A new strain of the coffee berry borer, a beetle that is the most common pest of coffee plants worldwide, "may represent a serious threat to the international coffee industry" because it is resistant to the most commonly used coffee insecticide, endosulfan, scientists say.
Because the beetle has an unusual means of reproduction, the gene that gives it protection from the pesticide may spread through the world population faster than might be expected with other insects.
Scientists at Purdue University, the University of Wisconsin and the Institut Francais de Recherchie Scientific pour le Development en Cooperation in Noume, New Caledonia, describe the coffee berry borer's unusual sexuality and its ability to resist the pesticide in a paper published in the October issue of the Proceedings of the National Academy of Science, U.S.A.
"The coffee berry borer is a cosmopolitan pest found wherever coffee is grown," says Jeff Stuart, an assistant professor of entomology at Purdue who specializes in insect resistance to pesticides. "As far as we know, this is the only strain of this pest that has developed a resistance to insecticides."
Coffee is a major worldwide crop that is grown in most countries in the tropical latitudes. In 1990, the worldwide crop of six million tons of coffee had an approximate value of $10 billion.
Luc Brun of the Institut Francais in New Caledonia first identified the resistance in this important beetle in his country in 1989. At that time, New Caledonia, which lies in the South Pacific Ocean approximately midway between Australia and the Fiji Islands, had many coffee farmers. Now, however, coffee farmers in that country are switching to other crops -- in part because of lower worldwide coffee prices, and in part because of the pest.
The small beetle was able to spread its genetic trait of pesticide resistance throughout the island because of its unique sexual biology. As their name suggests, the coffee berry borers (Hypothenemus hempei ) drill holes in the coffee berries and lay eggs inside the beans. Of the beetles that hatch, females outnumber males by a 10-to-1 ratio. The few males in the brood are unable to fly and never leave the coffee bean. These male beetles mate with their siblings before the mobile females flee the bean.
"This incestuous relationship increases the likelihood that offspring will receive two doses of the resistance gene," Stuart says. "Because of this, the resistance is likely to spread throughout the population much faster."
The genetics of the insecticide resistance were described by the researchers in the April 1995 issue of the scientific journal Nature.
Besides being of interest to java junkies and those interested in the sexual behaviors of insects, the coffee berry borer is intriguing to scientists because recent discoveries indicate that the beetle may be an intermediate step in the evolution of one of nature's genetic mysteries.
Most creatures, including humans, other mammals, birds and insects, have two sets of chromosomes or genes, one set inherited from the mother and one set inherited from the father. However, in one large class of insects that includes ants, wasps and bees, the males have only one set of chromosomes, which they inherit from the mother.
The coffee berry borer appears to be an unusual intermediate between the diplo-diploid insects, in which males have two sets of chromosomes, and haplo-haploid insects, in which males have a single set of chromosomes. In the coffee berry borer, the males receive both sets of chromosomes, but they shut off the set they receive from the father. In the paper in the Proceedings of the National Academy of Science, the researchers refer to this as "functional haplodiploidy."
Now that the researchers know what they're looking for, the next step will be to see if the resistance gene has gotten a foothold in coffee berry borer populations in other areas of the world.
"I believe that it is just as likely that it was brought into New Caledonia from some other country as it is that the resistance trait originated there," Stuart says. "So we're going to be looking at other coffee berry borer populations to see if we can find the gene there as well."
Even if the genetic trait originated in New Caledonia, that doesn't mean that other coffee-producing areas are safe from such a spray-proof beetle. "A similar mutation might arise again somewhere else," Stuart says.
Source: Jeff Stuart, (765) 494-4561; home, (765) 474-7881; Internet, firstname.lastname@example.org
Writer: Steve Tally, (765) 494-9809; home, (765) 463-4355; Internet, email@example.com
NOTE TO JOURNALISTS: A color print of a coffee berry borer invading a coffee berry is available from Purdue News Service, (765) 494-2096.
resistance in an important international insect pest
L.O. Brun and V. Gaudichon, Institut Francais de Recherchie Scientific pour le Development en Cooperation in Noume, New Caledonia; J. Stuart, Department of Entomology, Purdue University; and K. Aronstein and R.H. ffrench-Constant, Department of Entomology, University of Wisconsin, Madison, Wisconsin.
The coffee bean borer, Hypothenemus hempei , is the most important pest of coffee worldwide and has an unusual life history that ensures a high degree of inbreeding. Individual females lay a predominantly female brood within individual coffee berries and because the males are flightless there is almost entirely full sib mating. We investigated the genetics associated with this interesting life history after the important discovery of resistance to the cyclodiene type insecticide endosulfan. Both the inheritance of the resistance phenotype and the resistance-associated point mutation in the gamma-aminobutyric acid receptor gene Rdl were examined. Consistent with haplodiploidy, males failed to express and transmit paternally derived resistance alleles. Furthermore, while cytological examination revealed that males are diploid, one set of chromosomes were condensed, and probably nonfunctional, in the somaide cells of all males examined. Moreover, although two sets of chromosomes were present in primary spermocytes, the chromosomes failed to pair before the single meiotic division, and only one set was packaged in sperm. Thus, the coffee berry borer is "functionally" haplodiploid. Its genetics and life history may therefore represent an interesting intermediate step in the evolution of true haplodiploidy. The influence of this breeding system on the spread of insecticide resistance is discussed.
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