Age‐dependent responses of last instar larvae of Spodoptera mauritia to precocene II

ABSTRACT. Last instar larvae of Spodoptera mauritia Boisd. (Lepidoptera: Noctuidae) of various ages were treated with a single dose of 80 μg or 160 μg of precocene II (PII) and the effects of larval—pupal transformation were studied. Final instar (sixth) larvae treated on day 0, 1 or 2 with 80 μg P II showed a high mortality; P II treatment during subsequent days of this stadium showed a diminishing tendency for mortality. P II prolonged the larval—pupal period in all larvae but the effect was somewhat reduced in the mid‐stadium. Treatments of 160μg P II to 0‐day‐old, 1‐day‐old, 2‐day‐old and 3‐day‐old larvae were highly toxic. Treatments of 4‐day‐old and 5‐day‐old larvae with 160 μg P II delayed pupation by 1 day, but in addition the larvae often moulted into larval—pupal intermediates. Co‐application of 50μg juvenile hormone analogue (ZR 512) with 160 μg P II restored both normal morphogenesis and a normally‐timed moult.