The role of 20-hydroxyecdysone in the moulting of Biosteres longicaudatus, a parasite of the Caribbean fruit fly, Anastrepha suspensa

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Ecdysteroid levels in whole body extracts of parasitized and unparasitized Anastrepha suspensa peaked 24 h after initial puparium formation. Six to eight-hour old first instars of the parasite, Biosteres longicaudatus, dissected from the host 16–18 h prior to its ecdysteroid peak never moulted in 20-hydroxyecdysone free media, while > 15% removed 6–12 h afterwards (i.e. at 24–36 h old) did. Isolation of 6–8-h old parasites within ligated abdomens of pre-wandering host larvae inhibited the parasites' moult. However, topical applications of 20-hydroxyecdysone (1.3 μg) to each host abdomen 24 and 48 h after ligation elicited host pupariation and larval-pupal apolysis as well as parasite moulting. Pre-treatment of host larvae with 2.7 μg/g hydroprene prior to parasitization and ligation prolonged host larval life. Subsequent 20-hydroxecdysone therapy of these hydroprene-treated, ligated abdomens increased parasite moult above that of abdomens receiving 20-hydroxyecdysone treatments alone. Six to eight-h old parasite first instars incubated for 4 days in 20-hydroxyecdysone-free medium increased in length by 78.3% and in head-capsule width by 23.8%. After a 24-h pulse of 10 −6 M 20-hydroxyecdysone only those that exceeded 1400 μ [X̄ = 14.1 ± 0.9 μ (SD)] in length and 250 μ in headcapsule width, moulted. A comparison of parasite growth in vivo and in vitro suggested that size may also affect moulting competence.