals ivermectin's sublethal effects on non-target insects across multiple feeding guilds and trophic levels.

Findings

Ivermectin reduced pupal weight and survival in moth larvae.

Aphid colony establishment was inhibited in ivermectin-treated soil.

Parasitoid emergence rates were reduced from ivermectin-exposed host pupae.

Abstract

Our study evaluated the effects of ivermectin in sublethal doses on insects of different feeding guilds. We investigated the effects of ivermectin on weight and development when applied to the diet of two chewing herbivores, Spodoptera frugiperda and Helicoverpa armigera; the success of colony establishment of Acrythosiphon pisum on Pisum sativum grown in ivermectin-laced soil; and the reproductive success of the parasitoid Pachycrepoideus vindemmiae when parasitizing Drosophila melanogaster larvae fed with an ivermectin-laced diet. We found that in all experiments conducted in this study, ivermectin had significant negative effects on the insects involved, such as a reduction in pupal weight, prolonged development time, less successful establishment and reduced emergence from pupae. Since ivermectin and other macrocyclic lactones with similar properties are widely used as anthelmintics—dewormers for mammals—they are excreted into the environment in large amounts and can be taken up in similar circumstances such as those we have investigated here. We conclude that ivermectin can affect insects of different feeding guilds and have significant effects on different ecosystem processes. We recommend that ivermectin and comparable anthelmintics be used more cautiously in accordance with their negative effects on the environment and that the sublethal effects of seemingly harmless substances be researched more intensively in general.

Ivermectin, an anthelmintic used in livestock, is excreted in faeces and can therefore affect non-target organisms. While its effects on coprophagous insects have been well studied, recent research suggests that it can be taken up by plants, raising the possibility that it may affect a much wider range of invertebrates than previously known. Our study investigated the effects of ivermectin on insects from different feeding guilds. First, we tested its effects on the larvae of the noctuid moths Spodoptera frugiperda and Helicoverpa armigera (chewing herbivores) using an artificial diet. Secondly, we investigated the effects of its presence in the soil of pea plants Pisum sativum on the pea-feeding aphid Acyrthosiphon pisum (phloem-feeding herbivore). Thirdly, we tested ivermectin in an artificial diet for Drosophila melanogaster used as a host for the parasitoid Pachycrepoideus vindemmiae. Our results showed that ivermectin reduced pupal weight and survival in moth larvae, inhibited aphid colony establishment and reduced parasitoid emergence rates from ivermectin-exposed Drosophila pupae. These results highlight the potential of ivermectin to affect multiple trophic levels and emphasise the need for sustainable veterinary practices in the use of anthelmintics in free-ranging livestock and companion animals.

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