The Biosphere Blog

Fruit Fly

Posted by on 01 Dec 2020 in General Information, Jujube Cultivation and Horticulture, Pests and Diseases

Introduction

Fruit fly is an absolute scourge of a pest. If you have ever experienced just one infestation for yourself, then you will fully appreciate the devastation and its potential to literally wipe out the livelihood of commercial fruit growers overnight.

Professional growers are well aware of this problem, and millions of dollars are spent each year combating it. We all pay in some way, whether from lost crops, lost exports or costs passed on to the end consumer.

This post is written for the backyard/hobbyist fruit grower who may not yet have experienced fruit fly, or who has, but not known how to minimise future attacks.

Fruit Fly in Australia

This page states that there over 150 species of native fruit flies in Australia, while this one states over 300. Which to believe?! Whatever the number, the general consensus is that most of these do not attack commercial crops.

But without a doubt the two worst commercially are the native Queensland fruit fly (Bactrocera tryoni) and the introduced Mediterranean fruit fly (Ceratitis capitata), and both species readily attack jujubes.

Queensland Fruit Fly (Bactrocera tyyoni)

Queensland fruit fly (’Qfly’) hails from the subtropical rainforests of Queensland and northern New South Wales. Land clearing and the establishment of commercial orchards and backyard gardens has increased its range northwards into northern Queensland and into the Northern Territory, and southwards into southern New South Wales and Victoria. (Map here.) Increased irrigation and ease of watering in general has advanced its range further into drier regions too. A list of host fruits is here.

Mediterranean fruit fly (Ceratitis capitata)

Mediterranean fruit fly (’Medfly’), despite its name, apparently originates from sub-Saharan Africa and attacks over 200 fruit and vegetable crops. It was first found in Australia in 1895, in Claremont, a suburb of Perth, Western Australia, and is now endemic in that State. (Map here.)

Biology, Life Cycle and Identification of Fruit Fly Species

It’s beyond the scope of this post to cover these here, but for more detailed information on the biology, life cycle, and how to identify particular species, please go here for Queensland fruit fly, and here for Mediterranean fruit fly.

You may also find these videos and links interesting.

This site is an excellent resource for those with an entomological bent, or who just enjoy looking at truly stunning high-resolution, high-quality photomicrographs of tiny things! And the 360° Fruit Fly Rotator is well-worth a play!

Fruit Fly Damage in Jujube Fruit

Pictures speak a thousand words! The following photos were taken in February 2020.

Combating Fruit Fly

Commercial growers rely on large-scale, time-efficient monitoring, baiting, bait spraying and cover spraying such as outlined here. Some commercial jujube orchardists have their trees under large structures fully enclosed by nets for protection from both insects and birds.

Home gardeners may only have one or a small number of trees to protect, and control options include exclusion netting, fruit bags, traps and spraying. These options are covered here (with links on net application and how to make your own traps) and in this Gardening Australia video (with transcript).

A fruit fly control calendar can also be downloaded here. This doesn’t list jujubes, but the January – March ripening and harvest time for plum is a good guide for jujubes. November – December is the recommended time to start monitoring and control measures for that fruit species. (Which is why I’m even thinking of this subject and writing about it, as I’m doing this now for my trees!)

Pros and Cons of the Various Home Garden Options

All of the above options are effective control measures for fruit fly, and all have their pros and cons. I’ll cover these as best I can, which may help you to decide which is best for you. I’ll then mention my preferred choice, for what that’s worth.

If anyone has direct experiences or recommendations on any of these themselves, please do share in the comments!

Exclusion Nets

If going this route, please be sure to use the fine-mesh nets rated for insects, rather than the wider-holed netting rated for birds!

Pros
One outlay will provide you with a net(s) you can use over and over, and even on different trees within a year if they fruit months apart.

Cons
Nets are not only fiddly to apply, but you must make sure they are gathered tightly around the lower trunk and do not touch any fruit, as the female fruit fly’s ovipositor can still penetrate the mesh even if she can’t. You must also keep the tree pruned to a height of about 2 m or less to ensure the entire tree is adequately covered. (This could classify as a pro, as it forces all fruit to be within a reachable distance for picking!)

