New Guide Outlines Management for Mediterranean Fruit Fly in Egypt
By Mahfouz M. M. Abd-Elgawad, Ph.D.
The Mediterranean fruit fly (Ceratitis capitata) is a key pest of citrus fruit and can infect over 300 other economically important fruit-bearing plant species. As it has worldwide distribution, ability to tolerate variable climates better than most other species of fruit flies, and broad range of hosts, it is considered the most economically important fruit fly species in the world. Its larvae feed and develop on numerous deciduous, subtropical, and tropical fruits and some vegetables. Although it may be a major pest of citrus, often it is a more or equally serious pest of some other fruits, such as peach, guava, pear, plum, cherry, apricot, fig, mango, and apple.
The Mediterranean fruit fly, or medfly for short, is responsible for global annual losses of over $2 billion (U.S.) in crop size and quality. In the past, there have been outbreaks in Florida, California, and Texas, USA, but immediate actions were put in place to eliminate populations before they were established. In Egypt, meanwhile, the Ministry of Agriculture reported infestation of a variety of economically important hosts in 2009, including grapefruit (28.13 percent of national crop infested ), guava (27.1 percent), apricot (24.41 percent), peach (23.22 percent), fig (8.67 percent), orange (7 percent), and mango (6 percent). In a new guide published this month in the open-access Journal of Integrated Pest Management, I outline the fly’s life cycle and biology and available management methods for growers in Egypt.
The medfly can move to different hosts continuously, and in Egypt it has 8–10 overlapping generations per year. The female lays its eggs under the fruit peel and larvae use anterior mouth hooks to vigorously feed on fruit flesh until they reach the third and last instar. As tens of eggs are often deposited in a single spot, the fruit becomes juicy and inedible, and the flesh gets ruined by turning to liquid. Larval infection and feeding also facilitate the entry of fungi and microbes that cause the fruit to rot.
As a quarantine pest with high reproductive potential and dispersive ability, this pest is difficult to manage and poses a major threat to Egyptian citrus export because of concerns over infection or pesticide residues. Therefore, integrated pest management (IPM) programs consisting of regulatory, cultural, chemical, genetic, and biocontrol methods should be attempted in earnest to materialize the most effective strategies for medfly control. Regulatory and cultural practices should aim to block the insect diffusion and lower its population densities.
A partial spray application of synthetic insecticides is imposed by the Egyptian government to decrease the use of unsafe pesticides and replace them with benign, ecologically sound products for pest control in the context of sustainable agriculture. The use of fly traps aid in the detection of whether the medfly exists in a given area, delimiting traps define the boundaries of a region considered to be free from or infested by the pest, and monitoring traps record traits of the pest populations such as relative abundance and seasonal fluctuations. Surveys may examine the lure/attractant or trap efficiency, effectiveness of targeted programs, presence of fruit flies and host species, climate-related and seasonal fluctuations in medfly populations, and topography. Fly traps use sex pheromone and food attractants as lures and may be used separately to determine the male:female ratio.
Sterile insect technique (SIT) is utilized as an autocidal medfly control method. Mating between sterile males (sterilized by irradiation) and normal females produces no viable female offspring. Manipulating a self-limiting gene to disrupt insects’ normal development and prevent reproduction is also a promising method for the pest control. However, to achieve successful pest control with the SIT or by self-limiting genetic manipulation, cost-effective mass rearing methods and efficient generation of a male-only release group are required. Optimal inexpensive and rearing conditions for the medfly are currently being investigated.
With regard to natural enemies of the medfly, Egyptian farmers raise poultry in fruit groves without disturbing human-friendly birds such as hornbill (Ocyceros griseus) and hoopoe (Upupa africana), which feed on medflies, especially in their subterranean stages (fallen/last instar larvae and pupae). Members of the order Coleoptera and some ant species also prey on medfly at these stages. In Egypt, other organisms such as the earwig Labidura riparia and spiders attack medfly pupae in the soil and under fallen infested fruits. Entomopathogenic nematode spray on the ground under the tree canopies has also shown to optimize the pest control.
Setting threshold levels for fruit flies in various lure-based trapping systems is critical in different citrus-producing areas within a region to guide growers on the control strategies needed to achieve medfly-free orchards. Pest control measures should thus be implemented on a case-by-case basis. Ultimately, combining two or more compatible methods in holistic IPM programs is an effective strategy to rid citrus fruit of pesticide residues, pests, and diseases.
Journal of Integrated Pest Management
Mahfouz M. M. Abd-Elgawad, Ph.D., is a professor in the Plant Pathology Department, Agricultural and Biological Research Division at the National Research Centre in Giza, Egypt. Email: email@example.com.