Ovipositional response, developmental effects and toxicity of hexavalent chromium to Megaselia scalaris, a terrestrial detritivore

The effects of hexavalent chromium (Cr VI) on ovipositional response, development, and survival of a common terrestrial detritivore, Megaselia scalaris (Diptera: Phoridae), were assessed in the laboratory. Ovipositing females did not discriminate between substrates containing 0, 50, 500, or 1000 mug/g, indicating a lack of avoidance behavior. Eggs placed on artificial diets containing up to 1000 mug/g either did not absorb Cr VI or were unaffected as measured by eclosion rates. However, development and survival of larvae were significantly reduced at the higher concentrations tested. Concentrations of 500 mug/g in their food increased larval development times by nearly 65%. At 1000 mug/g, larval developmental times doubled. The time required from onset to completion of pupariation was not significantly different regardless of Cr VI concentration. Although males eclosed before females, there was no significant difference between the sexes in the time required for adult eclosion. In addition, there were no significant differences in the percentage of males and females emerging from any of the treatments. At concentrations of 500 or 1000 mug/g, Cr VI decreased larval survival. Survival was reduced by 44.3% at 500 mug/g as compared with the controls. There was no additional mortality from the onset of the puparial stage to adult eclosion for larvae fed diets containing 500 mug/g Cr VI. At 1000 mug/g Cr VI, larval survival decreased by 86.6%. An additional 7.4% mortality was recorded in the puparial stage, for a decrease in total survival (larval plus puparial stages) of 94%. Thus, nearly all of the observed mortality occurred during the larval stage rather than the puparial stage. The population level implications of lack of avoidance of contaminated food and the effects of increased developmental times and reduced survivorship are discussed.