Patti J. Elzen

Social encapsulation of beetle parasites by Cape honeybee colonies (Apis mellifera capensis Esch.)

Worker honeybees (Apis mellifera capensis) encapsulate the small hive beetle (Aethina tumida), a nest parasite, in propolis (tree resin collected by the bees). The encapsulation process lasts 1–4 days and the bees have a sophisticated guarding strategy for limiting the escape of beetles during encapsulation. Some encapsulated beetles died (4.9%) and a few escaped (1.6%). Encapsulation has probably evolved because the small hive beetle cannot easily be killed by the bees due to its hard exoskeleton and defensive behaviour.

Association of novel mutations in a sodium channel gene with fluvalinate resistance in the mite, Varroa destructor

SUMMARY Varroa (Varroa destructor) has recently become resistant to Apistan, a pyrethroid pesticide with tau-fluvalinate as its active ingredient. In many insect pests, resistance to pyrethroid insecticides is due to reduced target-site (sodium channel) sensitivity to pyrethroids in the nervous system, a phenomenon called knockdown resistance (kdr). A number of studies showed that kdr and kdr-type resistance is a result of point mutations in the para family of sodium channel genes. To investigate the molecular mechanism of resistance to fluvalinate in varroa, we have cloned and sequenced a large cDNA fragment corresponding to segment 3 of domain II (IIS3) to segment 6 of domain IV (IVS6) of a para-homologous sodium channel gene (VmNa) from susceptible and resistant mite populations. The deduced amino acid sequence from this cDNA shares 71%, 60%, and 50% identity with the corresponding region of the para-homologous protein of the Southern cattle tick, Boophilus microplus, Drosophila melanogaster Para, and rat brain type II sodium channel α-subunit, respectively. Sequence analysis revealed that four amino acid changes, F758L in IIIS6, L826P in the linker connecting domains III and IV, I982V in IVS5 and M1055I in IVS6, were correlated with fluvalinate resistance in both Florida and Michigan populations. Interestingly, the kdr or super-kdr (which confers much higher level resistance than kdr) mutation previously identified in insects was not detected in the resistant mites. These results support the emerging notion that distinct sodium channel gene mutations are selected in different insects and arachnids in response to pyrethroid selection.

Behaviour of African and European Subspecies of Apis Mellifera Toward the Small Hive Beetle, Aethina Tumida

SHB. We previously demonstrated that adult SHB will feed on European honey bee eggs in a laboratory setting, even in the presence of excess honey and pollen (Elzen et al., 1999). Five 0.473-litre jars were established with five adult beetles, a known number of Cape honey bee eggs in uncapped comb, and excess honey and pollen. Five control jars consisted of a known number of eggs in comb and excess honey and pollen (no beetles added). All 10 jars were held 24 h at 32°C and the number of eggs remaining were counted. Results showed overall, within 24 h the SHB ate 94% of the Cape honey bee eggs.

Effects of Soil Type, Moisture, and Density on Pupation Success of Aethina tumida (Coleoptera: Nitidulidae)

Abstract We tested the effects of different soils (soils A–F) representing four soil types, two moisture extremes (wet and dry), and two soil densities (packed and tilled) on the number of emerging Aethina tumida Murray (Coleoptera: Nitidulidae) adults. We further determined the effect of soil type and A. tumida sex on the time spent in the soil (where the beetle pupates). Three thousand A. tumida larvae were placed in the moist soil treatments (wet/packed and wet/tilled), of which 2,746 emerged from the soil as adults. Additionally, 3,000 larvae were placed in the dry soil treatments (dry/packed and dry/tilled), of which none emerged as adults. In only one soil were emersion rates different from those in other soils. For every soil, there were significantly more emerging A. tumida in the wet treatments than in the dry ones. Female A. tumida spent less time in the soil than male A. tumida but only by an average of less than half a day. Soil type did affect the length of time A. tumida spent as pupae, despite which average emersion as adults occurred within a tight range. The data suggest that biological requirements of A. tumida may limit/enhance their reproductive potential in various soil environments (especially in dry climates).

Small hive beetles survive in honeybee prisons by behavioural mimicry

Abstract. We report the results of a simple experiment to determine whether honeybees feed their small hive beetle nest parasites. Honeybees incarcerate the beetles in cells constructed of plant resins and continually guard them. The longevity of incarcerated beetles greatly exceeds their metabolic reserves. We show that survival of small hive beetles derives from behavioural mimicry by which the beetles induce the bees to feed them trophallactically. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at htpp://dx.doi.org/10.1007/s00114-002-0326-y.

