Turning into a monster

Turning into a monster

So what is it that turns this harmless solitary herbivore into part of an unstoppable cloud that consumes all that is in its path?

 

Well it all starts with a bit of rain followed by some nice weather that improves conditions in just the right way for the locust that then go onto reproduce at high numbers. How does this lead to these otherwise docile creatures turning into a swarm of ravenous monsters?

As their population size increase the levels of the locust change to suit the high densities by becoming more mobile but also more hungry…..

So what changes occur between the two types of locusts?

Physical

The brain of a gregarious locust grows to be about 30% large than a solitary locust, this helps the locust change their behaviour to suite a more generalist diet, where they need to remember what plants are best to consume over others. The larger brain will also help with the behavioural requirements needed to be part of a swarm such as having the ability to recognise the behaviours of other members of the swarm to reduce the effects of intraspecific competition. There is also a reduction in overall body size to allow the locust to be more mobile by reducing energy cost of having a larger body as well as an increased metabolism to help with the greater increase in energy output used by continuously moving over large distances.      

 Social/feeding

Solitary locusts do not occur in high densities and tend to move away from other locust they come in contact with each other.  whereas the gregarious locusts will swarm together in densities of more than  100 locusts m² and at these densities they will switch from eating a small range of host plants which become less available, too consuming a large range of plants unspecific plants that they come across as they travel across the land.

How do these locusts know that it’s time to swarm?

When the locusts come into close contact with each other they brush against hairs on their hind legs that trigger the release of serotonin this then compels the locusts to keep together as it gives them a chemical reward for being in close quarters with each other.  

Once the locust are together they start to march in columns that can be up to 6km long, they will continue this marching through the nymph stages of their life cycle but once they reach fall development they will fly in massive swarms that can cover large areas and eat everything they can that crosses their path until the population becomes too unstable to support as the resources start to deplete the locust can become cannibalistic as they need to feed constantly to support their high metabolisms.

These swarms are unpredictable as there is still a lot that isn’t know about them, there is also variation within the species of locust that can produces these swarms thus adding more complexity to what we need to know to understand the swarming behaviour that they exhibit and how to control them, so they do not cause millions of dollar of damage in the areas in which they occur .

 so until there is a time where we can control them people will always have to eyes to the skies and listen for the buzz of the swarm.

 

reference:

Ott SR, Rogers SM. 2010. Gregarious desert locusts have substantially larger brains with altered proportions compared with the solitarious phase. Proceedings of the Royal Society B-Biological Sciences 277(1697):3087-3096.

Simpson SJ, Despland E, Hagele BF, Dodgson T. 2001. Gregarious behavior in desert locusts is evoked by touching their back legs. Proceedings of the National Academy of Sciences of the United States of America 98(7):3895-3897.

 

Feeding the masses

How are leaf-cutter ants (Atta cephalotes and Acromyrmex echinatior) able to support their colonies of 1 million plus individuals on nothing but there home grown fungus? 

For the last 50 million years ants have been doing what we still are not fully able to do, managing a sustainable agricultural system. They do this by working symbiotically with Bactria to cultivate a single species of fungus into fungus gardens while protecting it from numerous weeds and parasites as well as other bacteria and insects. 

 

 What roles do the ants and bacteria have in the growing the fungus gardens?

Ants- the ant collects the resources required by the fungus to grow and as their common name suggest that is leafs. Once the leafs have been brought back to the nests the ant shred the leafs and “feed” it to the fungus. They protect the fungus from “weeds” by removing areas of the fungus garden that have other fungus growing from them and they also remove sections of dead fungus, some of the leaf-cutter ant species have areas used specifically for the disposal of the waste from their fungus gardens to ensure there is no spread of any unwanted pests and pathogens back to the garden. To stop weeds from establishing the ants lick the surface of the fungus to collect spores of unwanted fungus. Some ants also apply fecal waste to their gardens, this is thought to both help the degrade the plant martial to help their fungus digest the leafs and also help minimalize infection of other fungus because  high levels of chemicals like lignocellulases in the faeces . While preforming these tasks the ant will secret acids and other compounds from their metapleural gland that have antibacterial properties that also help maintain the fungal garden.

Bacteria- there are also some bacteria that work symbiotically with the ants, these bacteria mostly have antibacterial properties that can help inhibit the growth specialised paristies of the fungus and other less specific pathogens.

With the combination of the ants control methods and the bacteria the fungus gardens can maintain very controlled conditions that allow the ants to maintain a there agricultural system and protect it from any pests.

