Loving the fruit

Our apple and plum trees fruit in August, and there are many bugs that love them, some quite surprisingly. Slugs, springtails, woodlice and fruit flies gorge on fallen apples, and comma and speckled wood butterflies feed on blackberries, but recently I noticed a few new characters in our produce. Seven spot ladybirds clustered on overripe plums (we were away and failed to collect them) and honeybees and wasps joined them. The common wasp (Vespula vulgaris) above, kept coming back to feed on a damaged spot on this fallen apple. Sweet, sweet fruit!

7 spot ladybirds and a wasp

honeybee in plum

Celebrity flies

Continuing with the topical apple subject, I have been leaving damaged and rotten apples on the soil of a large pot. The place now is heaving with tiny fruit flies of the genus Drosophila - possibly the most famous and best known fly in biology, D. melanogaster. It is difficult to give an idea of how much research has been carried out using this fly but a quick search on the Google Scholar academic search engine yielded today under 3,000 hits on the common earwig, while D. melanogaster had 324,000 entries. Since the beginning of last century, experiments on fruit flies have generated much of the basic knowledge of genetics and evolution, and their genome sequence was published in 2000, before the human genome. Among the many reasons they have become such a popular model organism is that they are ubiquitous, easy to keep (who doesn't have fruit flies around the compost heap or fruit bowl?) and reproduce rapidly producing many eggs.
Much research has been carried out on fruit flies mating behaviour and the influence of genes on it. Despite their tiny size fruit flies can be easily watched performing their mating rituals on top of the rotting apples. Males are smaller and with a larger dark patch at the end of their abdomen. Females have a more stripy, and often distended abdomen.
According to Marla Sokolowski:

It might come as a surprise to some that D. melanogaster shows many exquisitely performed and complex patterns of behaviour. For example, the male fly shows courtship behaviour that is full of sensory stimuli and that requires the female to hear his song, feel his taps and licks, smell his odours and visually evaluate his stature...

As a primer, this figure (also from Sokolowski, 2001) illustrates the main steps of the fruit fly mating behaviour. Male 'song' is produced by wing vibration while keeping the wing tipped forward.

Check out the Drosophila melanogaster Wikipedia page for more info.

The lion springtail

Every day I go out in the garden and fetch the few apples that have fallen overnight. This springtail, Orchesella villosa, was resting on top of one today. It sat nicely for me and then jumped to pastures new.

Little pole vaulters

Pottering around in the conservatory the other day I noticed a large springtail walking on the floor. When I say 'large' of course, it is in relative terms as the animal was around half a centimetre long. Springtails, or Collembolans are small wingless hexapods less than 1 centimetre in length, some - one of the smallest insects- less than half a millimetre. Due to their small size they often remain unnoticed, until they jump. And jump they can: springtails can cover many times (I have read up to 20 times) their own length in a fraction of a second. Their name gives away the mechanism they use to jump. They have a prolongation of their abdomen (a forked 'tail' or furcula) which is normally folded under the insect and secured in place with a 'catch'. On being disturbed, the springtail releases the catch and the 'tail' pushes fast against the substrate, catapulting the springtail into the air away from danger.
 My conservatory springtail proved easy to identify thanks to a very exhuberant mane by WAB member Jason Green as Orchesella villosa. Going back to old photos I found one where a couple of individuals of the same species enjoy the underside of a fallen apple with some slugs and woodlice like a group of friends that have found paradise.

Many resources on springtails state that their relationships with insects is unclear, as some research showed they might be more related to crustaceans. To clarify this debate, a recent paper by Regier and collaborators, based on a phylogeny of 62 genes showed conclusively that collembolans are indeed hexapods and more closely related to insects.
More information
A very informative account on Collembollans by Steve Hopkin here.
Collembola.org by Frans Janssens.
Regier, J.C. et al. (2010) Arthropod relationships revealed by phylogenomic analysis of nuclear protein-coding sequences. Nature, 463:1079-1083. here.