## 4 Discussion
### Scg-Met Knockdown Severely Disrupts the Reproductive Development of Adult Male Locusts
_Met_[27] mutants showed reduced AG sizes. This could be ascribed to the overall reduced protein synthesis resulting from the impaired JH signaling [77]. Similar effects were observed after knocking down _Met_ or _Tai_ in the linden bug, _Pyrrhocoris apterus_[78; 79]. These studies demonstrated the participation of Met and Tai in generating the JH dependent effects on AG size in male _P. apterus_. Surprisingly, Met knockdown in this species did not reduce locomotor activity or mating behavior, in contrast to what is observed during adult reproductive diapause, which made the authors suggest that an additional photoperiod control mechanism might be situated in parallel, independent or upstream of JH [79]. In the red flour beetle, _T. castaneum_, a JHAMT knockdown reduced the AG size and production of seminal proteins, significantly affecting male fitness [80]. Moreover, in locust species, JH has previously been shown to be essential for the growth of the AG and associated protein content in this tissue [44; 46; 47]. Our results show that _Scg-Met_ knockdown in _S. gregaria_ produced effects opposite to JH itself, clearly illustrating the adverse consequences of a disabled transduction of the JH signal on the development of reproductive organs in adult male locusts. 4. Interestingly, both the size of the CA and the expression of _Scg-JHAMT_, which codes for a rate-limiting JH biosynthetic enzyme, were significantly increased upon sustained knockdown of _Scg-Met_ (Figure 2). These observations suggest the existence of homeostatic regulatory mechanisms for preserving a balance between JH synthesis and JH sensitivity. This is also supported by the observed increase in _Scg-JHAMT_ and _Scg-CYP15A1_ expression upon _Scg-Met_ knockdown in adult female _S. gregaria_[14]. A similar stimulation of JH production following Met knockdown was previously also described in the linden bug, _P. apterus_[78]. This homeostatic regulation may reside within the CA but could also be more complex and include inter-organ communication mechanisms. 5. Finally, knockdown of either component of the JH receptor complex induced very similar phenotypic effects in the desert locust (Figure 6). Recent studies revealed that Met forms a complex with Tai to become a functionally active JH-dependent receptor. Once JH is bound to Met, the JH-Met complex will subsequently interact with a Tai transcription factor domain to form an active JH signal transducer [10]. Our findings are in line with this mechanistic model for JH signaling and indicate that reproductive organ growth, yellow coloration and PAN pheromone emission in gregarious males are highly dependent on expression of both _Scg-Met_ and _Scg-Tai_. Profiles of _Scg-Met_, _Scg-Tai_, _Scg-Krh1_, _Scg-JHAMT_ and _Scg-CYP15A1_ in _Untreated Adult Males  
In this study, we have also analyzed the transcript profiles of _Scg-Met_, its dimerization partner _Scg-Tai_ and the downstream factor _Scg-Krh1_ during male adult development in four different tissues and on three different time points after the final molt (Figure S7). The abundance of the transcripts coding for these JH pathway components significantly increased in the fat body during male reproductive maturation, showing lowest levels when males were sexually immature (day 3), intermediate levels when they were maturing (day 7) and highest when they had reached sexual maturity (day 15) (Figure S7). On day 15, males in our gregarious desert locust colony have fully developed gonads, have a bright yellow colored cuticle and are sexually active as manifested by their mating behavior. That the levels of all three transcripts significantly increased from day 3, over day 7 to day 15 in male fat body indicates that JH directly interacts with male fat body. This increased expression of receptor components in the fat body seems to correlate with the significant rise of mRNA levels for the JH biosynthetic enzymes _Scg-_JHAMT and _Scg-_CYP15A1 in the CA, both crucial for JH biosynthesis.