Roots 'n' Shoots: Mediterranean Fruit Fly – Pest of the Month

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Sunday, 31 May 2015

Mediterranean Fruit Fly – Pest of the Month

Fruit Fly at a glance

Type of Damage
Chewing & secondary bacterial rot
Plant Symptoms
Misshaped fruits, up to 100% crop loss!
Favourite Plant
Several fruiting trees, vines & shrubs
Occurrence
Year-round in areas with mild winters (SA)
Distribution
Worldwide
Control
Difficult, chemical lures main control method, else avoid planning susceptible crops during fruit fly months

Mediterranean Fruit Fly,
Ceratitis capitata


Quick Intro

Fruit flies are the horror of commercial and backyard gardeners. Not only do they cause extensive damage to many fruiting plants, but they are hard to control due to their biology and lifecycle. The best route for the organic gardeners is to simply avoid planting host crops during the most active months of the fruit flies lifecycle (high summer, Jan-Mar in South Africa).

Science Stuff

The Mediterranean fruit fly (or medfly), Ceratitis capitata, originated in sub-Saharan Africa and quickly spread throughout the Mediterranean regions. Globally it has become a problematic invasive species worldwide. It belongs to the Tephritidae family of the Diptera order or ‘true flies’, where the second pair of wings has been reduce to ‘halters’ (spoon-shaped wings) used for balance during flight.

Distribution map of the Mediterranean fruit fly, Ceratitis capitata (Wied.)
© Copyright FAO IAEA 2013.



A similar species, native to southern & eastern Africa, is the Natal fruit fly, Ceratitis rosa. It has displaced the Mediterranean fruit fly in several regions and can be more economically damaging that the Mediterranean fruit fly. It is similar looking to the Mediterranean fruit fly, but is slightly larger and has differently patterned wings and black spots on its thorax.

The species we have a problem with is the Cucurbit Fruit Fly, Bactrocera cucurbitae. It is a widespread problem of many plants in the Cucurbitaceae family, which includes squash, cucumbers and melons.

Hosts

Both the Medflies and Natal fruit flies are polyphagous, meaning they feed on several varieties of fruiting plants. They prefer softer or thin skinned fruits, since the lay their eggs underneath the skins of fruits.

Here is a list of common host plants of importance for the backyard gardener:
Host plant
Mediterranean Fruit fly
Natal Fruit Fly
Apple
X
X
Apricot
X
X
Avocado
X
X
Blackberries
X

Citrus
X
X
Fig
X
X
Grapevine

X
Guava
X
X
Lilly-pilly, brush cherry
X

Mango
X
X
Peach
X
X
Pear
X
X
Peppers, capsicums
X
X
Persimmon
X
X
Plum
X
X
Prickly pear
X
X
Tomato
X
X


For an extensive list of Mediterranean fruit fly hosts see:  Featured Creatures: Mediterranean Fruit Fly.

For a comprehensive list of Natal fruit fly hosts see: Invasive Species Compendium.

We never had a big problem with the fruit flies, they usually attacked the apricots growing wildly in the veld and most of my produce was spared. For the past two years our spring rains where very late we have had an invasion of the Cucurbit fruit fly on my squash plants in the pumpkin patch, causing a 90% fruit loss of our second cropping round in January-March 2014. We had some losses in the main garden as well, but the largest point of invasion was in the pumpkin patch. The cucurbit fruit fly is slim and larger than the Medfly. It is red with yellow spots on it abdomen. Uncharacteristically, it has non-iridescent black eyes and clear wings. Here is a photo of one ovipositioning as well as the damage caused to cucumber and squash fruits as well as some tomatoes and peppers.

Cucurbit Fruit fly,
Bactrocera cucurbitae
Life Cycle

In optimum conditions the Medfly can complete its lifecycle (egg, larvae, pupae and adult) within 21 days. Whereas in cooler periods, below 10oC (50oF), the lifecycle either ceases or takes up to 100 days to complete. Females can lay up to 300 eggs during their life time. This effectively ensures a robust population that is challenging to control. Ovipositioning occurs underneath the skin of the fruit, where clusters of 75 eggs are laid. Larvae hatch after 1.5 – 3 days and immediately begin to feed and tunnel in the flesh. Larvae are typical white maggots between 7-11 mm in length. Larvae mature in 10-26 days depending on the host plant, after which they drop from the fruits to pupate in the surrounding soil. Pupae are 4 mm cylindrical shaped ‘pods’ resembling a cereal grain. Adults emerge in 6-13 days. Adults die within 4 months if no food is available (fruit, honeydew or plant sap). Some adults may overwinter cool temperatures or survive for up to 6 months in adverse conditions. Adult fruit flies are small (6 mm) and can disperse up to 20 km to seek a suitable host plant. Global fruit product trade has transported and introduced fruit flies to many new areas as well as re-introducing fruit flies to pre-exising populations.



