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Chiller bees
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Chiller bees
TIM MARTIN/NATUREPL.COM
Why did the super aggressive killer bees of Hollywood fame suddenly chill out on one tropical island? Ben Turner investigates
38 | New Scientist | 17 August 2019
S
TEPPING out of his house to survey the destruction, Hermes Conde felt like he had been transported to another world. “It was as if an atomic bomb had hit. Nothing was standing,” he says. “I couldn’t recognise the landscape around my own home.” It was 21 September 2017 and Hurricane Maria had just torn Puerto Rico to shreds. An estimated 2975 people died in the worst natural disaster the Caribbean island has ever witnessed. From the early hours of 20 September through to mid-afternoon the next day, Maria bisected Puerto Rico like a 100-kilometre-wide buzz saw. It plucked up trees and hurled roofs from homes like
After just a decade on Puerto Rico, killer bees like this had lost their famed aggression
Frisbees. The pounding rain sent flash floods, metres deep, rushing into populated areas. Downed trees and power lines blocked the roads. Electricity and water supplies were cut off for months after the storm. Conde’s first priority was to get petrol for his generator. It would take him 23 hours on foot, but fuel wasn’t the only thing he was looking for. Conde is a beekeeper and along the way he tapped into a network of fellow apiarists trying to discover the fate of their insects. The situation looked bleak. Hurricane Maria had almost annihilated Puerto Rico’s bees, but Conde was determined to rescue the survivors. It may sound like a strange mission in the middle of such chaos, but these are no ordinary bees. They are among the most incredible insects in modern evolutionary history. In just a decade, they have mysteriously transformed from killers to docile honey makers. They may even hold secrets that will help us breed disease-resistant bees in the future. Their story begins in Brazil, in 1956, with a local geneticist called Warwick Kerr. Honeybees aren’t native to the Americas, and at that time South American nations relied on imported European bees, Apis mellifera. The tropical heat, however, made them sluggish. Monks kept them to provide beeswax for church candles, but European bees were becoming increasingly unable to meet the Brazil’s demands for honey and crop pollination. So Kerr travelled to Tanzania to acquire some East African lowland bee queens for a breeding programme. This subspecies, Apis mellifera scutellata, is notoriously aggressive, but he hoped that by crossing them with their European cousins he could create a hybrid with the docility and honey yield of the European bee and the resistance to disease and heat of the African one. It would just take a little time. He hadn’t planned for his prototypes to escape, but that is exactly what happened the following year. Fleeing into the rainforest, the hybrids interbred with local honeybees, soon becoming dominant, first in Brazil then across the Americas. News of the bees’ advance was intermingled with tales of their legendary aggression. The truth didn’t need much embellishment. When European bees are provoked, about 10 per cent of hive members will attack, but these hybrid bees often retaliate en masse, emptying the hive in swarms of up to 800,000 individuals. They will give chase for up to half a kilometre and are content to wait it out if their target attempts to hide underwater, continuing the barrage of stings when the victim resurfaces for air.
Some people have died in such attacks, not because the bees’ venom is particularly potent, but due to the sheer number of stings. Hollywood cashed in on people’s fears with a string of horrifying bee movies. Films like The Swarm, Killer Bees and Deadly Invasion: The killer bee nightmare mythologised the insects, which began to spread across the southern US in the 1990s. By this time, “killer” bees had taken root in 20 countries on two continents. Then, at the height of their infamy, a queen stowed away aboard a ship in Texas. She was bound for Puerto Rico. Hybrid bees were first recorded on the eastern side of the island in 1994. From the start, they were just as quick to interbreed with local bees as they had been on the mainland – and just as aggressive. Records reveal four deaths, including a 2-year-old boy, in the first three years. The authorities were quick to respond. Emergency calls resulted in fire services spraying more than 2000 hives with a soapy solution that asphyxiated the inhabitants. Then, in September 1998, Hurricane Georges hit the island, sending bee numbers plummeting. It was during the post-Georges recovery that Tugrul Giray at the University of Puerto Rico got involved. He was keen to compare the island’s bees with those in Hawaii, which are of purely European origin. “The weird thing is that
“By the 1990s, killer bees had taken root in 20 countries on two continents” we were going up these trees expecting some kind of a fight on our hands,” he says. “We wanted to collect the baddest bees. But they were really just as sweet as can be.” This wasn’t the exception – Giray kept finding hive after docile hive everywhere he looked. Wondering whether the insects might be remnants of the island’s European bees, he decided to carry out some genetic tests. “Even the nicest colonies turned out to be of mixed African and European descent,” he says. “It was a total surprise.” It took a few years, but bee numbers eventually rebounded to their pre-Georges levels. Bee attacks, however, did not: these had dropped from 10,000 a year to 600. Giray’s bafflement grew. “We tried to scientifically > 17 August 2019 | New Scientist | 39
“What was the mystery force driving the bees’ remarkable transformation?”
