Humans and insects have been fighting over whose turn it is to eat the plants (and, in the case of mosquitoes, over whose blood is it, anyway?) for a very long time–but recent research may be about to give us two-legs a leg up over the six-legs.
More than 3,000 years ago, the Chinese used sulfur as a fumigant, the first known use of a pesticide. Much later, in the 16th century, they began using moderate amounts of arsenic-containing compounds to control garden pests. But pesticide use really took off with the rise of organic chemistry in the 1930s. Today, more than 400 pesticides, mostly synthetic chemicals, are registered with the U.S.’s Environmental Protection Agency. Even though they’re tailored to affect insects and not humans, pesticides are, by their very nature, toxic to some living organisms–and not necessarily just the targeted ones. According to the U.N., an estimated one million to five million cases of pesticide poisoning occur every year worldwide, resulting in several thousand fatalities.
So any news that might lead to less pesticide use is good news–and just such news surfaced over the past couple of weeks.
One story was on the work of Patricia Stock of the University of Arizona College of Agriculture and Life Sciences. Patricia Stock is a nematomologist: that is, she studies nematodes, a phylum of worms that includes a vast number of species, ranging in size from microscopic to menacing (Placentonema gigantisma, eight metres long, discovered in the placenta of a sperm whale, if you must know). Stock’s specific interest is in the microscopic entomopathogenic nematodes, or EPN, which have a symbiotic relationship with insect-killing bacteria.
EPNs either lurk where the larva of the insect they target are likely to feed, or actively hunt those larva. When they find one, get inside it through its natural openings or by drilling a hole. Once inside, they spit out the bacteria they carry, which kill the host within a day or two. The worms then grow and multiply inside the dead host, with one whole generation spending its entire life in the decaying grub. Finally, a new generation, 150,000-strong or more, exits the remains and crawls off in search of other hosts.
Nematodes make an excellent all-natural pesticide for several reasons. One, they can feed on a variety of insect species. Two, they kill quickly–within 48 hours. Three, they can be grown under artificial conditions. Fourth, they can stay viable for months if properly stored. Fifth, insects don’t seem to develop resistance to nematode bacteria, and sixth, they don’t harm anything else.
Unfortunately, they’re also harder to produce and store than chemical pesticides and can only be applied when environmental conditions are just right (moist enough, not too hot, not too cold). This makes them too expensive and unreliable for large plots of land. Still, they are being used for gardens and lawns, and Stock hopes to extend their use even further. In Arizona, they’re conducting pest control trials in citrus and iceberg lettuce, using local nematodes. In Jordan, they’re trying to develop new non-chemical and non-toxic pest control methods for desert and semi-desert areas. In both places, and in the rainforests of Costa Rica, they’re hoping to connect more insect-pathogenic nematodes with specific insect species, to broaden the possible applications of nematode-based insect control.
Meanwhile, a new discovery announced a couple of weeks ago holds out the possibility of obviating the need for pesticides by making insects turn up their noses at their usual food sources.
Leslie Vosshall and colleagues at Rockefeller University have discovered a gene, dubbed Or83b, that is central to the sense of smell in fruit flies–and very likely many other insects.
When the researchers created mutant fruit flies missing Or83b gene, the flies’ odor receptors picked up odor molecules from the air, but that information was never transferred to the flies’ nervous systems–so they ignored rotting fruit.
But when Or83b genes from three pest species, the medfly (a citrus pest), the corn earworm moth, and the malaria mosquito, were placed into the fruit flies, they regained their ability to smell properly–indicating Or83b likely plays the same central role in each of those species’ sense of smell.
If we can create a chemical that blocks the action of that gene, may not have to kill insects at all–because, unable to smell the plants or people they’re normally drawn to, they’ll simply ignore them.
Killer worms and smell-blinding: two potentially powerful new weapons in the age-old Battle of the Bug.