So why is it more beneficial for the ants to rely on the fungus over other food sources?

The fungus can break down plant polymers that the ants digestive system could not, so because of this the ants can get a higher return from the leafs they collect by using them to cultivate the fungus that has evolved with the ants to give an optimal return back to the ant.  In different ant communities the different fungus utilises different plant polymers that they break down into more easily digested compounds. (see refence paper for the list of different ants and funguses, pages 5-8)

    

So if these ants have been able to maintain such a heavily controlled agricultural system for the last 50 million years could we adapt this in a way to feed people more efficiently?  If so I hope you like mushrooms because you may be eating a lot of them someday .   

Aylward, F. O., Currie, C. R., & Suen, G. (2012). The evolutionary innovation of nutritional symbioses in leaf-cutter ants. Insects, 3(1), 41-61.

               

               

Destroying your body, controlling your mind

So imagine you’re a fly, you’re out and about doing fly things when you decide you’re a bit hungry so you stop by your favourite flower and have something to eat, you realise it tastes a bit different  but think nothing of cause you’re a fly, you don’t really think to start with. After a while you start to feel something strange and start to do things that as a fly you wouldn't normally do, then one day Bang! A hypha burst out your head and you die. You've just become a victim of an ENTOMOPATHOGENIC FUNGI!

(Cordyceps Fungus Infected Flesh Fly)

Entomopathogenic Fungi have been doing this for as long as there have been insects to infect, they come in many different forms and effect there hosts in different ways. A typical entomopathogenic fungi will slowly grow inside there host while consuming them, typically it is to the benefit of the fungi to keep the host alive for as long as possible so it can get enough resources from its host to reproduce successfully.  When the fungi is ready to reproduce it will manipulate its host to optimise its dispersal and survival ranging from killing it where it stands to changing its behaviour to find new host or increasing its range of dispersal.

Once infected an insect will change its behaviour ether as a defence against the fungus or due to the fungus taking control.

Some of these behaviours are:

  

BEHAVIORAL FEVER

Behavioural fever is the insect’s way of delaying the funguses growth or stopping it altogether. This is achieved by seeking out locations of higher temperature and increasing the internal temperature of the insect. This behavioural response has been seen in multiple species of insects including Musca domestica and locust and grasshopper species, and when these species has raised there temperatures they were more likely to live long enough to reproduce before succumbing to the fungi

FEEDING BEHAVIOR

In most case insect will reduces the amount of food they consume as they get closer to death, this is caused by the chemicals released by the fungi but in earlier stages of infection the feeding rate will normally not drop as the fungi wants the insect to consume as much as possible for its own benefit.  In some cases an infected insect will start to move away from the normal feeding site of the insect, this can be a result of the fungi driving the insect to places for better dispersal but in other case it is thought to be because the insect is trying to reduce the rate of infection to closely related insects by insuring that it is some distance away from its offspring or other close relatives before it dies and the fungus starts to produce spores  

REPRODUCTIVE BEHAVIOR

As expected the fungi will lower the reproductive rates of an insect weather it is because the fungi is reducing the amount of energy the insect can invest in reproduction or because of the effects of secondary metabolites that effect the growth and development of eggs and nymphs. In the case of M. domestica , when a female has died the fungus can release pheromones that attract males to mate with female that will then go on to mate with other females and spread the fungal spores to more flies.    

 
(Entomophthora muscae, anthomyiid)

SOCIAL BEHAVIOR

Eusocial insects typically live in environment that favour the growth of fungal pathogens, so when a entomopathogenic fungi is detected with in a colony the insects increase in there grooming habits to remove spores from there body and will also remove infected from their nest or bury the dead to control the spread of the infection but when all this fails they will abandon their nest and create one where the fungus is not present.

So as I have shown with these examples the behaviour of an infected insect will change after infection ether for its own benefit or because it has been driven to do so by the fungus and these responses can have a large effect on the host or fungus survival and fitness.

So next time you feel the need to lie in the sun with little appetite and no energy you better hope you don’t get a sudden erg to climb because thing are not going to end well for you, but then again you’re probably not an insect so you should be fine…….     

Roy, H. E., Steinkraus, D. C., Eilenberg, J., Hajek, A. E., & Pell, J. K. (2006). Bizarre interactions and endgames: Entomopathogenic fungi and their arthropod hosts. In Annual Review of Entomology (Vol. 51, pp. 331-357).