More about the research...

I read my past post and thought the part about the research could be explained more clearly or at least elaborated upon. I have also added an update about a new investigation I will soon start based upon recent observations.

The players:

Coccus viridis, green coffee scale
-A common pest of coffee, citrus, and in greenhouses. This insect lives stationary on the new growth and fruits of plants, feeding upon the sugars transported through the phloem of the plant

Azteca genus, tree dwelling ants
-An aggressive species of ant which obtains much of its diet by consuming carbohydrates excreted by scale insects and in turn, protecting the scale from predation. This mutualistic interaction between the ant and scale is expressed by saying, "the ants tend the scales"

Azya orbigera, lady beetle
-About the size and shape of a lady bug, but gray with two black dots. This beetle is a predator of C. viridis, the coffee scale. The larval form of the beetle is protected from the ants by a fluffy waxy coating and is generally found living on coffee bushes. The adult beetle is most often found in areas around trees with Azteca nests, where it can usually find a reasonable population of scales to eat. We did an estimate of the adult beetle population size by doing a typical mark and recapture estimate using modeling paint.

Inga genus, tree in the Fabaceae family
-The most common genus on the farm, this tree is often inhabited by Azteca. An interesting point is that this tree is commonly the host of a variety of scale and mealy bug species feeding on the tree's sugars, tended by ants. Otfen, C. viridis population levels are lower around this tree, theoretically due to indirect competition with the scales on the Inga itself.


The plot:

There is a common pest in coffee farms called Coccus viridis, a green scale insect that lives stationary on the young part of the stems of coffee bushes feeding on the sugars being transported by the plant. Being an immobile organism, the scale insect is usually very vulnurable to predation, except that in many cases, ants protect scale species because of a sugary substance secreted by the scale which the ants eat. So what ends up happening is ants (in this farm, ants of the genus Azteca are the most common) will nest in trees scattered throughout the farm, tending several coffee bushes near their nest in order to consume the sugars produced by the scale. Azteca keeps away not only the predators of the scale, but also general herbivores of coffee. This is an indiret benefit to the coffee, however, sometimes the population of C. viridis rises to pest levels. This is the focus of the research I am working on... What factors control the population of C. viridis and determine if it will rise to pest status? The past month, we have been looking into a species of lady beetle, Azya orbigera, that is a predator of the scale. A. orbigera has a unique larvae which is protected by a fluffy, waxy coating, allowing it to predate C. viridis even in the presence of Ateca. The idea is that the beetle A. orbigera is an important player in controlling populations of C. viridis.

ALSO, I recently noticed that there is a particular genus of shade trees (the Inga genus) that is used as a food source by other species of scale and mealy bug species. When Azteca is nested in an Inga tree, the ants will tend to scale living on the tree rather than leaving to tend C. viridis on coffee bushes. Therefore, it would seem that tree species composition is another factor influencing the pest status of C. viridus. This is the subject I and two undergraduate students are going to investigate this July.

This research is aimed at providing evidence of the way pests can be controlled in agricultural ecosystems through the maintainance and balance of ecological species communities. At this point in time, even the study of agricultural systems as ecosystems is a farily new idea. Though, given the economic and environmental costs of conventional, chemical based agriculture, agroecology is becoming an important field of study. In the particular case of coffee, the most important economic crop of much of Latin America, this research has large potential for practical application.