The effect of methylphenidate and its association with phenobarbital in the development of immatures of Chrysomya albiceps (Wiedemann) (Diptera: Calliphoridae)

Necrophagous insects associated with decaying bodies can assist in criminal investigations by providing information related to the cause of death, displacement of a corpse from the place where death originally occurred. In addition, it  is important in the estimation of postmortem interval (PMI). The calculation of PMI based on the age of the insect may be altered by numerous factors, including the presence of toxic substances or drugs in the tissues of a person who had used or died as a result of the use of the drug. Therefore, the objective of this study was to evaluate the development of Chrysomya albiceps (Wiedemann) (Diptera: Calliphoridae) under the effect of Methylphenidate (MPH) and the association with Phenobarbital (PB), drugs used respectively to treat attention-deficit hyperactivity disorder and as anticonvulsant. The drugs were added to an artificial in the following concentrations: (1) 10xDT of MPH + 1xDT of PB; (2) 50xDT of MPH + 3.3xDT of PB; (3) 100xDT of MPH + 6.7xDT of PB. These dosages were calculated considering that the therapeutic dosages (TD) are: 0.29 mg / kg for MPH and 2.5 mg / kg of PB. A group, reared without the addition of these substances was used as control. Every 12 hours, 10 larvae from each group were randomly removed from the diet and weighed until the pupal stage. Rates of survival and viability were also recorded. One-way ANOVA was performed to evaluate the effect of treatments on weight gain, and the Duncan test was used to check possible differences among the mean weights recorded. There was a significant difference in weight gain of immatures among all treatments (F = 109.21, p = 0.0001). A delay of 24 hours in total development time of immatures submitted to the MPH was observed, as well as a delay of 12h in the groups reared in the presence of PB. For the groups reared in the diet with the two drugs together, the effect was caused basically by PB. In the control group, pupation occurred at 168 h, whereas for the treated groups, it occurred at 192h and 180h to MPH for PB and association, respectively. The Duncan multiple comparisons tests also showed significant differences in the mass gain in all weight ranges were observed for both the control and treated groups. The results show that the presence of both MPH and PB can influence the time of development of immatures os C. albiceps. These differences should be considered in order to prevent an errors in the estimate of the PMI.