I’ve never used an exclusion net, but would imagine that they’d be a right pain to apply without touching any fruit. Jujubes only fruit on the deciduous fruiting branchlets, which are the most external structures of the whole tree. I’d also wonder how those branchlets would hold up to the constant movement of a net (such as from wind) rubbing on them. If I were to use a net I’d erect some kind of frame a small distance from and above the tree on which to hang the net. And even then you’d still want that net to be secured around the trunk, and not to the ground, as fruit flies pupate in the ground. Otherwise adult females may emerge from the soil enclosed by the net and attack your very carefully covered tree from within!

Fruit Protection Bags and Sleeves

Pros
Easier to apply than nets, I guess, not ever having used them. And again the one outlay can be used over and over. Be sure to keep a tree pruned to a manageable height to ensure topmost fruit can be reached and covered.

Cons
Bagging sounds an incredibly laborious and time-consuming method, but that’s just me — it might be a perfect solution for many others!

You’ll probably need many of the larger-sized bags or sleeves for a larger tree owing to the whorls of fruiting branchlets produced. Also bear in mind that jujube trees have an extended fruiting season over weeks and months unlike other fruit trees, so you may need more again. And again, I’m not sure how effective the mesh-style bags would be in not touching any fruit.

Traps

Pros
Very easy to set up and maintain, as well as being a visual indicator of whether fruit flies are even in your vicinity, as evidenced by their presence in the trap — something exclusion nets and bags can’t provide.

Cons
Buying commercial traps and refills can be expensive upfront if many are needed, and there is an ongoing cost in topping them up. There may also be a time-cost, depending on how frequently and how many must be topped up. Making your own traps and bait is cheaper, but may be a false economy for some if costly in time.

Sprays

Cover sprays are insecticides. Bait sprays are a food attractant laced with small amounts of insecticide — the insect is attracted to the bait, ingests the poison along with the food, and dies. Always follow label directions, for any formulation you apply, diligently.

Pros
A good way to treat numbers of trees at once. Bait sprays generally are safe to use, do not harm non-target insects, and do not have a withholding period. (Check the label to be sure.) Some cover sprays also have these features, especially the ones aimed at the home grower.

Cons
Reapplications may be necessary throughout a season, and may need to be timed carefully. A cover spray may be indiscriminate and target beneficial insects, as well as have a withholding period, during which fruit must not be consumed. Weather conditions will dictate the spraying window — ideally when there is no wind and/or rain.

My Choice, For What It’s Worth

Hands down I prefer a commercial trap. The one I use currently is the Cera-Trap^® by Amgrow. (I do not receive any remuneration or other benefit for saying this, and this is not to be taken as an endorsement.) This trap contains a liquid protein solution that attracts both males and females of both Qfly and Medfly. Flies enter the trap, drown in this liquid and sink to the bottom out of the way of yet more flies entering and drowning!

I especially like how the liquid solution lasts a whole season. Set and forget for months, unless regularly stopping by to gloat over the rapid accumulation of little bodies along the bottom! The liquid does slowly evaporate over time, but not enough to evaporate dry. Should the liquid become less liquid from dehydraton, it can be rehydrated with water. Should levels go down too much overall in the trap, these can be replenished from a refill bottle if necessary.

The contents are completely compostable — it says so on the box!

The recommended application is one per tree or one per 20 m² when trees are touching.

Yes, you can make your own traps and bait (methods and recipes galore are easily found via a search), but for me these are a false economy owing to the number of traps I would need (smaller effective range of usually every 2 m), the time required to make up the solutions, and the frequency with which the home-made ones need to be topped up (weekly). I’m just not interested! Though I fully understand why others would — it might even be a fun activity for some!

Disposal of Infested Fruit

Infested fruit will contain maggots and eggs, and these need to be killed so as to break the breeding cycle. Place all such fruit in a plastic bag and leave this in the sun to cook over a few days. Throw this in the bin, or, less wastefully, add the nitrogen-rich contents to the compost!