Attractants are widely used in lures for pest control and the attraction of small hive beetles to honeybee colonies, particularly after they have been opened by beekeepers (Delaplane, 1998), suggests that a lure may be successful. Such a lure could be used in association with a trap or chemical control method in a similar way to control methods for the related Carpophilus species (sap beetles) (James et al., 1996). Such lures may be based on the beetles own pheromones, in a similar way to the use of aggregation pheromones in Carpophilus species, or using food associated volatiles which attract the beetles (James et al., 1996).
Volatiles from Aethina tumida
The ISI web of science and Edina BIOSIS were both searched using the following search parameters: (AETHINA TUMIDA OR SMALL HIVE BEETLE) AND (ATTRACT* OR BAIT OR LURE OR ODO*R OR PHEROMON* OR SEMIOCHEMI* OR BEHAVIO*R OR DETECT* OR TRAP*)
No information on any pheromone(s) released by the SHB or any artificial synthetic chemical attractant developed for the SHB to date was found in the literature. Only one relevant article was found regarding the attraction of SHB (Elzen et al., 1999). In a laboratory bioassay, a combination of honey, pollen, and adult bee volatiles was very attractive to the SHB. However, volatiles from honey plus pollen elicited no response from the SHB, whilst volatiles from adult bees alone were found to be only slightly attractive. Honey and pollen were not tested separately, and therefore it is not known whether the attractive volatile component(s) are from honey or pollen or both. The observation of attraction is encouraging because it suggests that a lure for this beetle could be developed however, no specific chemical attractants were identified. This approach has been used as part of a physical control measure in the USA (see the section on in-hive physical control measures). However, the persistence of this as an attractant, i.e. the practical life of the lure, is questionable and a pheromone based lure is a more practicable option.
Volatiles from Nitidulid beetles other than A. tumida
As no specific chemicals were identified as being attractants for the SHB the Edina BIOSIS was searched for attractants of Nitidulid beetles other than A. .tumida using the following search parameters:
(NITIDULID*) AND (ATTRACT)
Many species of Nitidulid beetles are attracted to volatiles produced by yeasts, fungi, and fruit volatiles that are also present in honey, especially ethanol. The sap beetle, Carpophilus humeralis, is attracted to ethanol, 2-methylpropanol and 3-methylbutanol produced by the fungus Fusarium verticilloides (Bartelt and Wiklow, 1999). These volatiles are also found commonly in honey (Perez et al., 2002). In other work, the same species was attracted to ethanol and 3-hydroxy-2-butanone. These volatiles are produced by yeasts grown on sweetcorn and are also present in honey (Nout and Bartelt, 1998).
An article on the synthesis of one Nitidulid beetle pheromone was found, that of the dried fruit beetle, Carpophilus hemipterus (L.) (Bartelt et al., 1990). The pheromone components were different branched tetraenes, including: (2E,4E,6E,8E)-3,5,7-trimethyl-2,4,6-decatetraene. These reports of food volatiles and pheromones of other Nitidulid species are encouraging as it suggests testing the former against the SHB may prove successful since they are unlikely to be species specific.
Volatiles from honey, pollen and adult honeybees (Apis mellifera)
An additional search was conducted into honey volatiles using ISI web of science and Edina BIOSIS using the following keywords:
Volatiles from honey
(HONEY) AND (VOLATIL*)
Several of the articles described the analysis of honey volatiles by Gas Chromatography-Mass Spectrometry (GC-MS) and its use in the characterisation of honeys of different floral origin and also in authenticity. The aroma profiles of honeys can vary widely depending on their floral origin. Five Spanish honeys (orange, eucalyptus, rosemary, lavender, and thyme) were analysed by SPME-GC-MS and found widely varying aroma profiles (Perez et al., 2002). However, several volatiles were common to all five honeys: ethanol, acetone, dimethylsulphide, acetic acid, 1-hydroxy-2-propanone, 3-hydroxy-2-butanone, 2,3-butandiol, furfural, benzaldehyde, benzene acetaldehyde, and 2-phenyl ethanol. These volatiles would be worth testing as attractants for the SHB.
(POLLEN) AND (VOLATIL*)
No specific pollen volatiles were identified in any of the 72 articles from the literature search. All of the volatiles identified in these articles were released by the flowers themselves and not by the pollen.
Volatiles from honeybees
A search of volatiles produced by honeybees was conducted using ISI web of science:
(HONEYBEE*) AND (VOLATIL*)
A total of 42 articles were found, of which the following two were of particular interest.
(I) Nasanov secretion:
Cassier and Lensky (1994) studied the attraction of pheromones secreted by worker honeybees to other honeybees. These pheromones are produced in the abdominal scent (Nasanov) gland of worker bees, which the drones and the queen do not possess. The pheromone secretion is composed of several terpene compounds: geraniol, nerolic acid, geranic acid, E-2-citral, (Z)-citral, (E,E)-farnesol, and nerol. The most abundant compound in the Nasanov secretion is geraniol. Geranic acid and a racemic mixture of trans (E) and cis (Z) isomers of citral are both commercially available and genaric acid and (E)-citral are thought to be the attractive components for bees based on their antennal responses and effects in the field and laboratory (Winston, 1987). Nasanov pheromones are used by bees in orientation and particularly in entrance finding following disturbance of the colony (Winston, 1987), which may be a cue for the SHB when colonies are disturbed during beekeeping activities (Delaplane, 1998). However, the Nasanov pheromone is also used by bees to indicate water sources (due to the relative lack of odour of the resource) and artificial food sources and therefore any trap using these lures must exclude bees that may also be attracted.
(II) Sting pheromones:
The sting alarm pheromone is released by worker bees and recruits other workers to attract any intruder and consists of iso-pentyl acetate (IPA) as the most abundant active compound (Grandperrin, 1983). Seven other chemicals were also isolated from worker bee sting secretion: n-butyl acetate, isoamyl alcohol, n-hexyl acetate, 2-nonanol, n-decyl acetate, benzyl acetate, and benzyl alcohol. It is less likely that the SHB would be attracted by sting pheromone.
Queen female sex pheromone:
A. mellifera queens produce two pheromone components: 9-oxo-(E)-2-decenoic acid (9-ODA) which was discovered by Gary (1962), and 9-hydroxy-(E)-2-decenoic acid (9-HDA) by Callow et al. (1964). As these pheromones are only released by the queen and not by worker bees neither of these two pheromones is likely to be responsible for the attraction of A. tumida found in the study by Elzen et al. (1999). Similarly, the sting pheromone should only be released by bees if they are disturbed, so this is unlikely to be responsible for the attraction of the SHB to bees. Thus of the pheromones listed above the Nasanov secreted materials are the most likely to be the attractive volatiles released by the adult worker bees in the study by Elzen et al. (1999).
Other bee pheromones
The attraction of the SHB to honeybee colonies may also be due to other pheromones produced by brood although these have not been completely identified (Winston 1987). The work of Elzen et al. (1999) showed that adult beetles were not attracted to uninfested comb, comb, pollen and honey, brood or infested comb (whereas they were attacted to honey, pollen and adult bees and to adult bees alone) suggesting there were no pheromones attracting the beetles to colonies in the absence of adult bees. However, there is conflicting information from South Africa that the brood is highly attractive to adult SHB (Mike Allsopp, pers.comm.) which suggests it may be worth further investigation.