New way to beat pest

It is only 5 millimeters long, but the light brown insect with iridescent wings is the olive oil industry’s greatest enemy. Bactrocera oleae, the olive fruit fly, is the most harmful pest in Greek agriculture. Until now it has been dealt with by spraying – either by the Agriculture Ministry or by farmers themselves – with a powerful pesticide to which the insects have gradually built up a resistance. Meanwhile, the pesticide enters the soil and, from there, the food chain. Recently, however, researchers at the University of Crete and its Technology and Research Institute have found a way to reduce the population of fruit flies with the aid of genetic science. They have discovered a technique that releases sterile male insects into the environment. The females mate with them but do not reproduce, gradually reducing the population. Until now, the mass reproduction of this insect caused problems due to its demands for food. Greek scientists have found an effective way to distinguish male and female insects and to sterilize the males without changing their characteristics. Their results were recently published in the online edition of the journal Insect Molecular Biology. «This is a very important discovery,» said Costas Mathiopoulos, professor emeritus of molecular biology at Thessaly University’s Department of Biotechnology. Fighting the problem with pesticides was a dead end since the insects have simply developed a resistance. «Still, if it is not controlled, the fruit fly can destroy up to 80 percent of the crop,» Mathiopoulos said. «It increases the acidity of the olive oil and affects the quality of the fruit.» He claimed that releasing sterilized insects into the environment poses no risks to the balance of nature. «It is not like putting a completely foreign organism into a genetically modified corn gene,» he said. «Here we are ‘playing’ with the fruit fly’s own genes so as to distinguish the males from the females.» He said that the widespread appearance of these fruit flies in nature is unnatural. «It is the result of intensive farming,» he said. «This technique will allow us to control the population.» The technique has been used abroad with other insects such as the Cochliomyia himinivorax in the US, an insect that laid its eggs on the skin of cattle, resulting in a very painful death for the animal, or in dealing with the Mediterranean fly (related to the olive fruit fly) in California and Latin America, where it is particularly harmful to over 200 species of plants. The tsetse fly, which causes sleeping sickness in Africa, and other fruit flies in the Far East and in Australia have also been examined using the technique. In organic farming, the fruit fly is dealt with using natural methods such as hanging traps on trees. «The strange thing is that on Crete, one area produces organic olive oil without any trace of pesticide while in another there is great resistance among fruit flies to pesticides through use of the latter,» said Mathiopoulos. The project was carried out with contributions by Professor Aristides Economopoulos, PhD candidate Chronis Reboulakis from Crete University’s applied entomology laboratory, Professor Haralambos Savvakis and PhD candidate Martha Koukidou from the molecular biology laboratory and the Institute for Molecular Biology and Biotechnology.