Pity the poor mosquito!

You are probably, dear reader, a little prejudiced against mosquitoes. Take Aedes scapularis. Whilst it´s true that it is a vector for yellow fever, and  human and Venezuelan equine encephalitis, poor A. scapularis has a hard life. In 2002, Casanova and do Prado studied them in the pastureland around a farm near Campinas, in Sao Paulo state, Brazil.

During the hot rainy season (October to March) muddy puddles form all over the land, and the drought resistant eggs of Aedes scapularis hatch, little larvae swimming off hopefully into the water. It seems a good life in a hot bath full of rich organic matter, but little scapularis does not realise the horrors ahead.

For a start, it might rain, it might not, it might rain a LOT. Aedes only needs 9 days from hatching to adulthood, but even that might be too long. Of the 58 populations studied by Casanova and do Prado, 27 were wiped out by their ponds drying up, and 15 were washed away by floods, they never stood a chance.

Life in the 16 remaining pools was better, but not by much. The good news was that starvation was almost unknown, the bad news that all those mosquitoes ensured that starvation was unknown for their predators too. Estimates of total mortality from tiny larvae to emerging adults varied from 68 to a massive 96% per pool!

Predators included........

Giant water bugs "Baratas d' aqua" (Belostomatidae), aggressively predaceous insects who feed on, well, anything, injecting a digestive saliva and sucking out the remains. One of the most painful bites of any insects to us, let alone to a little mosquito.

Giant Water Bug larva (Wikipedia)

Water scorpions (Nepidae) - actually another type of insect

Diving beetles (Dytiscidae) -  you can eat these, if you want to,  in Mexico the adults are roasted and salted and added to tacos

Dragonfly larvae - there are, incredibly, at least 267 species of dragon- and damsel-fly in Sao Paulo state alone, and many of these eat mosquitoes

Last, but not least, larvae of a predatory mosquito, Psorophora ciliata. Don´t start to feel too grateful to this one, they feed on us as well, and infact are the largest blood feeding species found in the USA.

So, the little larva hatching into a warm, muddy, pool will almost certainly desiccate, be swept away, or be eaten. No wonder they are so angry!

Reference
Key-factor analysis of immature stages of Aedes scapularis (Diptera: Culicidae) populations in southeastern Brazil byC. Casanova and A.P. do Prado (Bull. Entomol. Res. 92, 271-7)

Beware the wings of Summer!

Christmas is coming

Bruxas in the flat
please put the aircon on
and squash the mossies flat

Summer is coming to the Mata Atlantica, which means hot days and nights, and rain - perfect conditions for insects. This, not Halloween, is the time for witches, "bruxas", huge (up to 16cm) moths the size of bats who invade your house at night. As I mentioned in a previous blog, bruxas, (Ascalapha odorata) are of course completely harmless, if occasionally annoying, and they feed on rotten fruit. They'll probably be around until January.

Bruxas might be harmless, but other summer visitors not so much. Termites ("cupims") swarm at this time of year, males and females abandoning their nests and flying out into the sky. They are weak fliers, and blown hither and thither by the wind. When they land they shed their wings and, if they are lucky, start to make a nest from the wet trees and timber they have landed on, so if you see discarded insect wings on your furniature, watch out! Mated queens produce huge quantities of workers that build the nest where they will all live, either underground, in mounds in the pampas or fields, or as nests on the side of trees and fence posts.


As many house holders have found to their cost, termites are very good at digesting wood, which is beyond most creatures. Although some can actually do this by themselves, most have colonies of microbes in their gut who do the work for them. Humans though are having their revenge. Firstly, termites are edible and easily caught when swarming. Apparently they are best lightly grilled on a hot plate, their natural oils supplying the cooking fat. Secondly, they are potentially a source of fuel - producing hydrogen from waste wood, although nobody has quite made a termite power station yet.

And worst of all are the mosquitoes, their life cycles speeded up by the heat, and with plenty of puddles to lay their eggs. Development time for Aedes aegypti, from egg to adult, goes from 33 days at 16C to 9 days at 32, although if it's any consolation they do die younger. With more mosquitoes comes more disease, the incidence of Dengue fever for example starts to rise steeply in December before peaking in March to May.

So beware, the time of the insects is coming!

Fever in the forest - addendum

Lots of good questions! Thanks guys, it´s really nice to get feedback.

Steve, from what I know, Aedes aegypti can feed during the day, but they are more active around dusk. It´s complicated though, as Vitoria is being invaded by another species that can transmit Dengue, Aedes albopictus, and this is around all day. Worse still, it´s very nervous and flits away before finishing a good meal, so it has to bite lots of people.