Laboratory rearing of small hive beetles Aethina tumida (Coleoptera, Nitidulidae)

The small hive beetle (Aethina tumida, SHB) is a common honey bee (Apis mellifera) parasite in Africa that causes little damage to strong colonies (Lundie, 1940). However, it is a serious threat in the Western Hemisphere where the beetle has been introduced recently (Elzen et al., 1999) and where host colonies lack the behavioural resistance mechanisms of African honey bees (Neumann et al., 2001). Captive breeding of this parasite is an important research technique to produce SHB under controlled conditions for experiments. Here we report on a simple technique for rearing SHB in the laboratory.

Social encapsulation of the small hive beetle (Aethina tumida Murray) by European honeybees (Apis mellifera L.)

SummaryEuropean and African subspecies of honeybees (Apis mellifera L.) utilize social encapsulation to contain the small hive beetle (Aethina tumida Murray), a honeybee colony scavenger. Using social encapsulation, African honeybees successfully limit beetle reproduction that can devastate host colonies. In sharp contrast, European honeybees often fail to contain beetles, possibly because their social encapsulation skills may be less developed than those of African honeybees. In this study, we quantify beetle and European honeybee behaviours associated with social encapsulation, describe colony and time (morning and evening) differences in these behaviours (to identify possible circadian rhythms), and detail intra-colonial, encapsulated beetle distributions. The data help explain the susceptibility of European honeybees to depredation by small hive beetles. There were significant colony differences in a number of social encapsulation behaviours (the number of beetle prisons and beetles per prison, and the proportion of prison guard bees biting at encapsulated beetles) suggesting that successful encapsulation of beetles by European bees varies between colonies. We also found evidence for the existence of circadian rhythms in small hive beetles, as they were more active in the evening rather than morning. In response to increased beetle activity during the evening, there was an increase in the number of prison guard bees during evening. Additionally, the bees successfully kept most (~93%) beetles out of the combs at all times, suggesting that social encapsulation by European honeybees is sufficient to control small populations of beetles (as seen in this study) but may ultimately fail if beetle populations are high.

Oviposition by small hive beetles elicits hygienic responses from Cape honeybees

Two novel behaviours, both adaptations of small hive beetles (Aethina tumida Murray) and Cape honeybees (Apis mellifera capensis Esch.), are described. Beetles puncture the sides of empty cells and oviposit under the pupae in adjoining cells. However, bees detect this ruse and remove infested brood (hygienic behaviour), even under such well-disguised conditions. Indeed, bees removed 91% of treatment brood (brood cells with punctured walls caused by beetles) but only 2% of control brood (brood not exposed to beetles). Only 91% of treatment brood actually contained beetle eggs; the data therefore suggest that bees remove only that brood containing beetle eggs and leave uninfected brood alone, even if beetles have accessed (but not oviposited on) the brood. Although this unique oviposition strategy by beetles appears both elusive and adaptive, Cape honeybees are able to detect and remove virtually all of the infested brood.

Hygienic Behavior of Cape and European Apis mellifera (Hymenoptera: Apidae) toward Aethina tumida (Coleoptera: Nitidulidae) Eggs Oviposited in Sealed Bee Brood

Abstract In this study, we tested for the presence and efficacy of hygienic behavior by Cape honey bees in South Africa and European honey bees, Apis mellifera L. (Hymenoptera: Apidae), of mixed origin in the United States toward Aethina tumida Murray (Coleoptera: Nitidulidae) eggs oviposited in sealed bee brood. We looked for colony differences in removal rates of brood in cells with cappings perforated by A. tumida within each subspecies to identify colonies within location that display superior hygienic behavior. Finally, we determined the oviposition rate (number of A. tumida-perforated cells actually oviposited in by A. tumida/total number of A. tumida-perforated cells) in A. tumida-perforated cells and the number of A. tumida eggs oviposited in each cell. There were no colony differences within subspecies for the removal of normal capped brood, artificially perforated brood (capped cells perforated by experimenter with a pin), and A. tumida-perforated brood. For both subspecies, the bees removed significantly more A. tumida-perforated brood than either normal or artificially perforated brood. A. tumida oviposited significantly more eggs per cell in Cape colonies than in European colonies, but the oviposition rate in A. tumida-perforated cells did not differ between Cape and European colonies. Both subspecies removed a proportion of A. tumida-perforated brood statistically indistinguishable from the proportion of A. tumida-perforated brood containing A. tumida eggs. Thus, both Cape and European A. mellifera preferentially remove the contents of A. tumida-perforated cells in which A. tumida have actually oviposited.

