Variables affecting the practical use of juvenile hormone analogues for control of the western spruce budworm (Choristoneura occidentalis) (Lepidoptera: Tortricidae)

Robertson, JL.; Kimball, RA.

Variables affecting the efficacy of 7 juvenile hormone analogs [JHA] on western spruce budworm, C. occidentalis Freeman, were examined in laboratory bioassays. Those tested were epofenonane, hydroprene, kinoprene, methoprene, triprene, ZR-587 [ethyl (ZE,4E)-11-hydroxy-3,7,11-trimethyl-2,4-dodecadienoate] and ZR-1662 [ethyl (ZE,4E)-10-methoxy-3,7,11-trimethyl-2,4-dodecadienoate]. Selected intrinsic variables, stage of development, sex and extent of direct contact with sprays, were examined in bioassays involving direct exposure of 3rd instars, direct applications to 3 pupal age classes and indirect applications to 6th instars. An extrinsic variable, persistence in the environment, was assessed by determining the residual effectiveness of each JHA to 6th instars. Sixth instars, rather than 3rd instars, appeared to be the target of choice for 2 reasons: less active ingredient would be required for equivalent mortality by the time of adult eclosion; and greater, more consistent, deleterious reproductive effects coupled with a lower incidence of sexual variation in lethal effectiveness, would occur. Pharate pupae and untanned pupae were very susceptible to most of the chemicals and may provide a secondary target for the primary target, 6th instars. The importance of direct chemical-insect contact in achieving maximum reproductive inhibition suggests that these chemicals might be used most effectively in ways such that contact can be maximized, as in good applications. Finally, some JHA such as epofenonane and ZR-1662 appeared to persist long enough to permit flexibility with respect to instar distribution in a population.