The results of the literature searching undertaken here provided little direct evidence for precedents on which to base the development of a lure for A. tumida. It might be worth testing the attraction of SHB to volatiles identified from yeasts, fungi, fruit and honey and the components of the honeybee Nasanov secretion. However, the likelihood of success is limited. Greater chances of success should come by more detailed study of A. tumida itself. The work of Elzen et al. (1999) suggests that some kind of advantageous behavioural modification may be possible by using a mixture of volatiles obtained from honey, pollen and adult honeybees in combination. First, this finding needs to be confirmed under UK conditions and with sufficient replication to be convincing. Since the practicality of obtaining this mixture of volatiles from their natural origins would be both costly and of variable quality, the next step would be to identify, obtain and test those individual components in the mixture which are together responsible for the observed attraction. To do this, the volatile components of honey, pollen and adult bees could be isolated by Solid-Phase Microextraction (SPME) separated from each other by gas chromatography. Since it appears that A. tumida is attracted only to blends of volatiles rather than individual components, each volatile should then be analysed by electroantennography to identify those which elicit an electrical response in A. tumida. These volatiles would then be subjected to behavioural bioassay to identify those which are attractive to A. tumida. The chemical structures of the attractive components could then be identified by Gas Chromatography-Mass Spectrometry (GC-MS). The artificial mixture of volatiles could be formulated for use in an appropriate design of trap.
It would be necessary to ensure that the lure and trap combination did not attract honeybees. This is most easily achieved by using a physical control, by using a design of trap which allowed access to A. tumida whilst preventing the entry of A. mellifera, e.g. a 3mm mesh.
An alternative chemical approach to achieve this selectivity would be to use a semiochemical which is specific for A. tumida. At the time of writing, it is not known whether A. tumida uses or even produces pheromones which could be exploited in this way, although the USDA are pursuing this avenue (Elzen, pers comm.). It is even unclear whether the SHB mates inside or outside the honeybee colony, although it is thought it mates prior to entering the honeybee colony (M. Allsopp, pers. comm.) and the SHB readily mates and breeds under laboratory conditions (Neumann et al., 2002). The first step to establish this would be a detailed study of the key aspects of its behaviour, e.g. whether males produce aggregation pheromones. If this were to give encouraging results, the most pressing need would be to identify the putative pheromones. This would involve isolation of the pheromone(s) by either sweeping headspace above the beetles onto a porous polymer trap or by direct solvent extraction of the beetles, followed by separation and analysis as described above.
The effective use of trap and lure combinations, whether for early detection, monitoring of populations or control purposes, demands that both the lure and the trap are optimised. Development in the laboratory of a lure would therefore have to be followed by the testing of existing designs of trap, or the introduction of a new design if necessary, in combination with the lure. In this way, the chances of successfully interrupting the natural behaviour of A. tumida would be maximised.
Repellency as a control method
An alternative approach to control of SHB is in repelling adults beetles from entering honeybee colonies. It is unclear how effective this may be as 1) the effects on bees should be minimal and 2) the beetles are likely to only be deflected to colonies with a lower level of repellency or to native bee colonies, e.g. bumble bees. Therefore, if a compound with differential repellency to SHB can be identified, it may be more useful in association with other lure based control methods.
A number of essential oils have been identified with repellent properties towards beetles, e.g. grain beetles (Papachristos and Stamopoulos, 2002; ObengOfori, and Reichmuth, 1997). Many essential oils are also toxic and have ovicidal effects, decrease fecundity and increase larval mortality. However, some essential oils have been used as in-hive treatments for varroa (e.g. thymol in Apiguard and a mixture of essential oils in Apilife Var) (Whittington et al., 2000). As essential oils are already used in beekeeping in many countries their effects on infestation of colonies by the SHB could be readily evaluated.
Cinnanamide is a contact repellent for a number of invertebrate, and vertebrate, species (Mossom et al., 1996; Watkins, 1996). However, its effects on honeybees have not yet been evaluated and this would be key to its success in hive protection.
The repellency of neem extracts and azadirachtin have also been evaluated against stored product beetles (Xie et al., 1995). Azadirachtin has been proposed as a novel varroacide by some researchers (Melathopoulos et al., 2000; Whittington et al., 2000), however, work ongoing at the NBU suggests it may have adverse effects on overwintering colonies as it is an ecdysteroid synthesis inhibitor.
An alternative use of repellents is in masking the odours of colonies, e.g. Nasanov pheromone, that attract SHB to colonies. Thus an essential oil aerosol may be effective in masking the colony odour after routine beekeeping inspections. This could be readily evaluated under laboratory conditions.
There are three areas in which control of the small hive beetle may be effective in limiting damage: in-hive control of adult beetles and larvae, soil treatments for the control of pupating larvae and emerging beetles and treatment of combs during storage. This section will describe the use of chemicals, biocontrol methods and physical control methods in each of these areas