Saturday, 26 November 2011

Insects in medicine

I woke up this morning with a strange thought in my head - why aren't insects used more often in medicine? Off the top of my head I could only think of one example (for all of you shouting 'leeches!' they are not insects but worms).

No, the example I was thinking of was the use of blow worm maggots to clean up certain wounds as they will eat the dead tissue reducing the likelihood of infection. An example can be seen here though this is absolutely not for the squeamish!

The real question though was not about the mechanical application of insects but about the use of chemicals derived from insects as medicines. I have often heard about medicines derived from plant chemicals (the obvious example is Aspirin (from Willow if you were wondering)) but not any from insects.

A quick internet search shows that there are some examples, but not much with any really solid evidence behind them. Is there a phytocentric approach to medicinal discovery? You certainly hear of pharmaceutical companies utilising botanists to try and find new drugs and indeed indigenous communities complaining of biopiracy but never have I come across talk of anyone considering the massive variety of insect fauna as a source of new medicines.

So, why not?

It's certainly not because of numbers - there are thought to be around 300 thousand species of plant, but at least 1.3 million species of insect. Perhaps its just that the knowledge of the medicinal effects of plants is better and not close to being exhausted that the harder to find (and more likely to run/fly away) insects are not being considered.

Perhaps more likely though is that plants can't run away and therefore need another form of defence against being eaten. It is often the secondary metabolites produced by the plant to reduce herbivory that are used as medicines. Insects probably produce fewer additional chemicals as a defence mechanism, leading to fewer possible opportunities for finding insects with medicinal properties.

Alternatively, maybe it is just too difficult to convince someone who is ill to eat a beetle...

Thursday, 26 May 2011

Trichogramma in flight

Parasitic wasps of the genus Trichogramma lay their eggs inside the eggs of other insects (see here for a vid). As such, they are very small, typically less than 1mm in length and are known to hitch hike on their host insects to get around (this is more complicated than it sounds - see this excellent 'Not Exactly Rocket Science' post for more detail).

However the reason behind this post is not to discuss the fascinating habits of these tiny insects but to point out a news item on the Flight Artists from Wageningen University, who have used a high-speed camera (apparently 22,000 frames per second) to capture Trichogramma in flight.

This is well worth a quick look, not least because it shows that they can beat their wings at 350 strokes per second but they also appear prone to landing on their faces!

Watch the video here.

Saturday, 12 March 2011

Don't (just) blame the aphids!

I spend a certain amount of time working with and thinking about aphids (AKA greenfly, blackfly, plant lice…) and have to admit to a certain amount of affection for them. I doubt that many farmers and gardeners feel the same way as they are significant pests of most crops and many garden plants. One of their most serious effects is through the transmission of plant viruses as these can cause massive economic damage to crops (eg BYDV, PVY). Note I am not getting into the different virus transmission types (persistent, semi-persistent and non-persistent), but you can read about the differences here. The discussion below is about a non-persistent virus. 

Although it is the virus that causes the damage it is generally the aphid that is seen as the villain in this scenario and it is always the aphid that is the target of any control options.  Often all aphids are seen as a problem, even if only a small number of species (there are over 500 in the UK alone) are actually capable of transmitting a particular virus. At the most basic level, the aphid picks up the virus by feeding on or tasting an infected plant, then moves to another plant and transmits the virus by feeding/tasting again. I think it is often assumed that the virus is passive in this process and that the aphid [maliciously?] skips around spreading as much virus as possible.

However, the relationship between the virus, the plant and the vector is always a complex one that has been shaped over time by natural selection. A number of investigations have shown that, in some plant-virus-vector relationships at least, it is the virus that manipulates the situation to maximise it’s chances of being spread between plants. A relatively recent example is that of the Cucumber mosaic virus and two aphid species Myzus persicae and Aphis gossypii (Mauck et al, 2010). They have shown that the aphid is attracted to infected plants to pick up the virus and then repelled from those plants leading to an increased likelihood of transmission to a healthy plant.

So, how does this work?
  1. The virus in an infected plant
    1. Affects the nutritional balance of the plant so it is not a good host for the aphids
    2. Affects the plant chemistry so that the volatiles escaping from the plant suggest that it is an extremely good host for the aphids
  2. The aphid arrives in the field
    1. Uses plant volatiles to find suitable hosts leading to a good chance that they will land on an infected plant as the plant is giving the signal of ‘very good host’
    2. Once they have landed and tasted the plant (picking up the virus) the actual nutritional balance of the plant suggests it is not a good host and there is a good chance that the aphid will fly of in search of another, more nutritious plant.
    3. Eventually they will come across a good host, which is likely to be an uninfected plant and transmit the virus to a new host.
So the manipulation of the plants biochemistry by the virus essentially tricks the aphid into giving it a ride to healthy plants where it can multiply and continue the process.

There is (probably) nothing in this for the aphid – it is just a dupe, and ultimately not to blame!

This shows that, as with many biological relationships (and indeed many other things), what may appear simple on the surface can actually be a much more complex situation once the detail is investigated.

Reference: Mauck KE, De Moraes CM, Mescher MC. 2010. Deceptive chemical signals attract insect vectors to inferior hosts. Proc Natl Acad Sci 107 (8): 3600–3605. [LINK]

Saturday, 12 February 2011

Entomological Haikus

Though to be fair, these are actually more specific than that as they are all crop protection haikus. These have come about as I spotted the link on Bug Girl’s blog about the 4th Annual Hexapod Haiku Challenge sponsored by the North Carolina State University Insect Museum. I spent a couple of bus journeys contemplating verse rather than damaging my hearing by listening to my pod at full tilt. These are the results:

An attempt to distil the complex epidemiology of Parsnip Yellow Fleck Virus into 17 syllables 

Spring umbellifers
Aphids, virus coincide
Carrots wilt and die

Orange wheat blossom midge is an occasional problem in wheat if the conditions and timing is right and there is only one effective option in the UK

Still summer evenings
Blossom midge flits. Right growth stage?
Chlorpyrifos: death

IPM is used in many closed systems to keep pest populations under control (in this case Trialeurodes vaporariorum and Encarsia formosa)

Glasshouse whitefly blooms
Parasitic wasp controls
Residue free food

Easier than I thought to fit some things into 17 syllables and for it to still make sense! However, I am sure that aficionados of the genre will point out, perhaps using these as evidence, that it takes far more effort than a 20 minute bus journey to produce good quality Haikus.

I have submitted these to the competition and await my prize!

Comments welcome!