Platynereis nadiae sp. n. (Polychaeta: Nereididae) from Italian coasts

A new species, Platynereis nadiae sp. n. (Polychacta: Ncrcididac), from thc Mediterranean Sea is described. It is clearly distinguished from the other Platynereis species by the distribution and the morphology of the homogomph falciger setae and by the structure of thc tcntacular cirri.     

Influence of environmental factors on the wandering phase and pupariation in stable fly, Stomoxys calcitrans, larvae

Abstract. Components of the wandering phase of mature stable fly ( Stomoxys calcitrans L. (Diptera: Muscidae)) larvae were examined. The mean length of the wandering phase was estimated to be 10.6 ± 3.5 h. In a factorial experiment in which wandering larvae were allowed to pupate in media with three levels each of moisture, temperature and light, the mean time to 50% pupariation was delayed and the rate of pupariation was lowest at high moisture levels, but this latter effect was seen only at the moderate light level. Pupae in media with higher moisture contents had significantly higher fresh weights. However, none of the three factors affected dry weight of pupae. A significant interaction was observed between the effects of moisture and temperature on survival; only at highest moisture content and at the highest temperature did a significant decrease in survival occur. In a separate experiment, density was found to have no effect on mean time to 50% pupariation or the rate of pupariation. Puparium formation appeared to be random under a LD 169 h photocycle, showing no apparent circadian rhythm.     

A fast algorithm for the exact likelihood of stationary and partially nonstationary vector autoregressive-moving average processes

An expression for the likelihood function of a stationary vectorautoregressive-moving average process is developed. The expressionis very efficient numerically and applies to any stationarybut not necessarily invertible model. In particular, when themultivariate process is autoregressive, the exact likelihoodcan be evaluated with a small number of operations dependingon the order of the autoregressive operator and the processdimension, but not on the size of the observed series. The expressionalso provides an efficient method for the evaluation of theexact likelihood of a partially nonstationary vector autoregressive-movingaverage process, for which the determinant of the autoregressiveoperator has at least one unit root and the remaining rootsare outside the unit circle. This method does not require differencingthe series, so that complications caused by over-differencingthe series, such as noninvertibility and parameter identifiabilityproblems, are avoided. The results for autoregressive modelsare also applied to testing the stationarity and invertibilityof any autoregressive-moving average model with given parametervalues.     

Effect of host instar on host discrimination of heterospecific‐parasitised hosts by sympatric parasitoids

1. Interspecific competition among hymenopteran parasitoids may shape their behavioural strategies for host resource exploitation. In order to reduce or prevent competition, many parasitoid species have evolved the ability to discriminate between unparasitised hosts and hosts parasitised by another parasitoid species (i.e. heterospecific host discrimination). However, discriminatory ability might be affected by host instar. 2. This study reports the first results on whether host instar can influence the use of heterospecific‐parasitised hosts by sympatric parasitoids of the genus Aphytis (Hymenoptera: Aphelinidae). 3. Aphytis melinus and Aphytis chrysomphali discriminated between unparasitised and heterospecific‐parasitised hosts when they found a third‐instar host (high quality), with a tendency to multi‐parasitise. However, this discrimination was not observed in the second instar (lower size). 4. The behavioural strategies adopted towards multi‐parasitise third‐instar hosts varied between both species. Aphytis chrysomphali reduced its clutch size in heterospecific‐parasitised hosts, whereas A. melinus tended to probe them for longer than healthy hosts. 5. Overall, our results highlight the importance of host instar in the study of intrinsic competition between parasitoids.     

Eco-physiology of Palaemonetes antennarius (Crustacea, Decapoda): the influence of temperature and salinity on cardiac frequency

Abstract.  The effect of different temperatures and salinities on the cardiac frequency of the freshwater shrimp Palaemonetes antennarius is investigated. The results show that both temperature and salinity influence heart rate. Variations in water temperature are associated with changes in heart rate: variations higher than 8°C in 6 h affect not only heart rate, but also shrimp survival. After an initial rapid increase, the heart rate returns to initial values at saline concentrations of 15‰ and 30‰, whereas, at 20‰ salinity, the shrimps show a persistent decrease of heart rate throughout the test. The marked tolerance of variations of temperature and salinity suggests that P.   antennarius is well adapted to waters with large salinity and temperature oscillations. Cardiac frequency can be used as a valid indicator of physiological stress in this species.