I'm not sure that socks give you such immunity! Mosquitoes hunt you down by first following a trail of CO2, which is why some buzz around your face, and then smelling your sweat, which means exposed skin. Now, feet can be quite a potent source of er, odours, and the skin on the side is quite thin, hairless and easy to penetrate, so they make a good target, but not the only one. To diverge slightly, there was a famous experiment showing Limburger cheese as a good mosquito attractant, as the smell is similar to unwashed feet!

Bec, I know it sounds bizarre, but it might actually work! It is female mosquitoes that do the biting, and it´s only males that are released, after being sterilised. They mate with the females and produce infertile eggs (so you do get bitten now, just less in the future). This technique has been used to control insect pests like the Screw worm fly, or Mexican fruit flies, and in theory you don´t need any pesticides, but the problems are....
a) there is a high start up cost, you have to release lots of mossies, and sterilising them by radiation is fairly sophisticated
b) unless you live on an island, there will always be an influx of mosquitoes from outside. You just have to keep releasing indefinitely.
Still, it´s possible.

Mynah, I don´t know! They found antibodies, and virus gene sequence, but whether the bats, rodents etc would be a reservoir of infections for humans isn´t clear. In fact, what might be happening is that Dengue is evolving into Bat Dengue, Mouse Dengue etc, which wouldn´t be a problem (well, not for us).

Thanks again for the feedback!

Fever in the Forest

Now and again through the evening calm comes the sound of a powerful petrol motor, and soon afterwards the streets are filled with a thick grey cloud. This is insecticide, and they are fumigating against the mosquito Aedes aegypti. Aedes is one of the banes of mankind, in many ways, but the worry here is Dengue fever.

Dengue is a virus, and causes fever, joint pains and, even sometimes hemorrhage and death. It is incredibly common in tropical regions around the world, with about 50 million cases a year. You can´t catch it by shaking hands, or sneezing or eating the wrong foods, it has to be transmitted blood to blood, which in practice means the bite of a female mosquito of the Aedes genus. Hence the attempt to eradicate this little pest.

But does this really have anything to do with the Mata Atlantica? It´s not just the mosquito bite that causes a disease, there has to have been someone infectious to infect the insect. Or something infectious. Some animals act as reservoirs for human diseases, the sylvan equivalent of typhoid Mary. Yellow fever, for example, is notorious for infecting primate populations, so lumberjacks clearing forest are often particularly at risk.

In the Americas at least, that was thought not to be the case with Dengue, not least because it is not native here. It was brought over with slaves from Africa and immigrants from Asia, and so is not adapted for local wildlife. However, recent research in French Guyana, the French colony north of Brazil, found viral RNA in quite a few animals, including rodents, marsupials and bats. Several of these, such as the mouse opossum Marmosa murina are found in the Mata Atlantica and the presence of virus in their systems suggests that it is adapting. This is bad news for attempts to eradicate the disease.

Bromeliads

Bromeliads are one of the characteristic plants of Mata Atlantica region. As a type they normally have thick fleshy leaves growing from a central rosette, and range from tiny epiphytes sitting on branches in the forest to huge individual plants sitting on sandy ground of the coastal strip.

The problem with being a bromeliad is that you are stuck at ground level, and other plants can grow tall and shade you. However, there's also lots of advantages. They share with orchids and cacti a special metabolism based on crassulacean acid, which means that they can "breathe" at night, drastically reducing water loss. Many also form a water tank by joining their leaves together, sometimes with over a litre of water. This means that they can evolve into epiphytes, which cling to high tree branches getting all their nutrients from the air and detritus on the branch around them, but close to the sun (thus redefining "ground"). Or lipophytes, which sit on bare rock free from competitors for sunlight, such as those found growing in cracks in the otherwise smooth rocky hills of Vitoria and Corcovado in Rio.

It has been estimated that up to 50,000 litres per hectare can be held in bromeliad tanks, and although the normal quantity is much, much, smaller, it is a permanent enough habitat to form an attractive option for small creatures in need of a home. Dragonfly larvae can be fund there, and even the tadpoles of many frogs such as the Brazilian Hylid frog found in Espirito Santo. There are spiders that live exclusively in the MA bromeliads, and at least 43 species of ants (there really are an awful lots of ants in Brazil).

More importantly, from a human perspective, they are a significant habitat for the Aedes mosquito, carrier of Dengue fever. Not only do larvae wiggle in the forest bromeliads of the Mata Atlantica, dreaming of the cities they will invade when they are grown up, but Aedes have been found in the large bromeliads found on the rocky mountain outcrops of Vitoria. Especially the Alcantarea genus which forms 90% of the bromeliad flora there. Aedes seem not to like bromeliads very much, and prefer to lay their eggs in shaded artifiical containers, but they are there.

Lastly, if you really want to see a bromeliad up close, buy a pineapple. Cut off the top and replant it, with luck it should grow. My grandmother did this on her kitchen window, and it is still common practice in small farms and households here.