Avermectins: a review of their impact on insects of cattle dung

Abstract

Avermectins administered to cattle for control of parasitic infections by injection or slow-release bolus are excreted in the faeces and have a variety of harmful effects upon Diptera and Coleoptera that develop in cow-pats: these effects are reviewed. Diptera Cyclorrhapha are severely affected, the extent of the response depending on the drug concentration in the dung. At high levels, larvae are killed or paralysed while at lower levels their metamorphosis is inhibited. At very low levels, adult emergence is reduced and a significant number of imagines show morphological abnormalities. These responses are induced by concentrations of avermectins well below levels occurring in faeces after routine treatment. Diptera Nematocera are less sensitive than Cyclorrhapha but larval and pupal development are affected at higher dose levels. Larval dung beetles and some immature adults cannot survive in the pats of recently dosed livestock. Mature adult beetles are more resistant, but contact with treated dung leads to impaired reproduction. Dung eliminated up to 5 weeks after cattle have been treated with a single injection or up to 14 days after topical dosing shows harmful activity against dung insects, and ivermectin-containing pats retain much of their toxicity after several weeks exposure on pastureland. The impact on dung insects is more pronounced and of longer duration when ivermectin is delivered daily at 40 (ig per kg cow by sustained-release bolus. Following topical or injection treatments, the rate of cow-pat degradation (measured by actual loss of biomass) is significantly delayed. When cattle are treated with a bolus delivering 40 mg ivermectin per kg cow per day, their dung remains intact on grassland for at least three months. The conclusions drawn from the various papers on these effects are compared and contrasted. In particular, attention is drawn to the general failure to recognize the importance of delayed reactions to non-lethal doses of avermectins, and to our lack of consideration of long-term consequences for cow-pat insects and the wider implications for ecology.

The negative effects of the residues of ivermectin in cattle dung using a sustained-release bolus on Aphodius constans (Duft.) (Coleoptera: Aphodiidae)

“…It is the same for other Diptera such as Neomyia cornicina [6,7,24] or Scatophaga stercoraria [19] whose larvae were unable to survive in dung collected up to one month after the cattle had been treated with ivermectin. In the same way, ivermectin has well-documented effects on a variety of beetles associated with dung and has been shown to have a wide range of sublethal effects in addition to its acute toxicity [17,18]. The fertility and the adult emergence rate decreased, whereas the mortality of newly hatched adults and the mortality of larvae could be important.…”

“…Ivermectin has a high potency at low concentrations against nematodes and arthropods, in particular against dung beetles and flies [8,18,20,21], and it has been demonstrated that dung pats containing ivermectin are degraded significantly slower than pats containing no ivermectin [3,13,20,21]. Although some authors [3,15] have previously recommended that cattle breeders treat their cattle with subcutaneous injection of ivermectin when there is negligible dung beetle activity, the spread of the use of Résumé -Effets négatifs des résidus d'ivermectine délivrés par un bolus à diffusion lente sur la survie du coprophage Aphodius constans (Duft.)…”

Treatment of reindeer with ivermectin - effect on dung insect fauna

“…Most of the dose given to an animal is excreted unaltered in the faeces (Halley et al, 1989). Studies on cattle show that ivermectin residues in faeces may have a negative effect on the dung fauna (Wall & Strong, 1987;Fincher, 1992;Strong, 1992Strong, , 1993Gunn & Sadd, 1994), and the wide use of ivermectin in reindeer (Rangifer tarandus) has given rise to a concern among reindeer herders, veterinarians, environmental authorities as well as the general public, on possible negative ecological effects on reindeer grazing areas, as reflected especially in Norwegian newspapers (Berg, 1991;Tonstad, 1991;Anonymous, 1992).…”

Use of anthelmintics in herbivores and evaluation of risks for the non target fauna of pastures

“…The environmental impact of antiparasitic chemotherapy depends on the deleterious effects which the agent or its metabolites have on an organism in the locus of excreta, the amount of the active agent excreted, the temporal nature of excretion and the stability of the ecotoxic residues [81]. The faecal concentration levels of ivermectin found in horse droppings [84] were all above concentrations that are lethal or sublethal to many dung breeding invertebrates of benefit to the ecosystem [50,100]. It has been demonstrated that ivermectin concentrations as low as 0.001 µg·g -1 (1 ng·g -1 ) wet weight are toxic to some dung breeding insects [101].…”

“…Faecal residues or metabolites of drugs belonging to the benzimidazole and levamisole/morantel groups are thought to be relatively harmless to dung fauna [81,110], on the contrary to other anthelmintics such as coumaphos, dichlorvos, phenothiazine, piperazine [12,64], synthetic pyrethroids [10,115], and most macrocyclic lactones [25,50,99,100,102] which have been shown to be highly toxic for dung beetles.…”