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Wolbachia bacterium offers promising new options for biocontrol

A bacterium naturally present in many insects has great potential for new methods of biocontrol, say scientists at the Agriculture and Agri-Food Canada (AAFC) Lethbridge Research Centre.

"The bacterium, Wolbachia, manipulates the reproductive system of its insect host," says Dr. George Kyei-Poku, an insect pathologist and microbiologist at AAFC. The effects of Wolbachia vary with different hosts and depending on the host's 'lifestyle,' the reproductive irregularity can be harnessed for the control of pest insects. Kyei-Poku works with Dr. Kevin Floate, an AAFC insect ecologist, on developing Wolbachia as a method to control pest flies affecting livestock.

"Wolbachia research has accelerated rapidly in the last 10 to 15 years and we are now beginning to learn how the bacteria works and develop it for application in pest control," says Kyei-Poku. The bacterium is thought to infect 20 to 70 percent of all known insect species in the world, and it displays an array of functions, some of which have potential crossover to medicine.

There are four rather complex mechanisms by which Wolbachia can affect their insect hosts, says Kyei-Poku. These mechanisms are feminization, selective killing of males, parthenogenesis-induction and cytoplasmic incompatibility.

Feminization occurs when Wolbachia transforms immature insects that are genetically programmed to become males into functional females, explains Kyei-Poku. This happens when Wolbachia suppresses production of insect hormones necessary for normal male development.

Selective male-killing occurs when infections of Wolbachia cause female eggs to hatch before male eggs. The young females then eat the unhatched eggs, thereby killing their male siblings.

Parthenogenesis-induction is limited to types of insects that normally produce male offspring from unfertilized eggs and female offspring from fertilized eggs, explains Kyei-Poku. Under normal conditions, unmated females will produce male offspring, but when infected with Wolbachia, they instead produce only female offspring.

"This mechanism is believed to be the most effective for use in biocontrol," he says. "Many biocontrol programs use beneficial insects that are parasites of pest species. Because only female parasites can lay eggs, use of Wolbachia to increase numbers of females is an ideal outcome."

The most common of the four mechanisms is cytoplasm incompatibility. Depending upon the type of insect, matings between Wolbachia-infected males and uninfected females, may produce either no offspring or only male offspring, says Kyei-Poku. These effects, however, are not observed in matings between uninfected males and infected females, or when both parents are either infected or uninfected.

"A number of pest insects could potentially be controlled with cytoplasm incompatibility," he says. For example, pest populations can be infected with Wolbachia to reduce the number of successful matings and, therefore, the size of the pest population in the next generation.

"The potential for using cytoplasm incompatible Wolbachia in biocontrol and other applications seems almost endless," says Kyei-Poku. In addition to pest control, this bacterium also provides an efficient and safe system for the biomedical community to analyze the spread of pathogens. As well, analyzing how Wolbachia disrupts the development of immature insects could provide valuable information to better understand the workings of pathogens in humans. Kyei-Poku notes, however, that there is no evidence of Wolbachia occurring in animals or humans.

Agriculture and Agri-Food Canada’s Lethbridge Research Centre has a mandate to promote innovation for growth, maintain security of the food system and protect the health of the environment.

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