Treatment of stored comb has been shown to be effective against wax moth (Galleria mellonella and Achroia grisella) by use of delta-endotoxin and spores of Bacillus thuringiensis Berliner var. aizawa, Serotype 7 (Certan). B. t. treatment may also be applicable to control of SHB in stored comb using a similar approach, although the same issue arises as in wax moth control in timing of the treatment to ensure exposure of the susceptible instars.
The only order that may be considered as a possible control system for the SHB in stored comb are the parasitic hymenoptera.
Hymenoptera are commonly used in biological control and include over 125,000 species (Gordh et al., 1999). There are several families which parasitise coleopterans. Among the Parasitica the host spectrum of the Ichneumonoidae is broad with focus on the Holometabola attacking larvae, pupae and immature cocoons. Adults are associated with moist habitats and ground cover. Aulacidae are cosmopolitan, solitary egg-larval endoparasites of wood-boring coleoptera. Chalcididae are parasitoids of coleopterans typically developing as endoparasitoids of the last instar larva and pupa. The Prototrupidae (Serphidae) are solitary or gregarious internal parasitoids of coleoptera. Adults occur in damp concealed habitats under bark and in leaf litter, first instar larvae are quiescent and when the host is ready to pupate the larval parasitoid develops rapidly pupating externally on the host. Bethylidae are primarily external parasitoids of coleopteran larvae with females searching for hosts and stinging them into paralysis when egg laying occurs, the number of eggs laid being related to host size. Although they are not host specific species in certain genera are associated with certain host families.
A parasitic wasp has been reported for the strawberry sap beetle (Weiss and Williams, 1979). The wasp is a species of Microtonus and is the first parasite known to attack the adults of Nitidulidae. The female oviposits on the adult and the larva feeds on the organs of the beetle causing sterility and then death. The parasitic wasp Trichogramma is used in the control of wax moth in stored comb (Clay, 2001).
Physical control methods
There are a number of physical methods that have been trialled for control of SHB. These range from use of chickens (Letter to the American Bee Journal, November 2001), modified hive entrances (Ellis et al., 2002b) and an inside hive trap (Hood, 2001). In addition, there are approaches to control of stored product beetles that may be applicable to stored comb.
The modified entrance (Ellis et al., 2002b) consisted of an approx 2cm PVC pipe entrance 8-10cm above the bottom board of the colony with all other entrances sealed. The modified entrance appeared to reduce the number of adult small hive beetles within the colony but had adverse impacts on brood production, thermoregulation, removal of floor debris and water drainage. Many of these problems are addressed by use of a 3.8cm PVC pipe together with a screened bottom board to increased ventilation (Delaplane and Ellis, 2001).
The inside trap (Hood, 2001) was a 152x80x25 mm plastic box with 2.5mm width vent in the top and was mounted on the bottom bar of a brood frame. The trap was baited with a variety of materials, e.g. beer, mineral oil. The two that resulted in greatest efficacy were apple cider vinegar and mineral oil but the levels of efficacy were not suitable as control methods. If the trap can be designed to exclude bees, more acutely toxic in-hive treatments could be used in combination with the lure or trap to increase efficacy.
An alternative inside trap is described in which a hole is cut in the bottom board of a colony, and a jar, one-third filled with irradiated (to prevent disease spread) honey and pollen, placed so it is held at the neck. The jar is covered by a square of perspex placed on washers and fixed with bolts to the bottom board to give a 3mm gap between the top of the jar and the perspex.
Larvae may be prevented from leaving the colony to pupate, although the colony damage will continue to occur as long as the adults are present laying eggs. SHB adults are not deterred by standard insect barrier glues, e.g. Tanglefoot (Frazier and Steinhauer, 2000) but, apparently untested, the larvae may be more sensitive. An alternative is similar to an approach used in South Africa to reduce ant damage. The legs of the hive are kept in oil reservoirs to prevent insects crawling into the colony. Again this approach would prevent larvae leaving the colony but adult SHB are likely to fly to the entrance and therefore would not be deterred.
Outside the hive
Apart from the use of chickens to control larvae and pupae in soil around the apiary (Letter to ABJ, 2001) traps have been developed to detect and control SHB within apiaries (Elzen et al., 1999). Honey buckets (7.6 litre) with lids and four 7cm diameter holes in the sides covered with mesh of a size to allow SHB entry but exclude bees can be used. As beetles are approx 3.2+0.01 mm in width a mesh size of 3mm will exclude honeybees but allow SHBs entry (Ellis et al., 2002a). A combination of live adult honeybees, pollen and honey was reported to be most attractive to SHBs (Elzen et al., 1999).
For stored combs there are three possible methods of non-chemical control – freezing, irradiation and diatomaceous earth.
Freezing for 24-48hrs (-20oC) may offer an option for stored comb which will destroy hatched SHB larvae and eggs (Frazier and Steinhauer, 2000). This is a technique frequently used in wax moth control but should be monitored carefully to ensure reinfestation does not occur.
The effects of irradiation on species of Carpophilus have been investigated (Brower et al., 1973). Irradiation of eggs and larvae with 5,000 rad (50 grays) prevented development of adults. Some adults emerged from pupae irradiated with up to 100,000 rad (1000 grays) but their longevity was reduced.
Diatomaceous earth is used in stored grain for control of mites and beetles and may be a suitable control method in stored comb (www.diatomaceousearth.co.uk) (Lord, 2001; Cook and Armitage, 2000). It is the fossil remains of diatoms (algae) which are amorphous (non-crystalline) silica. It kills and repels insects by dehydrating them, making it unsuitable for use within honeybee colonies. The sharp edges of the diatoms are drawn to the insect by static electricity, puncture the cuticle and the insect dehydrates and dies. If consumed by the insect the silica interferes with digestion and reproduction. Although this appears an attractive route for control of beetles in honey-houses the safety of treated combs returned to the hive requires investigation as it may have deleterious effects on adult bees or brood.