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 10^oC (50^oF), 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:

R. Sapkota, K. C. Dahal and R. B. Thapa. 2010. Damage assessment and management of cucurbit fruit flies in spring-summer squash. Journal of Entomology and Nematology Vol. 2(1), pp. 007-012

M.K. Dhillon, Ram Singh, J.S. Naresh and H.C. Sharma. 2005. The melon fruit fly, Bactrocera cucurbitae: A review of its biology and management. Journal of Insect Science. 5:40, available online: insectscience.org/5.40. 

The Mediterranean Fruit Fly: PDF

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Please share with fellow gardening enthusiasts via the various sharing buttons at the end of posts/pages! Else you can vote for posts through the Google reactions bar at the end of articles. To stay up to date I have provided several reader and social networking platforms with which to subscribe: Twitter, Pinterest, RSS Feed Reader or Email/Follow directly using the Blog Followers widget on the left hand side toolbar. Thank you for reading and please feel free to ask if questions arise - I appreciate comments and ideas too! 😆

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Sustainable, Productive and Economical Vegetable Gardening (Part 4): Vegetable Garden Planting Guide & Management

When you consider an ideal vegetable garden I imagine that many of you (as well as myself at one point too) had the following image in mind: Vegetables arranged in neat regimented lines or blocks containing one type of vegetable, perfectly bordered by some type of hedging and clear weed free paths between the planted beds. No weeds, no bugs – simply a beautiful garden with lots of bursting fruits…

Chateau Villandry potager

Vegetable garden at Ham House Estate

Sadly, this reality is rarely achievable due to the high maintenance of such a garden. Also vegetable production, soil health and pest control will be very poor. Let me give you a breakdown of the impact of the 'perfect, clean and neat' garden design has on food production and its ecosystem;

1) Mono-cropping of vegetables, either as rows or blocks has the following implications:

a) Soil becomes depleted of a certain type of nutrient. For instance, a block of leafy veggies will consume a lot of soil nitrogen, a nutrient required for leaf growth. This creates a large imbalance in the NPK ratio of the soil in that area.

b) Plots are separated by barren soil – this are likely walkways, which prevent soil compaction in growing beds, but these separate areas of beneficial insects and limits/prevents their spread to other areas.

c) Disease spread like wildfire through mono-cropped plants resulting in large losses.

Solution: Increase diversity of plants by planting multiple types and species of crops in each bed – resulting in a mixed plant population. Allow separated beds to become connected by adding an organic soil cover, either living or dead.

Maize monocropping

2) No organic soil cover on the bare soil paths or planted beds, leads to:

a) Extensive erosion of soil by all the elements, including topsoil loss through wind, rainwater runoff and leaching of nutrient, as well as the loss of moisture through excessive sun.

b) Soil structure breakdown, due to erosion, which has a direct impact on soil health, where micro- and macroscopic soil animals cannot flourish and their biochemical processing of the soil is at a minimum resulting increase nutrient depletion of the soil.

Solution: Add an organic soil cover, either living or dead. It increases soil nutrients and soil life during decomposition, as well as preventing erosion of soil structure and leaching of soil nutrients.

Soil erosion on farm

3) The rigid design of the vegetable garden, either as rows or squares, results in:

a) Lots of labour, not only in the initial setup of the garden, but the maintenance as well. Weeding will be a constant battle as bare soil becomes a haven for them. Plants are sickly due to mono-cropping and require lots of pest control (usually in the form of chemical control as beneficial insects are non-existent). Soil structure is poor leading to tillage, which breaks down soil structure even more, leading to nutrient loss that needs to be replaced by synthetic fertilisers for a quick fix instead of organically derived sources.

b) Plants are disturbed regularly by pruning and pulling of plants to fit exact plant spacing, which leads to a marked decrease in beneficial insects that would have assisted with pest control.

Solution: Let the plant become a bit wild - do still prune them to shape, for exposure to maximum sunlight and optimum production, but allow them to become intertwined. Disturb them as little as possible, but when you prune, give the prunings a vigorous shake to return any beneficial insects to the garden. A more ‘wild’ vegetable garden scheme will allow less weeds, pests and fertilising - as well as an increase in crop production, health and overall enjoyment of the garden.

The solutions I have posed are aimed at letting Mother Nature work with you during your food growing endeavours, where beneficial insects keep pests at a minimum level (pest will never be eradicated!), organic soil covers provide nutrients to the soil and acts as weed barriers, lastly the diverse and dense plantings decrease pests and diseases as well as assisting with balanced soil nutrient consumption and improved soil health (through a diverse soil life that inhabits plant roots).

