Roger Huybrechts

Female anautogenous Sarcophaga flesh flies need a protein meal to start large‐scale yolk polypeptides (YPs) production and oocyte maturation. Protein meal rapidly elicits a brain‐dependent increase in midgut proteolytic activity. Trypsin and chymotrypsin together represent over 80% of protease activity in liver‐fed flies. Abdominal injection of 6‐hydroxydopamine (6‐OHDA) dose‐dependently prohibits this increase in proteolytic activity at translational level in a similar way as post liver feeding decapitation. Delayed injection of 6‐OHDA later than 6 h post liver meal has no effect. In flesh flies, chemical decapitation by 6‐OHDA, by interrupting the brain‐gut dopaminergic signaling, can be used as tool for the controlled inhibition of midgut proteolytic activity and subsequent ovarial development. Inhibition of ovarial development is probably indirect due to a deficit in circulating amino acids needed for YPs synthesis.

Insect cell cultures played central roles in unraveling many insect physiological and immunological processes. Regardless, despite imminent needs, insect cell lines were developed primarily from Dipteran and Lepidopteran orders, leaving many important insects such as Orthopteran locusts under-represented. Besides the lack of cell lines, the slow progress in development of in vitro techniques is attributed to poor communications between different laboratories regarding optimized primary cell cultures. Therefore, we report here about methods developed for primary cell culture of Locusta migratoria hemocyte and phagocytic tissue cells by which we could maintain viable hemocytes in vitro for over 5 d and phagocytic tissue cells for over 12 d. 2-Mercaptoethanol and phenyl-thiourea supplements in Grace’s medium together with addition of fetal bovine serum 30 min after cell seeding resulted in a successful setup of the primary cell cultures and a week-long survival of the hemocytes and phagocytic tissue cells in vitro.

Drastic changes in the environment during a lifetime require developmental and physiological flexibility to ensure animal survival. Desert locusts, Schistocerca gregaria, live in an extremely changeable environment, which alternates between periods of rainfall and abundant food and periods of drought and starvation. In order to survive, locusts display an extreme form of phenotypic plasticity that allows them to rapidly cope with these changing conditions by converting from a cryptic solitarious phase to a swarming, voracious gregarious phase. To accomplish this, locusts possess different conserved mediators of phenotypic plasticity. Recently, attention has been drawn to the possible roles of protein kinases in this process. In addition to cyclic AMP‐dependent protein kinase (PKA), also cyclic GMP‐dependent protein kinase (PKG), which was shown to be involved in changes of food‐related behavior in a variety of insects, has been associated with locust phenotypic plasticity. In this article, we study the transcript levels of the S. gregaria orthologue of the foraging gene that encodes a PKG in different food‐related, developmental and crowding conditions. Transcript levels of the S. gregaria foraging orthologue are highest in different parts of the gut and differ between isolated and crowd‐reared locusts. They change when the availability of food is altered, display a distinct pattern with higher levels after a moult and decrease with age during postembryonic development.