ATP-dependent carbon transport in perfused Chara cells

Carbon transport across the plasma membrane, and carbon fixation were measured in perfused Chara internodal cells. These parameters were measured in external media of pH 5·5 and pH 8·5, where CO₂ and HCO₃^- are, respectively, the predominant carbon species in both light and dark conditions. Cells perfused with medium containing ATP could utilize both CO₂ and HCO₃^- from the external medium in the light. Photosynthetic carbon fixation activity was always higher at pH 5·5 than at pH 8·5. When cells were perfused either with medium containing hexokinase and 2-deoxyglucose to deplete ATP from the cytosol (HK medium) or with medium containing vanadate, a specific inhibitor of the plasma membrane H⁺_-ATPase (V medium), photosynthetic carbon fixation was strongly inhibited at both pH 5·5 and 8·5. Perfusion of cells with medium containing pyruvate kinase and phosphoenolpyruvate (PEP) to maximally activate the H⁺_-ATPase (PK medium), stimulated the photosynthetic carbon fixation activities. Oxygen evolution of isolated chloroplasts and the carbon fixation of cells supplied ¹⁴C intracellularly were not inhibited by perfusion media containing either hexokinase and 2-deoxyglucose or vanadate. The results indicate that Chara cells possess CO₂ and HCO₃^- transport systems energized by ATP and sensitive to vanadate in the light. In the dark, intact cells also fix carbon. By contrast, in cells perfused with medium containing ATP, no carbon fixation was detected in 1 mol m ^-3 total dissolved inorganic carbon (TDIC) at pH 8·5. By increasing TDIC to 10 mol m^-3, dark fixation became detectable, although it was still lower than that of intact cells at 1mol m^-3 TDIC. Addition of PEP or PEP and PEP carboxylase to the perfusion media significantly increased the dark-carbon fixation. Perfusion with vanadate had no effect on the dark-carbon fixation.     

Development of a genetic sexing strain of Anopheles arabiensis for KwaZulu‐Natal,South Africa

An efficient sexing system is important for the release of sterile males for any control programme using the sterile insect technique. This study describes the development and characterization of a new genetic sexing strain from South Africa (GMK), needed for the planned implementation of such a programme in northern KwaZulu‐Natal Province. The base colony used was a locally modified laboratory strain of Anopheles arabiensis containing a sex‐linked gene conferring dieldrin resistance to male mosquitoes. Female A. arabiensis mosquitoes from northern KwaZulu‐Natal were mated with these males and backcrossed to introduce the dieldrin resistance gene to the Y chromosome. The resulting strain therefore had an overall genotype representing the local population but with the Y chromosome containing the dieldrin resistance gene. Life‐history characteristics, stability of the sex‐linked resistance marker, and reduction in dieldrin waste were investigated. The strain showed semi‐sterility exhibited by low egg hatch rates, faster development in the immature stages and longer adult survivorship compared with the parental strains. While the GMK strain carrying the dieldrin‐resistant gene was successfully established, the stability of the gene is limited, requiring periodic purification. Dieldrin waste can be limited by treating many more eggs than currently recommended.     

Do fledgling and pre‐breeding Common Swifts Apus apus take part in aerial roosting? An answer from a radiotracking experiment

This study has shown that fledgling Common Swifts Apus apus spend the first post-fledging night of their life on the wing and that pre-breeders also spend the full night on the wing. Even though this work was conducted during an unusually cold, wet period, the results show that fledglings do not return to their natal colony in the week after fledging. It also demonstrates that yearlings are only slightly more likely than fledglings to spend any time at a particular colony, but are more likely to move from colony to colony. Older pre-breeders are more likely to spend more time at and revisit a particular colony more often than yearlings. It is our observation that only right at the end of the breeding duties will the parents participate in an evening ascent, and even then many of them return to their nest for the evening. Breeding adults displayed the greatest devotion to a particular colony. But even among such adults we detected some that ceased caring for their young a few days prior to their fledging. Adults roost in their nestbox if they meet with bad weather.     

Behavioural study of plasticity in host preferences of Trichogramma maidis (Hym.: Trichogrammatidae)

Abstract. To test the relative importance of genetic and environmental factors in host preferences of Trichogramma maidis Pint. & Voeg., a polyphagous parasitoid, the oviposition behaviour was analysed on two host species: Anagasta kuehniella used for mass rearing) and Ostrinia nubilalis a target pest). Females were compared according to the species on which they had been reared, and to that on which they had an oviposition experience. To quantify an oviposition sequence, the most frequent behavioural succession was established for each experimental situation, individual sequences were then compared with this standard one to count the number of additional behaviours. An affinity coefficient positively related to host acceptance was then calculated from these additional behaviours. A preference for O.nubilalis versus A kuehniella appeared, but rearing on A. kuehniella enhanced the level of spontaneous affinity for this unnatural host. These initial preferences were modified by an oviposition experience: the affinity for a given host was higher after an oviposition on the same species, which suggests a female's ability to learn. This learning ability was higher on the non-preferred host, which led to an equivalent final parasitic performance on both hosts. Moreover, the learning ability was specific to a given host, since the oviposition on a given species did not provide any improvement in the level of affinity for the other species.