Porcupine! 16 - Cute little Mayfly... How inportant you are

I have been interested in insects since my first degree in Chile where I studied plant resistance to aphids. Some years later while in England I did an MSc at the University of London and my project involved the use of baculoviruses to control the cabbage looper. Until then I had been mainly in the laboratory doing biochemistry, plant physiology and chemistry with only a few opportunities of actually doing field work (which I greatly enjoyed). Life brought me to Hong Kong (the opposite place on earth to Chile) where I met Dr. Dudgeon (now Professor Dudgeon), who after chatting for a while about jobs and research possibilities in Hong Kong suggested I might do a PhD. I said yes but only if insects are involved in it. So in 1995 1 started working in stream ecology with a very cute subject, mayflies (have you seen those big watery eyes..?). Because I had no previous experience in ecological methods I started by researching in the library for the first few months in order to get a grip on the more common techniques to apply in my project and also to learn how to recognize stream insects.

The first question is why to study mayflies? They are one of the most abundant taxa found in Hong Kong streams which may indicate their importance in the food chain, both as primary consumers and as prey for higher taxa. In this project I am trying to determine how important mayflies are in energy transfer in streams, which involves posing two questions: How fast do they grow? (growth rate) and How many are present in streams? (biomass). For the last two years I have been measuring the biomass of several species of mayflies belonging to three major families at three sites in Hong Kong: two forest streams with different abundance of insects and one polluted stream which has the advantage of presenting two different habitats (open and shaded sites). I have used enclosures (cages) in two sites in order to measure the growth of mayflies 'in situ'. I have to collect the animals and measure them in the field using a measuring magnifier (I look rather strange staring into a tray with my little magnifier), then after some days I measure them again in order to obtain their growth rate. Measuring biomass involves a lot of field work (collecting samples every two weeks), and lots of sorting and measuring under the microscope (which strangely enough I like to do).

Food availability and temperature are well known factors affecting the growth of animals so two basic questions arise: Is food limiting the growth of mayflies in different streams? What about temperature? By studying the growth of mayflies during a year in the polluted site (open and shaded habitats having different food inputs), I expect to be able to answer these questions (if everything goes okay and my cages are not stolen or washed away). Also if time allows I would like to compare the growth and production of mayflies with other taxa which have different feeding habits, i.e. predators. At this point in my research (very close to its end but before statistical analysis) I will be cautious not to give results yet, but I can say that all the species I have studied are growing 'very fast' and their growth is higher in the open site than in the shaded one. Implications of higher annual secondary production levels are expected.

Cute little Mayfly... How important you are

Maria Salas