Induction of macroptery, precocious metamorphosis, and retarded ovarian growth by topical application of precocene II, with evidence for its non-systemic allaticidal effects in the brown planthopper, Nilaparvata lugens

Two strains of the brown planthopper, Nilaparvata lugens, exhibiting predominantly macropterous or brachypterous wing form in a broad range of population densities were topically treated with precocene II at different nymphal stages. The developmental profile, wing dimorphism and ovarian growth were investigated to know the effects of reduction/prevention of juvenile hormone synthesis by precocene II application on these characteristics. The results demonstrated that the sensitive periods to precocene II treatment for induction of precocious metamorphosis differed between the two strains: 2nd and early 3rd nymphal stadia in the presumptive brachypterous strain, while the 3rd and 4th (penultimate) nymphal stadia were sensitive in the macropterous strain. All of the precocious metamorphosis was induced in the 4th stadium and a dose-dependent response was observed for the disruption of metamorphosis. Changes in wing-form by precocene II treatment were observed only in the presumptive brachypterous strain. There was an overlap in the sensitive periods necessary for the disruption of metamorphosis and the induction of long wing forms in the presumptive brachypters, although the sensitive period for the disruption of metamorphosis was shorter. Macroptery induction was more prominent in males than in females. These results support that endocrinological events proceed differently from 2nd stadium between the two strains, and precocene II indirectly exerts its effects in the penultimate and last nymphal stadia to reduce juvenile hormone titer to change genetically moderated events; but the titer being too high in the penultimate stadium of the presumptive brachypterous strain to cause observable change(s) when precocene II was applied at this stadium. Moreover, our results showed that a single application of precocene II at the 2nd, 3rd, 4th or 5th stadia failed to have any effect(s) on ovarian growth, although metamorphosis and wing dimorphism were disrupted. When the chemical was applied twice before adult emergence, ovarian growth was reduced drastically in the insects in which the two applications were carried out in the later stadia (4th and 5th). The lack of any effect(s) on ovarian growth in the single applications suggest that precocene II is not a systemic allatocidin but acts only to suppress the activity of the corpora allata and does not destroy it entirely.