After working with the Hine’s emerald dragonfly for almost 20 years, both the U.S. Fish and Wildlife Service and University of South Dakota are finding out there is still much to learn! At the beginning of the captive rearing program at the Genoa National Fish Hatchery (NFH) in 2014, there were thought to be three “absolutes” regarding the species (later found to be assumptions!)
Number 1: After the eggs were deposited by the females in the wetlands, they would develop to the point of eye spots over the summer and fall and then hold off at that point until spring. Number 2: In March or April 95% of the eggs would complete development and then begin hatching right around April 1st for about 2-3 weeks total. Number 3: The larvae would grow and molt through several instars over the next 3-5 years before they were ready to emerge.
In the first year of working with the larvae at Genoa NFH, the Hine’s emerald dragonfly shattered assumption Number 3! By having a plentiful food source available to them in the hatchery ponds, the larvae went from newly hatched to their last instar during that summer, with some of them emerging the following spring. Early concerns were that the emerging dragonflies would be under-developed or not up to the normal adult size, possibly causing issues with reproduction. Measurements taken on the newly emerged adults laid those concerns to rest, the dragonflies were up to normal size and no issues with flight were seen as they were released. In following years, the Illinois Dragonfly Rearing Facility managed by University of South Dakota and the DuPage Forest Preserve District’s Urban Stream Research Center began to change their rearing techniques. They incorporated more natural water sources with a larger variety of zooplankton and experienced similar growth patterns. So it would seem the dragonfly larvae grow according to temperature, water availability and food availability, similar to most other aquatic species.
In the second year of the grant, the hatchery received eggs to hatch out, and the Hine’s emerald dragonfly decided to shatter assumption Number 2! That year, the eggs hatched over a three month span, it is thought perhaps they were placed in the cooler to go dormant over the winter too soon, throwing off development timeline. This pattern is still being studied and has repeated over the last couple years.
the growing season. Credit: Angela Baran
During the summer months of 2017, the dragonfly shattered the final assumption remaining, that they would only hatch in the spring. Eggs collected early in the summer began hatching a couple of weeks after they were collected. Originally it was thought this was a survival technique, by holding off until spring, the resulting larvae would be hatching at a time when the water would be warming and food would be present. This pattern was seen again over the summer in 2018, but the early hatching larvae in 2017 still grew enough to have sufficient energy stored to survive the winter and continue growing the following spring. Perhaps the survival technique is still the reasoning, but on years when the weather supports it, they can start the process early.
This species continually challenges all partners working with it and with each passing year, a wealth of knowledge continues to be collected. This knowledge is applied to each facility in different ways for new methods of rearing and has made huge impacts to the recovery programs. To date, 2018 seems to be a successful year, 43 newly emerged adult dragonflies were released in Illinois, bringing the total released since 2016 up to 64 individuals. After working with fish and mussels, these numbers seem very small, but when you consider the Illinois population is estimated at 86-313 total adults each year it gives hope for the future of the species. This summer was also a good one for egg collections, with more than 3500 collected in Illinois and over 2000 eggs collected from the Wisconsin population. So early indications show there should be a strong year class in 2019. The hope and goal of the program is to stabilize the genetically diverse population in Illinois and then to increase the population and begin to restore historic habitats throughout their range.