The small hive beetle (SHB) is closely related to a common pest species of fruit - Carpophilus sp. - and a number of chemical control methods have been developed in both fruit growing and storage situations. Many of these methods use highly toxic insecticides, e.g. carbamate insecticides (Harrison and Richardson, 1979) that are likely to adversely impact honeybee colonies and therefore cannot be considered for use as in-hive SHB control methods. The major problem with treatments within the hive is the need to ensure exposure, and thus control, of all life-stages of the beetle. Thus powder or liquid formulations are more likely to be effective against all life stages of the SHB than strip formulations as they are more widely distributed around the hive, e.g. into honey and over comb surfaces, by the bees. However, the greater distribution around the colony also raises issues of residues in honey.
There are a number of chemicals used for varroa control within colonies that could be screened for activity against the small hive beetle. Coumaphos is a varroacide currently also used as a treatment for the SHB in the USA (Elzen et al., 1999). Strips are stapled to the underside of pieces of corrugated card that are placed on the floor of the colony so that the beetles are attracted to the gaps underneath and thus are exposed to the chemical. Elzen et al. (1999) investigated the effectiveness of coumaphos treatment in infested colonies. After 24 hours treatment 60-77% of adult and larvae beetles present on the bottom boards were killed with total of 85-90% adult beetles and 94% larvae killed over a 48-hour treatment period. It was noted that the smaller larvae were not killed as they remained on the combs and therefore were not exposed to the treatment. The quoted efficacy is likely to be over-estimated as assessments were only made of the numbers of adult beetles and larvae present on the bottom board rather than throughout the colony, i.e. larvae within combs were not exposed to the treatment and were not included in the assessment. In the UK the only two varroacides currently registered are pyrethroids and, although they have good efficacy against SHB in the laboratory, no control was observed in colonies containing impregnated plastic strips (Elzen et al., 1999). Higher doses or alternative treatment methods may increase the efficacy of pyrethroids in colonies, but due care should be taken to establish a safety factor for honeybees. Amitraz is used in some areas of Europe but has acaricidal rather than insecticidal activity and there are no reports of its effectiveness in control of the SHB.
Other pesticides may be suitable if they have specificity against coleopteran pests, e.g. ecdysone agonists. These compounds bind to the receptor site of the insect moulting hormone ecdysone lethally accelerating moulting, decreasing feeding and growth, reducing fecundity of treated adults and also have ovicidal properties (BCPC, 2001; Smagge and Degheele, 1994; Darvas et al., 1992). As ecdysteroids vary in structure across insect species (de Fur et al., 1999) ecdysone agonists may offer species selectivity between the SHB and honeybees. There are four diacylhydrazine (nonsteroidal) ecdysone agonists, which have been developed as pesticides methoxyfenozide, chromafenozide, tebufenozide and halofenozide. Of these only halofenozide is active against coleopteran pests (BCPC, 2001). Further evaluation of this approach would require studies on the toxic effects in both adult and larval stages of SHB and honeybees to determine the safety factor. The toxicity of halofenozide to adult honeybees is reported to be low (greater than 100 μg/bee by contact) but data are not available for the, more sensitive, honeybee larval stages. In addition there are wide species differences in sensitivity reported amongst coleopterans. Cowles et al. (1999) showed that, for halofenozide, Asiatic garden beetles (Maladera castanea) were insensitive and the European chafer (Rhizotrogus majalis) was less sensitive than Japanese beetles (Popillia japonica) or oriental beetles (Exomala orientalis). The stage of development and physiological condition of coleopteran larvae also affect sensitivity with first and second instar larvae more susceptible to halofenozide than third instars (Cowles and Villani, 1996). The only ecdysone agonist currently registered as a pesticide in the UK is methoxyfenozide (lepidopteran specific). The costs of evaluating efficacy and generating the required safety data for control of SHB solely for registration as a veterinary medicine may be prohibitive in the absence of support from the agrochemical industry.
There are a wide range of soil treatments/sterilants which could be used to control the pupating SHB larvae or emerging beetle. Permethrin is used in the USA as a drench to treat the soil around affected colonies (Y-Tex Gardstar 40% Livestock and Premise Insecticide (Frazier and Steinhauer, 2000)). A survey of the pesticides currently registered for use in the UK as soil treatments showed a range of compounds which are applied as spray applications, granules or drenches and have potential for control of SHB in soil due to their insecticidal activity. Granules and sprays may require specialist equipment for applications and therefore the most readily usable treatments would be drenches. The two insecticides which could be most readily used as soil drenches around apiary sites are chlorpyrifos and permethrin. This would require approval from the PSD to ensure that “off-label approval” would be granted for this use. The only approved use of permethrin as a drench (Permethrin 12ED (12% nominal ai)) has been withdrawn and use is not permitted after December 2003.
Combs during storage
The suitability of chemicals for treatment of combs during storage, e.g. after honey extraction, depends on not only the efficacy against the SHB but also any effects on bees on the return of the combs to the hive. Effects may be toxicity related due to residues remaining on the comb (which may affect adults and/or brood) or repellency, with bees absconding from the hive in which the combs are placed. Therefore many of the issues pertaining to in-hive use are also relevant for use on stored comb. A range of household products have been tested for use in control of the small hive beetle in honey houses and the safety assessed on reintroduction of the combs into colonies (Park et al., 2002). The most promising of these in terms of effectiveness in controlling small hive beetle larvae, killing 100% within 4 hours, and the acceptance of the combs on return to the colony (with a delay after treatment of 24 hours) was household bleach. As use of these chemicals relates to control of pests they should be registered as pesticides before their use is recommended.