measure their aggressiveness by kicking the hive or throwing a brick at it,” he says. “Some of them even had zero response. They didn’t want to sting at all.” These insects looked like hybrid bees, but they didn’t act like them. Giray was forced to conclude that, sometime during the decade since their arrival, the once-vicious killers had evolved into bees as docile as their European cousins. Nature had finished what Kerr had started. What was the mysterious force driving this transformation? Giray’s first thought was that it had something to do with habitat. Islands tend to have fewer predators than the mainland, but the challenge of island living is to get by with scarcer, seasonally available resources. As a result, species often adapt to focus on energy efficiency and ensuring they have calories for leaner times, making them fat and docile. The turkey-sized dodo, for example, evolved from a small, airborne pigeon that arrived on Mauritius. This “harsh seasonality” could have had a similar effect on Puerto Rico’s bees, forcing them to forage well and pick their battles. Hurricanes would have played a part too, by killing off
all but the most skilful hoarders. There is another possible explanation. Giray’s collaborator, Arian Avalos, now at the US Department of Agriculture, suggested that the bee’s rapid evolution might be connected to the island having the highest human population density of anywhere in the hybrid honeybee’s range. This could have led to unwitting human selection because people regularly encountered hives and those containing the most aggressive bees were systematically destroyed, leaving only the calmer bees to repopulate the isolated island.
Disease-resistant bees The likelihood is that all these factors played a part. What is truly amazing is that the bees have evolved incredibly rapidly, yet have retained an enormous amount of genetic variation even though their numbers have crashed on several occasions (see “The killer that changed its stripes”, below). The result is a remarkable creature that isn’t just docile, but resistant to disease and good at producing honey.
The killer that changed its stripes Social insects, such as ants and many bee and wasp species, have a remarkable ability to rapidly adapt to changing environments. In Puerto Rico, honeybees evolved from being highly aggressive killers to gentle foragers in just a decade (see main story). This rate of change seems extraordinary, even given the recent realisation that evolution can happen surprisingly quickly. It is easy to see how a bacterium, reproducing every 20 minutes or so, can evolve immunity to a drug, but the generation time of bees is far longer. Worker honeybees live for around a month, drones survive for five to 10 weeks and the queen can make it to three years or more. So if rapid reproduction isn’t the key, what has allowed Puerto Rico’s bees to evolve so quickly? In part, it is the fact that when bees produce eggs and sperm, their genes are more thoroughly shuffled than in other species and the mutation rate is very high. This creates lots of different
40 | New Scientist | 17 August 2019
genetic combinations, increasing the potential to produce highly variable offspring able to survive in a wide variety of environments. Although this sounds like a winning formula, there is a reason most animals don’t adopt it: mutations are more often harmful than helpful. When so many occur during the production of sex cells there is a risk of losing vital bits of genetic information and ultimately the entire species. But bees, and some other colonial insects, have a trump card to get around this problem: the haplodiploid sex system. It works like this. Male drones develop from unfertilised eggs and have only one pair of chromosomes: they are haploid. Female workers develop from fertilised eggs and have both pairs of chromosomes, and so are diploid. The queen is the only fertile female in the colony and mates with about 12 to 20 males to produce the hive’s population. Because drones only have one pair of her chromosomes, any harmful mutations that arise have no alternative versions of the genes to counteract the
bad ones. So, if one of the hive’s lines of descendants mutates too far, the drones it produces will die or be unable to mate, removing the line from the gene pool. This combination of haplodiploidy and high mutation rates creates enormous genetic diversity in colonial insects. It is this that allows the colony to respond rapidly, and with nuance, to subtle alterations in the environment – as if it were a single organism. In Puerto Rico, the environment seems to have favoured active foragers over aggressive individuals and the drive to change was so strong that it happened in just a few years. Yet despite such remarkable adaptability, bees and other colonial insects are declining in numbers worldwide. Marla Spivak at the University of Minnesota sees this as an indictment of the environmental conditions humans are imposing upon them. “The fact they’re struggling right now really shows that they are being pushed to, or beyond, their tipping points,” she says.