Control

Fruit flies cause extensive crop damage by the initial ovipositioning of females and the feeding of larvae. Both expose fleshy parts of the fruit which quickly become infected with secondary bacterial/fungal rot. The initial oviposition point causes a pitting of the skin and fruit, this makes the fruit grow at an angle (bend at the pitting point) thereafter larvae feeding and rots make the fruit soft and sunken. Most fruits cannot be rescued and the best remedy is simply removing the host plant before larvae fall from the fruits to pupate in the soil (resulting in re-infestation next season).

When it comes to fruit fly invasions, there is little to do on the organic side as most products available in South Africa are nasty chemicals or expensive lures based on pheromones. We decided not to fight the invasion, after failed attempts at making my own lures and bagging each fruit individually was much too laborious. Thus, we plant a huge amount of summer squash early in the season and rip them all out after their first cropping in December. Larger winter squash (Butter nuts, Flat white boers and Hubbards) are more resistant as their skins are very hard to pierce, if smaller fruit become infected – soak them in water for 2 days to drown any larvae and throw away. Fruit fly populations are reduced drastically when there are no suitable host plants, therefore not providing any are the best way to control fruit flies organically.

For those of you with more serious invasion of multiple fruits, there is a Natal fruit fly lure available from Ever Green Growers and Fruit Fly Africa are working on sterile male release technology to reduce population expansions. 

Improved fruit fly lure trap

Something Interesting: Sterile Insect Technique

One type of biological control of many pest species, especially flies, is to release sterile males into the environment. Males from a fly species are radiated to make them sterile. Afterwards they are released into the environment to compete with wild-type males and mate with females. No offspring are produced from sterile males and hence the population decreases with each successive fly generation and the release of sterile males each season. Unfortunately, irradiated males are less fit than wild-type males and often compete at a diminished capacity. 

This technique has been successfully used on screw-fly, Cochliomyia hominivorax, a pest of cattle. It has also been implemented for the Medfly and Mexican fruit fly, Anastrepha ludens. This technique has been extended to several human pathogenic carriers such as:
Anopheles mosquito, carrier of Malaria,
Tsetse fly, carrier of Sleeping sickness,
Aedes mosquito, carrier of filariasis, dengue and yellow fever.


References:



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4 comments:

  1. Shroom - Thanks for all the info. I find it incredibly frustrating that fruit fly traps are not available in SA. I have written to FFA only to e informed by them that they do not supply the public (grrrrrr) Importing traps - not an option - too costly and not a good trasnport footprint - especially when there is a product available locally...

    An Houw Hoek farmer had to destroy an entire orchard due to woolly fruit fly infestation a year or so ago. Surely making the bait / traps available to the public would help stem the infestation countrywide?

    ReplyDelete
  2. Flies are notoriously difficult to control and for the organic gardener it is a nightmare. For instance the chemical pesticides are an absolute no-no in my garden due to their general insect target range not to mention toxicity to us and even more so to our cats. The pheromone lures have inconsistent efficacy whereas those yellow-sticky paper traps are also not very effective and I have found many other beneficial insect victims stuck to them in the past.

    On a commercial scale however I can understand that the farmers would use chemicals as a means for control, at least until an alternative with the same efficacy and cost presents itself. I imagine that the FFA do not want to supply the pheromone lures to the public as it contains a natural pesticide called GF 120 Spinosad, which likely needs to be applied/used by professionals ... although it is in very low doses and would likely not do sufficient harm to humans, it is a problem for birds & aquatic life. The Spinosad lures/baits also seem to attract biological control parasitoid flies as unintended victims, which again make the lures more general than one would like.

    So, unfortunately, one is stuck again with limiting the population by not providing host crops - and as with many of SA's problems; proper quarantine & trade regulations are at the top of the list as it would go a long way to limiting & even preventing the spread of such invasive species. Until then it remains with us backyard wacky-doodles to come up with environmentally friendly ways of keeping the pests at bay whilst feeding ourselves at the same time - sad as it may be. Yet, I am sure one could train a couple of people in each province to provide Spinosad application services to the public...

    ReplyDelete
  3. Is there any work being done with nemetodes?

    ReplyDelete
  4. Are you referring to sterile nematode techniques or control techniques overall? I am not cued up on nematode research but I can make a few comment overall. The sterile male technique would likely be ineffective due to the scale of the nematode population, I wuold assume that something such as a fungal control would be preferable, such as the parasitic/predatory Trichoderma genus of fungi - who ensnare nematodes and consume them. I know of an established nematode research group at Wits University, but more specific details I'll have to read up on first.
    Hope that helps!

    ReplyDelete

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