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

Abstract

This study examined the lethal and sublethal effects on the beneficial insect Bombus terrestris by two classes of insect growth regulators (IGRs) that are commercially used in agriculture to control pest insects. Three juvenile hormones analogues (JHAs) (pyriproxyfen, fenoxycarb and kinoprene) and two ecdysone agonists or moulting accelerating compounds (MACs) (tebufenozide and methoxyfenozide) were tested. The bumblebee workers were exposed to the insecticides via three different routes of exposure: dermally by topical contact, and orally via the drinking sugar water or the pollen. In the first series of experiments the IGRs were applied at their respective maximum field recommended concentration (MFRC). These risk hazard tests showed that the tested IGRs caused no acute toxicity on the workers, and any compound had an adverse effect on reproduction (production of males). In addition, larval development was followed in the treated nests compared with the controls. After application of the two MACs and the JHA fenoxycarb no adverse effects were observed on larval development. However, in the nests where the workers were exposed to the JHAs pyriproxyfen and kinoprene higher numbers of dead larvae were scored. These larvae were third and fourth instars, implying a lethal blockage of development before metamorphosis. In a second test, a series of dilutions was made for kinoprene, and these results revealed that only the MFRC caused a toxic effect on the larval development. On the other hand, kinoprene at lower concentrations (0.0650 mg ai/l) had a stimulatory effect on brood production. It was remarkable that ovaries of such treated dominant workers were longer and contained more eggs than in the controls. In a last experiment, the cuticular uptake was determined for a JHA and MAC to evaluate to what extent worker bees accumulate these classes of IGRs. Cuticular uptake ranged from 34 to 83% at 24 h after topical application. Overall, the obtained results indicate that the tested IGRs at their recommended concentration are safe to be used in combination with B. terrestris.

Risk assessment for side-effects of neonicotinoids against bumblebees with and without impairing foraging behavior

“…Coop. Apihurdes, Pinofranqueado-Cáceres, Spain) as energy and protein source, respectively, as described by Mommaerts et al (2006).…”

“…The experimental setup consisted of one artificial nest (box A) (Mommaerts et al 2006). In brief, in each nest box a worker became dominant, developed her ovaries and laid eggs within a week, thus playing the role of a queen.…”

“…In the artificial nest boxes, worker survival was evaluated daily for the first 3 days post treatment and then on a weekly basis for a period of 11 weeks. The treatments were scored in accordance with the classification of IOBC (International Organization for Biological Control of Noxious Animals and Plants): 1 = less than 25% effect, non-toxic; 2 = 25-50% effect, weakly toxic; 3 = 50-75% effect, moderately toxic; and 4 = more than 75% effect, highly toxic (Mommaerts et al 2006). Subsequently, the adverse sublethal effects on reproduction were monitored on a weekly basis for 11 weeks by scoring the numbers of drones produced per nest.…”

Ecdysteroid hormone action

“…Ecdysone agonists can even be used if beneficial insects like bumblebees are present simultaneously [123]. The search for suitable new diacylhadrazine derivatives to increase the toxic potential and the selectivity for certain pest organisms important for agriculture gave rise to the development of tests for mass screening [124].…”

“…Consequently, due to this benign pharmacology, ecdysteroids and nonsteroidal agonists are attractive tools for application in medicine [140]. The retinoid X receptoralpha/ecdysone receptor system can also be used in conjunction with other receptors with no detectable overlap of activity, thus enabling concurrent and temporal regulation of multiple genes within the same cell [123]. The receptor proteins showed negligible basal regulation in the absence of ligand [141,142].…”