Biology and laboratory rearing of Cricotopus lebetis (Diptera: Chironomidae), a natural enemy of the aquatic weed hydrilla (Hydrocharitaceae)

Abstract

Field and laboratory studies were conducted on Cricotopus lebetis Sublette, a midge of unknown origin that causes widespread damage to the aquatic weed hydrilla, Hydrilla verticillata (L.f.) Royle, at Crystal River, FL, USA. The larvae of C. lebetis burrow into the submersed apical meristems of the hydrilla plant and destroy shoot tips during their development. Abscission of the hydrilla stem tip usually occurs when the last instar excavates a tunnel inside the stem for pupation. Mining damage caused by the feeding larvae induces stunting and basal branching that alters the normal growth pattern of hydrilla. Larval populations of C. lebetis and damaged hydrilla shoot tips were highest in the summer (May and June) and fall months (October and November) during 1997 and 1998. In June 1998, more than 70% of the hydrilla shoot tips were damaged by midge larvae. Adults lived <2 d in the laboratory, and nuptial flights were not a prerequisite for mating. Females deposited a single egg string containing an average of 154 eggs inside a gelatinous matrix. The eggs took ≈2 d to complete development and neonate eclosion was synchronized. The larval stage had four instars and required ≈14 d to develop to the pupal stage, which lasted an additional 2 d. Although most larval chironomids feed on algae or detritus, the larvae of C. lebetis fed and developed entirely on the living stem tissue of hydrilla.