The susceptibility of tubers of potato cultivars to black dot (Colletotrichum coccodes (Walk.) Hughes)

In experiments with commercial seed of different cultivars at Rothamsted and Woburn, Bedfordshire in 1985 – 88 the severity of black dot on daughter tubers at harvest differed between cultivars. The disease was most severe on Desiree tubers. Amounts of disease were similar at both sites in 1986 – 88 but in 1985 it was more severe at Woburn than at Rothamsted. Disease-free seed of 12 (1987) or 15 (1988) cultivars were planted in experiments at Rothamsted (inoculated with Colletotrichum coccodes or not) and at Mepal, Cambridgeshire (not inoculated) and black dot assessed at harvest in October 1987 and in September and October 1988. There were significant differences in the amount of disease on different cultivars and the order of severity was similar at the two sites, on the two harvest dates in 1988 and in both years. Desiree, Maris Piper, Maris Peer and Record were amongst those cultivars severely affected whereas Cara, Pentland Crown and Romano were least affected. Skin discoloration caused by black dot was more noticeable on white-skinned than red-skinned cultivars and was severe on the Dutch cultivars Estima, Marfona, Santé and Wilja.     

The paramedial neurosecretory cells of the suboesophageal ganglion of the cricket,Teleogryllus commodus (Walk.)

Summary Ovariectomy, performed immediately after the final hatch, caused a reduction of stainable (neurosecretory?) material in the paramedial neurosecretory cells (PNC) (A-type) of the suboesophageal ganglion in 10 day-old females of Teleogryllus commodus (Walk.). A concomitant increase in nuclear volume and in the incorporation of ³⁵S-cysteine indicates increased synthesis of neurosecretory material. From these findings it is concluded that more stainable material is secreted in the cerebral neurohaemal organ after Ovariectomy. A functional relationship between the PNC and the ovaries is suggested.     

The paramedial neurosecretory cells of the suboesophageal ganglion in the cricket,Teleogryllus commodus (Walk.)

Summary The paramedian neurosecretory cells (PNC) (A-type) in the suboesophageal ganglion of the cricket, Teleogryllus commodus (Walk.), have been studied by electron microscopy. In control animals (10 day-old virgin females) three different cell stages could be distinguished: Stage 1 shows a variable content of elementary granules and characteristics of actively synthesising cells. Stage 2 is characterised by the presence of numerous fusion bodies, which are formed by the coalescence of elementary granules, presumably for storage purposes. In stage 3 granules are degraded in lysosomes (?). While the production of material rich in cysteine increases after ovariectomy (Dürnberger et al., 1978), the fine structure of the cells is essentially unchanged. The only noted differences are an increased lysosomal synthetic activity and the existence of stages intermediate between 2 and 3, which were never found in control animals. The functional significance of the different stages is discussed.     

The effect of age on the ultrastructure of the mid-gut cells of the hymenopteran Nasonia vitripennis (Walk.) (Hymenoptera,Pteromalidae)

Summary The ultrastructure of the mid-gut cells of aged female Nasonia vitripennis is described. The mid-gut is a shrunken and distorted organ in the aged animal. The individual cells are highly disorganised and the organelle components are altered. The small lipid droplets formed in the apical cell region do not coalesce to form the large central lipid inclusions characteristic of the young animal. The rough endoplasmic reticulum is reduced and some of the mitochondria enlarge. The mid- and apical cell regions also contain large numbers of cytolysosomes. The basal cell region is essentially unchanged, but the channels formed by the infolded basal plasma membranes are dilated. The changes observed are discussed in relation to previous observations on other insect species.We are indebted to Professor E.W. Knight-Jones in whose Department this work was carried out, and to the Science Research Council for financial support to one of us (I.D.)     

Environmentally cued size variation in the light-brown apple moth,Epiphyas postvittana (Walk.) (Tortricidae), and its adaptive value in dispersal

Summary Adult males and females of the light brown apple moth,Epiphyas postivittana (Walk.) (Tortricidae) showed seasonal, cyclic variations in size at two study areas. These variations are caused by the quality of the food available and temperature. Large individuals occur during the cool wet months of the year (autumn-winter generation moths that fly during September–November) and small individuals occur during the warm dry months of the year (from January to May when late-spring and summer generation moths fly). The ratios of body length to wing-length showed that the wing-loadings of the smaller individuals are significantly lower than those of large individuals, even though the latter have longer wings. Those with low wing-loading would be expected to be more adapted for dispersal. It is suggested that the type of flight dimorphism ofE. postvittana which is associated with the size of the insect has survival value in enabling the moth to disperse when habitats become adverse for breeding.     

