Quote of the moment: Jonathan Weiner’s Pulitzer-winning explanation of mosquitoes developing immunity to DDT

April 30, 2010

When evolutionists study these worldwide resistance movements, they see four classes of adaptations arising, because an insect under attack has four possible routes to survival.

Jonathan Weiner, author of The Beak of the Finch

Jonathan Weiner, author of The Beak of the Finch, a story of evolution in our time

First, it can simply dodge. Strains of malarial mosquitoes in Africa used to fly into a hut, sting someone, and then land on the hut wall to digest their meals. In the 1950s and 1960s health workers began spraying hut walls with DDT. Unfortunately in every village there were always a few mosquitoes that would fly in through the window, bite, and fly right back out. Millions of mosquitoes died, but these few survived and multiplied. Within a short time almost all of the mosquitoes in the villages were hit-and-run mosquitoes.

Second, if an insect cannot dodge, it can evolve a way to keep the poison from getting under its cuticle. Some diamondback moths, if they land on a leaf that is tainted with pyrethroids, will fly off and leave their poisoned legs behind, an adaptive trick known as “legdrop.”

Third, if the insect can’t keep the poison out, it may evolve an antidote. A mosquito species called Culex pipiens can now survive massive doses of organophosphate insecticides. The mosquitoes actually digest the poison, using a suite of enzymes known as esterases. The genes that make these esterases are known as alleles B1 and B2. Many strains of Culex pipiens now carry as many as 250 copies of the B1 allele and 60 copies of the B2.

Because these genes are virtually identical, letter by letter, from continent to continent, it seems likely that they came from a single lucky mosquito. The mutant, the founder of this particular resistance movement, is thought to have lived in the 1960s, somewhere in Africa or Asia. The genes first appeared in Californian mosquitoes in 1984, in Italian mosquitoes in 1985, and in French mosquitoes in 1986.

Cover of Jonathan Weiner's book, The Beak of the Finch, a story of evolution in our time

Finally, if the insect can’t evolve an antidote,it can sometimes find an internal dodge. The poison has a target somewhere inside the insect’s body. The insect can shrink this target, or move it, or lose it. Of the four types of adaptations, the four survival strategies, this is the hardest for evolution to bring off — but [entomologist Martin] Taylor thinks this is how Heliothis [virescens, a cotton boll-eating moth] is evolving now.

“It always seems amazing to me that evolutionists pay so little attention to this kind of thing,” says Taylor. “And that cotton growers are having to deal with these pests in the very states whose legislatures are so hostile to the theory of evolution. Because it is evolution itself they are struggling against in their fields each season. These people are trying to ban the teaching of evolution while their own cotton crops are failing because of evolution. How can you be a creationist farmer any more?”

Jonathan Weiner, The Beak of the Finch, a story of evolution in our time, Alfred A. Knopf 1994, pp. 254-255. The book won the Pulitzer Prize for general non-fiction in 1995.


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