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Ceratitis capitata, commonly known as the Mediterranean fruit fly or medfly, is a yellow and brown, fruit pest that originates from sub-Saharan Africa. While C. capitata has no near relatives in the Western Hemisphere, it is considered to be one of the most destructive fruit pests in the world. Despite this, there have been occasional medfly infestations in the states of California, Florida, and Texas that required extensive eradication efforts to prevent the fly from establishing itself in the US. C. capitata is the most economically important fruit fly species because of its ability survive in cooler climates more successfully than most other fly species, and its ability to inhabit over 200+ tropical fruits and vegetables to which it causes severe destruction and degradation. Eradication efforts practiced on the medfly after its introduction into a new environment can be extremely difficult and extremely expensive. Moreover, infestation of C. capitata will induce lower crop yields and costly sorting processes for fresh fruits and vegetables.
- 1 Physical description
- 2 Distribution
- 3 Life cycle
- 4 Food resources
- 5 Mating Behavior
- 6 Genetics
- 7 Immunity
- 8 Aggression
- 9 Invasions
- 10 References
- 11 Further reading
- 12 External links
C. capitata eggs are characterized by their curved shape, shiny white color, and smooth features. Each egg is approximately 1 mm in length; as seen in other fruit flies, the egg possess a micropylar region with a clearly tubercular shape.
Larvae of the C. capitata have been described as having a common fruit fly larval shape that is cylindrical with a narrow anterior end and flattened caudal tail. By the end of the third and final instar of the medfly, the larvae measure between 7 and 9 mm and about 8 fusiform areas. 
The adult fly is typically 3 to 5 mm in length. There are numerous visually defining characteristics of the C. capitata’s bodily features. To begin with, the thorax is a creamy white to yellow with a characteristic pattern of black blotches; the abdomen is tinted brown with fine black bristles located on the dorsal surface and two light bands on the basal half. The medfly’s wings contain a band across the middle of the wing with dark streaks and spots in the middle of the wing cells. In a study done by Siomava et. al, researchers utilized geometric morphometrics to analyze wing shape in three different fly species including C. capitata. Through their findings, the researchers were able to show that the medfly exhibits extensive sexual shape dimorphism (SShD) between the proximal and distal part of the wing between males and females; this difference can be used to distinguish between the two sexes since male wings tend to be wider and shorter in comparison to females. This anatomical difference is important because this allows males to displace more air and create a more audible “buzzing” effect during mate attraction.
The Geographic Distribution Map of C. capitata (Updated December 2013).
This map provides information on the distribution of the Mediterranean fruit fly, C. capitata, throughout the world. The information is mainly based on available Mediterranean fruit fly national surveillance reports. Therefore, the map displays assessments of the presence of this pest at the national level and in some cases at sub-national levels.
The four stages of the C. capitata are the egg, larvae, pupae and adult stages. Female medflies lay eggs in groups of roughly 10-14 eggs and deposit them just under the skin surface of their host fruit. Once eggs are deposited below the skin, they hatch in only a few days, emerging as maggots or larvae. C. capitata flies are known to disperse up to distances of 12 miles in search of host fruit. In the instances where plentiful host fruit is situated in their current locations, they will not disperse beyond 300–700 feet.
In optimum conditions, medflies can complete their cycles in 21 days. In cooler temperatures, the life cycle of the medfly can take up to 100 days to complete. In temperatures that are below 50 °F, development of the fly ceases. Oviposition in females ceases to occur in temperatures below 60 °F.
The lifespan of the C. capitata is quite short with half of most populations dead in under 60 days. However, cool conditions and proper sustenance can enable some flies to live 6 months or even up to a year. In most lab conditions, under controlled diets of sugar and protein, females have a longer life expectancy than males by 1.5 days. On average, the lifespans of flies in captivity are 10 days longer than lifespans of those in the wild.
Among fruit fly species, C. capitata have the largest variety of host-fruits, ranging over 200 different types of fruits and vegetables. These fruits include but are not limited to akee, star apple, oranges, grapefruit, guava, mango, plum, and pears. C. capitata in the adult and larval stage feed in different ways.
Because nutrition is a crucial determinant of adult size and development, larva prefer to eat fleshy host fruit. Higher concentrations of glucose and sucrose boost development and the percentage of emerging larva in comparison to high starch and maltose diets.
While larva go for the middle of the fruit, adults prefer the fruit portion that contains more nutritional value in comparison to the flesh. Adults tend to gain their carbohydrate intake from ripe fruit and protein from decomposing fruit or leftover bird feces, their diet preferences have been proven by studies in which medflies placed at the top of oranges and papayas consistently moved lower to the nutrient dense parts whereas flies placed near the bottom remained in their starting location. Adult flies typically feed in the mid-morning/late afternoon.
