Alderfly (Megaloptera: Sialidae) Larval Emergence and Pupation Site Selection at Intermediate Lake, Antrim County, Michigan

Larvae of the alderfly Sialis mohri Ross were collected in barrier pitfall traps along the shoreline of Intermediate Lake during a 3-year period (2015–2017). Two barriers (each 1-m long) were used per trap in 2015 and 2016, being placed on opposite sides of a central collection cup that was about 1 m from the shoreline at time of deployment. In 2015, with two traps monitored at 4–to 18-day intervals from 19 April to 29 June, larvae were collected first during the 19 April – 7 May period and last during 16–31 May. In 2016, using the same two trap locations, with traps monitored (often daily) from 15 April through 9 June, larvae were collected first on 19 April, they peaked on 5 May, and were last collected on 7 June. In 2017, four traps (with one plastic barrier each) were placed near each other but with the collection cups at different distances from the shoreline (1, 2, 4 and 6 m), and checked from 15 April through 1 June. Overall, 71.1% of the larvae were collected at 1 m, 19.5% at 2 m, 8.9% at 4 m, and 0.5% at 6 m. During periods when traps were checked daily in the morning, 99% of all larvae collected in 2016 were trapped when it had rained the previous night (14.7%) or previous day (84.6%), and similarly 58% (46.1% and 12.1%, respectively) in 2017. This study documented timing of S. mohri larval emergence in spring, indicated that wet conditions favored emergence, and indicated that nearly all pupation sites were within 4 m of the shoreline.