No wonder Puerto Rico’s beekeepers have taken these insects to their heart, and nobody more so than Conde. A lifelong apiarist, following in the tradition of his grandmother, he was also a police captain in the 1990s. He was there when the emergency services were being called out to exterminate killer bees, and he was torn up by their fate. So, after retiring in 2011, he established the Eastern Apiculture Academy. Rather than teaching people about honey production, its sole aim is to protect Puerto Rico’s hybrid bees. This explains Conde’s activities in the weeks after Hurricane Maria. An estimated 90 per cent of the island’s bees were dead and the remainder needed help – fast. “The bees had lost so many of their homes, and were so hungry that we were finding them everywhere,” he says. “Bins, drink cans, postboxes, dogs’ houses, dolls’ houses, abandoned homes.” With Giray’s assistance, Conde and 30 volunteers worked in shifts around the clock to move colonies to safety. “The most difficult were those hanging from electrical cables, but fortunately I’m a helicopter pilot,” says Conde. In total, they rescued around 65 hives. This brush with fate has brought Puerto Rico’s bees to the attention of US beekeepers, whose own hives of European bees have been devastated by a phenomenon
MANUEL GIANNONI GUZMAN
HERMES CONDE
A young apiarist helps protect Puerto Rico’s hybrid bees, which are both diseaseresistant and good honey producers
called colony collapse disorder. The hybrids spend far longer grooming themselves than European honeybees, making them twice as likely to dislodge the varroa mite, a parasite that carries various pathogens and is a factor in colony collapse. As a result, some see Puerto Rico’s bees as a silver bullet that can solve a problem that has plagued beekeepers in the US and elsewhere for a decade. “The prospect of importing the bees is promising,” says Avalos. But it may not be the solution. “The bees’ adaptability is remarkable, but colony collapse emerged from poor nutrition, pesticides, pests and pathogens. They can handle one of these, but we don’t know how they will handle the others. You can adapt to a higher water level, but you’re not going to grow gills.” Other entomologists share his reservations. They include Marla Spivak at the University of Minnesota, who is breeding varieties of honeybees that are better able to detect and remove pathogens and mites. She thinks Puerto Rican bees would struggle to cope with the intensive agricultural systems, greater urbanisation and high concentration of mites in the US. “What makes Puerto Rico’s story amazing is how they’ve found such a great way of working with their bees,” she says. “The same solution wouldn’t work everywhere. We want multiple great solutions for multiple places.”
