Tiny pests plague olives
By Susan Felker, Outreach and International Affairs
Fine olive oil wins the praise of gourmets around the world and has grown in popularity over the past two decades. Even local supermarkets in the United States carry a wide array of olive oil products, ranging from simple “olive oil” to the deluxe “extra virgin olive oil.” It is not hard to spot the premium price that the latter brings at the cash register, but most consumers don’t know that a high level of acidity in the oil means a lower quality – and lower income for the farmer who produces it.
That’s what Albanian olive farmers face – low-quality, acidic olive oil produced from their annual crops.
The culprit was the Mediterranean olive fruit fly, Bactrocera oleae, a tiny insect that meant big trouble because it was laying its eggs on maturing olives. The larva not only damaged the olives, but also rendered them bitter. “Most people would respond by suggesting insecticides,” says Doug Pfeiffer, professor of entomology in the College of Agriculture and Life Sciences, “but we need to look at the big picture and think about cost and environmental impact – in short, the importance of controlling the pest with minimum collateral damage.”
Pfeiffer chairs the Albanian Integrated Pest Management Collaborative Research Support Program (IPM CRSP) under Virginia Tech’s Office of International Research, Education, and Development with funding from the U.S. Agency for International Development. IPM CRSP programs tackle pests that damage or destroy crops, placing priority on natural controls and limiting or eliminating pesticide use.
The reddish-brown olive fruit fly is slightly under a quarter of an inch in length and is distinguished by three dark stripes running lengthwise on top of its thorax and a white scutellum at the rear of the thorax. A single dark spot marks the apex of its wings. In Albania, the fly has three generations each year. The third brood causes the most damage.
The female lays an egg in the olive with a sharp ovipositor – a needle-like tube on her belly that cuts a hole in the fruit. She then smears olive juice around the hole to alert other egg-laying females that the olive has already been used. She repeats the process on many olives. When the olive fruit fly population is especially high, females ignore the marking and lay eggs on the same olive as other females. When the larvae hatch, they feed on the olives, damaging the pulp, making it more acidic, and causing it to rot. The larvae pupate over the winter either in the earth beneath the trees or in the olive itself.
The collapse in the early 1990s of the former communist government in Albania, a country slightly smaller than Maryland and located on the Adriatic and Ionic seacoasts, led to widespread economic hardship. Over the next few years, large numbers of Albanians fell prey to pyramid schemes as they adapted to a free market economy, further impoverishing the country of 35 million people.
Collective farms produced olives for oil and table use under the old economy, controlling the three major insect pests that attack the crop – the olive fruit fly, the olive moth, and black scale – using pesticides. When the government privatized the olive groves about 15 years ago, each family received a number of trees, usually 7 to 20 per person, using a formula based on village population and the quantity of trees in the area. Farmers were no longer able to afford insecticides, so the olive fruit fly thrived. Those who tried sprays were thwarted if the farmer owning the next block of trees in the orchard didn’t spray too. The quality of their olives – and their income – dropped.
Olive oil is the primary source of dietary fat for residents of many Mediterranean countries, including Albania, and is a key ingredient in local cuisines. A solution to the olive fruit fly problem was critical.
IPM work began in Albania during the previous decade, Pfeiffer notes. He first traveled there in the summer of 1998 for a “participatory appraisal,” the term used for an analysis of problems that includes researchers from the country in question and the farmers themselves. The international team then developed a research plan.
They decided to focus on six IPM CRSP projects:
• Monitoring crop pests and their natural enemies;
• Determining the effects of harvest timing on olive fly infestation, olive oil yields, and olive oil quality;
• Introducing organic methods of vegetation management and olive insect control;
• Determining the effect of pruning on production, infestation by black scale, and the incidence of olive knot and timing of copper sprays to control leaf spot and olive knot;
• Introducing pheromone-based integrated pest management in olive groves and effects on non-targeted species; and
• Determining the socio-economic impacts.
After studying the insect’s life cycle and habits, an Albanian scientist suggested that the team of U.S. researchers and other Albanian scientists study the olive crop to determine the amount and the quality of oil produced. A first step was delivering three short courses in statistical analysis for Albanian scientists, who then began analyzing gains in weight and accumulation of oil in the olive crop.
“We also took olive oil samples and had then analyzed at a laboratory in Greece,” Pfeiffer says. “The pH factor is the main determinant of quality in olive oil, so we wanted to determine the point at which fruit fly damage increased the most rapidly.”
Albanian scientists continued to record the weight gain of olives and oil content as the crop matured.
The results were a bit surprising. The team discovered that, contrary to traditional belief, there was almost as much oil in the olives two weeks before the traditional harvest date that marked peak oil content. During those final two weeks, the third brood of olive fruit flies caused the most damage and acid levels increased the most.
“By the simple expedient of moving the harvest date forward by two weeks, farmers will be able to produce low-acid extra virgin olive oil from their crops and they will see an immediate financial return,” Pfeiffer says. “The harvest timing is something any farmer can do – there is no financial obstacle. For this reason, it should be widely adopted.”
The technique works for the most widely produced varieties of olives grown in Albania, but may not work for late-harvest varieties.
The IPM team launched a farmer education program to disseminate information about this easy method for improving crop quality and is hoping that word of mouth will accelerate adoption of the early harvest technique. “We were looking for a low-cost solution, but we found a no-cost solution,” Pfeiffer says. “The benefit to the Albanian economy of this measure alone will be $39 million over the next 30 years.”
The IPM team also investigated the use of paper sack olive fly traps, which have a pheromone on the outside and bait on the inside. The traps also have an insecticide coating, so as the olive flies congregate on the traps, they die. The result was drastic drops in the olive fly population in groves where the traps were used compared to groves with no traps.
“Unfortunately,” says Pfeiffer, “at $1 each, the traps are too expensive for most farmers.” In a country where the per capita gross domestic product (GDP) is $4,900 (compared to $41,800 per capita GDP in the United States), $1 traps that need to be replaced if they get wet, dusty, or contaminated with non-target insects can be prohibitively expensive.
A second Albanian CRSP, this time combined with programs in Moldova and the Ukraine, received funding under the IPM CRSP funding cycle that began in 2005. The new initiative is investigating alternative crops and livestock that could help boost farm productivity and farmer income. Pfeiffer led another series of participatory appraisal meetings to determine farmer – and research – priorities.
“I really get a lot of satisfaction out of working with local scientists and farmers to tackle problems that are obstacles to a better life,” Pfeiffer says. “I’ve learned a lot from my colleagues in Albania.”