Assessment of the toxic and disruptive effects of Precocene II on growth and metamorphosis of the grasshopper Euprepocnemis plorans plorans (Charp.) (Orthoptera: Acrididae).

Abstract

As reported in Egypt, the grasshopper Euprepocnemis plorans plorans is considered as a serious pest to crops in some regions. The objective of the current investigation was to evaluate the toxic and disruptive effects of the anti-JH compound, Precocene II (PII), on this pest. Nymphs of the newly moulted 2nd and 4th (penultimate) instars had been exposed to the doses: 60, 40, 20 and 10 µg/cm2. Complete mortality of nymphs was observed within 24 h of exposure of 2nd instar nymphs to the higher two doses. At other doses, PII exhibited a remarkably extended low toxicity on the subsequently moulted nymphal instars and emerged adults. After exposure of the 4th instar nymphs to PII, no complete mortality was observed, but various mortalities had been recorded among the treated nymphs, 5th instar nymphs and adults. LD50 values of PII were calculated as 0.388 and 17.022µg/cm2, after treatment of 2nd and 4th instar nymphs, respectively. After treatment of 2nd instar nymphs with PII, the nymphal growth of both 4th and 5th instars was insignificantly inhibited, regardless the dose. Exposure of 2nd instar nymphs to the lowest dose of PII led to 3.33% precociously moulted nymphs into 4th instar, skipping off the 3rd instar. On the other hand, exposure of 4th instar nymphs to the higher tow doses of PII induced some treated nymphs to precociously metamorphose into adultoids, skipping over the 5th instar. Some permanent nymphs (3.85%) appeared among the 2nd instar nymphs after exposure only to 20µg/cm2. Also, similar permanent nymphs were induced during the 4th instar. No permanent nymphs had been induced after exposure of 4th instar nymphs to PII.