Return of the Medfly

By: Virginia Hayes

Here they come again: The Medfly has been spotted in our area.
It’s been just over 30 years since the first outbreak of the
Mediterranean fruit fly (Ceratitis capitata) in Southern
California. This first incidence caused widespread panic both in
the agricultural industry and the urban landscape where it
occurred. This little fly has the nasty habit of laying its eggs
just under the skin of a variety of fruits. There, the larvae that
hatch start eating the juicy insides of the fruit, causing a wound
that soon supports one or more fungi to ruin it. Most fall from the
tree a rotten mess to the ground, where the larvae burrow into the
soil to complete their life cycle, emerging as flying adults to
carry on the devastation. Since the Medfly is native to the
Mediterranean region of Western Africa with a climate very similar
to ours, it could adapt easily to this area. In a state with an
agricultural industry measured in the tens of billions, the
establishment of such a pest is not a scenario officials and
growers want to contemplate.

So, state officials sprayed the area in Los Angeles from
helicopters with a sticky concoction laced with Malathion (thus the
panic of the populace) and eradicated the flies. They’ve been back
to California periodically since then: in 1980, 1982, 1987, 1988,
1989, 1990, and 1994. Where are they coming from and how are they
getting here? Extensive inspections of illegal shipments of fruit
by commercial producers revealed only part of the problem. Tourists
are as often to blame. Contraband fruit is subject to confiscation
upon entering the state; so many people try to circumvent the
inspections by mailing fruit from infected areas such as Hawaii. In
one investigation, 124 larvae, 18 pupae, and two adults were found
in 324 packages mailed from Honolulu to California. Today, the
state maintains 130,000 traps to monitor potential outbreaks. If a
single Medfly is trapped, intensive trapping in the area begins. If
two are found within a three-mile radius or if one mated female,
one larvae, or one pupae is found, eradication begins. One method
of eradication involves releasing large numbers of sterile males,
resulting in a failure of the intruders to reproduce. A more direct
approach, called “male annihilation,” uses a pheromone, emitted by
females to attract males, suspended in a gel containing a pesticide
that kills the males when they contact or ingest it. This gel is
sprayed on the trunks of trees and utility poles at a height of 8
to 12 feet. Applications are made throughout the affected area and
out to a radius one-and-a-half miles in each direction from the
sites where the fruit flies were found. For a map of the region,
visit, click on Oriental Fruit Fly
Information, then click CDFA Eradication Treatment Area Map. You
will also find a schedule of treatments.

The pesticide is applied at that height to “keep it out of reach
of passers-by and pets,” according to the County Agricultural
Commission’s Web site. They also identify the pesticide as Dibrom.
Thanks to some diligent monitoring by a few residents, it isn’t at
all clear that the gel applications actually end up where they are
supposed to. One witness said she saw the gel, which is sprayed
from a truck, also fall on the surrounding area. While it’s a far
cry from aerial spraying with Malathion in the dead of night,
repeated applications of any pesticide over such a wide area, even
though directed at specific targets, are cause for some concern.
For residents in the area, vigilance is suggested and children and
pets should be contained if you have reason to believe the gel is
in reach.

Dibrom, also known as Naled and Fly Killer-D, is in the class of
pesticides known as organophosphates. Purported to be moderately
toxic both orally and through skin exposure, it can cause
dermatitis and other skin allergic reactions on contact. Chronic
exposure can lead to neurological or neuromuscular problems.
Luckily, it is also very fast-acting and has a reported half-life
of less than a day, rapidly degrading in the presence of sunlight
to dichlorvos. Soil microorganisms break it down in the soil and
plants also eliminate the bromine component to form dichlorvos.
Dichlorvos remains a nerve toxin until it, too, is broken down;
another half-life of 24 to 36 hours. So exposure to the sprayed gel
should be avoided for a minimum of 3 days to avoid experiencing any
toxic effects. Sensitive people (children and seniors) should avoid
all contact.

The loss of crops and agriculture-related jobs should the Medfly
become established California would be immense. Until the tide of
illegal fruit arriving in the state is stemmed, limited use of
pesticides will probably still be the best way to treat such


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