Villa Carpe Diem, Maroni

We started to harvest our ‘eating olives’ today. They were noticeably  fewer in number than last year when we had a bumper crop. The eating olive is the larger of the olives that we grow. About the size of a very large grape and shaped like a rugby ball is how I would describe them. You may have guessed that I am not well informed in matters ‘olive’.

In the kitchen after washing the olives in cold water, I settled down with a sharp knife to cut two incisions into each of the washed olives prior to placing them in brine. They never reached the brining stage as olive after olive that I cut into I had to reject.  I  split a few open and noticed (with the aid of reading glasses)  a very small almost immobile  maggot in the brown ruined flesh of our olives. What had caused this? Had our lovely trees become infected?  Is there a cure? If there is a cure what must be done?

A quick search on Google identified a couple of useful sources of detailed information. They each confirmed  the cause of the  problem as the olive fruit fly. This is my first encounter with said fruit fly and I knew I needed to know more before confronting our newest garden enemy!

It is considered the most devastating insect pest of olives in the Mediterranean region, where it has occurred for more than 2,000 years.

Description The adult olive fruit fly is about 3/16” (approximately 5 mm), reddish brown in color, with large reddish eyes and small antennae. The body is long with clear wings containing dark veins and a small dark spot at the wing tip. The head, thorax, and abdomen are brown with darker markings, and the thorax has several white or yellow patches on each side. The end of the male fly’s abdomen is blunt, whereas females have a large black ovipositor at the end of their abdomen that is visible to the naked eye. Larvae are yellowish-white maggots with a pointed head.

Life Cycle First, the most basic concepts: the female olive fly mates and lays eggs into the olive fruits. Each egg hatches into a tiny larva (maggot) that feeds throughout the olive and develops into a pupa (pupates) in a hollow area just beneath the outer skin. The adult fly emerges from the pupa. And the cycle starts again. The olive fruit fly has three, and perhaps as many as six, generations per year depending on local conditions.  the olive fly can overwinter as an adult; alternatively, it can spend the winter as a pupa in the soil or in fallen fruit. Overwintered adult populations decline to low levels by February or March. First generation new adults from overwintered pupae start emerging in early spring. The first females can lay eggs in un-harvested fruit from the previous year’s crop; later emerging flies can lay eggs directly into new fruit. Olive fruit susceptibility begins at the time of pit hardening, in July or earlier depending on climactic conditions.

DETECTION
As seen above, olive fruit flies in the larval stage cause the most damage. This damage is not always obvious to people unfamiliar with olive fly infestation signs. When we ask new growers whether they use olive fruit fly control measures for their trees, before accepting the fruit for milling, they often respond that they “don’t have the fly.” Once we tell them exactly what to look for, they invariably call back to say that in fact they did find damage.

In order to detect fruit fly damage, fallen winter fruit and fruit on the tree should be visually inspected for oviposition stings, maggots, or tunneling and decay. Adult flies can best be discovered by trapping. The olive fly can be monitored with McPhail, Olipe, or Yellow Sticky Traps. McPhail traps have proven to be more effective than yellow sticky traps in catching larger numbers of olive fruit flies and catching them earlier in the season.

While there is no relationship between fruit damage and the number of insects found in traps, surveying trap catches can evaluate treatment efficacy by comparing trap catches before and after treatment.

For all trap types, the traps should be placed in fruiting trees before March 1 in the second tree row or further in to reduce dust accumulation in the traps. Hang the traps mid-canopy, in the shade (north side of the tree), and in an open area to avoid leaves blocking the trap. The number of flies trapped weekly should be recorded. Preliminary research indicates that applications of bait sprays should begin when trap captures begin to increase in early summer.

Olives are the only breeding host plants. The larger olive varieties, e.g. Manzanillo, Sevillano, or Mission, are preferred for oviposition by the female. All olive varieties, however, are susceptible. Flies have been trapped in other plants or crop orchards where the adults are looking for food or refuge. http://en.wikipedia.org/wiki/Olive_fruit_fly