Slave labour

日期:2017-08-23 01:59:32 作者:闾丘钟 阅读:

By Jon Copley A VORACIOUS appetite for pests makes ladybirds, or ladybugs, a gardener’s best friend. But there is a problem with these biological pest-killers—they tend to fly off before they’ve finished the job. Now, however, French researchers have patented a way of breeding ladybirds that can’t fly, which ensures that they stay around to eat the pests. Using predators to control pests is widely seen as less harmful to the environment than pesticides. Ladybirds make ideal predators, since both larvae and adults feed on other insects. The larvae are already used to protect growing crops. The trouble starts when the insects grow wings. When an American species was introduced onto lime trees in the Netherlands, for instance, most of the 30 million adults flew away in just three weeks. André Ferran and his colleagues at the National Institute of Agronomic Research in Antibes have now found a way to produce mutant multicoloured Asian ladybirds (Harmonia axyridis) that are unable to fly. Starting with a normal population, they induced random mutations by exposing the insects to ionising radiation and treating them with a mutagen known as ethyl methyl sulphonate. They picked out individual mutants that couldn’t fly and bred from them. “We carried out selective breeding to produce a population of 95 per cent flightless ladybirds,” says Ludovic Guide, who was a member of the team. Flightless mutants occur naturally in various ladybird species, but they tend to have deformed wings and are generally unfit, so they are little use in pest control. Ferran’s mutants, however, seem just as healthy as their flying counterparts. “They have a normal wing morphology,” he says. They also reproduce normally. Ferran proposes introducing a limited number of adults onto plants and allowing them to breed to develop captive local populations of predators that eat a broad range of creatures, including aphid, scale insects, mites and mealybugs. In tests, the flightless ladybirds have already been successful in keeping pests off cucumbers and melons. In the US, normal H. axyridis are used to control pests on crops such as pecans, apples and peaches—which means being able to feed high in the trees. Whether their flightless relatives will be able to do this is unclear. “Certainly this is an interesting advance,” says Mike Majerus at the University of Cambridge, who heads a group researching the population genetics of ladybirds. “Field trials are necessary to find out how efficient this is, and not just in greenhouses.” But Majerus also urges caution. “This is a very hardy ladybird—very tolerant of adverse winter conditions. We can keep them at 4 °C for up to 18 months.” That hardiness, he points out, could have its drawbacks. In the US, for instance, H. axyridis introduced for biological control have ousted other species to become one of the most common ladybirds. Flightless populations would have a less widespread impact,