Joint actions of deltamethrin and azole fungicides on honey bee thermoregulation Re ´my Vandame, Luc P. Belzunces* INRA, Phytopharmacie, Unite ´ de Toxicologie, Site Agroparc, 84914 Avignon Cedex 9, France Received 28 January 1998; received in revised form 11 June 1998; accepted 12 June 1998 Abstract The effects of sublethal doses of deltamethrin, a pyrethroid insecticide, and prochloraz and difenoconazole, two azole fungi- cides, on honey bee thermoregulation were investigated by infrared thermography of honey bees kept at 22°C. Deltamethrin at doses of 0.5 and 1.5 ng/bee did not elicit any significant effect on bee thermogenesis whereas doses of 2.5 and 4.5 ng / bee caused a severe hypothermia. Similarly, prochloraz and difenoconazole did not elicit any significant effect on thermogenesis at doses of up to 850 ng / bee whereas they triggered hypothermia at 1250 ng / bee. When associated with prochloraz or difenoco- nazole at 850 ng / bee, deltamethrin elicited a joint hypothermia at doses that did not induce a significant effect on thermoregula- tion when used alone.  1998 Elsevier Science Ireland Ltd. All rights reserved Keywords: Thermoregulation; Pyrethroid insecticide; Azole fungicide; Insect; Synergy; Apis mellifera The honey bee Apis mellifera is now widely recognized as a beneficial arthropod of agronomical, ecological and scientific importance. Its thermogenesis is essentially due to tetanic contractions of indirect flight muscles achieved by a discreet movement of the scutelum that prevents the stretch activation of flight muscles. The increase of thoracic temperature is always associated with muscular contraction and action potentials, and all action potentials trigger mus- cle contractions [7]. Deltamethrin is a type II pyrethroid insecticide that affects nerve transmission. Its primary target is the vol- tage-dependent sodium channel [17]. Azole fungicides, such as triazoles and imidazoles, are molecules that inhibit ergosterol biosynthesis by preventing the cytochrome P- 450-dependent 14a-demethylation of lanosterol. They can also inhibit the cytochrome P-450-dependent metabolism of both endogenous and exogenous compounds [16]. In the honey bee, very low sublethal doses of pyrethroids alter systems controlled either by an aminergic pathway, such as glycemia, or by both aminergic and cholinergic pathways, such as memory [4,10,11]. Thus, considering that an aminergic pathway is involved in honey bee thermo- genesis, the pyrethroids are representative of products that could potentially alter thermoregulation [2]. The possible effects on honey bee thermoregulation was studied with sublethal doses of deltamethrin that do not alter flight mus- cle activity [19]. Deltamethrin was applied either alone or in association with sublethal doses of prochloraz and difeno- conazole, two azole fungicides known to act in synergy with pyrethroids [5]. In our study, the body temperature of honey bees has been analyzed by infrared thermography [2]. Honey bee foragers (Apis mellifera) were placed in obser- vation boxes (10 per box) and were left to recover for 24 h at 28°C and at 65% relative humidity, and with 50% (w/v) sucrose solution ad lib. They were treated by a calibrated spraying [19] and kept at 22°C, with 50% sucrose solution ad lib, for thermographic analysis [2]. The thermographic measurements were achieved with an Inframetrics camera Model 760-LW/BB with a resolution of 0.04°C. The abso- lute thoracic surface temperature was calculated using an emissivity of 0.97 [18]. The accuracy was 0.3°C for relative measurements and 0.7°C for absolute measurements. Ther- mographic images were analyzed using image analysis soft- ware. For each image, the warmest point was used as an indication of the external temperature. Values at 4 h were Neuroscience Letters 251 (1998) 57–60 0304-3940/98/$19.00  1998 Elsevier Science Ireland Ltd. All rights reserved PII S0304-3940(98)00494-7 * Corresponding author. Tel.: +33 490316057; fax: +33 490896905; e-mail: belzunce@avignon.inra.fr