STRONTIUM LABELLING OF THE SHELL OF THE ANTARCTIC LIMPET NACELLA CONCINNA (STREBEL, 1908)

Nacella concinna (Strebel, 1908) held in seawater enriched withSr, partially replaced Ca in their shells with Sr The bandslaid down were clearly visible In back-scattered, scanning electronmicroscope images, and such bands could be used to mark carbonateskeletons in field investigations of growth Sr directly replacedCa in the carbonate shells, although not entirely, and newlysecreted shell material always contained less Sr than wouldbe expected from the levels used in treatments. Specimens heldin water with atomic Ca:Sr ratios of 114:1 (control seawater,no added Sr), 4.4:1, 2.2:1 and 1.1.1 produced shell ratios ofca. 635:1, 11.0.1, 3.1:1, and 8.1:1 respectively These valueswere between 1.4 and 7 4 tunes higher than expected, indicatingthat, when shell was laid down Sr was discriminated againstby a factor of around 4. Growth rates were similar before andafter placing specimens in experimental treatments and feedingrates were not significantly different between treatments andcontrols, indicating that the enhanced Sr regimes caused littlestress for the limpets. Limpets were exposed to the experimentaltreatments for 12 days. However, in specimens where growth bandswere visible, it was only possible to distinguish between 5and 8 micro-growth lines. In specimens removed after 3 daysexposure, there was no detectable area of enhanced Sr in theshell. These two observations were interpreted as either meaningthat it takes around 5 days for Sr to enter the extra-pallialfluids which are used for laying down shell, or that the limpetsdid not produce any shell growth during that period. Experimentsplacing Sr in food and not in the treatment water, and vice-versa,suggested that Sr taken directly from the water may be moreimportant than uptake from food. (Received 24 October 1995; accepted 13 December 1995)     

Elevation of pheromone response threshold in almond moth males pre-exposed to pheromone spray

Abstract. High percentages of naive Cadra cautella (Walker) (Lepidoptera: Pyralidae) males not pre-exposed to pheromone flew upwind to sources containing 50 ng (83%) and 500 ng (97%) of pheromone, but not to sources containing 5 μg (23%) and 50 μg (4%).Of the naive males that flew upwind in response to 50 ng sources, 67% located and landed on the source, whereas fewer than 19% of the naive males that flew upwind in response to higher doses located and landed on the sources.A 2-minute pre-exposure of C.cautella males to a spray cloud containing 50 ng, 500 ng, 5 μg or 50 μg of pheromone, induced shifts in response levels such that in wind-tunnel bioassays performed 1 h later, there was an increase in the doses that optimally elicited upwind flight and landing on the source that was proportional to the pre-exposure dose.Few of the pre-exposed males flew upwind to (10–43%) and landed on (0–33%) 50 ng sources, whereas they now perferentially flew upwind to(58–81% and 52–73%) and landed on (33–68% and 55–60%) pheromone sources of doses of 500 ng and 5 μg, respectively.Therefore pre-exposure to pheromone promoted a shift of threshold for response, and not an overall reduction in responsiveness to pheromone.