Tarsal contact chemoreceptor for the host marking pheromone of the cherry fruit fly, Rhagoletis cerasi: responses to natural and synthetic compounds

Abstract. The European cherry fruit fly (Rhagoletis cerasi L.; Diptera, Tephritidae) marks cherries (Prunus avium L.) after oviposition with a host marking pheromone (HMP). The marking trail prevents additional oviposition by the same or other females into the same fruit. On the ventral side of the tarsi of both sexes, contact-chemoreceptor sensilla were identified which contain a receptor cell selectively sensitive to HMP. The HMP receptors of males were slightly more sensitive than those of females, suggesting that the more general term ‘host-marking pheromone’ is more appropriate than the previously used ‘oviposition deterring pheromone (ODP)’. The four structural isomers of the HMP, N(15R, S(β-glucopyranosyl)-oxy-8RS-hydroxypalmitoyl)-taurine, and various derivatives were synthesized and tested in an electrophysiological bioassay. Both the 8R,15R and the 8S,15RS isomers of the HMP were equally active with a threshold of about 2 times 10^-10M, and were shown to be present in the female faeces in similar proportions. The two 15S HMP isomers were about 13 times less active. Testing synthetic derivatives of the HMP molecule revealed that the presence of the four moieties of the molecule are important for the activity: taurine, palmitic acid, C₍₈₎ hydroxyl group, and glucose (C₍₁₅₎). The chain length of the fatty acid, the hydroxyl group at C₍₈₎ and the position of glucose at C₍₁₅₎ also influenced the activity. Only minor loss of activity (factor 2) relative to the natural molecule was observed when the methyl group in the C₍₁₅₎ position was removed. The removal of the β-glycosidically linked glucose (replaced by a hydroxyl group) resulted in about a 4-fold loss of activity. The cation of the HMP molecule seemed to have no effect on its activity, whereas both low and high pH reduced it significantly. Based on these results, field experiments have been initiated to control oviposition by cherry fruit flies on cherries applying the 15-desmethyl-HMP derivative.     

Ontogeny of the Molluscan Shell Field: a Review

In the gastropod, scaphopod, lamellibranch, and cephalopod gastrulae a thickened portion of the posttrochal region is referred to as the embryonic shell field. It invaginates and gives rise to the shell gland. In species with an at least temporarily external shell, the shell gland evaginates and again forms a shell field. In lamellibranchs, the shell field grows into two halves connected by the ligament-secreting isthmus. In polyplacophorans plate fields are produced without invagination. Slugs and endocochleate cephalopods overgrow the embryonic shell field to form an internal shell sac. The calcified part of the shell is secreted by the flattened central region. The periostracum has its origin in the permanently thickened peripheral region of the shell field. In many forms, this region is depressed in a periostracal groove. If the shell is external, the central region of flattened cells, the mantle roof, along with the two or three marginal folds of the free mantle edge and, in species with internal shell, the shell sac are parts of the mantle. The shell field descends from the first somatoblasts. Either of 2 d or 2 c alone is able to form the shell field. There are arguments that the formation of the embryonic shell field is not autonomic, but induced by the entoderm during a period of contact. The shell gland and the shell field grow by mitotic cell divisions. Cells secreting organic material are highly prismatic, have a well developed ergastoplasm and large dictyosornes, and contain much peroxidase. The secretion of calcium manifests itself in very flat cells, rich in alkaline phosphatase and glycogen. The shell gland and the rosette of ectocochleate conchifera together are homologous to the proximal part of the shell sac in slugs and endocochleate cephalopods.     

The orientation of walking honeybees in odour fields with small concentration gradients

The behaviour of walking honeybees in small gradient odour fields was investigated by means of a simulation technique. The bee was kept in one place by a locomotion compensator (‘running sphere’). This compensator allowed for a precise reconstruction of the bee's actual locomotion on the sphere, and presented the bee with a stimulating odour whose concentration was controlled by feedback from the reconstructed locomotion. This rendered possible the application of well-defined odour fields and revealed that: (1) honeybees are capable of finding odour sources in the absence of optical cues and with concentration gradients too small to allow tropotactic or klinotactic orientation; (2) bees are capable of memorizing odour concentrations with a high degree of accuracy; (3) this orientation system is based on a switching over from negative to positive anemotaxis at a ‘reference’ concentration; (4) this reference is a function of the odour concentration at which a sugar reward is given. The results do not support any hypothesis for an orientation system based on the detection and comparison of successive values of odour concentration. A hypothesis on the nature of the ‘reference value’ is discussed and supported by experiments.