Review: Carneiro et al. (2007). Neotropical Entomology, 36: 949-952

Written: October 22, 2008

Posted: 10/23/08

Word count: 728

Question: Are Africanized bees less prone to varroa mites?

Answer: Not as much as they used to be!

It’s a general biological principle that life in the tropics is more diverse and therefore a lot more competitive. This, of course, stems from the fact that temperatures are higher and there is more sunshine around the equator, which permits for more plant growth (and thus the struggle over eating them; nature, red in tooth and claw, after all). With more life comes more lifeforms that try to make a living off of other lifeforms (pests, parasites, and pathogens). Just think about it; virtually all of the really bad diseases in the world at least derived in the tropics. You don’t have to get a litany of immunizations whenever you travel to Iceland!

It is not surprising, therefore, that tropical honey bees are a bit on the defensive side. If our honey bees had to put up with elephant and giraffe predation on a daily basis (and no, I’m not making that up), perhaps ours would be too. But with increased defensiveness comes certain side effects. For example, African bees are a lot more paranoid about robbing, so their guard bees are ever vigilant. This, presumably, cuts down on colony mortality and honey losses, and even reduces disease transmission.

There’s yet another benefit. African bees develop more quickly than European bees, and are thus a tad smaller in adult body size (the two are not linked, however; smaller bees are not necessarily more defensive). This enables African colonies to reproduce slightly faster, to build up more quickly, and to rebound from population crashes more readily. This trait also results on perhaps the single-most important trait for honey bees today: resistance to varroa mites.

Mites enter brood cells just before they are capped, hiding out in the brood food out of sight until they are sealed in. Once securely behind closed doors, they then make a cut in the side of the pupa and start feeding on its hemolymph (“bee blood”)—no wonder they’re sometimes referred to as the vampire mite. The female then lays one egg at 30-hour intervals: first a daughter, then a son, then the rest daughters. The more time the mother mite has—that is, the longer the pupal development time—the more daughter mites she can raise. This is why varroa prefers drone brood; they’re longer development time means a dramatic increase in their own reproductive success.

It is this same reason why Africanized honey bees are thought to bee less susceptible to varroa. If the AHB develops faster, the mite levels within their colonies won’t build up to the same levels to pose a problem. In the neotropics of Latin America, beekeepers have seen this first hand.

But a new study out of Brazil gives pause to the complacency of tropical beekeepers, and casts doubt on the AHB’s ability to withstand the varroa mite. A research team lead by Francisco Carneiro measure the reproductive ability of varroa in Africanized bees, comparing numbers today to those measured in the mid-1980s (when the mite was first introduced). They also measured colonies over the course of an entire year to determine seasonality. They measured mite reproduction by percent fertility, percent of mites that reproduced, and number of offspring per mite. In all of these measures, and in all of the months of the year, they found that varroa reproduction has risen since they were first recorded 20 years ago.

It is unfortunate that there was no comparison to rates of varroa reproduction in European colonies in this study, as that would indicate the relative degree to which the AHB may still be tolerant of mites. Nonetheless, it is fairly obvious that Africanized bees may not be as resistant to parasites as we once thought, and may even becoming more susceptible over time. It seems that the competitive nature of the tropics continues, and the general biological principle marches on.

Reference

Carneiro, F. E., R. R. Torres, R. Strapazzon, S. A. Ramírez, J. C.V. Guerra Jr, D. F. Koling, and G. Moretto. (2007). Changes in the reproductive ability of the mite Varroa destructor (Anderson and Trueman) in Africanized honey bees (Apis mellifera L.) (Hymenoptera: Apidae) colonies in southern Brazil. Neotropical Entomology, 36: 949-952.