COMPARATIVE TESTING OF SEVERAL JUVENILE-HORMONE ANALOGS IN 2 SPECIES OF LOCUSTS, LOCUSTA-MIGRATORIA MIGRATORIOIDES AND SCHISTOCERCA-GREGARIA

Effective treatment with juvenile hormone analogues (JHAs) of early pe nultimate or early last-instar locust hoppers induces a supernumerary 'extra' nymphal instar. These 'extra' nymphs, also termed 'adultoids', die in the course of, or shortly after, an 'extra' moult. Less effect ive treatment results in imperfect adults with crumpled twisted wings which presumably limit their flight and migratory abilities. Extremely effective treatment leads to death in the next moult. Comparing dose- response relations of (7S)-methoprene, fenoxycarb, pyriproxyfen and a new JHA, R70-1 (ethyl droxycyclohep-1-ylmethyl)phenoxy]ethyl}carbamate ), we revealed that route of administration, instar of the recipient h opper, and species may alter over 1000-fold the ED50 for the same JHA. Locusta migratoria migratorioides is much more susceptible to JHAs th an Schistocerca gregaria. The lowest ED50 found to induce adultoids an d subsequent death in the 'extra' moult was 0.12 mu g pyriproxyfen inj ected in olive oil to early penultimate instar hoppers of L. m, migrat orioides (about 0.5 mu g g(-1) fresh weight). R70-1 was more active th an pyriproxyfen following the more practical topical application to ea rly last-instar hoppers of L. m. migratorioides, 5.9 mu g and 46 mu g per hopper, respectively (about 10 mu g g(-1) and 78 mu g g(-1) fresh weight). The high susceptibility of last-instar L. rn. migratorioides nymphs to topically applied R70-1 is promising from the practical stan dpoint.