Male sexual enhancement after methoprene treatment in Anastrepha fraterculus (Diptera: Tephritidae): A sustained response that does not fade away after sexual maturation

Abstract

The juvenile hormone (JH) of insects triggers physiological changes related to reproduction in adults of both sexes. Methoprene is a sesquiterpene with some effects that are analogous to those of JH. Treatments with methoprene accelerate sexual maturation in males of the South American fruit fly Anastrepha fraterculus, giving young males a mating advantage over non-treated males of the same age. Here, we evaluated the effects of methoprene treatment on A. fraterculus males after the sexual maturation phase and tested whether this compound provides a long-term mating advantage. Moreover, we took the first step to unravel the mechanisms that underlie male sexual enhancement. We treated males 1day or 8days after adult emergence and compared mate choice between recently matured (young) females and females that had been mature for ca. 10days (aged females). We also addressed methoprene treatment effects on male sexual signalling. We found that methoprene treatment enhanced male sexual competitiveness even after the sexual maturation phase, and the effect did not decrease until males were older than 20days. However, when methoprene treatment was carried out close to sexual maturity, the mating enhancement was no longer observed, suggesting a non-immediate effect and excluding the possibility that methoprene acts as a pheromonal compound. Young and aged females tended to mate more frequently with treated-males. This might indicate that in a context of sexual selection, the potential benefits associated with reproductive success would be similar for females of both ages. Treated males released larger amounts of pheromonal compounds than non-treated males, but their courtship behaviour was not altered to the same extent, suggesting that methoprene treatment may accelerate differently the components of male courtship. We discuss potential benefits of using methoprene to increase the efficiency of the sterile insect technique, which is an environmentally safe method to control this important South American fruit pest.

Mate choice confers direct benefits to females ofAnastrepha fraterculus(Diptera: Tephritidae)

“…[42] and Bachmann et al . [43,44] observed that A. fraterculus females prefer males that had been exposed to volatiles of guava fruit (one of its main hosts) or treated with methoprene (an artificial analogue of JH). Here, we verified these patterns of sexual selection and investigated whether female preferences can be explained on the basis of a direct fitness benefit.…”

“…relating their preference with direct fitness benefits) is misleading. In this scenario, methoprene would induce a higher rate of pheromone release in males, which triggers female acceptance over non-treated males [44] by exploiting females’ sensory channel with no reward in terms of their own potential fecundity. However, juvenile hormone analogues do exist in nature [45–47] and some insects consume them, increasing their reproductive output [48].…”

“…Males were 12-14 d old; ; whereas females were 14-18 d old. These experimental arenas have been extensively used in A. fraterculus as a valid experimental approach to study female mate choice [42–44,55,56]. Males were marked on their thorax with a dot of non-toxic, water-based paint for identification [54].…”

“…Despite evidence showing that guava fruit volatiles and mimics of natural compounds (like methoprene) enhance male mating success in different Anastrepha species, no prior investigation has measured the potential fitness benefits gained by females that mate with those enhanced males. Even though guava volatiles are natural compounds and methoprene is synthetic, they both stimulate males to release larger amounts of pheromone and increased male mating success [43,44]. Furthemore, plants produce several natural analogues of the juvenile hormone (termed juvenoids), which protect them from herbivore larvae [45–47].…”

Effects of the juvenile hormone mimic NC-184 on the development of the reproductive organs and mating behaviour of nymphs of the desert locust, Schistocerca gregaria (Orthoptera: Acrididae)

“…Drosophila melanogaster Meigen also shows JH-dependent male mating behaviour (Wijesekera et al, 2016). On the other hand, in the South American fruit fl y, Anastrepha frateculus (Wiedemann), treatment with methoprene accelerate sexual maturation of males, but not the enhancement of mating in males close to sexual maturation, suggesting methoprene might act as a pheromone (Bachmann et al, 2017). In the Asian comma butterfl y, Polygonia aureum L., transplantation of active corpora allata into adult butterfl ies in diapause does not induce males to copulate (Endo, 1973), although methoprene or active corpora allata promotes reproductive development in both sexes (Hiroyoshi et al, 2017).…”