Even so, these extraordinary bees will be vital in the future battle to strengthen global bee populations. The next step is to use recent discoveries about how their genome differs from those of their African and European ancestors to isolate the genes responsible for aggression and mite resistance. That work is already under way, and the researchers are very excited at the possibility of uncovering the complex genetics underpinning the bees’ rapid evolution. “By triangulating among African, European and Puerto Rican bees, we could uncover the genetic variants responsible for docility and disease resistance,” says geneticist Gene Robinson at the University of Illinois at Urbana-Champaign, who, along with his colleague Matt Hudson, is collaborating with Avalos and Giray. Their work could prove an enormous boon to beekeepers hoping to use genetics to create more resilient bees. Who knows what the next chapter of this story will bring. But when the protagonist is an insect that has transformed from a killer to a potential saviour in the blink of an evolutionary eye, anything seems possible. ❚
Ben Turner is a writer based in London. Follow him on Twitter @usuallyjustben
17 August 2019 | New Scientist | 41
Chiller bees
TIM MARTIN/NATUREPL.COM
Why did the super aggressive killer bees of Hollywood fame suddenly chill out on one tropical island? Ben Turner investigates
38 | New Scientist | 17 August 2019
S
TEPPING out of his house to survey the destruction, Hermes Conde felt like he had been transported to another world. “It was as if an atomic bomb had hit. Nothing was standing,” he says. “I couldn’t recognise the landscape around my own home.” It was 21 September 2017 and Hurricane Maria had just torn Puerto Rico to shreds. An estimated 2975 people died in the worst natural disaster the Caribbean island has ever witnessed. From the early hours of 20 September through to mid-afternoon the next day, Maria bisected Puerto Rico like a 100-kilometre-wide buzz saw. It plucked up trees and hurled roofs from homes like
After just a decade on Puerto Rico, killer bees like this had lost their famed aggression
Frisbees. The pounding rain sent flash floods, metres deep, rushing into populated areas. Downed trees and power lines blocked the roads. Electricity and water supplies were cut off for months after the storm. Conde’s first priority was to get petrol for his generator. It would take him 23 hours on foot, but fuel wasn’t the only thing he was looking for. Conde is a beekeeper and along the way he tapped into a network of fellow apiarists trying to discover the fate of their insects. The situation looked bleak. Hurricane Maria had almost annihilated Puerto Rico’s bees, but Conde was determined to rescue the survivors. It may sound like a strange mission in the middle of such chaos, but these are no ordinary bees. They are among the most incredible insects in modern evolutionary history. In just a decade, they have mysteriously transformed from killers to docile honey makers. They may even hold secrets that will help us breed disease-resistant bees in the future. Their story begins in Brazil, in 1956, with a local geneticist called Warwick Kerr. Honeybees aren’t native to the Americas, and at that time South American nations relied on imported European bees, Apis mellifera. The tropical heat, however, made them sluggish. Monks kept them to provide beeswax for church candles, but European bees were becoming increasingly unable to meet the Brazil’s demands for honey and crop pollination. So Kerr travelled to Tanzania to acquire some East African lowland bee queens for a breeding programme. This subspecies, Apis mellifera scutellata, is notoriously aggressive, but he hoped that by crossing them with their European cousins he could create a hybrid with the docility and honey yield of the European bee and the resistance to disease and heat of the African one. It would just take a little time. He hadn’t planned for his prototypes to escape, but that is exactly what happened the following year. Fleeing into the rainforest, the hybrids interbred with local honeybees, soon becoming dominant, first in Brazil then across the Americas. News of the bees’ advance was intermingled with tales of their legendary aggression. The truth didn’t need much embellishment. When European bees are provoked, about 10 per cent of hive members will attack, but these hybrid bees often retaliate en masse, emptying the hive in swarms of up to 800,000 individuals. They will give chase for up to half a kilometre and are content to wait it out if their target attempts to hide underwater, continuing the barrage of stings when the victim resurfaces for air.
Some people have died in such attacks, not because the bees’ venom is particularly potent, but due to the sheer number of stings. Hollywood cashed in on people’s fears with a string of horrifying bee movies. Films like The Swarm, Killer Bees and Deadly Invasion: The killer bee nightmare mythologised the insects, which began to spread across the southern US in the 1990s. By this time, “killer” bees had taken root in 20 countries on two continents. Then, at the height of their infamy, a queen stowed away aboard a ship in Texas. She was bound for Puerto Rico. Hybrid bees were first recorded on the eastern side of the island in 1994. From the start, they were just as quick to interbreed with local bees as they had been on the mainland – and just as aggressive. Records reveal four deaths, including a 2-year-old boy, in the first three years. The authorities were quick to respond. Emergency calls resulted in fire services spraying more than 2000 hives with a soapy solution that asphyxiated the inhabitants. Then, in September 1998, Hurricane Georges hit the island, sending bee numbers plummeting. It was during the post-Georges recovery that Tugrul Giray at the University of Puerto Rico got involved. He was keen to compare the island’s bees with those in Hawaii, which are of purely European origin. “The weird thing is that
“By the 1990s, killer bees had taken root in 20 countries on two continents” we were going up these trees expecting some kind of a fight on our hands,” he says. “We wanted to collect the baddest bees. But they were really just as sweet as can be.” This wasn’t the exception – Giray kept finding hive after docile hive everywhere he looked. Wondering whether the insects might be remnants of the island’s European bees, he decided to carry out some genetic tests. “Even the nicest colonies turned out to be of mixed African and European descent,” he says. “It was a total surprise.” It took a few years, but bee numbers eventually rebounded to their pre-Georges levels. Bee attacks, however, did not: these had dropped from 10,000 a year to 600. Giray’s bafflement grew. “We tried to scientifically > 17 August 2019 | New Scientist | 39
“What was the mystery force driving the bees’ remarkable transformation?”
