Bionomics and Instar Determination of Synanthedon rhododendri (Lepidoptera: Sesiidae) on Rhododendron

Male moths generally emerged in advance of females and constituted 56% of the population. Mated females collected in the field produced a mean of 40 eggs. The egg of Synanthedon rhododendri (Beutenmüller) is bilaterally concave, has a mean length of 0.44 mm, and a mean width at the center of 0.22 mm. Eggs incubated at 26°C developed in 11.4 days; eggs held at ambient temperatures developed in 14 to 15 days. Seven groups of head widths were identified by morphometric analysis and separated with a scatter diagram. Head-capsule width increased instar by instar by a factor of 1.28. Head-width analysis indicated that all instars were present in late September and early October. Thus, some larvae may require a 2-year developmental period. Mean length of pupae is 7.10 mm for females and 6.78 mm for males. The venter of the pupal terminalia was examined by scanning electron micrographs and is illustrated. Female calling on the host plant is described as well as male behavioral response, and secondary host plant associates are listed.