Hazards and uptake of chitin synthesis inhibitors in bumblebees Bombus terrestris

Abstract

This research project examined the potential hazards of a major class of insect growth regulators (IGRs) to survival, reproduction and larval growth in bumblebees Bombus terrestris L. Eight chitin synthesis inhibitors (CSIs) were tested: buprofezin, cyromazine, diflubenzuron, flucycloxuron, flufenoxuron, lufenuron, novaluron and teflubenzuron. These different IGRs, which are important in the control of pest insects in greenhouses, were applied via three different routes of exposure under laboratory conditions: dermal contact, and orally via the drinking of sugar/water and via pollen. The compounds were tested at their respective maximum field recommended concentrations (MFRC) and also in dose-response assays to calculate LC(50) values. In general, none of the CSIs showed acute worker toxicity. However, there was a dramatic reduction in brood production, especially after oral treatment with pollen and sugar/water. Conspicuously, egg fertility was reduced in all treatments with diflubenzuron and teflubenzuron. In addition to egg mortality, the worker bumblebees removed larvae from the treated nest, and in most cases these individuals were dead first-second instars. Under a binocular microscope, such larvae showed an abnormally formed cuticle leading to mechanical weakness and death. In another series of experiments using (14)C-diflubenzuron and (14)C-flufenoxuron, cuticular penetration in workers was studied for a better understanding of the differences in toxicity. With (14)C-diflubenzuron, transovarial transport and accumulation in the deposited eggs supported the strong reproductive effects. Overall, the present results suggest that CSIs should be applied with caution in combination with bumblebees. The compatibility of each compound to be used in combination with B. terrestris is discussed in relation to calculated LC(50) values, routes of uptake and effects.

Regionalization of surface lipids in insects

“…have been found to be very effective in DTT and pyrethrum uptake [41]. Beyond that, diflubenzuron and flufenoxuron, two derivatives of the lipophilic benzoylurea-based chitin synthesis inhibitors, pass through the bumblebee (Bombus terrestris) cuticle with different efficiencies [42]. Taking these arguments together, knowledge about the preferred region of cuticle penetration and identification of the respective CHCs may help to optimize the impact of an insecticide by chemical modifications.…”

Plasticity in the gut microbial community and uptake of Enterobacteriaceae (Gammaproteobacteria) in Bombus terrestris bumblebees’ nests when reared indoors and moved to an outdoor environment

“…Coop. Apihurdes, Pinofranqueado-Caceres, Spain) as energy and protein sources, respectively (Mommaerts et al 2006). For the six bumblebee nests, we labeled the queen and then also each newborn worker adult on a daily basis with a unique marking disc (Bijenhof, Bissegem, Belgium) to the dorsal thorax.…”

Bumblebees can be used in combination with juvenile hormone analogues and ecdysone agonists

“…After 1 week, the dominant worker started to produce eggs that develop into males. The nests were kept under standardized laboratory conditions in the dark at 28 ± 2°C and 60 ± 10% RH, and commercial pollen and sugar water were provided as food (Mommaerts et al 2006). …”