http://ucanr.org/repository/CAO/landingpage.cfm?article=ca.v052n02p9&fulltext=yes
peer-reviewed research article
Blessing or curse? Varroa mite impacts Africanized bee spread and beekeeping
authors
Robert E. Page, Department of Entomology
publication information
California Agriculture 52(2):9-13. DOI: 10.3733/ca.v052n02p9. March-April 1998.
abstract
Africanized honey bees were first detected in California in October 1994. Since then, they have established a foothold in the Imperial Valley and have spread toward San Diego and into Palm Springs. However, their spread has been much slower than originally expected. What has slowed them? The best guess is Varroa jacobsoni, an exotic ectoparasite of honey bees recently introduced into North America. The effects of varroa on Africanized honey bees may be both a blessing and a curse; the latter is especially true if Africanized bees become resistant to varroa and commercial honey bees do not.
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In 1990, before varroa became a serious problem, we conducted a study of the feral honey bee population of California. Samples of bees were collected from 208 feral colonies distributed widely in nest sites throughout the state. We failed to find any colonies infested with varroa (Kraus and Page 1995a). In 1993, we reinspected 124 of the original nest sites and the findings were alarming. Around Sacramento — an area with intensive commercial beekeeping — only 25% of the original nest sites still had colonies of bees living in them. All surviving colonies were infested with varroa. Honey bees nest in enclosed cavities that are usually not easily accessible. However, in some cases the inside of an empty nest was exposed and could be inspected. In every case, dead varroa were found in the bottom of the nest — the smoking gun. The surviving colonies were examined again the following spring (1994). Only one remained and it was heavily infested and unlikely to survive.
Regions of California that had smaller populations of commercial hives in 1993 (as a result of less commercial beekeeping) had reduced levels of infestation of varroa and higher survival in the feral bees. It appears that varroa spread through the feral population aided by the activities of commercial beekeeping. We used estimates of reoccupation rates and rates of survival to estimate life expectancy. Estimations of nest site reoccupation rates following the death of a feral colony and rates of survival resulted in an estimate of the life expectancy of a feral colony before and after the arrival of varroa in areas with intensive commercial beekeeping. Prior to varroa's arrival, the life expectancy was 3.5 years; after varroa arrived the life expectancy was only 6 months to a year. In 3 short years, varroa had reduced the feral population to a tiny fraction of what it had been in 1990. As a consequence of varroa, the feral population of California is greatly reduced to about 15% of its original size in areas with extensive commercial beekeeping. Feral bees are therefore expected to have a greatly reduced effect on the gene pool of the invading AHB. Also, a smaller feral population should result in less competition for invading AHB for food and nest site resources. This is especially true if the AHB are relatively resistant to varroa.
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of the feral colonies in some areas of California.
Resistance to varroa?
For many years, reports have been coming from Brazil that AHB are resistant to varroa. These reports have been confounded with results demonstrating that varroa have a less severe effect on all colonies, even European, in tropical versus temperate climates (Moretto et al. 1991). Resistance, however, is plausible because of the greatly reduced effect that varroa have on their natural host, A. cerana, a close relative of our western honey bee. Recent evidence from Brazilian researchers suggests that, like A. cerana, Brazilian AHB have the ability to detect varroa on the bodies of adult workers and remove them (Moretto et al. 1993). This may provide a mechanism for resistance. Varroa were introduced into southern Brazil in 1972, after the spread of AHB, so the proposed resistance may have been selected in Brazil and may not be a characteristic of the spreading population of AHB. Or, AHB may be “preadapted” to be more resistant to varroa than are bees of European origins. The AHB population spreading into California did not encounter varroa until after it had invaded Mexico and Texas.
Regards,
peer-reviewed research article
Blessing or curse? Varroa mite impacts Africanized bee spread and beekeeping
authors
Robert E. Page, Department of Entomology
publication information
California Agriculture 52(2):9-13. DOI: 10.3733/ca.v052n02p9. March-April 1998.
abstract
Africanized honey bees were first detected in California in October 1994. Since then, they have established a foothold in the Imperial Valley and have spread toward San Diego and into Palm Springs. However, their spread has been much slower than originally expected. What has slowed them? The best guess is Varroa jacobsoni, an exotic ectoparasite of honey bees recently introduced into North America. The effects of varroa on Africanized honey bees may be both a blessing and a curse; the latter is especially true if Africanized bees become resistant to varroa and commercial honey bees do not.
----------------------------------------------------------------------------------------------------------------
In 1990, before varroa became a serious problem, we conducted a study of the feral honey bee population of California. Samples of bees were collected from 208 feral colonies distributed widely in nest sites throughout the state. We failed to find any colonies infested with varroa (Kraus and Page 1995a). In 1993, we reinspected 124 of the original nest sites and the findings were alarming. Around Sacramento — an area with intensive commercial beekeeping — only 25% of the original nest sites still had colonies of bees living in them. All surviving colonies were infested with varroa. Honey bees nest in enclosed cavities that are usually not easily accessible. However, in some cases the inside of an empty nest was exposed and could be inspected. In every case, dead varroa were found in the bottom of the nest — the smoking gun. The surviving colonies were examined again the following spring (1994). Only one remained and it was heavily infested and unlikely to survive.
Regions of California that had smaller populations of commercial hives in 1993 (as a result of less commercial beekeeping) had reduced levels of infestation of varroa and higher survival in the feral bees. It appears that varroa spread through the feral population aided by the activities of commercial beekeeping. We used estimates of reoccupation rates and rates of survival to estimate life expectancy. Estimations of nest site reoccupation rates following the death of a feral colony and rates of survival resulted in an estimate of the life expectancy of a feral colony before and after the arrival of varroa in areas with intensive commercial beekeeping. Prior to varroa's arrival, the life expectancy was 3.5 years; after varroa arrived the life expectancy was only 6 months to a year. In 3 short years, varroa had reduced the feral population to a tiny fraction of what it had been in 1990. As a consequence of varroa, the feral population of California is greatly reduced to about 15% of its original size in areas with extensive commercial beekeeping. Feral bees are therefore expected to have a greatly reduced effect on the gene pool of the invading AHB. Also, a smaller feral population should result in less competition for invading AHB for food and nest site resources. This is especially true if the AHB are relatively resistant to varroa.
-----------------------------------------------------------------------------------------------------------
of the feral colonies in some areas of California.
Resistance to varroa?
For many years, reports have been coming from Brazil that AHB are resistant to varroa. These reports have been confounded with results demonstrating that varroa have a less severe effect on all colonies, even European, in tropical versus temperate climates (Moretto et al. 1991). Resistance, however, is plausible because of the greatly reduced effect that varroa have on their natural host, A. cerana, a close relative of our western honey bee. Recent evidence from Brazilian researchers suggests that, like A. cerana, Brazilian AHB have the ability to detect varroa on the bodies of adult workers and remove them (Moretto et al. 1993). This may provide a mechanism for resistance. Varroa were introduced into southern Brazil in 1972, after the spread of AHB, so the proposed resistance may have been selected in Brazil and may not be a characteristic of the spreading population of AHB. Or, AHB may be “preadapted” to be more resistant to varroa than are bees of European origins. The AHB population spreading into California did not encounter varroa until after it had invaded Mexico and Texas.
Regards,
