Mexfly No Stranger to U.S. Researchers : Persistent pest: An American expert spent 30 years in Mexico studying how to deal with the insect and its threat to agriculture.

Meet Anastrepha ludens. About the size of a housefly, it has green eyes, a yellowish-brown body and not much of a sweet tooth.

A. ludens for short, this hardy Mexican fruit fly has 150 to 200 cousins spread throughout Mexico, the Caribbean and Central and South America. But the Mexican fruit fly is by far the one most likely to be found in California.

And, if those doing battle against the Mexfly in San Diego County know much about it, it’s because John Gilbert Shaw spent nearly three decades finding it out.

Shaw was in Mexico City from 1937 to 1965, studying the Mexican fruit fly in the lab and in the orchards of nearby Morelos state for the U.S. Department of Agriculture. He helped figure out how long the fly lived, what it liked best to eat, and how to get rid of it.

Shaw was sent to Mexico to study the fruit fly because it had been found in citrus along the Rio Grande Valley in Texas.

“They tried to eradicate it, but they found out they couldn’t do it because the fly continued to move in from Mexico, right across the river,” said Shaw, now retired and living in Riverside.

When talking about the Mexican fruit fly, let’s get first things first, Shaw says: It’s only very distantly and coincidentally related to the more notorious Mediterranean fruit fly.

The Medfly is an insect thought to have originated in Africa and to have spread over many years to Mediterranean countries. It’s in a completely separate genus ( Ceratitis ) from the Mexfly. The Mexfly originated in the subtropical areas of the New World, along with 150 to 200 others in the Anastrepha genus.

The Medfly and Mexfly also differ in size. The Mexfly is about the size of a housefly or a little larger; the Medfly is about half as big.

Other tidbits Shaw shares about the pest that kept him in Mexico City for so long:

The Mexfly’s yellowish-brown body is punctuated on its middle section, or thorax, with long bands of a slightly lighter color. Its wings have yellow and brown bands across them, one of the bands V-shaped.

Females are slightly larger than males. Like Medflies, female Mexflies have a long thin “ovipositor” on their back end. But this attachment for injecting eggs into fruit is longer than that of the Medfly--one reason the Mexfly’s favorite fruit can be citrus. Mangoes are second-best.

The female mates and begins depositing eggs in fruit, in small clutches of several eggs each. This process is repeated every few days for about a month.

The ovipositor under magnification looks like a thin, serrated knife. The female Mexfly withdraws a protective membrane from around this barbed protrusion and uses it to slice a hole about as thick as a pencil lead and about one-quarter of an inch deep into the fruit.

She leaves several eggs in the fruit, pulls the ovipositor out and proceeds to do the same thing again, in that fruit or another one. All told, a fertilized female produces about 1,000 eggs--the number can run as high as 4,000 in the most ideal food and temperature conditions.

The eggs hatch into small white larvae in four to six days. The larvae spend the next 25 days with their pincer-like mouths attached to the fruit’s internal flesh, growing to about the size of a grain of rice. They make the fruit ripen more quickly, but their feces also make it taste bad.

After 25 days, the larvae crawl out of the fruit and drop to the ground, where they spend 15-18 days as pupae before hatching into flying insects ready for mating. All told, the life cycle is 45 to 60 days, depending on conditions such as temperature and availability of food.

Mexfies prefer citrus, their favorite being grapefruit. In some locales, they favor mangoes instead. But, if neither is available, they move into other types of citrus or other fruits such as apples, peaches and quince. Avocadoes are relatively safe from them because of their tough skin.

Like Medflies, Mexflies prefer subtropical temperatures of 75 to 80 degrees. Cool nights or hot days will slow reproduction, but some will survive even intermittent freezing.

Back-yard fruit that is infested with Mexflies can be found in several ways. It often will fall off the tree, and tiny holes in the skin can be seen. Also, if fruit is picked and set aside, larvae will begin crawling out, apparently because of the movement of the fruit.

But, while the back-yard signs of Mexfly infestations are obvious, they prove harder for agricultural officials to track. This is partly because they are strong fliers. It also is because the Mexfly is a lot harder to catch in traps than the Medfly is, said James E. Carey, a UC Davis entomologist.

Medflies are lured to widely spaced government traps with a sex hormone attractant; Mexflies have to find the traps without such potent chemical signposts, Carey said.

So, when a trap does contain a Mexfly, it’s because the infestation has progressed well beyond its earliest stages, Carey said.