Decreased severity of potato common scab after foliar sprays of 3,5 -dichlorophenoxyacetic acid, a possible antipathogenic agent

Glasshouse tests on the potato cultivars Majestic and Maris Bard measured the effects of single early foliar sprays of ring-substituted phenoxyacetic acids (0.9 × 10–³ M) on the incidence of potato common scab, caused by soil-borne Streptomyces scabies. The most effective compound was 3,5-dichlorophenoxyacetic acid (3,5-D), which decreased scab by about 90%; its action was preventative, early sprays being more effective than late However, it slightly decreased yield, and increased the number of tubers per plant and the proportion of deformed tubers. The trichloro- and tetrachloro- acids containing the 3,5-dichloro- group also decreased scab, though to lesser extents; the most active of these was the 2,3,4,5-tetrachloro- acid, which had the same side effects as 3,5-D. The herbicide 2,4-D almost halved scab incidence, but seriously decreased yield. Other acids tested had little or no effect on scab. In tests against S. scabies in culture, 3,5-D was no more toxic than other disubstituted acids which were inactive, or weakly active, against the disease in vivo. 3,5-D may be an ‘antipathogenic agent’, preventing scab development by altering tuber metabolism.     

Aphid colonization of spring cereals

In 1970-1, Metopolophium dirhodum, Rhopalosiphum padi and Sitobion avenae were the commonest alatae trapped from April/May to August, with most in July and early August. The first alatae appeared in the Rothamsted survey suction trap 0–34 days before aphids were found on the cereals, but during May and June no relationship was found between the numbers trapped and the number on the crop. Most species occurred first near the sheltered edge of the crop, but M. dirhodum was widespread over the field. Most infestations were quickly dispersed by the movements of older morphs; adults only stayed in one place for about 2 days. Alate M. dirhodum moved more often than apterae, but both morphs of S. avenae moved equally often and more frequently between larvipositions than did those of M. dirhodum. Apterae deposited more nymphs in a ‘group’ than alatae, and M. dirhodum deposited more than S. avenae. Few ‘groups’ persisted for more than a week. Although M. dirhodum occupied the crop area faster than S. avenae, all 0–3 m lengths of row sampled being infested within 2–5 wk of their first appearance, most or all of the tillers were colonized only in late July 1970.     

Application of the names Crataegus calycina Peterm. and C. oxyacantha L.

Authentic herbarium material of Crataegus calycina Petermann (1849) supports Hrabetová-Uhrová's contention in 1969 that this is conspecific with C. macrocarpa Hegetschweiler; the name C. calycina , for which a Petermann specimen in Musée Botanique Cantonal, Lausanne is designated as lectotype, had been incorrectly applied in Flora Europaea.
Examination of the specimens in the Linnaean Herbarium has led to acceptance of Dandy's proposal in 1946 that sheet 643.12 should be designated as the lectotype of C. oxyacantha L. (1753). This specimen is not, as frequently assumed, C. laevigata (Poiret) DC. (C oxyacanthoides Thuill.) but the species described in Flora Europaea as "C. calycina Peterm. subsp. curvisepala (Lindman) Franco". It is suggested that the name C. oxyacantha L. is a source of confusion and should be rejected under Article 69 of the International Code of Botanical Nomenclature. This gives priority to the name C. curvisepala Lindman, which should replace C. calycina Peterm. in Flora Europaea.     

THE SPECIFIC CHARACTERS OF THE CRESTED PORCUPINES, SUBGENUS HYSTRIX

The characters used for specific diagnosis in the subgenus Hystrix have been studied to determine their constancy as specific characters and their geographical variation within the species. As a result three species are recognized, namely H. indica, H. cristata and H. africaeaustralis. H. galeata is considered a synonym of H. cristata , and H. stegmanni a synonym of H. africaeaustralis . The morphological differences between cristata and africaeaustralis in East Africa are not continued clinally within these species. Between cristata and indica some of the diagnostic characters vary clinally, others change abruptly.     

