Emergent body size of mayfly survivors

Abstract

1. Employing field-deployed mesocosms, we examined the effects of 12-h pulse and 20-day press (continuous) exposures of the common agricultural insecticide, imidacloprid, on nymph abundance, emergence patterns and adult body size of Epeorus spp. (Heptageniidae) and Baetis spp. (Baetidae). 2. In press exposures, reduced nymph density was driven by reduced survivorship; in pulse exposures, reduced nymph density may reflect increased emergence because of stress. 3. Once exposed to imidacloprid, Epeorus and Baetis mayflies developed less and emerged smaller than their control counterparts. Concentrations as low as 0.1 lg L )1 (12-h pulse) reduced head length in Baetis and thorax length in Epeorus. 4. In all of the Baetis and Epeorus examined, effects were only found in males. Male survivorship and body size can affect population dynamics. Sublethal doses of this widely applied agricultural insecticide have the potential to reduce reproductive success of mayfly populations.

Structural and functional responses of benthic invertebrates to imidacloprid in outdoor stream mesocosms

“…In fact, Alexander et al (2008) showed that exposure to sub-lethal concentrations of imidacloprid caused mayflies to mature earlier at a smaller size, leading to impaired reproductive fitness. Several diversity and biotic indices commonly calculated in rapid bioassessment protocols failed to discriminate effects of pesticide contamination on natural benthic communities.…”

“…The artificial streams were designed to simulate lotic habitats by encompassing a portion of substratum and of the benthic invertebrate community collected in the Nashwaak River, New Brunswick, Canada (46 14 294 0 N, 66 36 722 0 W) in semi-field conditions Culp and Baird, 2006). A complete description of the artificial streams characteristics, inoculation of fine and coarse natural substratum and pesticide contamination can be found elsewhere (Alexander et al, 2008) Once inoculated with natural substratum and after deploying the leaf bags (see above), the streams were allowed to equilibrate for 2 days prior to the addition of benthic invertebrates. Benthic invertebrates were collected upstream of the gravel collection site on the Nashwaak River with U-nets (area ¼ 0.06-m 2 ) (Scrimgeour et al, 1993).…”

Conclusion on the peer review of the pesticide risk assessment for aquatic organisms for the active substance imidacloprid

“…Furthermore, this conclusion was also supported by the additional information derived from the publicly available mesocosm studies, which indicated effects on Ephemeroptera at concentrations below the mesocosm NOECs (Alexander et al, 2008 andColombo et al, 2013; see the study evaluation notes, section 5.5; EFSA, 2014b).…”

“…EFSA, 2014b) were also included in the literature search performed by the applicant. However, these additional studies, with some exceptions (Alexander et al, 2008;Colombo et al, 2013 andPestana et al, 2009b), were not considered useful for risk assessment, because either the exposure was not relevant or worst case (e.g. addition of contaminated leaves to the micro/mesocosm, paddy micro/mesocosm or indoor micro/mesocosm), or only one concentration was tested or an endpoint could not be derived, or there were concerns on the representativeness of the environmental conditions in Europe.…”

The effects of the psychiatric drug carbamazepine on freshwater invertebrate communities and ecosystem dynamics

“…The reduction in adult body dimensions may be due to acceleration of development to avoid unfavorable habitat conditions and maximize overall fitness. Exposure to anthropogenic contaminants can prompt nymphs to accelerate development at the cost of future reproductive success (Alexander et al 2008, Palmquist et al 2008, Conley et al 2009 …”