Local population differences in emergence of cabbage root flies from south-west Lancashire: implications for pest forecasting and population divergence

ABSTRACT.

• 1 Emergence of cabbage root fly, Delia radicum (L.), from overwintering populations of puparia collected from twenty-one sites in south-west Lancashire, was extremely variable.
• 2 The patterns of emergence indicated that there were two extreme biotypes, one with early- and the other with late-emerging flies. There was also evidence of an intermediate biotype, tending more to early than to late emergence.
• 3 This gradient of biotypes, or clinal divergence, was maintained by populations breeding at different times and by females mating close to their sites of emergence. Non-dispersive females then perpetuated their genotype within their own locality.
• 4 The time of emergence was not obviously associated with the type of host-crop on which larvae had developed.
• 5 The late-emerging biotype was most prevalent around Halsall. The minimum distance between populations of the late- and the early-emerging biotypes was 16 km. 20 km south-east from Halsall only half of the fly population was early-emerging, possibly a result of a displacement of the Halsall biotype by the prevailing NW wind.
• 6 Regional-based forecasts will need to take into account the emergence characteristics of the populations to predict the peak periods of cabbage root fly activity adequately in south-west Lancashire and other areas where emergence patterns differ.

     

Completion of diapause in field populations of the cabbage root fly (Delia radicum)

The various diapause and post-diapause stages entered by cabbage root fly pupae during the overwintering period are shown schematically. Although diapause induction started in mid-Aug., the early-pupating insects did not develop further but were maintained in diapause by the warm autumn temperatures. Therefore, diapause development was simultaneous in all Wellesbourne pupae, whether of second or third generation origin. Diapause development started only in mid-Oct., when mean soil temperatures fell below 10°. In the field, 90% of the overwintering population of cabbage root fly pupae had completed pleted diapause by 5 March 1980, 17 Feb. 1981 and 18 Feb. 1982. This was equivalent to a duration of 19 weeks from mid-Oct. onwards, during the winters of 1979–80, 1980–81 and 1981–82 respectively. A further break between the completion of diapause and the warm conditions required to start post-diapause development also helps to condense the emergence of flies in the spring. Hence, an accurate forecast of the time of spring attack by populations of flies similar to those at Wellesbourne should be possible.This study was financed partly by the Commission of the European Communities as CEC Contract No. 0771.     

Nutrition of winter wheat during the life cycle. I. Yield and accumulation of dry matter and minerals

Mineral uptake by winter wheat (Trilicum aestivum L. cv. Martonvasari 8) was studied throughout the life cycle. Accumulation of macronutrients (i.e. total nitrogen, phosphorus, potassium, sodium, magnesium and calcium) and the water content of roots and shoots of plants grown in complete nutrient solution were higher than those of plants grown in two types of soils. The supply of macronutrients was in some cases limiting for soil-grown plants as revealed by a comparison of available and accumulated amounts of these nutrients. Their supply was abundant, however, for solution-grown plants. This led to a doubling of grain yield for the latter plants with a three fold increase in accumulation of dry matter and a five-fold increase in fresh weight. The efficiency ratios of solution-grown plants to soil-grown plants were approximately 1 for N and Na, 0.5 for Mg and Ca, and 0.3 for P and K.     

Histopathology of Selected cultivars of Tobacco infected with Meloidogyne species

Rates of nematode penetration and the histopathology of root infections in fluecured tobacco cultivars ''McNair-944,'' ''Speight G-28,'' and ''NC-89'' with either Meloidogyne arenaria, M. incognita, M. hapla, or M. javanica were investigated. Penetration of root tips by juveniles of all species into the M. incognita-resistant NC-89 and G-28 was much less than that on the susceptible McNair-944. Few juveniles of M. incognita were detected in resistant cultivars 7 and 14 days after inoculation. Infection sites exhibited some cavities and extensive necrotic tissue at 14 days; less necrotic tissue and no intact nematodes were observed 35 days after inoculation. Although some females of M. arenaria reached maturity and produced eggs, considerable necrosis was induced in the resistant cultivars. Meloidogyne hapla and M. javanica developed on all cultivars, but there was necrotic tissue at some infection sites in the resistant cultivars. The occurrence of single multistructured nuclei in the syncytia of most M. hapla infections differed from the numerous small nuclei found in syncytia caused by the other three species.     

