Crops
Dacus ciliatus Loew
Ethiopian Cucurbit Fly
General
- Insect belonging to the order Diptera and the family Tephritidae.
- Native to Africa where it has a very wide distribution throughout the continent. It is also present in East Asia (from Bangladesh to Pakistan) and throughout the Arabian Peninsula. Its presence in the Indian Ocean was first detected in Mauritius, then in Reunion, Madagascar and the Comoros.
- Oligophagous species that only attacks plants of the Cucurbitaceae family.
- Sensitive botanical family (s)
| Cucurbits* |
* cultivated : calabash, darling, pumpkin, cucumber, zucchini, bitter gourd, melon, watermelon, snake gourd, pipangaille, melon; uncultivated: calabash-ivy, wild bitter melon .
- Affected production areas :
| Mayotte | Reunion |
- Organs attacked
| Fruits |
Symptoms, damage
- Symptoms :
- Only the females cause the damage.
- Thanks to their ovipositor, they lay their eggs in the epidermis of the fruits, which causes the appearance of areas of dark green to blackish bites which soften and become hollow (figures 1 to 3, and 5).
- The numerous larvae emerging from the eggs develop rapidly inside the fruit by eating the pulp (figure 4).
- Rotting and decomposition of fruits linked to the development of opportunistic micro-organisms penetrating them via the egg-laying holes (bites).
- Signs : Presence of female flies on the fruits and in the crop (figures 6 and 7) and of larvae inside the fruits (figures 4). Eggs are sometimes visible at the level of the egg-laying holes (figure 3).
- Possible confusion : Other Cucurbit fly species such as Bactrocera cucurbitae or Dacus demmerezi .
Biology
- Biological cycle : It takes between 28 and 15 days between the egg stage and the emergence of adults over temperature ranges ranging from 35°C to 20°C.
- The whitish, fusiform eggs remain in the state for 15 to 28 days.
- The larval stages last from 7 to 4 days then the larvae leave the fruit and fall to the ground following a sudden release. They then burrow into the ground to pass to the pupa stage.
- The duration of the pupation can vary from 9.5 to 18 days. Beyond 35°C the pupae are no longer viable.
- The adults (figures 6 and 7) are characterized by an orange-brown color and the presence on their wings of a thin costal band punctuated by an elongated spot at their end. They have a size that varies between 6 to 18 mm, the males are smaller than the females which are distinguished by the presence of an apparent auger on the abdomen which allows them to lay eggs.
- A large part of the adult populations live outside the cultivated plot, on refuge plants (such as maize) where they live a large part of their lives. Only the females go to the crop or to wild host plants to lay eggs during the day, which leads to low effectiveness of chemical phytosanitary control.
Protection
- Weed the crop and its surroundings and eliminate the various reservoir host plants that may be found near the production plots.
- Collect and destroy regularly and imperatively bitten fruits (burial, bagging, burning, animals, etc.) in order to reduce fly populations. This measure sometimes proves to be sufficient provided that it is also practiced by neighboring farmers.
- Use an augmentorium (1) with an optimized mesh size net to confine flies while letting out associated insect parasitoids.
- Install canvases at shelter openings. In the open field, use mesh-covered containment tunnels. Under strong heat, it is preferable to use larger meshes which will allow better ventilation, but will allow other pests and also auxiliaries to pass. In this case, provide manual pollination (zucchini) or open the tunnels for a few hours early in the morning to allow the bees to enter, then close the shelter (zucchini and other Cucurbitaceae).
- Favor natural enemies in field cultivation or under open shelters (2).
- Install pheromone traps outside the shelter. (3)
- When regulations permit, "attract and kill" type attractants can reduce fly populations when they are sprayed on refuge plants (maize) planted at the edge of plots (GAMOUR method in Reunion).
- Mass trapping based on food attractant and insecticide is not yet developed for Cucurbitaceae flies.
- Chemical protection on the crop is not effective given the fact that a large part of the fly populations live outside the treated plot.
(1) Structure resembling a closed tent in which infested fruits collected in the field are regularly placed. The augmentorium thus prevents the re-infestation of the agroecosystem by a new generation of adult flies that emerge in the augmentorium, while a net with an appropriate mesh, placed on the roof of the augmentorium, makes it possible to release fly parasitoids into the wild.
(2) Certain natural auxiliaries can help to limit fly populations. To encourage their presence, it is necessary to maintain favorable habitats made up of refuge plants inside and outside the cultivated plots. In addition, insecticide treatments must be rationalized as much as possible to limit their negative impact on auxiliaries.
(3) There are pheromones to use traps (McPhail type) to capture the males of certain species of harmful Cucurbitaceae flies (Cue-Lure® effective on Bactrocera cucurbitae and Dacus demmerezi ) to monitor populations. However, there is currently no known attractant pheromone to trap male Dacus ciliatus .