Sensilla coeloconica ringed by microtrichia in host‐seeking biting midges

The distribution and morphology of antennal sensilla coeloconica in parasitic and predaceous biting midges were studied in females of Forcipomyia (feeding on the blood of frogs), Atrichopogon (feeding on haemolymph), Austroconops, Culicoides (feeding on the blood of birds and mammals) and Brachypogon (feeding on haemolymph and dissolved tissues of insects) (all: Diptera: Ceratopogonidae). A Lower Cretaceous female of Archiculicoides (Diptera: Ceratopogonidae) from Lebanese amber, which fed on the blood of unknown vertebrates, was also examined. In sensilla coeloconica ringed by microtrichia, the peg is grooved longitudinally and protrudes distinctly from the pit. We suggest that the microtrichia encircling the protruding peg form a structure resembling a picket fence in order to maintain a higher level of humidity, which facilitates the capture and transport of odour molecules through the channels in the peg wall. Sensilla coeloconica ringed by microtrichia function as very effective chemoreceptors in host‐ and prey‐seeking activity. During the evolution of Ceratopogonidae, sensilla coeloconica with a fence of microtrichia have evolved twice in groups feeding on the blood of vertebrates (i.e. in the basal lineage: Lower Cretaceous or earlier) and in the subgenus Lasiohelea of Forcipomyia (Palaeogene). Sensilla coeloconica ringed by microtrichia are described for the first time in the relict genus Austroconops.     

Cuticle hydrolysis in four medically important fly species by enzymes of the entomopathogenic fungus Conidiobolus coronatus

Entomopathogenic fungi infect insects via penetration through the cuticle, which varies remarkably in chemical composition across species and life stages. Fungal infection involves the production of enzymes that hydrolyse cuticular proteins, chitin and lipids. Host specificity is associated with fungus–cuticle interactions related to substrate utilization and resistance to host‐specific inhibitors. The soil fungus Conidiobolus coronatus (Constantin) (Entomophthorales: Ancylistaceae) shows virulence against susceptible species. The larvae and pupae of Calliphora vicina (Robineau‐Desvoidy) (Diptera: Calliphoridae), Calliphora vomitoria (Linnaeus), Lucilia sericata (Meigen) (Diptera: Calliphoridae) and Musca domestica (Linnaeus) (Diptera: Muscidae) are resistant, but adults exposed to C. coronatus quickly perish. Fungus was cultivated for 3 weeks in a minimal medium. Cell‐free filtrate, for which activity of elastase, N‐acetylglucosaminidase, chitobiosidase and lipase was determined, was used for in vitro hydrolysis of the cuticle from larvae, puparia and adults. Amounts of amino acids, N‐glucosamine and fatty acids released were measured after 8 h of incubation. The effectiveness of fungal enzymes was correlated with concentrations of compounds detected in the cuticles of tested insects. Positive correlations suggest compounds used by the fungus as nutrients, whereas negative correlations may indicate compounds responsible for insect resistance. Adult deaths result from the ingestion of conidia or fungal excretions.     

On the relationship between sweet taste and seasonal body weight changes in a primate (Microcebus murinus)

The relationship between obesity and taste, especially sweettaste, has been and is of interest. From this point of viewof a small primate, the lesser mouse lemur (Microcebus murinus),is of particular interest. It goes through a yearly cycle ofphysiological changes, one of which is an extreme variationin body weight of up to 100%. This occurs concomitantly withsignificant changes of the animal's liking for sucrose; measuredby two-bottle preference tests, the threshold for sucrose changesfrom 28–45 in lean to 77–105 mM in obese animals.It is possible that a change in peripheral taste sensitivitymight be the cause for these preference changes. To test thispossibility we studied the ability of M.murinus to taste sucrosewith electrophysiological and conditioned taste aversion techniques.The electrophysiological recordings were obtained from the chordatympani proper nerve in two heavy and three lean animals. Wedid not record any difference between the two groups in theirneural response to a series of sucrose concentrations. Conditionedtaste aversion experiments with 200 mM sucrose as conditioningstimulus and 50 and 200 mM sucrose as test stimuli gave similarresults. No difference was found between three heavy and fourlean animals; both groups rejected the sucrose concentrations.The results support the notion that the seasonal variationsin preference threshold to sucrose were unrelated to the abilityof M.murinus to taste sucrose.     

On the sense of taste in two Malagasy Primates (Microcebus murinus and Eulemur mongoz)

The relationship between phylogeny and taste is of growing interest.In this study we present recordings from the chorda tympaniproper (CT) nerve of two lemuriforme primates, the lesser mouselemur (Microcebus murinus) and the mongoose lemur (Eulemur mongoz),to an array of taste stimuli which included the sweeteners acesulfame-K,alitame, aspartame, D-glucose, dulcin, monellin, neohesperidindihydrochalcone (NHDHC), saccharin, sodium superaspartame, stevioside,sucralose (TGS), sucrose, suosan, thaumatin and xylitol, aswell as the non–sweet stimuli NaC1, citric acid, tanninand quinine hydrochloride. In M.murinus the effects of the tastemodifiers gymnemic acid and miraculin on the CT response wererecorded. Conditioned taste aversion (CTA) experiments in M.murinusand two-bottle preference (TBP) tests in E.mongoz were alsoconducted. We found that all of the above tastants except thaumatinelicited a CT response in both species. The CTA technique showedthat M.murinus generalized from sucrose to monellin but notto thaumatin. The intake of aspartame, ranging in concentrationfrom 0.1 to 30 mM was measured in E.mongoz with TBP tests. Atno concentration did we see a preference, but there was a significantrejection of 10 and 30 mM aspartame (P