Olive insect is hot topic
If late summer heat is uncomfortable for those in California's agricultural production areas, it is just as bothersome for one co-habitating insect pest, the olive fruit fly.
But that's only one important fact that researchers have learned about this persistent pest which has the potential to derail the fast-growing California olive oil industry and its enormous economic potential.
The tiny olive fruit fly rivals pizza lovers in its desire for olives. The difference is that it doesn't eat them, but uses the ripening fruit as a place to lay its eggs. Whether the fruit is canned whole or crushed for oil, the presence of insect eggs results in lowered quality and reduced acceptance.
The researchers are learning all they can about the insect and the predator insects that like to munch on its eggs, hoping they can recommend to olive growers an effective method of biological control. Growers and researchers alike prefer reducing populations that way rather than using pesticides late in the season when picking time is near.
It is fairly late in the season when hot weather overtakes the flies, July and August in popular growing areas such as Tulare, Fresno, Kern and Madera counties. Measurements of the olive fruit fly populations have shown that the insect definitely slows its egg-laying proclivity during hot summer days.
The list of the institutions of the seven investigators who wrote the recent report on the fly's characteristics reads like a cross section of the major facilities prominent in much of California's agricultural research. M.W. Johnson, X.-G. Wang, K. Lynn Patterson and Kent Danne are with the University of California, Johnson from Riverside, Wang and Danne from Berkeley, and Patterson from the Kearney Agricultural Center in Parlier. H. Nadel is with the U.S. Department of Agriculture, Susan Opp is at California State University East Bay, and J. Stewart Leslie operates at the Consolidated Central Valley Table Grape Pest and Disease Control District in Exeter.
Their report was published in the January-March issue of UC's peer-reviewed journal California Agriculture. All but 10 of the issue's 48 pages were dedicated to various aspects of olive production. The information will be vital to growers and others in the industry as the acreage occupied by olive trees continues to expand in California.
Because olive trees that are grown specifically for oil differ in several ways from those that produce fruit for canning — called table olives — the whole realm of olive production is being evaluated. One of the noticeable differences is the close spacing of the oil varieties and their upright growth, characteristics lending to harvest by machines that straddle the tree rows, similar to the way wine grapes are harvested.
But the damage done by the insidious olive fruit fly is most pronounced in olives destined for canning. One infested olive can result in rejection of an entire load. Fruit to be pressed for oil can tolerate some fly damage as long as it has not rotted.
The search for natural enemies of the fly began in 2003, concentrated in Africa, where the researchers suspect it originated. Natural enemies, first reported there in 1912, have been sought in South Africa, Namibia, Kenya, Reunion and the Canary Is-lands as well as Morocco, Pakistan, India and China.
Although the use of natural enemies to control the pest can be disrupted by insecticides, even those designated as reduced-risk, research is showing that biological control can be a practical and economically effective means of fruit fly control, if they can just find the right natural enemy.
The thermometer will be counted on for an assist.
CONTACT Don Curlee at agwriter1@sbcglobal.net
