Microhabitats boost insect abundance

Posted on July 20, 2015

Although the emergence and dispersal of adult insects from streams is significant in terms of energy export and ecological connections between aquatic and terrestrial systems, the environmental factors that encourage insect emergence remain unclear. This is partly due to the fact that most studies have been carried out at the habitat, rather than microhabitat, scale. To assess the relative importance of available microhabitats and the size of the bottom-dwelling larval stock on the abundance of emerging adults, emergence traps and bottom-sampling nets were positioned along a 40 m reach of Cabin Creek in northern Minnesota, U.S.A. in May and July 2010. A range of environmental parameters were scored at each sampling site. Data analysis revealed that insect emergence (which was dominated by flies and mayflies) was positively related to the size of the larval stock, the shallowness of the water, and the amount of wood, periphyton, detritus and fine material in the stream. Wood may assist emergence by intercepting drifting insects before they leave the water, and by providing surfaces for the new adults to exit from. The significance of periphyton is probably related to its association with high light levels, which are known to attract emerging insects. Detritus and fine material may assist emergence by concentrating burrowing larvae, and shallow water increases the chance that insects will emerge from the water close to their original location rather than further downstream. These results show that microhabitat variables have a significant influence on insect emergence, independent of the size of the larval population. Insect numbers can be maximised by managing the riparian zone and the shape of the channel so as to maintain the supply of wood and patches of fine material.

Reference: Merten, E.C. et al. 2014. Microhabitat influences on stream insect emergence. Aquatic Sciences 76, 165–172. http://link.springer.com/article/10.1007%2Fs00027-013-0326-3#page-1