Tomato fly – revisited

An email conversation with an entomologist from New South Wales prompted the addition of a paragraph (in bold) to this article from about a year ago.

I picked a tomato off the bush the other day and noticed a little hole in it. I cut it open and saw that the contents were looking a bit ordinary, as if it was about to rot. Under higher magnification I could see the culprits – fly larvae – yep, maggots! The image below shows a close-up of one.

tomato fly larva

Queensland fruit fly (Bactrocera tryoni) and Mediterranean fruit fly (Ceratitis capitata) are known to lay their eggs in tomatoes, but neither of these species is found in my region of Victoria. The larvae of vinegar fly (Drosophila melanogaster) – known in America as “fruit fly” – feed in fallen rotting fruit, but this tomato was on the plant. So what species of fly produced the larvae?

I put the offending tomato in a plastic container and waited. Over a few days the larvae grew bigger, allowing me to take the photograph above, and started to jump around the container. I knew this was a sign the larvae didn’t want to be in the moist tomato pulp anymore, and were looking for somewhere dry to pupate. I shepherded as many jumping larvae as I could into a dry container with some tissue paper at the bottom, and by the following day they were all pupae.

The flies haven’t emerged yet, but I know what species they are because I went through this same exercise last year. Behold, the metallic-green tomato fly Lamprolonchaea brouniana (Diptera: Lonchaeidae).

metallic green tomato fly

These little flies are only about 4mm long, so they might be a bit hard to see in the garden. The good news is that, in my garden anyway, they are not in very large numbers and don’t lay eggs in every tomato. It is an endemic species that has been most commonly collected from the temperate south. Those wanting to learn more about this pretty little fly could jump onto the Australian Fauna Directory here.

(Note – The “jumping” behaviour of the larvae of these flies is not unique. Queensland fruit fly larvae also “jump” when they leave the larval substrate to pupate. My NSW correspondent suggested that this has led to some confusion in Victoria where people are assuming these metallic-green tomato fly larvae are Queensland fruit fly larvae. Then they wonder why their Queensland fruit fly traps and baits, which are specific to QFF, aren’t working. This illustrates why accurate identification is vital in pest management.)

One more thing about the vinegar flies mentioned above. Don’t be alarmed if you find lots of little flies in your compost. Vinegar fly larvae help with the decomposition process. You don’t need to “get rid of them”! Vinegar flies are about 3.5 mm long and look like this (below).

drosophila

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Where do insects go in winter?

Insects are ectothermic meaning they don’t generate their own body heat, and rely on external sources to regulate their body temperature. Freezing temperatures are life threatening to many insects, so how do they survive winter?

One July morning I went down to my vegetable garden to see how the plants had survived the deep freeze (-3°C) of the night before. I wasn’t surprised to find my brassicas were covered in ice crystals, but I didn’t expect to find a cabbage white butterfly (Pieris rapae) larva also encrusted in ice. I decided to keep an eye on it, so after the day warmed up a bit I revisited the garden to find the caterpillar happily munching on the plant. How did it do it?

Cabbage white larva Continue reading Where do insects go in winter?

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Return of the Green Scarab

Green scarab beetleDuring November swarms of green scarab beetles (Diphucephala colaspidoides) descended on my place. They are notorious leaf eaters noted for stripping the leaves from a variety of plants. The beetles tend to feed in large groups so plant damage can happen quickly and be quite devastating. Can plants recover after such damage? Continue reading Return of the Green Scarab

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