Effects of pyriproxyfen on engorged females and newly oviposited eggs of the lone star tick (Acari:Ixodidae).

Engorged females and 1- to 3-d-old eggs of the lone star tick, Amblyomma americanum (L), were exposed to 9 treatments of pyriproxyfen (4, 8, and 16 micrograms/cm2) in glass vials at exposure periods of 7 d, 14 d, and continuous at each dosage level. Treatment of newly engorged females did not affect the number of females ovipositing, but the number of eggs oviposited decreased as dosage and exposure time increased. Complete inhibition of egg hatch occurred at all treatment levels except that of the lowest dosage and exposure time where 99.9% inhibition was observed. Egg masses from treated females contained eggs that turned a dark amber color and imploded, retained normal shape and color without visible evidence of embryogenesis, or had developed embryos that were unable to emerge. Treatments of 1-to 3-d-old eggs were effective in reducing hatch and larval survivorship to 25 d after emergence only at the continuous exposures of dosages of 4, 8, and 16 micrograms/cm2. Larvae emerging from eggs treated at the lower dosage rates of 0.2 and 0.02 microgram/cm2 were as successful in feeding on chickens and subsequently molting as acetone treated control ticks.