Randy wrote:
> The subspecies was likely "preadapted" before the mite arrived (not my idea or term, but can't remember the source).
Peter:
* Going back to the facts: Why do African bees seem to be able to resist mites?
> In Apis cerana (the original host of Varroa), mite reproduction occurs only in the small number of sealed male (drone) honeybee brood cells. Consequently, mite populations within an A. cerana colony are low (< 800) and no adverse effects are seen. In A. mellifera EHB colonies, V. destructor also reproduces in the much more numerous worker brood cells, enabling mite populations to increase up to 2000-fold annually, causing colony death within one year. However, mite populations in similar-sized AHB colonies stabilize at 1000–3000 mites per colony, allowing colonies to survive indefinitely, although the resistance mechanism, until now, has remained elusive.
> The short adult longevity of AHB (21 days versus 25–180 days for EHB) as a result of the tropical or sub-tropical climate indicates that more than 12 000 mites are needed to kill an AHB colony. Therefore, although DWV is present in AHB and A. cerana colonies, mite populations stabilize at levels well below that required to kill the colony.
> It is unlikely that AHB evolved Varroa tolerance after the AHB hybrid was created as a result of increased hygienic behaviour or brood attractiveness because such factors are unlikely to lead to a stabilized mite population. Instead, tolerance has probably resulted from pre-existing resistance characteristics fortuitously coming together in the hybrid. That is a high level of mite offspring mortality in worker brood and a short life span in the adult honeybee.
from: "Africanized honeybees have unique tolerance to Varroa mites" by
Stephen J. Martin and Luis M. Medina
* * *
> Africanized honey bee workers have a shorter development period, shorter life span, and start foraging at younger ages than European honey bees. Requirements of cavities for nesting are less stringent in Africanized honey bees. In fact, in contrast with European honey bees, Africanized honey bees frequently construct exposed nests, which are smaller and store a lower amount of honey. Differences in reproductive biology are also striking with swarming rates and extent of drone production considerably larger in Africanized than in European honey bees. In addition to swarming, Africanized honey bees have spread in the neotropics due to absconding. Africanized colonies may promptly abandon their nest when disturbed or when food resources are scarce. Absconding swarms may travel as far as 160 km or more.
from "TEMPORAL GENETIC STRUCTURE OF FERAL HONEY BEES (HYMENOPTERA:
APIDAE) IN A COASTAL PRAIRIE HABITAT OF SOUTHERN TEXAS: IMPACT OF
AFRICANIZATION", A Dissertation by MARIA ALICE DA SILVA PINTO
* * *
> No single factor determines the ability of African bees to displace European bees. The continuity of the African genome in the Americas arises from a complex interaction of population dynamics, genetic phenomena, and physiological and behavioral mechanisms. In this presentation, I focus on four factors that we have studied recently: 1) African-patriline advantages during queen replacement; 2) differential use of African and European sperm by queens; 3) nest usurpation by African swarms; and 4) decreased developmental stability in hybrid workers. Each of these factors may be involved in the asymmetrical gene flow between African and European populations and contribute to the prevalence of African bees in areas that were once dominated by European honeybees.
from "Mechanisms that Favor the Continuity of the African Honeybee
Genome in the Americas" by
Stanley S. Schneider and Gloria DeGrandi-Hoffman
* * *
It is important to realize that animal behaviors may be linked. By
selecting for one trait you may also be inadvertently selecting for
another. For example:
1 AHBs experience rapid colony growth and frequent swarming at small
colony sizes
2 AHBs are less selective in choice of nest sites
3 AHB colonies produce and maintain larger numbers of drones
4 AHBs are better individual foragers than group foragers. This leads
to greater honey production when nectar is in short supply
5 AHBs forage more for pollen
6 AHBs have a greater tendency to swarm
7 AHBs are more tolerant to certain classes of insecticides
8 AHBs forage at an earlier age
9 AHBs show greater responsiveness to alarm pheromone
10 AHBs store less honey
11 AHBs exhibit differences in diet selection
12 AHBs have a lower mean age of worker bee
13 AHBs have shorter worker bee life spans
14 AHBs have smaller colony size
15 AHBs have a greater susceptibility to pollination-management stress
16 AHBs reproduce more frequently and rapidly
17 AHBs have shorter reaction times in response to disturbances
18 AHBs have foraging patterns that are quick and furtive
19 AHBs enter the hive entrance at a greater rate of speed
20 AHBs exhibit shorter visits to food sources
21 AHBs show less persistence to a food patch
22 AHBs initiate faster defensive behavior
23 AHBs exhibit faster initiation of grooming behavior in response to
infestation of Varroa mites
24 AHBs exhibit less hoarding of a sucrose solution
25 AHBs exhibit differential sensitivity to changes in reward frequency
26 AHBs exhibit lower levels of being able to learning a proboscis
conditioning task
from "Behavioral Studies of Learning in the Africanized Honey Bee
(Apis mellifera L.)" by Charles I. Abramson and Italo S. Aquino
* * *
more detailed references available on request. pb
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