THE NEUROENDOCRINE SYSTEM AND STOMATOGASTRIC NERVOUS SYSTEM OF THE ADULT TSETSE FLY GLOSSINA MORSITANS

The brain of Glossina morsitans Westwood contains four groups of neurosecretory cells which are stainable with chrome haematozylin and phloxin. The axons of these cells form a pair of nervi corporis cardiaci which pass posteriorly from the brain and innervate the corpora cardiaca and corpus allatum before uniting with a small ganglion posterior to the corpora cardiaca. This ganglion is considered to represent the fusion of the fusion of the hypocerebral and ventricular ganglia which remain separate in other insects.
There is no frontal ganglion in the adult Glossina and the recurrent nerve fuses with one of the nervi corporis cardiaci immediately behind the brain. The oesophageal nerves arising from the fused hypocerebral and ventricular ganglia innervate the oesophagus in the anterior part of the thorax, the proventriculus and the posterior extension of the oesophagus close to the crop. These nerves possess both sensory and motor nerve endings. The differences which exist between Glossina and other cyclorrhaphous Diptera with respect to their neuroendocrine/stomatogastric system are noted and considered in terms of the control of neuroendocrine function.     

NEW SPECIES AND RECORDS OF POLYCHAETA FROM CEYLON

A collection of polychaetes made by the author in December 1961 and April 1962 from a number of places on the coast of Ceylon was examined. Seven new species and one new subspecies are described and sixteen species are recorded new to the fauna of Ceylon. The holotypes and lectotypes have been deposited in the British Museum (Natural History).     

Multiplication of the agent of X-disease in a non-vector leafhopper Macrostelesfascifrons

The relative titre of the causal agent of X-disease of stone fruits in the non-vector leafhopper Macrosteles fascifrons was tested by injecting dilutions of M. fascifrons extracts into non-infective Colladonus montanus leafhopper vectors. The recipient C. montanus were fed on celery test plants which were then observed for X-disease symptoms. M. fascifrons were assayed at various intervals for up to 37 days after they were fed on X-diseased celery or injected with infectious extracts of the X-agent. Infectivity was detected in M. fascifrons only after 25 or 37 days in separate trials. Whole body extracts but not extracts from detached heads of M. fascifrons that had fed on X-diseased celery were infectious, whereas extracts prepared from the heads of M. fascifrons previously injected with X-agent extracts were infectious. This infectivity was retained for up to four serial passages in M. fascifrons. Electron microscopy of M. fascifrons that had been injected with extracts of the X-disease agent revealed mycoplasma-like organisms (MLO) only intercellularly and appressed to various organs in the haemocoele. No MLO were observed in uninjected M. fascifrons or those injected with extracts from non-infectious C. montanus. These results suggest that, despite multiplication of the X-agent in vivo. barriers in the gut and salivary glands prevent its transmission to plants by M. fascifrons.     

The effect of introducing aphid-pathogenic Entomophthoraceae into field populations of Aphis fabae

During two warm, dry seasons (1975 and 1976) aphid-pathogenic species of Entomophthoraceae introduced into Aphis fabae populations on field beans established briefly but failed to spread. In cool moist seasons (1977 and 1978), the fungi, principally Erynia neoaphidis and Neozygites fresenii, spread more rapidly in treated than untreated plots. In 1977, the maximum aphid population in plots treated with fungi reached a mean of 9000/plant on 19 July compared with 16 000/plant 1 wk later in untreated plots. The corresponding yield of beans in treated plots was twice that in untreated plots though only half that in plots kept free of aphids with pirimicarb. In two experiments in 1978, the maximum aphid population in treated areas was 700/plant, half that in untreated areas and 1 to 2 wk earlier. Yields from treated plots, however, were not significantly different from those from untreated plots. In nature, the fungi attack A. fabae populations in England only after they have become damaging, partly because fungal inoculum is sparse when the aphid population is small.     

Cytotaxonomic studies in the Adiantum caudatum complex of Africa and Asia

Study of meiosis in synthesized hybrids has permitted a genome analysis to be carried out with respect to the holotype of A. indicum Ghatak, 4x, originally found wild near Calcutta. The two differentiated diploids from which A. indicum , 4x, seems to have arisen are represented in the analysis by A. zollingeri from Ceylon and by two strains of an Indian diploid provisionally designated A. incisum sens. lat. 2x. Supplementary information excluding an autopolyploid origin for A. indicum is provided by hybrids between A. indicum 4x and an unrelated tetraploid, A. malesianum Ghatak. Ecological information is supplied for the material of A. zollingeri , indicating that it occupies a specialized habitat which might be found in India if search is made in the right kind of territory. A. incisum 2x is shown to be much more widespread and to be present in hill country, or occasionally in lowlands, from the Himalayas to South India inclusive. It contains a number of genetically determined biotypes differing slightly in morphology but behaving as members of one species when combined into hybrids. Further morphological information and a revised key for separating the specimens used in the investigation is provided in an Appendix.