Seasonal variation in hemolymph juvenile hormone of adult monarchs (Danaus p. plexippus: Lepidoptera)

Abstract

The Galleria wax test was used to quantify juvenile hormone (JH) activity in the hemolymph of adult monarch butterflies captured in the field at monthly intervals. In animals of both sexes captured in June and July, high levels of hemolymph JH activity were found. By contrast, both sexes had generally lower JH titers from August through January. These results are in general agreement with the state of the JH-sensitive reproductive tract components during these months. Nevertheless, there were notable exceptions, including males in February and September and females in October. During these months relatively high levels of JH were obtained for some hemolymph samples, while in general, reproductive tract development during these periods was variable. This result suggested that temperature, photoperiod, nutrition, flight, JH sensitivity, or some other variable may be important in the triggering of JH-induced reproductive tract growth during these periods. Verification procedures for the assay itself and for the biological material included construction of dose responses for JHI, JHII, JHIII, and Ayerst JH (AJH) (i.e. 16 isomers of JHI), tests for hemolymph JH activity inhibition, effect of allatectomy on JH titer, and comparison of the JH activity of field- and laboratory-collected hemolymph.