Accumulation and metabolism of aldicarb by the free-living nematodes Aphelenchus avenae and Panagrellus redivivus

The accumulation and metabolism of aldicarb has been compared in two species of free-living soil nematodes, Aphelenchus avenae and Panagrellus redivivus, which differ considerably in their sensitivity to this and other pesticides. Similar levels of aldicarb were found to accumulate in the two species. The results showed that although the rate of uptake of aldicarb was greater in P. redivivus, so also was the rate of metabolism and elimination. Levels of toxic metabolites of aldicarb were two to three times higher in the more susceptible species A. avenae after 24 h incubation than in the less susceptible P. redivivus. The toxicological significance of these findings is discussed in relation to previous work with the organophosphorus pesticide phorate and its effects on the same two nematode species.     

Effect of temperature and sex on growth patterns in nymphs of the mayfly Hexagenia hilineata in the laboratory

SUMMARY. Eggs collected from Hexagenia bilineata females were successfully reared in the laboratory at temperatures of 15, 20, 25 and 30°C. Eggs did not hatch at 10°C and although hatching was successful at 35°C, all nymphs at this temperature died while in early instars.
Survival of nymphs between the approximate size interval of 4–14 mm showed a significant decrease with increased temperatures. Nymphs at 15°C, however, generally did not survive transformation to the subaduit stage.
The growth pattern of individual nymphs was well described by a logistic curve at most temperatures. Furthermore, growth pattern was significantly affected by both temperature and sex.
Rate of development from oviposition to first emergence increased with increasing temperatures in a linear fashion between 15 and 30°C. The relationship was equally well described by a hyperbolic equation and a power-law equation. By extrapolation from the hyperbolic equation, the lower threshold temperature for development was estimated to be 10.1°C3.1°C. The degree (°C)-days required for development from oviposition to first emergence was calculated to be 2337 days with 95% confidence limits of 2045–2727 days under laboratory conditions.     

Incidence, importance and virulence of Puccinia hordei on barley in New Zealand

Brown rust of barley (Puccinia hordei) is widespread in New Zealand and causes crop losses in some years. The cultivars presently grown lack adequate genetic resistance but a highly resistant line has been produced. Twelve different virulence combinations were identified in the pathogen population using the Welsh differential lines; there were differences between North Island and South Island isolates; and no virulence was observed for resistance conferred by factors Pa 3 and Pa 7.     

Behaviour of the systemic nematicide oxamyl in plants in relation to control of invasion and development of Meloidogyne incognita

A single foliar application of oxamyl (12.5 μg) in acetone significantly reduced invasion of cucumber seedlings by Meloidogyne incognita juveniles for at least 21 days but did not affect the early stages of development of juveniles which had already invaded the roots. In contrast, application of oxamyl to the roots significantly reduced both invasion and development of juveniles. Concurrent studies using radiolabelled oxamyl showed that the amount of toxicant in the roots after 3 days was 13 times greater following root application than after foliar treatment. It is probable that oxamyl concentrates at the sites of nematode attack as an overall concentration of only 3 ng oxamyl g^-1 root was sufficient to prevent invasion. Much greater concentrations than this were required to affect the nematode in vitro. Oxamyl appeared to be lost from the roots into the soil principally in the form of its non-toxic oxime and it is suggested that the site of action following foliar application is at the root surface or outer cortex. Studies on the invasion behaviour of M. incognita juveniles on agar showed that the action of oxamyl had a sensory component.     

Frequency and geographical distribution of specific virulence factors in Bremia lactucae populations in England from 1973 to 1975

Samples of lettuces infected with Bremia lactucae were collected from seven areas of England during 1973-5. These were tested under controlled environmental conditions on a range of differentially resistant cultivars to determine the frequency of virulence (V) factors in the pathogen population. In most cases the results could be accommodated by the relationship advanced by Crate & Johnson (1976). A virulence phenotype was determined for each isolate and individual virulences within isolates were identified as present at high or low frequencies. The most common V factors were V3, V4, V6 and V8 which reflected the resistance (R) factor complement of lettuce cultivars currently in commercial production. There were few gross differences in the geographical distribution of virulence factors between the seven areas. In the West Central region, however, which encompasses the Evesham and Lancashire production areas, results indicated that the use of cultivars containing resistance (R) factors 2 and 8 respectively would have provided protection from the disease during 1974. There were differences in virulence combinations at the holding or locality level within each large area, which could be exploited by growers providing testing was done in their particular locality. Universally susceptible cultivars and those with only limited resistance factors were often found to be infected with B. lactucae populations which contained large numbers of V-factors. It might have been expected that these pathogen populations would have been restricted to cultivars with large numbers of R-factors. This finding conflicts with the suggestion that pathogen populations with complex virulence patterns are ‘unfit’ as compared with those with more simple virulence components.     

Male mating success in an aquatically mating pinniped, the harbour seal (Phoca vitulina), assessed by microsatellite DNA markers

Similar to many other pinniped species, harbour seals ( Phoca vitulina ) mate exclusively at sea. Here we present the first attempt to measure male mating success in an aquatically mating pinniped. Male mating success was estimated by paternity analysis in two cohorts of pups born at Sable Island, Nova Scotia, Canada, using microsatellite DNA markers. The genotypes of 275 pups born in 1994 and 1995 were compared to those of 90 candidate males at six microsatellite loci using a likelihood approach to resolve paternity. Paternity could be assigned for two, 22, 40 and 85 pups at confidence levels of 95, 80, 65 and 50%, respectively. Most successful males were assigned the paternity of a single offspring, suggesting a low variance in male mating success relative to most pinniped species. The proportion of paternal half sibs within cohorts and between maternally related sibs estimated by maximum likelihood were not significantly different from zero. It is thus unlikely that most offspring were sired by a small number of highly successful unsampled males, and that female harbour seals do not usually exhibit fidelity to the same male in sequential breeding seasons. A low level of polygyny in Sable Island harbour seals is consistent with predictions based on their breeding ecology, as females are highly mobile and widely dispersed in the aquatic mating environment at Sable Island.