Stimulation of root and somatic embryo production in Euonymus europaeus L. by an inhibitor of polyamine biosynthesis

In vitro formation of roots and somatic embryos is obtained from cotyledon explants of a Spindle tree (Euonymus europaeus L.) cultured on two different media: a medium inducing callus formation and the production of roots, and a medium inducing callus formation, root and somatic embryo production. We studied the effects of -difluoromethylornithine (DFMO), a specific, irreversible inhibitor of ornithine decarboxylase (ODC) on root and somatic embryo production, growth and titers of putrescine in Euonymus explants and explant-derived calli. Early changes in putrescine levels were detected in both cultures before the visible emergence of roots or somatic embryos. DFMO rapidly inhibited putrescine accumulation and growth in non-embryogenic calli and highly stimulated rooting activity. DFMO partially inhibited putrescine accumulation in embryogenic calli. This inhibition had no effects on callus growth but significantly reduced the time of emergence of roots and highly stimulated somatic embryo production. The relationship among putrescine, putrescine metabolism, growth, root and somatic embryo formation is discussed.     

Fatty Acid Composition of the Peribacteroid Membrane and the ER in Nodules of Glycine max Varies after Infection by Different Strains of the Microsymbiont Bradyrhizobiumjaponicum

The fatty acid composition of ER, Golgi and peribacteroid membrane (PBM) from root nodules formed on Glycine max after infection with different strains of Bradyrhizobium japonicum has been analysed by gas chromatography. In each plant-microsymbiont combination the fatty acid composition (FAC) of the PBM is distinct from ER and Golgi. The similarity between ER and PBM fatty acid composition is significantly stronger than between Golgi and PBM. In addition the fatty acid composition of all membrane systems in nodules is affected by the microsymbiont strain. A comparison of four strains of Bradyrhizobium japonicum grown in agar surface culture and isolated as the symbiotic bacteroids reveals a decrease in oleic acid during bacteroid differentiation.     

湿地松与茶树间作根系分布状况的研究

湿地松(Pinus elliottii)是阳性乔木,茶树(Camellia sinensis)是阴性灌木。这两种树种间作,形成针阔、乔灌两层树冠结构的茶园复合生态系统,可以改善茶树生态条件,提高茶叶的产量和品质。但间作存在胁地现象。一般认为这是上层树木的过度遮荫和根系间的竞争造成的。为了解这两种树种根系的分布状况和相互关系,并为间作茶园的合理配置和加强这种茶园的耕作管理提供依据,我们进行了湿地松与茶树间作根系分布状况的研究。     

Screening Subterranean Clover (Trifolium spp.) Germplasm for Resistance to Meloidogyne species

This study was conducted to identify lines of subterranean clover (Trifolium spp.) with resistance to Meloidogyne arenaria (Neal, 1989) Chitwood, 1949, race 1; M. incognita (Kofoid and White, 1919) Chitwood, 1949, race 3; and M. javanica (Treub, 1885) Chitwood, 1949. A collection of 134 subterranean clover lines was evaluated and all had intermediate to high susceptibility. Root galling was negatively correlated with both seed and dry matter yields. Soil fumigation significantly reduced the nematode population in the field. Results indicate there is limited genetic resistance to root-knot nematodes among subterranean clover lines. Alternative sources of variation for this trait should be investigated.     

Root respiration during grain filling in sunflower: The effects of water stress

Instantaneous rates of (soil + root) respiration were measured periodically during grain filling in sunflower crops that were i) irrigated at weekly intervals and ii) subjected to water stress for the last 25 days of the 40-day grain filling period. Daily (soil + root) respiration was calculated using instantaneous respiration rates, an empirically determined temperature response function, and diurnal records of soil temperature. Daily soil respiration was estimated using empirically determined functions linking soil respiration to soil temperature and water content. Between anthesis and maturity, daily root respiration of the irrigated crop dropped by about one half from ca. 1.8 g C m^-2 d^-1, exhibiting a strong association with daily crop gross photosynthesis. Water stress brought about a rapid decrease in root respiration, which fell to about 0.1 g C m^-2 d^-1 at maturity. Root respiration during grain filling was 46 and 30 g C m^-2 for irrigated and stressed crops, respectively.