Foraging depth of Cricotopus lebetis Sublette larvae

Authors: KARIUKI, EUTYCHUS - University Of Florida; CUDA, JAMES - University Of Florida; Hight, Stephen; HIX, RAYMOND - Florida A & M University; GETTYS, LYN - University Of Florida; GILLETT-KAUFMAN, JENNIFER - University Of Florida

Submitted to: Journal of Aquatic Plant Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2018
Publication Date: 7/30/2019
Citation: Kariuki, E.M., Cuda, J.P., Hight, S.D., Hix, R.L., Gettys, L.A., Gillett-Kaufman, J.L. 2019. Foraging depth of Cricotopus lebetis Sublette larvae. Journal of Aquatic Plant Management. 57:69-78.

Interpretive Summary: The aquatic weed hydrilla is one of the most destructive and invasive aquatic weeds in U.S. freshwater ecosystems. Hydrilla displaces other aquatic vegetation, harms many fish and other aquatic life because it interrupts native food webs, and forms dense surface mats which interfere with recreational and commercial water-use activities. Scientists with the USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology, Tallahassee, Florida, and Florida A&M University, and the University of Florida, Gainesville, Florida, determined that a naturally occurring insect that feeds on hydrilla shoot tips could attack hydrilla from the surface to at least three feet underwater. This feeding depth covers most of the plants’ occurrence in Florida’s shallow lakes and streams. Since hydrilla has become resistant to several of the most commonly used herbicides that are used to control the plant, this stem mining midge may help manage hydrilla by stunting the growth of the plant.

Technical Abstract: Evidence from previous studies indicates Cricotopus lebetis Sublette (Diptera: Chironomidae) may have value as an augmentative biological control agent for hydrilla, [Hydrilla verticillata (L.f.) Royle]. Although several aspects of the insect’s biology, impact on hydrilla, and host-finding behavior, have been investigated extensively, it is not known how deep neonates of C. lebetis can swim or drift in the water column to locate and infest hydrilla. In Florida, hydrilla typically grows to depths of up to 3 m, with half of its biomass occurring within the upper 0.5 m of the water column. To determine the foraging depth of the insect, experiments were conducted in controlled greenhouse studies with hydrilla placed at known depths (0 m, 0.9 m, 1.8 m, and 2.7 m) and in Lake Istokopoga to investigate the foraging depth of C. lebetis under natural conditions. The greenhouse studies demonstrated C. lebetis can attack submersed hydrilla at depths ranging from 0 m to at least 2.7 m. Field studies demonstrated the ability of C. lebetis to attack hydrilla ranging from the water surface level to the hydrosoil, which occurred at a depth of approximately 0.9 m. Our results showed most of the hydrilla in Florida’s shallow lakes grows within a depth range accessible to larvae of C. lebetis.