Helpful weevils

Eurasian milfoil (Myriophyllum spicatum)

Eurasian milfoil (Myriophyllum spicatum), a submerged aquatic plant that grows in still or slow-moving water, is one of the worst aquatic plant pests in North America. Like native aquatic milfoils, it has feather-like underwater leaves and emergent flower spikes. Usually leaf shape and size can be used to distinguish it from other milfoil species. However, Eurasian milfoil is a variable species, often making it difficult to identify without chemical or DNA analysis. It has been known to crowd out native plants and create dense mats that interfere with recreational activity. Eurasian milfoil can grow from broken off stems which increases the rate in which the plant can spread and grow. 

One of the many lakes that are heavily invested with this invasive plant is Christina Lake in British Columbia, Canada. In the lake milfoil is currently controlled by having dive teams who manually extract the plant from June until October. Those teams work seven days a week with one overlapping day just to keep the nasty aquatic weed at bay. 

Milfoil weevil (Euhrychiopsis lecontei)

Obviously it would be much easier and cost-effective to develop biological pest control strategies and there are a few species that have been discussed and used. The water veneer moth (Acentria ephemerella), feeds upon and damages this water milfoil. It has been used as biocontrol but carefully, as it lacks host specificity and attacks other plant species, including natives. In addition it is also an introduced species. Another method for biocontrol is grass carp, (Ctenopharyngodon idella), is sometimes released into affected areas, since these fish primarily feed on aquatic plants and have proven effective at controlling the spread. However, the carp prefers native species before turning against Eurasian milfoil and more imporantly it has become a serious pest in North American lakes as well. That leaves us with the milfoil weevil (Euhrychiopsis lecontei), a native species that specifically loves to eat the new growth on the pest thereby stunting the plant’s growth and propagation.  that a weevil that lives in the region is actually this native species, making it possible to rear and release more of the bug. In the case of Christina Lake it needed DNA tests to confirm that the right kind of weevil naturally occurs in the lake. This makes it possible to rear and release more of the bug as it will be easier to get permission to introduce more of them to help control the ever growing milfoil. Regional authorities now hope that a pilot project can be started as early as coming summer. Eventually they would like to see a business created that will raise weevils to release not only into Christina Lake, but other lakes around the province to naturally control the alien species of Eurasian Milfoil.