Cryptic species identification: a simple diagnostic tool for discriminating between two problematic bumblebee species

Distinguishing between cryptic species is a perennial problem for biologists. Bombus ruderatus and Bombus hortorum are two species of bumblebee, which can be indistinguishable from their morphology. The former species is in decline, whereas the latter is ubiquitous. In the UK, isolated records of B. ruderatus occur amongst many for B. hortorum. For ecological studies of B. ruderatus to be feasible, the two species need to be reliably distinguishable. We present a diagnostic tool for quick and reliable identification of problematic individuals based on a restriction enzyme digest of the cytochrome b region of mitochondrial DNA.     

Influence of environmental conditions on spore dispersal and infection by Septoria nodorum

In field experiments using healthy trap plants it was found that pycniospores of S. nodorum were dispersed from diseased wheat plants whenever rain fell and occasionally in the absence of rain. Of two spring wheats tested, cv. Kolibri seemed a better ‘source’ plant and cv. Maris Butler a better ‘receptor’ when rainfall was light, but this difference was not apparent when rainfall was heavy. On 44 occasions, plants of Kolibri and M. Butler were also exposed to natural conditions immediately following artificial inoculation with S. nodorum. Infection of plants occurred on 10 occasions and was associated with the following minimum conditions: r.h, at inoculation >63%; and in the following 24 h, minimum temperature <6°C, at least 4 h with r.h. >90% and not more than 4 h with r.h. >60%.     

Influence of cocksfoot streak virus on the growth of cocksfoot swards

Small experimental swards of three types-healthy, 50% and 100% streak-virus-infected-were established from single tillers of randomly selected cocksfoot genotypes. In these swards 44% of infected plants died within 2 years compared with 21% of healthy plants. Mortality of infected plants was not increased by the presence of healthy plants in the same sward. In swards containing both healthy and infected plants, increased growth of healthy plants compensated for the low yield of infected ones only when the swards were frequently defoliated. Infrequent cutting apparently allowed infected plants to check the growth of healthy ones, and 50% infected swards yielded little more than 100% infected swards. This difference in response was attributed to differences in the growth habits of healthy and infected plants. Few initially healthy plants became infected during 2 years of the experiment.     

A comparison of the effects of sward improvement on invertebrates, sward establishment and herbage yield

Field experiments were done at two widely separated sites in England (Tadcaster, North Yorkshire and North Wyke, Devon). In each case an old permanent sward was re-seeded after ploughing or by direct drilling, or was left intact and fertilised. The carbamate pesticide aldicarb was applied to half of each experimental plot. The effects of sward improvement and pesticide on various soil invertebrate groups were assessed. Soil-dwelling macrofauna arthropods were scarce at both sites. Stem-boring dipterous larvae, however, were numerous at both sites. At Tadcaster, Oscinella vastator was the only species present in the original sward, but 0. frit was by far the most prevalent species in re-seeded areas. These can only have arisen from direct oviposition of eggs by adults on or near the emerging seedlings and not by migration of larvae from buried turf or the desiccated old pasture.
Mites and Collembola were abundant. Their numbers were reduced initially by cultivation and pesticide usage, but the effects of these practices were transient and their numbers recovered to previous levels usually within 10 wk.
Earthworms were present at both sites. Deep burrowing species, e.g. Lumbricus terrestris and Allolobophora longa were less affected by the treatments imposed than species such as A. chlorotica and L. rubelius which usually live close to the soil surface. Effects on their numbers were in any case, short-lived.
No improvement method consistently provided the greatest herbage dry matter yield. Pesticide application, however, greatly increased seedling stand and/or herbage yield at both sites and showed the benefits of using crop protectants, especially on direct-drilled re-seeds.