Feeding behavior of Simulium vittatum larvae in response to various suspended materials: implications for control using biological larvicides

Abstract

Biologically based larvicides used to suppress nuisance populations of black flies (Diptera: Simuliidae) require that the larvae ingest the larvicide for mortality to occur. Materials present in the habitat that alter larval feeding behavior may reduce the effectiveness of the larvicide. This study was conducted to determine the effects that commonly occurring materials in larval habitats have on Simulium vittatum Zetterstedt feeding behavior. Larvae were exposed to 50 p.p.m. of kaolinite clay and 4 p.p.m. of purified diatom frustules. Larvae were also exposed to 10 000 cells or colonies per ml of viable green algae, Chlorella vulgaris Pratt and Scenedesmus quadricauda (Turp) Bréb, and the diatom Cyclotella meneghiniana Kützing to determine the effects that these materials have on larval feeding behavior. Individual larvae were recorded using a digital camcorder to determine the average number of times the larvae extended and retracted their cephalic fans per min (flick rate) in each medium. Following exposure to the selected material, neon red particles (NRP) (DayGlo) were added to the larval medium for 20 min. A spectrophotometric analysis was conducted to determine the average quantity of NRP consumed by larvae per min in each medium. The flick rate and quantity of NRP consumed by larvae was not significantly affected by clay material or viable Chlorella cells. When Scenedesmus colonies or Cyclotella cells were present in the larval medium, larval flick rate and NRP ingestion was significantly reduced. The presence of diatom frustules in the medium resulted in the most severe reduction in larval flick rate and NRP ingestion. The results suggest that larval flick rate can change depending on environmental conditions, and that suppression programs using biologically based larvicides may benefit from investigating the potential correlation between algal counts and treatment efficacy.

Evaluation of Larval Medium in the Controlled Current Toxicity Test

“…Interestingly, subsequent work conducted by Iburg et al (2011Iburg et al ( , 2016 demonstrated that different types of seston could affect the efficacy of a Bti-based larvicide. In an effort to evaluate the effect of suspended nutrients in the standard CCTT larval medium and determine if a physiologically more natural medium was more conducive to Bti-based larvicide evaluations, 3 alternative larval mediums were evaluated.…”

“…The premise for this protocol was that the larvae needed some food material to be present to stimulate and maintain normal larval feeding in the flask environment. However, subsequent work (Iburg et al 2011(Iburg et al , 2015(Iburg et al , 2016 has demonstrated that suspended materials in the larval environment can have an impact on mortality levels produced by Bti-based larvicides.…”