measure their aggressiveness by kicking the hive or throwing a brick at it,” he says. “Some of them even had zero response. They didn’t want to sting at all.” These insects looked like hybrid bees, but they didn’t act like them. Giray was forced to conclude that, sometime during the decade since their arrival, the once-vicious killers had evolved into bees as docile as their European cousins. Nature had finished what Kerr had started. What was the mysterious force driving this transformation? Giray’s first thought was that it had something to do with habitat. Islands tend to have fewer predators than the mainland, but the challenge of island living is to get by with scarcer, seasonally available resources. As a result, species often adapt to focus on energy efficiency and ensuring they have calories for leaner times, making them fat and docile. The turkey-sized dodo, for example, evolved from a small, airborne pigeon that arrived on Mauritius. This “harsh seasonality” could have had a similar effect on Puerto Rico’s bees, forcing them to forage well and pick their battles. Hurricanes would have played a part too, by killing off
all but the most skilful hoarders. There is another possible explanation. Giray’s collaborator, Arian Avalos, now at the US Department of Agriculture, suggested that the bee’s rapid evolution might be connected to the island having the highest human population density of anywhere in the hybrid honeybee’s range. This could have led to unwitting human selection because people regularly encountered hives and those containing the most aggressive bees were systematically destroyed, leaving only the calmer bees to repopulate the isolated island.
Disease-resistant bees The likelihood is that all these factors played a part. What is truly amazing is that the bees have evolved incredibly rapidly, yet have retained an enormous amount of genetic variation even though their numbers have crashed on several occasions (see “The killer that changed its stripes”, below). The result is a remarkable creature that isn’t just docile, but resistant to disease and good at producing honey.
The killer that changed its stripes Social insects, such as ants and many bee and wasp species, have a remarkable ability to rapidly adapt to changing environments. In Puerto Rico, honeybees evolved from being highly aggressive killers to gentle foragers in just a decade (see main story). This rate of change seems extraordinary, even given the recent realisation that evolution can happen surprisingly quickly. It is easy to see how a bacterium, reproducing every 20 minutes or so, can evolve immunity to a drug, but the generation time of bees is far longer. Worker honeybees live for around a month, drones survive for five to 10 weeks and the queen can make it to three years or more. So if rapid reproduction isn’t the key, what has allowed Puerto Rico’s bees to evolve so quickly? In part, it is the fact that when bees produce eggs and sperm, their genes are more thoroughly shuffled than in other species and the mutation rate is very high. This creates lots of different
40 | New Scientist | 17 August 2019
genetic combinations, increasing the potential to produce highly variable offspring able to survive in a wide variety of environments. Although this sounds like a winning formula, there is a reason most animals don’t adopt it: mutations are more often harmful than helpful. When so many occur during the production of sex cells there is a risk of losing vital bits of genetic information and ultimately the entire species. But bees, and some other colonial insects, have a trump card to get around this problem: the haplodiploid sex system. It works like this. Male drones develop from unfertilised eggs and have only one pair of chromosomes: they are haploid. Female workers develop from fertilised eggs and have both pairs of chromosomes, and so are diploid. The queen is the only fertile female in the colony and mates with about 12 to 20 males to produce the hive’s population. Because drones only have one pair of her chromosomes, any harmful mutations that arise have no alternative versions of the genes to counteract the
bad ones. So, if one of the hive’s lines of descendants mutates too far, the drones it produces will die or be unable to mate, removing the line from the gene pool. This combination of haplodiploidy and high mutation rates creates enormous genetic diversity in colonial insects. It is this that allows the colony to respond rapidly, and with nuance, to subtle alterations in the environment – as if it were a single organism. In Puerto Rico, the environment seems to have favoured active foragers over aggressive individuals and the drive to change was so strong that it happened in just a few years. Yet despite such remarkable adaptability, bees and other colonial insects are declining in numbers worldwide. Marla Spivak at the University of Minnesota sees this as an indictment of the environmental conditions humans are imposing upon them. “The fact they’re struggling right now really shows that they are being pushed to, or beyond, their tipping points,” she says.