Mating in the C. capitata fly typically begins with males stationed at the bottom of the surface of leaves during the late morning or early afternoon. Once males are stationed at these locations, they begin the mating process by forming leks and releasing sex pheromones to attract virgin females. If successful, mating will occur during this time period. Another important location for copulation is on the fruit itself during the late morning or early afternoon. Males position themselves here in an attempt to copulate with already-mated females through seduction or force. In a study conducted by Chuchill-Stanland et al., it was shown that a male’s size can dictate their mating success rate. Researchers found that flies that were approximately 8–9 mg had optimum mating success while flies that were smaller than this (i.e <6 mg) had significantly less mating success. Furthermore, when males were equal or larger in size, mating frequency was equal and events such as eclosion, flying, and mating speed were positively correlated with pupal size.
It has been shown that during mating, females experience a switch in olfactory-mediated behaviors. Specifically, virgin females prefer the pheromones of sexually developed males over the host fruit odor. Females continue to exhibit this preference until mating occurs, following which, they prefer the host fruit odor; this finding has been evidenced by a specific protein, CcapObp22, that shows approximately 37% identity with the pheromone binding protein of Drosophila melanogaster. In a recent study, this protein was shown to bind male pheromone components, specifically farnesene, a highly strong hydrophobic terpene.
Sex determination in C. capitata is by the familiar XY system. Unusually for a dipteran and for a frugivore, medflies do not have an opsin gene for blue light perception as shown from the whole-genome sequencing project completed in September 2016. In study done by Spanos et al. in 2001, researchers were able to sequence the entire mitochondrial genome. They found that the genome was 15,980 base pairs long with 22 tRNA genes and 13 genes encoding mitochondrial proteins. Using this information, researchers were able to use this genome sequence as a diagnostic tool for population analysis and a method to determine the source of recent introductions.
In a 1987 study completed by Postlethwait et al., researchers assessed the immune response of the medfly using bacterial inoculation. After inoculating the medfly with Enerobacter clocae, the researcher extracted the haemolymph from the males and found that it contained potent antibacterial factors compared to the haemolymph of controls. Through further testing, they were able to show that these potent factors were generated within 3 hours of inoculation and lasted for approximately 8 days; this finding indicated that the medflies does contain an adaptive immune response that is similar to the Drosophila melanogaster.
Studies have shown that wild C. capitata flies were found to partake in more head-butting behavior, direct opponent contact, and less likely to cede an occupied leaf to an invader. Furthermore, it was found that sounds that are produced during body vibration constitutes threat behavior. Aggressive sounds are substantially higher in pitch (roughly around 1–3 kHz) while sounds produced during non-aggressive moments such as courtship times tended to be around 0.16-0.35 kHz.
In the United States, C. capitata has invaded four states (Hawaii, California, Texas, and Florida), but has been eradicated from all but Hawaii. Reintroduced populations of the medfly have been spotted in California as recently as 2009, requiring additional eradication and quarantine efforts, it has also been eradicated from New Zealand and Chile.
California medfly crises
Much research has been dedicated to means of controlling the medfly. In particular, use of the sterile insect technique has allowed the species to be eradicated from several areas.
In 1981, California Governor Jerry Brown, who had established a reputation as a strong environmentalist, was confronted with a serious medfly infestation in the San Francisco Bay Area, he was advised by the state's agricultural industry and the US Department of Agriculture's Animal and Plant Health Inspection service (APHIS) to authorize airborne spraying of the region. Initially, in accordance with his environmental protection stance, he chose to authorize ground-level spraying only. Unfortunately, the infestation spread as the medfly reproductive cycle outpaced the spraying. After more than a month, millions of dollars of crops had been destroyed and billions of dollars more were threatened. Governor Brown then authorized a massive response to the infestation. Fleets of helicopters sprayed malathion at night, and the California National Guard set up highway checkpoints and collected many tons of local fruit. In the final stage of the campaign, entomologists released millions of sterile male medflies in an attempt to disrupt the insects' reproductive cycle.
Ultimately, the infestation was eradicated, but both the governor’s delay and the scale of the action has remained controversial ever since; some people claimed that malathion was toxic to humans, as well as insects. In response to such concerns, Brown's chief of staff, B. T. Collins, staged a news conference during which he publicly drank a small glass of malathion. Many people complained that, while the malathion may not have been very toxic to humans, the aerosol spray containing it was corrosive to car paint.
During the week of September 9, 2007, adult flies and their larvae were found in Dixon, California; the California Department of Food and Agriculture and cooperating county and federal agricultural officials started eradication and quarantine efforts in the area. Eradication was declared on August 8, 2008, when no "wild" (i.e. non-sterile) medflies were detected for three generations.
On November 14, 2008, four adult flies were found in El Cajon, California; the San Diego County Agricultural Commission implemented a treatment plan, including distributing millions of sterile male flies, local produce quarantines, and ground spraying with organic pesticides.
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|Wikimedia Commons has media related to Ceratitis capitata.|
- University of Hawaii. "Crop Knowledge Master".
- "Global Invasive Species Database".
- The 1981 California Medfly Panic
- CISR Summary on Mediterranean Fruit Fly
- Species Profile - Mediterranean Fruit Fly (Ceratitis capitata), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Mediterranean fruit fly.
- Tephritid Workers Database