Tropilég - Cucurbit flies (B. cucurbitae, D. demmerezi)

$RITA$

Bactrocera cucurbitae (Coquillet)* - Melon fly

Dacus demmerezi (Bezzi) - Cucurbit fly of the Indian Ocean

Cucurbit flies

* Bactrocera cucurbitae is newly renamed Zeugodacus cucurbitae

General

Insects belonging to the order Diptera and the family Tephritidae.
In Reunion:
- Bactrocera cucurbitae is present from 0 to 700 m altitude.
- Dacus ciliatus is present at an altitude of 0 to 1,300 m.
- Dacus demmerezi is present from 500 to 1,500 m altitude.

Oligophagous species attacking only plants of the Cucurbitaceae family, Bactrocera cucurbitae can occasionally cause damage to passionflower or mango trees.

Sensitive botanical family (s)

Cucurbits*

* cultivated : calabash, chouchou, pumpkin, cucumber, zucchini, bitter gourd, melon, watermelon, snake gourd, pipangaille; uncultivated: calabash-ivy, wild bitter melon .

Affected production area :

	Mayotte	Reunion
*Bactrocera cucurbitae*
*Dacus ciliatus*
*Dacus demmerezi*

Organs attacked

Fruits

Symptoms, damage

Type of damage :
- The bites of the flies cause a wound on the epidermis of the fruits which can quickly lead to rotting of the flesh. Furthermore, the development of maggots inside the fruit makes it unsuitable for marketing.

Attack estimation and risk thresholds
- Damage is estimated by counting either the number of sorting reject crates over the number of crates harvested, or by counting the fruit stung on a certain number of plants. The risk threshold used is 5% sorting reject crates or 5% damaged fruit. Exceeding this percentage can lead to a significant increase in attacks.

Possible confusion : Little possible confusion except between the different species!

Biology

Cucurbit fruit flies sting the fruit using their ovipositor to lay their eggs (several dozen) at shallow depths. Upon hatching, the maggots feed on the pulp for several days before leaving the fruit to burrow into the ground and pupate. From this pupa will emerge an adult fly. The complete cycle from egg to adult lasts 20 to 30 days depending on the species and the climatic conditions. An important biological element lies in the fact that populations of adult flies mostly live outside the cultivated plot, in this case in the surrounding vegetation or on trap plants set up for this purpose (such as corn).

Protection

The most effective method of keeping cucurbit fruit fly damage to an acceptable level is to interfere with the insect's reproductive cycle by eliminating bitten fruits during sorting rejects. These fruits are thrown into an augmentorium, which stores them throughout their degradation. The augmentorium has a window closed with a canvas whose mesh (about 2 mm) prevents the exit of emerging flies but allows the exit of parasitoid insects from fly larvae. If there is no augmentorium, you can use a barrel or a dustbin with a net attached to the lid.
Stung vegetables can also be given to animals (chickens, ducks, pigs...).
The application of spot treatments using Synéïs bait every five days is complementary to the elimination of bitten fruits:
- on chouchou, bitter gourd: spray by spot on yellow plastic supports spaced every 10 m under the trellis;
- on zucchini, cucumber, pumpkin, melon...: spray every 10 m on the corn rows surrounding the plot because flies spend 90% of their time around the plot on attractive plants such as corn.