Impacts of macrocyclic lactones on larval survival, growth and development of three dung beetle species (Coleoptera: Scarabaeidae)

Abstract

Macrocyclic lactones (MLs) are some of the most pervasive chemicals used in cattle management to control internal parasites. However, the drenches can have a range of lethal and sublethal impacts, potentially impacting the efficiency of adult dung beetles at burying dung and negatively impacting their larval growth, development and survival. Here, we assess the impacts of adult dung beetles provisioning their larvae with cattle faecal residues containing three commonly used cattle drenches in Australiamoxidectin, abamectin and doramectin. We used the larvae of two introduced tunnelling (paracoprid) species: Onthophagus binodis and Onitis viridulus, and one introduced rolling (telecoprid) species: Sisyphus rubrus. We anticipated that dung beetle larvae feeding on dung containing an ML would have altered growth patterns to those larvae feeding on untreated dung. Further, beetle larvae exposed to an ML in the dung would have different growth patterns, depending on the time the chemical took to be excreted from the treated cattle, with the anticipation that the chemical may have a peak excretion time. We also expected that dung beetle larvae feeding on dung containing an ML would have a decreased survival rate compared to dung beetle larvae feeding on untreated dung. We found that abamectin and doramectin were more toxic to beetle larvae than moxidectin and control dung, across all three species, and these chemicals also had the greatest negative impact on larval growth and development. Abamectin excreted 7 days after treatment resulted in few live larvae. Overall, moxidectin was the least toxic ML to the larvae assessed, and generally, the drench impacts were reduced as time since exposure increased.

Environmental impacts of equine parasiticide treatment: The UK perspective

“…When horses are treated with ivermectin, dispersal of manure by decomposer insects is markedly delayed (Herd et al., 1993). In contrast, moxidectin is unlikely to have such a deleterious effect on the faecal fauna (Floate et al., 2005; Herd, 1995; Kadiri et al., 1999; Lumaret & Errouissi, 2002), with little to no effect on growth and reproduction of various dung‐colonising insects (Doherty et al., 1994; Mackenzie et al., 2022; Strong & Wall, 1994). The systematic patterns of variability in toxicity in ivermectin and moxidectin can be attributed largely to differences in the toxicity of active ingredients, their formulation/lipophilicity, and/or the susceptibility of the insect species (Floate et al., 2005).…”

Season‐Long Simplification of Insect Communities in Dung From Cattle Treated With an Extended‐Release Formulation of the Parasiticide Eprinomectin

“…(Merial, 2010b) The latter sentence in this statement is misleading. There is no debate that endectocide residues in dung adversely impact coprophilous insects (Finch et al, 2020;Floate et al, 2005;Floate et al, 2016;Junco et al, 2021;Lumaret et al, 2012;Mackenzie et al, 2021;Nieman et al, 2018). However, the consequences of these effects on ecosystem function at the level of the pasture are unclear and may be undetectable (but see Kruger & Scholtz, 1998;Verdú et al, 2018).…”

“…Residues may prevent insects from developing in dung of cattle treated weeks or months previously. Insects that survive residue exposure may experience delayed development, subtle morphological changes, or impaired locomotion (Mackenzie et al, 2021; Verdú et al, 2015; Villada‐Bedoya et al, 2022). Sublethal exposure also can reduce insect fecundity by affecting ovarian morphology and vitellogenesis (Martínez et al, 2017).…”