Mexican fruit fly larvae travel the world… in infested fruits.
Cousin to the dreaded MedFly, melon flies, and spotted wing drosophila, just to name a few, Mexican fruit flies (Anastrepha ludens), or MexFlies, are a major agricultural pest. Currently, in California, there is one active Mexican fruit fly quarantine in effect in San Diego County, but this is an on-going battle, so it’s a good idea to check the CDFA quarantine listing, or your local Department of Agriculture, regularly to see if your area is included.
History of Mexican fruit flies in California
First found in the U.S., in Texas, in 1903, Mexican fruit flies were seen again in 1927. By 1954, they had spread to Florida, Arizona, and California. It is estimated that these pests have cost farmers $1.44 billion in damages. Mexican fruit flies are subject to eradication programs that include capturing, sterilizing, and releasing males that interrupt the breeding cycle.
Mexican fruit flies have been expanding their range for several years now, and it’s not simply by catching a ride on an infested piece of fruit. Commercial agriculture brings crops to non-native regions, introducing them to local pests and diseases. For example, the mango, from India, only became a popular food of Mexican fruit flies after it started being grown in Central American and Mexico.
Mexican fruit flies prefer grapefruit, oranges, tangerines, mango, apple, peaches, nectarines, avocado, and pear. More recently, they have been found on figs, bananas, prickly pear cactus, cashews, papaya, guava, pomegranate, peppers, tomatoes, squash, beans, quince, Japanese persimmon, passionfruit, pummelo, and arabica coffee. [Coffee?!!?} Not only is the Mexican fruit fly range expanding, but so is their diet.
Mexican fruit fly description
Slightly larger than a housefly, Mexican fruit flies are 1/3 to 1/2 of an inch long. They have a yellow or brown body and distinctive wing patterns. Also, adult females have extra long ovipositor sheathes (egg-laying tubes). The wing patterns include a costal spot (C), an inverted-V, and a sideways S shape. Larvae are slender white grubs with mouth hooks, and a slightly flattened back end.
Mexican fruit fly lifecycle
As far as fruit flies go, this particular species is relatively long-lived. Individuals can survive for 11 to 16 months. Females lay over 1500 eggs in their lifetime. Eggs are laid in groups of 10, on the skin of a fruit, preferably one that is slightly damaged. This provides an easy point of entry for Mexican fruit fly larvae, along with many other pests and diseases. In a week or so, after being deposited, the eggs hatch out larvae that burrow into the fruit and start feeding. As they feed, the larvae take on the color of the fruit their are eating, so you may not notice right way, after taking a bite of an infected fruit.
Larval feeding continues for 3 or 4 weeks, depending on temperatures. Then, larvae drop to the ground, where they pupate in the soil. During this seeming pause in development, the slug-like larva is converted into a winged adult that begins breeding immediately after emerging, starting the whole process over.
Controlling Mexican fruit flies
Because they spend most of their lives inside fruit, insecticides are not effective against Mexican fruit flies in the larval, egg, or pupal stages. There is a tiny, repeated window of opportunity for treatment of adults, but only if direct contact is made with the insecticide. Generally, adults will simply fly away from treated trees and return a few days later, after it has worn off. Commercial growers use complex bait and trap methods that are unavailable to small scale growers.
So, they only thing you can do if you suspect Mexican fruit flies have found their way to your garden is to immediately contact the California Pest Hotline at 1-800-491-1899, or your local Department of Agriculture. It is best to leave controlling these pests to the pros.
You can grow a surprising amount of food in your own yard. Ask me how!