Temperature‐independent arrest in female reproduction in a tropical fruit fly (Diptera: Tephritidae)

Abstract

Polyphagous tropical fruit flies of the genus Bactrocera are generally assumed to undergo continuous breeding on the basis that hosts and temperature are not limiting. However, in their endemic monsoonal rainforest habitats, breeding hosts are not always available, and repeatable seasonal population depression for Bactrocera species has been documented. This has led to a recent hypothesis that some species in the genus may undergo seasonal reproductive arrest during the year. Working with outdoor‐maintained mixed‐sex colonies at a subtropical site, we documented changes in Bactrocera tryoni (Froggatt) female reproductive status and fecundity over time, with an emphasis on the period from May to August (winter), when population numbers in the field decline and then rebuild. Based on dissection, female flies emerging in mid‐May did not contain mature eggs in the ovaries until mid‐July, while sperm in the spermathecae was not observed until early August. Based on day degree accumulation and normal development, sexual maturation should have occurred by mid‐June; that it did not provides evidence for delayed sexual development acting independently of ambient temperature. Fecundity was greatly suppressed in July compared to egg production in spring and summer, and mating was again delayed. Flies surviving from May through to September laid 70% of the egg load of new‐generation spring flies emerging and had a similar egg fertility, showing large reproductive potential of ‘old’ flies. The results support a hypothesis for a seasonal break in breeding by B. tryoni that is not solely temperature related.