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Honeybee workers counterattack their natural enemies using stingers to protect their colony. The stinger is hooked and detaches from the abdomen after the attack, which causes death of the attacker bee. This is a typical altruistic behavior that is performed for their kin at the expense of their own lives, which is characteristic of social animals. We aim to clarify the molecular basis underlying this altruistic attacking behavior.
One of the natural enemies of the honeybee in Japan is the giant hornet. Interestingly, the aggressiveness of the individual worker towards the hornets differs even within the colony. Some of the guard bees (attackers) are the first to counterattack a giant hornet presented as a decoy, whereas some of the in-hive workers (escapers) escape from the hornet. This enables us to collect aggressive and non-aggressive workers separately using the giant hornets as decoys. With the aim of identifying the genes involved in worker aggressiveness, we compared the gene expression patterns in the brains between attackers and escapers. Using differential display and RT-PCR methods, we identified a novel RNA that was specifically detected in the attacker brains, termed Kakugo RNA, which means gready to attack and dieh in Japanese. Sequence analysis and subsequent experiments revealed that Kakugo RNA is the genomic RNA of a novel insect picorna-like virus (Kakugo virus; KV), indicating that the attacker brains were infected with this virus, KV (Fujiyuki et al, 2004).
Our recent epidemiologic analysis revealed that the prevalence of KV differs between colonies. KV was detected only from the attackers in two colonies that were examined at our early research stages, whereas it was detected from various worker populations in three other colonies that were heavily infested with KV. Some of the KV-infected colonies were parasitized by Varroa mites, which are believed to be a vector of various pathogenic bee viruses, suggesting that the mites mediate the prevalence of KV in the honeybee colonies (Fujiyuki et al, 2006). To our knowledge, this is the first report of the prevalence of a virus in honeybee colonies.
The relation between KV infection and honeybee aggressiveness is an interesting subject, which remains to be solved. Because KV was detected specifically in the brains of attackers in our early research, we first speculated that KV infection might relate to the aggressiveness of the guards, i.e., KV infection might promote aggressiveness of the guards or, vice versa, aggressive guards are susceptible to KV infection (Fujiyuki et al, 2004; 2005). As KV infection sometimes prevails over the entire colony, however, it is now important to examine whether KV infection relates to the aggressiveness of various workers at the individual level. As we often experience different levels of aggression among honeybee colonies, we plan to examine the possible correlation between KV infection and aggressiveness of the honeybee colonies as a whole, and to isolate an infectious KV clone to examine whether artificial KV infection promotes worker aggressiveness.
The deformed wing virus (DWV) closely relates to KV. DWV is a pathogenic virus believed to cause wing deformity in honeybees in Europe and the US. Its RNA genome is highly homologous to Kakugo RNA. Phylogenetic analysis of KV genomic RNA revealed that the KV substrains detected in Japan are distinct from any DWV strains detected in other countries, suggesting that KV and DWV are similar but distinct substrains of the same virus with different pathogenecities, and KV is specific to Japan or Asian areas (Fujiyuki et al, 2006). How KV differs from DWV in virologic characteristics requires further research.
Microbe infection sometimes affects animal behaviors, whereas most of them are pathogenic influence. We are interested in the possibility that KV infection causes gphysiologich rather than gpathogenich changes in honeybee behavior, since KV infection might not have been clarified without the molecular biological techniques, and that KV has co-evolved with the honeybee to modify their inherent aggressive behaviors.
(25, Jan, 2007)
| Original papers |
1.Novel insect picorna-like virus identified in the brains of aggressive worker honeybees. Fujyiuki T, Takeuchi H, Ono M, Ohka S, Sasaki T, Nomoto A, and Kubo T (2004) Journal of Virology, 78(3), 1093-1100.Prevalence and phylogeny of Kakugo virus, a novel insect picorna-like virus that infects the honeybee (Apis mellifera L.), under various colony conditions.
Tomoko Fujiyuki, Seii Ohka, Hideaki Takeuchi, Masato Ono, Akio Nomoto, and Takeo Kubo. (2006) J Virol. 80, 11528-11538.
Novel insect picorna-like virus identified in the brains of aggressive worker honeybees.
Fujyiuki T, Takeuchi H, Ono M, Ohka S, Sasaki T, Nomoto A, and Kubo T (2004) J. Virol. 78(3), 1093-1100.
| Review |
Kakugo virus from brains of aggressive worker honeybees.
Tomoko Fujiyuki, Hideaki Takeuchi, Masato Ono, Seii Ohka, Tetsuhiko Sasaki, Akio Nomoto, and Takeo Kubo. (2005) Advances in Virus Research, 65, 1-27.