Walk this way

The neural mechanisms that decide when and where to walk are not well understood. In this issue of Neuron, Felsen and Mainen use an olfactory-guided orienting task to show that the superior colliculus is necessary in rodents for the normal execution of spatial locomotor choices.     

The effect of diet on the ultrastructure of the mid-gut cells of Nasonia vitripennis (Walk.) (Insecta: Hymenoptera) at various ages

Summary The ultrastructure of mid-gut cells of female Nasonia fed on a diet of 10% sterile sucrose is described. There are extensive alterations in cell organelles, particularly the mitochondria, rough endoplasmic reticulum (R.E.R.) and lipid inclusions, when compared to similar insects fed a normal diet of dipteran pupae. A proportion of the mitochondria found in the apical cell region are enlarged in size and contain electron-dense granules. The remaining mitochondria are smaller, but also contain electron-dense granules. Cytochrome-c oxidase activity appears to be absent from the enlarged mitochondria. The R.E.R. appears reduced in many cells of the 1 day old, sugar-fed insects, however, this component fluctuates throughout the remaining life span. The lipid inclusions prominent in the 1 day old, pupae-fed insects are not present in sucrose-fed females of the same age, but lipid deposition was recorded later in the life span. There are many large residual bodies and cytolysosomes present in the old, sugar-fed insects. These changes in ultrastructure are discussed in relation to diet and longevity.     

In vitro release of digestive enzymes by FMRF amide related neuropeptides and analogues in the lepidopteran insect Opisina arenosella (Walk.)

The insect neuropeptides FMRF amide, leucomyosupressin (LMS) and neuropeptide analogues leucosulfakinins (FLSK and LSK II Ser (SO(3)H)), perisulfakinin (PSK), proleucosulfakinin (PLSK), 14A[phi1]WP-I, 542phi1, and 378A[5b]WP-I were assayed for their effects on the release of amylase and protease from the midgut tissue of larvae of Opisina arenosella. In the bioassay, empty midgut tubes ligated at both ends using hair were incubated with insect saline containing neuropeptides/analogues in a bioassay apparatus at 37 degrees C for 30 min. After incubation the contents of the midgut preparations were analyzed for amylase and protease activity. In control experiments, the midgut preparations were incubated in insect saline without neuropeptides. The results of the study reveal that for stimulating amylase release from midgut tissue, the peptides require an FXRF amide (X may be methionine or leucine) sequence at the C-terminal. The presence of HMRF amide at C-terminal of peptides may inhibit the release of amylase. Meanwhile, peptides with both FMRF and HMRF amide sequence at the C-terminal are found to be effective in stimulating protease release. The tetrapeptide segment at the C-terminal probably represent the active core of the neuropeptide.     

Flight thresholds and seasonal variations in flight activity of the light-brown apple moth,Epiphyas postvittana (Walk.) (Tortricidae), in Victoria,Australia

Summary The flight activity of Epiphyas postvittana was studied at two sites near Melbourne with the aid of suction traps, over a period of 4 years. Maximum numbers were found to fly during the period September to March with peak activity coinciding with the emergence of winter, spring and summer generation moths. E. postivittana is predominantly a nocturnal flier with maximum activity around 20.00–24.00 h. The lower temperature threshold of flight was 8–11°C. The upper temperature threshold varied from 20–21°C, 24–25°C and 27–28°C for the winter, spring and summer generation moths respectively. Flight was highly influenced by the prevailing wind. The lower wind speed threshold was 0.5–0.8 m^-s and the upper wind speed threshold was 2.6–2.7 m^-s. The relationship between wind speed and the amount of flight was non-linear, with the frequency of flights decreasing sharply with increasing wind speed. No flights occurred at wind speeds greater than 2.8 m^-s. Variation in relative humidity had no influence on flight, but lack of rain favoured flight. The amount of flight activity and the amount of rainfall were negatively correlated; flights did not occur when the daily precipitation exceeded 32.5 mm, and with a precipitation exceeding 39 mm no flights could be expected. The value of these findings to pest control programmes is discussed.