Modelling adult survival in the laboratory of diapause and non-diapause Colorado beetle Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) from Normandy, France

Adult Leptinotarsa decemlineata from a culture originally from Normandy, France were kept in a controlled environment and fed daily on potato foliage. Dead beetles were scored and removed. Setting up the experiment was spread over 212 days and 1135 beetles were used. After 21 days each group was divided into two, some remained active and others were induced to diapause for 221 days before becoming active once again. Life span varied from 1 to 504 days and could be extended to 770 days by diapause. A model was derived which describes the mortality over time by assuming that a proportion of the population had an exponential distribution of lifetime and the remainder had a Weibull distribution which allowed for a hazard rate increasing with time. In the model 17% were short-lived, having a mean lifetime of 8 days, and the remainder were long-lived having a mean lifetime of 139.5 days. An exponential survivor function describes the post-diapause cohort, which had a mean lifetime of 129 days after diapause.     

Melanosomal Tyrosine Transport in Normal and Pink-eyed Dilution Murine Melanocytes

Tyrosine is the endogenous substrate for melanin production within melanosomes, but the method of tyrosine transport into the melanosome has not been investigated. In the mouse, melanogenesis is disrupted by mutations in the p gene resulting in the pink-eyed dilution phenotype; it has been suggested that the p gene codes for a tyrosine transport protein. We determined that normal (melan-a) melanosome-rich granular fractions take up 10 μm [³H]tyrosine at 21.1 ± 6.1 (SEM, standard error of the mean) pmol/min/mg protein (N=7) compared with 21.3 ± 5.8 SEM pmol/min/mg protein (N=5) for pink-eyed dilution, whose plasma membrane tyrosine transport was also normal (K_m 89 μM; V_max 302 pmol/min/mg cell protein). We also demonstrated that pink-eyed dilution melanosomes are immature by virtue of their low density, high hexosaminidase activity, and lack of pigment. These data indicate that a tyrosine transport system exists in the melanosomal membrane and that the p gene does not encode a tyrosine transporter of critical importance.