Where have all the butterflies gone?... Parasites part II

A bit over three weeks into my stay here at La Selva, I’m sad to report that I’m not having much luck finding my butterflies. Although many of the same species occur here as at my other sites in Ecuador and Panama, they are not visiting my traps as frequently as in those places. I’ve only collected about 6 species in total, and although they are all things that I would expect to find, 5 of the 6 are represented by a single individual (the other, Zaretis itys, is actually quite abundant). Thinking that perhaps the butterflies here might have a different bait preference (I typically use rotting fish, whereas most people working with butterflies in Costa Rica use rotten or over-ripe fruits), I began to experiment with a  mixture of old bananas and sugar – but still, almost no butterflies. While this is, in itself, an interesting phenomenon, it makes the difficult, dirty work in the field feel decidedly futile, and the situation is overall quite discouraging. I think that abundance is generally just lower here than in other places – for example, in Ecuador one regularly sees butterflies in my target groups patrolling forest edges and light gaps, something I have rarely witnessed here so far. The weather is almost certainly a factor, as it has rained almost every day since my arrival, and butterflies generally do not fly without at least some sun. Some folks here have also suggested that pesticides might be a factor – the area surrounding the station is heavily planted with banana and pineapple, which are both heavily sprayed with pesticides. While I personally doubt it is very important, especially considering all the other insects that I typically expect in my traps, including many flies and beetles, are extremely abundant, there is a possibility that pesticides are drifting over from adjacent fields and affecting butterflies. Whatever the cause, it is making for a very frustrating time.

An Adelpha butterfly, one that I would expect to find in my traps.

Another of my guys - this one is Opsiphanes.

On a brighter note, my cutaneous larva migrans has grown by leaps and bounds! It started just on the upper side of my left hand, and has now spread around to my palm and to two spots on my chest and left shoulder. And all this after taking two different nematicides! I’m thinking it’s time for medication round two… for now, maybe I can at least spin this as a Halloween costume?? I just need to return from the field and I’m dirty, smelly, parasite-ridden field biologist man!

It grows!! And itches like mad!

Tropical Parasites

Thursday, 20 October 2011

The tropical rainforest is not a place that lends itself readily to simple generalizations, but if I had to chose just one word to describe this place, I’d probably go with ‘diversity’. That’s one of the biggest reasons I’m in Costa Rica – the rainforest here at La Selva contains an almost overwhelming and beautiful diversity of plants and animals. Another dimension of tropical diversity though, one which relatively few people are interested in, is a staggering variety of tropical parasitic diseases. Everyone knows of a few – malaria, for example, is a global scourge caused by parasitic Plasmodium protists that kills nearly a million people a year worldwide. But there are myriad others, and while many are far less dangerous than malaria, they are nonetheless highly problematic and often exceedingly disgusting. An array of fungi attack every imaginable part of the body, like mycosis, which is highly prevalent in the tropics. Other microorganisms, like bacteria, protists, and a large assortment of various tiny worms cause dreadful diseases like leishmaniasis, schistosomiasis, elephantiasis, typhoid, cholera, and Chaga’s disease. Yet others simply feed on the human body without resulting in ‘disease’; one such organism, a small nematode worm known as cutaneous larva migrans, has recently made it my first Costa Rican parasite for 2011!

I noticed it a few days ago, though I thought I had just another itchy bug bite. When the ‘bite’ began to take on a serpentine shape, I started to suspect something more sinister. Sure enough, my symptoms matched perfectly with cutaneous larva migrans, a disease caused by tiny hookworms buried under the skin. The worms are unable to penetrate the deeper layers of the skin, hence the visible pathways they follow as the feed. Whatever they are and whatever they’re doing in me, they itch like crazy and I want them gone!

Cutaneous larva migrans, the hookworms that are making doodle art out of my hand

That might be pretty gross, but it’s nothing compared to perhaps the most infamous tropical parasite of all – the botfly. I had the bad luck (or good luck??) of getting four of them this past summer on a trip to Panama. The eggs of the fly are vectored by another insect, often a mosquito – the female botfly captures the mosquito and deposits a number of eggs on her. Then, when the mosquito approaches its warm-blooded host, the botfly eggs hatch and the larvae burrow into the host (in the case of the human botfly, the human) where they develop. When ready to pupate, they simply drop out of the host and then complete the life cycle. I think I may have been bitten by the same mosquito four times, because I had four botfly larvae of approximately equal age, one on each arm, one on my back, and a very painful one on the webbing between two of my fingers. They shift under the skin periodically, causing bleeding and extreme pain. It’s funny – despite that pain and blood, it didn’t occur to me that I even had botflies until I could actually see the larvae breathing through their tiny holes in my skin!

Baby botfly larva, how cute!

La Selva, Costa Rica

A few days ago I arrived in San Jose, Costa Rica, and headed down to the Caribbean lowlands to La Selva, the Organization for Tropical Studies’ (OTS) flagship tropical rainforest research site. At the moment the station is very busy (it usually is), with several short- and long-term tropical biology courses and a number of researchers, research assistants, and even natural history tourists visiting. Indeed, over the years thousands of students have been trained in a variety of courses at both the graduate and undergraduate levels, and a multitude of scientific papers have been published based on work conducted at La Selva and other OTS research sites spanning a variety of topics ranging from evolution and systematics to ecosystem-level studies.

La Selva itself is located on a 1,600 hectare reserve in the Sarapiqui canton of northwestern Costa Rica. To the south the property borders Braulio Carrillo National Park, which at 46,000 hectares forms the core conservation unit of the Cordillera Volcanica Central Biosphere Reserve. Together, these protected areas form a vast forested corridor that extends from low elevations at La Selva (ca. 30 – 100m) to over 2,900 meters at Volcan Barva in Braulio Carrillo. Four protected life zones provide refuge for a large number of plants and animals, including over 5,000 species of vascular plants, over 400 species of resident and migratory birds, diverse mammals and herpetofauna (reptiles and amphibians), and innumerable arthropods (bugs!).

Stone Bridge connects the two halves of the La Selva campus divided by Rio Puerto Viejo and provides access to the reserve.

I’m here at La Selva for several reasons, all related to my graduate work at the University of Florida (UF) on the relationship between abundance and distribution in Neotropical butterflies. First, I hope to expand my consideration of scale. For my master’s degree at UF, I showed that there was no relationship between abundance and distribution among butterfly species in eastern Ecuador. As I’ve detailed in previous posts, I collected abundance measures at 5 sites there, covering a large portion of the eastern lowlands. However, I compared those abundance measures to those species’ global range-sizes, which almost always extended well beyond the region in which I gathered abundance data, and occasionally even throughout the entire Neotropical zone. Abundance data from Costa Rica will help to minimize the difference in scale between measures of abundance and distribution. In addition, there are a number of species that I expect to find here that are not present in South America, thereby increasing the number of species in my analyses. Finally, I hope to begin to prepare for a future trip to Peru that I plan for 2012-2013 in which I will be looking at the breadth of host-plant utilization among ithomiine butterflies, in an attempt to explain some of the patterns that I have observed. Learning their host plants is an obvious requisite for that, and I will spend some time here teaching myself plant identification.  

I’ll be here for the next month or so, and I’ll have lots more to say about this place and what I’m doing here, stay tuned!