The role of direct chilling injury and inoculative freezing in cold tolerance of Amblyomma americanum, Dermacentor variabilis and Ixodes scapularis

Abstract. Supercooling points and chill tolerance were compared among nymphs and adults of the ixodid ticks Dermacentor variabilis, Amblyomma americanum and Ixodes scapularis (Acari: Ixodidae).Supercooling points in the range of <-22 to -18°C were observed for nymphs, and -22 to -8°C for adults.The lower lethal temperatures observed under dry conditions, -14 to -10°C, were warmer than the supercooling points, but still much colder than -4.8°C, the lowest temperature recorded from a likely tick habitat in southwestern Ohio.Based on our experiments, spontaneous freezing and direct chilling injury are not significant mortality factors in these species in the field.Mortality was observed between -5 and -3°C for A.americanum and D.variabilis nymphs chilled for 2 h while in direct contact with ice.This mortality is probably due to inoculative freezing.Given the requirement for a rather humid microhabitat for off-host survival, these findings suggest that inoculative freezing is an important cause of overwintering mortality in these medically important species.     

Acoustic recognition of sibling species within the holarctic lacewing Chrysoperla carnea (Neuroptera: Chrysopidae)

Abstract. Individuals of Chrysoperla curnea (Stephens) from central Europe exhibit courtship songs that are radically different from those of nearctic members of the same species. Additionally, the two geographically distinct populations will not hybridize under laboratory conditions. It is likely, therefore, that the two song morphs are distinct, sibling species; consequently Chrysoperla plorabunda (Fitch) is raised from synonymy, to include New World specimens formerly placed in C.camea. Within the nearctic region, other plorabunda -like individuals have been found to possess uniquely different calls, suggesting that the carnea-plorabunda complex may in fact consist of numerous morphologically indistinguishable species.     

Vocal individuality in the roding calls of Woodcock Scolopax rusticola and their use to validate a survey method

The Woodcock Scolopax rusticola is a difficult species to survey in the breeding season because of its cryptic plumage and, with the exception of courtship flights, secretive behaviour. Sparse data from general bird surveys prohibit reliable estimation of population sizes and trends, and a new species-specific method to provide baseline information on population status and to enable reliable future monitoring is required. Counts of displaying, or 'roding', males at dawn or dusk potentially provide such a method but their value is unclear because it is impossible for an observer to distinguish different birds. We examined the vocal individuality of 39 roding males and were able to attribute calls to individuals correctly in 95% of cases on the basis of five parameters measured from spectrograms. Using calls, we determined the number of individual males at 43 sites. Roding activity differed between males at one site, with the two most active birds accounting for, on average, 55 and 27% of passes. There was no evidence of sequential roding by different males. We quantified the relationship between numbers of males and numbers of passes of roding birds during a 1-h period at dusk. This relationship was not affected by region, month, habitat or woodland size class. We conclude that counts of roding males provide a suitable index for monitoring populations of this species.     

Grain aphid clones vary in frost resistance,but this trait is not influenced by facultative endosymbionts

1. Facultative endosymbiotic bacteria of insects are known to affect life‐history traits of their hosts, and can provide important fitness benefits under certain environmental conditions. While several distinct endosymbiont‐induced effects have been reported, there is no data on whether heritable facultative endosymbionts in any species affect their hosts' performance at low temperatures, something that could have a major effect on insect physiology and survival, and thus population structure and distribution. 2. The original facultative endosymbionts were experimentally removed from five clonal genotypes of the grain aphid, Sitobion avenae Fab., which were then exposed to frost. 3. Aphid genotypes differed considerably in survival following the exposure and in fecundity of the survivors. However, the presence of the facultative symbionts had no overall effect on the studied traits. 4. The results suggest that the facultative symbionts have limited effects on the cold hardiness of their grain aphid hosts.     

Effective population size and persistence of Anopheles arabiensis during the dry season in West Africa

Abstract. The way that the malaria vectors Anopheles arabiensis and An.gambiae survive the dry season in sub-saharan Sahel or northern Savanna areas of Africa remains enigmatic. We examined this problem by calculating the effective sizes (N_e) of An.arabiensis populations for several locations in West Africa. An indirect/genetic procedure was used, comparing gene frequencies at several time intervals. The amount of drift which occurred provides an estimate of N_e. Most estimates of N_e were approximately 2000 individuals, probably close to the yearly minimum. This supports the hypothesis that populations of An.arabiensis in this region are continuous throughout the year, with many individuals surviving through the dry season, perhaps in a physiologically altered state, rather than extinction or severe bottlenecks during the dry season, followed by recolonization by a few individual survivors or immigrants in the subsequent rainy season.     

Xylem Transfer of Organic Solutes inSantalum albumL. (Indian Sandalwood) in Association with Legume and Non-legume Hosts

Indian sandalwood (Santalum album), a commercially importantroot hemi-parasitic angiosperm, was partnered singly in potculture with one of three nitrogen-fixing legumes or a eucalypthost. Xylem (tracheal) sap of stems of host and parasite andethanolic extracts of endophytic tissue of haustoria of theparasite were analysed for amino acids, organic acids and sugarsto determine which sets of solutes were available to and obtainedby the parasite from different hosts. There were high concentrationsof asparagine, followed by glutamate, aspartate and