When a honey bee colony that contains Africanized and European worker honey bees is disturbed, which group of workers respond by exhibiting defensive behavior? When honey bees defend their hive they release alarm pheromone which in turn stimulates other bees to defend the nest. If the Africanized workers stimulate their European half-sisters to defend the hive, a colony would not have to be totally Africanized (i.e., an Africanized queen mated to only Africanized drones) to exhibit the colony defense behavior commonly associated with Africanized honey bees (AHB). To answer this question, we established colonies headed by either European or Africanized queen honey bees mated to European and Africanized drones either alone or in combination. We used the Cordovan line of European honey bees so that we could tell our European patriline (i.e., the daughters of the Cordovan drones)from the Africanized (daughters of the Africanized drones) by the color of the workers' cuticle. Cordovan bees have a distinctive light brown color.
After establishing the colonies, we needed a way to quantify
nest defense behavior. This is very difficult if more than one
colony is to be tested for defensive behavior because the
responding bees not only attack the target set out by the
investigator, but the bees attack the investigator as well. With
a cloud of aroused bees following the investigator from colony to
colony, it difficult to determine from which colony the
responding bees originated. To solve this problem, we constructed
a new trap to help quantify nest defense behavior.
The trap is made of 15 inch wide computer paper folded
into the shape of a cone. On one end is an opening that is 1 inch
in diameter. This end fits snugly into a colony whose entrance
has been reduced to an auger hole 1 inch in diameter. The other
end of the cone has a clear plastic bag attached to it to capture
the responding bees. Inside the cone is a small patch of black
velcro attached to an elastic string that serves as a target for
the responding bees.
We quantified nest defense behavior by first placing a cone
trap without the black velcro patch in the colony entrance for 30
seconds. Next, we inserted a long plastic tube
into the colony entrance, and exhaled into it three times.
Human breath serves as an excellent stimulus to
provoke defensive behavior in honey bees. We removed the tube and
immediately placed the cone trap with the velcro patch in the
colony entrance. After 30 seconds, we removed the
cone trap and placed corks into the entrances of the colony and
the trap.
The sample of bees was placed into an
ice chest, and the remaining colonies were sampled using the same
procedure. All samples were frozen, and the bees were later
identified as having either European or Africanized patrilines
depending upon the color of their cuticle.
The most defensive colonies in our experiment were those where the queen was mated to only Africanized drones. This occurred whether the queen was European or Africanized. Colonies with European or Africanized queens that were mated to both European and Africanized drones were equally defensive. In these colonies, >85% of the bees responding to our colony disturbance had Africanized patrilines. Colonies where Africanized queens were mated to European drones were the least defensive hives. These results indicate that the proportion of Africanized drones that mate with either Africanized or European queens will largely determine the defensive behavior of a colony. Our results also suggest that queen type has a limited effect on colony defensive behavior which appears to be influenced more by drone type. Consequently, introducing a virgin European queen to reduce defensive behavior might not be effective if she can mate with Africanized drones.