The effect of methanol and ethylene glycol on the development and survival of Cochliomyia macellaria (Fabricius; Diptera: Calliphoridae)

Entomotoxicology, a subdiscipline of forensic entomology, in part focuses on how the ingestion of chemicals by necrophagous blow flies affects their development and potentially alters development rates, which is key for determining the time of colonization as related to the minimum postmortem interval (mPMI) estimation given certain assumptions. The effects of methanol and ethylene glycol on the development and survival of Cochliomyia macellaria (Fabricius; Diptera: Calliphoridae), the secondary screwworm, were determined. Cochliomyia macellaria eggs were placed on homogenized beef liver treated with one of four different dosages for each drug: control (no drug), quarter-lethal, half-lethal, and lethal dosages. Dosages were based on reported human lethal doses. Each developmental treatment was destructively sampled to determine the minimum duration of development, average larval length and weight over time, average pupal length and weight, and average adult weight and sex ratio. For the survival experiment, 100 first instars were reared on tissue treated with different dosages of methanol and ethylene glycol. Observations were made twice daily until all resulting adults perished. All dosages of methanol increased the average total minimum duration of development from egg to adult by 19%. This increase was primarily due to an increased duration of the feeding third instar for the lethal (69%) and half-lethal dosages (50%) and pupal stages (8% on average). Additionally, methanol skewed the sex ratio toward males by 23% on average. Methanol had no significant effect on larval length and weight over time, pupal length and weight, adult weight, or survival. The lethal dose of ethylene glycol significantly decreased the length and weight of larval (9% and 29% respectively) and pupal stages (19% and 36% respectively), and the adult weight (33%). Ethylene glycol also had an effect on life stage duration; however, the drug’s effects were unclear. There was no significant relationship between ethylene glycol dosage and survival or sex ratio. In conclusion, the results show that methanol and ethylene glycol affected the development of C. macellaria which could cause errors in estimating the time of colonization as related to the mPMI estimate given certain assumptions.