You will notice that much of this introduction is aligned with two other posts: the Conservation Agriculture and my Insectary post. These two posts cover the main ‘natural’ principles to keep in mind, but I would replace crop rotation with diverse plantings rather (where multiple crops are planted in the same bed) in the Conservation Agriculture's principles list. Leading from this new approach to gardening, let me give you an example of what my garden looked like last summer (2014-2015 season):

Vegetable Garden Summer 2015

Now you will likely tell me that it looks like a royal mess! – it does seem a bit untamed, but it actually took a bit of planning to get it this way and I have not yet perfected the technique. Therefore, my ‘Vegetable Garden Design’ will not be a set of measurements and crop groupings as many books and internet design software will dictate. This is mainly due to the fact that;

1) Each garden is unique. My sizes are not standard, therefore I have to work around this.

2) Everybody eats differently. Many of us will eat different types of vegetables and in different amounts – for instance we eat a lot of tomatoes, but don’t plant any chillies, therefore the garden will look different to someone who loves chillies.

3) Trial and error is part and parcel of working with Mother Nature. You will have to grow a bunch of different vegetables with different vegetable layouts to discover what works for your garden. This is where record keeping is integral, note down where the cucumbers did well, or the radishes suffered, which pests are prevalent and what plant(s) to include in the garden next year for attracting beneficial insects to assist with that specific pest problem.

Although, I am not going to put down an exact fool-proof universal planting method here, I will provide an example of my garden plan…

Now I have a very strange garden outlay with 8 beds and three sides of the garden is surrounded by walls. One bed is permanently occupied by herbs (blocks indicate their relative overlap with one another), whereas the others are open for planting. The pathways between the beds are paved with bricks and the bare soils in the pathways are occupied mostly by penny royal. The bare soil areas outside the garden beds are occupied by penny royal that spilled from the pathways and some parsley as well as an ice plant/vygie (Mesembryanthemaceae).

Parsley weed barriers on the outside of the vegetable garden:
See Post on How to Grow Parsley

I roughly divided the plots into 36 circles for approximate planting position. Large vegetables such as the tomatoes, potatoes, peppers and cucumbers have one plant occupying a circle, whereas root vegetables and onions contain multiple plants. I have white clover (Trifolium repens) in my two left-most plots (the top and side one), the other two top beds have sweet potato as a ground cover as it occupies the whole bed between the other vegetables, whereas the rest of the plots have the lesser trefoil (Trifolium dubium) clover as ground cover.

Lesser/suckling hop trefoil,
Trifolium dubium clover

I want to change this garden plan for next year to have all the different root veg (radish, carrot and beets) in one plot as the larger vegetables outcompete the root veg for light in this current setting. I will likely mixed the root seeds with a bid of soil and scatter them randomly in the plot – no rows or blocks of any kind. The cucumber, sweet potato and potato’s positions would likely remain the same, as the cucumber likes the evening sun it gets from that current position, whereas the potatoes and sweet potatoes enjoy the more shaded beds at the back near the walls.

I have planted out the winter vegetables for this season in a mix-match planting setting similar to the summer garden and will report on the success of the set up later on. Lastly I want to show you two pictures of vastly different vegetation types - do you see the resemblance?

Cape Fynbos Vegetation

Savannah Grassland Vegetation

Both systems have diverse and dense plantings with no bare soil to see, as well as a permanent ground cover supplied by many different low growing plants. This is how Mother Nature intended natural vegetation to grow and it would be beneficial to mimic this system in the vegetable garden. Some of you might notice that my proposed system has a lot in common with Permaculture and The Seven System of the Food Forest. The concepts behind Food Forest are great should you create a 'native food garden' with plants suited to that growing system, whereas vegetables have long lost those traits due to their domestication. Since I discovered that planting carrots under tomatoes only gives you poor carrots due to their battle for sunlight - I am working on a different version of the same concept... stay tuned for updates and let me know whether you have implemented a similar system and what you relative successes are.

Related Posts:

Sustainable, Productive and Economical Vegetable Gardening Series
Part 1: Vegetables Worth Growing
Part 2: Conservation Agriculture
Part 3: Integrated Organic Gardening

Insectary: Beneficial Insects & Garden Security Force
Lunar Gardening: Planting by the Phases of the Moon
Biodynamics: Lunar Gardening Revisited
Penny Royal: The Living Mulch
Green Manures: Cover Crops & Green Forage

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Please share with fellow gardening enthusiasts via the various sharing buttons at the end of posts/pages! Else you can vote for posts through the Google reactions bar at the end of articles. To stay up to date I have provided several reader and social networking platforms with which to subscribe: Twitter, Pinterest, RSS Feed Reader or Email/Follow directly using the Blog Followers widget on the left hand side toolbar. Thank you for reading and please feel free to ask if questions arise - I appreciate comments and ideas too! 😆

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