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Letís talk about top pheromones in insects

Let’s talk about top pheromones in insects. The possible extent to which colony pheromone odour normally has a genetic basis needs reinvestigation. The colonies used should be headed by queens t...

Let’s talk about top pheromones in insects. The possible extent to which colony pheromone odour normally has a genetic basis needs reinvestigation. The colonies used should be headed by queens that have been articially inseminated so all the offspring within a colony are of identical parentage.

If top pheromone odour does prove to be genetically determined individual bees must learn the odours of their half-sisters as well as their own odour shared by their true sisters. Getz and Smith (1983) raised workers of different genetic constitution in the same colony. On emergence they were kept with their full sisters in groups of ten. After ve days, bees within a group were more antagonistic to strangers that were half-sisters than to strangers that were full sisters. It is not clear whether this was because the bees innately responded more favourably to their full sisters’ odour or whether it was because they had become conditioned to its presence on the other nine workers with which they were conned. The former alternative receives support from an experiment by Getz et al. (1982), who found that within a colony workers of different male parentage segregate non-randomly during colony swarming. They suggested that kin recognition could be responsible for this non-random grouping

Bumblebee colonies also have distinctive pheromone odours although no food transfer occurs between individual bees. Anaesthetized workers (Bombus pascuorum and B. lucorum) were attacked when introduced to a strange colony of their own species, but anaesthetized nestmates of the recipient colonies were not. Bumblebee colony odour may be acquired from the nest atmosphere. Individual workers are attacked on return to their own nest after being conned to combs of strong colonies of the same species from which the rightful occupants have been removed, or after being suspended above the combs of strong colonies for one or two hours (Free, 1958). This includes pheromone signals.

There remains the possibility that top-rated pheromone odours are genetically determined. This was discounted by Kalmus and Ribbands (1952) because the split halves of a colony produced by a single queen had separately distinct pheromone scents after a few days. However, it is now known that a queen receives sperm from several males so her workers are genetically heterogeneous and it is unlikely that offspring from different fathers will be evenly distributed in any articial colony division. Breed (1983) has provided strong evidence that recognition can be by genetically determined pheromone odours. Workers produced from the eggs of different queens were reared in the same colony and kept in the same environment for ve days after emergence. When presented to strange bees they were less likely to receive an aggresive reception if they had come from eggs laid in the recipient bees’ own colony. If pheromone odours are (at least in part) genetically determined it would help explain why foragers on return to their hives are accepted as belonging to the colonies concerned, even though each has probably visited only one ower species during its foraging trip and so may be saturated with only onepheromone odour. Indeed, bees that have collected loads of pollen are readily recognized as alien when introduced to the hive entrance of a strange colony (Butler and FreeFree Reprint Articles, 1952).

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Alexander P is a blogger from Los Angeles that studies pheromones.

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