No wonder Puerto Rico’s beekeepers have taken these insects to their heart, and nobody more so than Conde. A lifelong apiarist, following in the tradition of his grandmother, he was also a police captain in the 1990s. He was there when the emergency services were being called out to exterminate killer bees, and he was torn up by their fate. So, after retiring in 2011, he established the Eastern Apiculture Academy. Rather than teaching people about honey production, its sole aim is to protect Puerto Rico’s hybrid bees. This explains Conde’s activities in the weeks after Hurricane Maria. An estimated 90 per cent of the island’s bees were dead and the remainder needed help – fast. “The bees had lost so many of their homes, and were so hungry that we were finding them everywhere,” he says. “Bins, drink cans, postboxes, dogs’ houses, dolls’ houses, abandoned homes.” With Giray’s assistance, Conde and 30 volunteers worked in shifts around the clock to move colonies to safety. “The most difficult were those hanging from electrical cables, but fortunately I’m a helicopter pilot,” says Conde. In total, they rescued around 65 hives. This brush with fate has brought Puerto Rico’s bees to the attention of US beekeepers, whose own hives of European bees have been devastated by a phenomenon
MANUEL GIANNONI GUZMAN
HERMES CONDE
A young apiarist helps protect Puerto Rico’s hybrid bees, which are both diseaseresistant and good honey producers
called colony collapse disorder. The hybrids spend far longer grooming themselves than European honeybees, making them twice as likely to dislodge the varroa mite, a parasite that carries various pathogens and is a factor in colony collapse. As a result, some see Puerto Rico’s bees as a silver bullet that can solve a problem that has plagued beekeepers in the US and elsewhere for a decade. “The prospect of importing the bees is promising,” says Avalos. But it may not be the solution. “The bees’ adaptability is remarkable, but colony collapse emerged from poor nutrition, pesticides, pests and pathogens. They can handle one of these, but we don’t know how they will handle the others. You can adapt to a higher water level, but you’re not going to grow gills.” Other entomologists share his reservations. They include Marla Spivak at the University of Minnesota, who is breeding varieties of honeybees that are better able to detect and remove pathogens and mites. She thinks Puerto Rican bees would struggle to cope with the intensive agricultural systems, greater urbanisation and high concentration of mites in the US. “What makes Puerto Rico’s story amazing is how they’ve found such a great way of working with their bees,” she says. “The same solution wouldn’t work everywhere. We want multiple great solutions for multiple places.”
Even so, these extraordinary bees will be vital in the future battle to strengthen global bee populations. The next step is to use recent discoveries about how their genome differs from those of their African and European ancestors to isolate the genes responsible for aggression and mite resistance. That work is already under way, and the researchers are very excited at the possibility of uncovering the complex genetics underpinning the bees’ rapid evolution. “By triangulating among African, European and Puerto Rican bees, we could uncover the genetic variants responsible for docility and disease resistance,” says geneticist Gene Robinson at the University of Illinois at Urbana-Champaign, who, along with his colleague Matt Hudson, is collaborating with Avalos and Giray. Their work could prove an enormous boon to beekeepers hoping to use genetics to create more resilient bees. Who knows what the next chapter of this story will bring. But when the protagonist is an insect that has transformed from a killer to a potential saviour in the blink of an evolutionary eye, anything seems possible. ❚
Ben Turner is a writer based in London. Follow him on Twitter @usuallyjustben
17 August 2019 | New Scientist | 41