Juvenile hormone metabolism during the fourth stadium and pupal stage of the southern house mosquito, Culex quinquefasciatus Say

Abstract

Juvenile hormone (JH) esterase activity did not change significantly during the fourth stadium in Culex quinquefasciatus, but JH epoxide hydrolase activity peaked in 36-h-old fourth instars and pharate pupae at levels 5.7- and 3.0-times that of JH esterase, respectively. JH epoxide hydrolase activity was greater than the JH esterase activity throughout larval development and in 0-h-old pupae. Both activities declined and were equivalent in pupae more than 8-h-old. 1-Naphthyl acetate (NA) esterase activity remained constant during the fourth stadium and peaked in pupae 16–24-h-old. Different isoelectric forms of JH esterase and epoxide hydrolase were found in fourth instars and pharate pupae. Subcellular distribution studies indicated that the majority of JH esterase and JH epoxide hydrolase were membrane bound. Inhibition of larval JH esterase with O,O-diisopropyl phosphorofluoridate revealed an I 50 3000-times that of 1-NA esterase but both enzymes had approximately equivalent I 50 values in pupae that were more than 8-h-old. Methoprene treatment of fourth instars significantly extended the duration of the fourth stadium, but did not extend the duration of the pupal stage. Methoprene also eliminated the normal peaks in JH epoxide hydrolase activity found during the last stadium, increased the 1-NA esterase activity, but had no effect on JH esterase activity. Methoprene treatment of fourth instars had no effect on the pupal JH epoxide hydrolase and JH esterase activity but depressed the overall 1-NA esterase activity eliminating the pupal 1-NA esterase peak.