Infectivity of entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) against the small hive beetle Aethina tumida (Coleoptera: Nitidulidae).

Small hive beetles (SHB), Aethina tumida Murray, are nest invaders of honey bees, Apis mellifera L., and have become a global threat to apiculture and wild bee populations (Neumann & Elzen, 2004). Entomopathogenic nematodes (EPN) possess high virulence against target insect pests, yet pose no threat to crops, wildlife, or humans. Currently there is no information on the efficacy of EPN against the SHB. Although honey bee colonies are not affected by EPN (Georgis et al., 1991; Baur et al., 19950), EPN can control similar beetles (Vega et al., 1994). Since A. tumida is most vulnerable when the larvae leave the hive to pupate in the soil, our objective was to determine the susceptibility of the SHB wandering larvae to three commercially available EPN. Heterorhabditis megidis (‘HO 1’ strain) and Steinernema carpocapsae (‘All’ strain) were obtained from ARBICO Environmentals (Tucson, Arizona), and S. riobrave (Texas strain) was obtained from our laboratory (Weslaco, TX). Wandering larvae and soil were collected from beehives heavily infested with this beetle at Tony York’s bee yard in Port St. Lucie, Florida in August 1998. The experiment was performed at Ft. Pierce, Florida. Nematodes, stored for one wk (10° C) with 100% viability, were applied to a St. Lucie, Florida sandy soil type at four nematode concentrations (0, 50, 100, 200 infective juveniles [Ijs] per insect). Control insects were treated with water only. Nematodes were sprayed with a hand sprayer in 5 ml sterile distilled water suspension on the soil surface of each dish (100 x 15 mm) containing fifty grams of autoclaved soil (20% soil moisture). Seven larvae were placed in each of five replicate dishes (100 x 15 mm) for each of the four treatments and incubated in the dark at 25° C, 59% RH. Insect mortality was recorded daily for 5 consecutive days and dead insects dissected to examine nematode presence. Mortality data were analyzed by the SAS PROBIT procedure (SAS Institute, 1994). Lethal concentrations required to kill 50% of the insects (LC50) were calculated and estimated the 95% fiducial limits (FL) for the LC50. Infectivity tests indicated that SHB larvae were susceptible to these nematodes (Fig. 1). Although the LC50 was lower for S. riobrave (157 IJs; 95% FL = 120-231) than those for H. megidis (164 IJs; 95% FL = 124-262) and S. carpocapsae (204 IJs; 95% FL = 150-504), their fiducial limits showed no significant difference from each other in virulence. No mortality occurred in the controls. This paper presents the first data on the susceptibility of the SHB to EPN. Comparing the LC50 (157-204 IJs) for the SHB to other examples, it is similar to the S. riobrave LC50 (200 and 400 IJs per larvae) that caused 80 to 88% mortality in the driedfruit beetle (Vega, 1994), lower than S. carpocapsae strain All (4000 IJs) for S. frugiperda (Landazabal et al., 1981), but higher than S. riobrave (12 IJ) for boll weevil (BW) pupae (Cabanillas, 2003). There are limits to these comparisons; for example, the BW study used filter paper substrate while the present study used sand. Differences may also suggest a higher susceptibility in the sedentary stage of BW pupae, an easier target for nematode infection, than the active stage of SHB wandering larvae. It suggests that EPN may cause greater mortality in SHB if targeted to the pupal stage than prepupal stage, especially at times of year when beetles spend 15 to 60 days in the soil before adult emergence. Thus, insect mortality in our results could be higher by targeting the sedentary stage and allowing more than five days to evaluate nematode infectivity against the SHB. In conclusion, these results are significant because they show that EPN are infectious against the A. tumida prepupal stage, and until now neither parasites nor pathogens have been found against the small hive beetle (Neumann and Elzen, 2004). The utilization of EPN against A. tumida could affect SHB populations before adult emergence. Further research is necessary to use EPN more effectively against the small hive beetle. This information is novel and useful and may provide a foundation for building an integrated control program for the beetle. N OT E S A N D C O M M E N T S