Overwintering Host Research Articles

Variation in Developmental Rate on Different Hosts and Overwintering of the Sweetpotato Whitefly, Bemisia tabaci (Homoptera: Aleyrodidae)

Time required for Bemisia tabaci (Gennadius) to complete development from egg to adult at 26.7 ± 1°C was influenced by the host to which it was confined. Development was completed in 30% less time on lettuce, cucumber, eggplant, and squash than on broccoli or carrot. Five new hosts (carrot, guar, guayule, alfalfa, and lettuce) on which B. tabaci may complete its development are reported. Two-week lettuce leaf samples indicate one generation was completed from 27 October 1983 to 4 January 1984 under field conditions in the southern California desert. Field crops may serve as important overwintering hosts.

Development of Velvetbean Caterpillar, Anticarsia gemmatalis (Lepidoptera: Noctuidae), on Several Winter Hosts 1

Velvetbean caterpillar, Anticarsia gemmatalis (Hubner), larvae were reared on the following potentially important overwintering hosts in southern Florida: Dolichos lablab L. (hyacinth bean); Galactia speciformis Torr and Gray; Glycine max (L.) Merrill (soybean); Indigofera hirsuta L. (hairy indigo); Melilotus alba Desr. (sweet clover); Phaseolus lathyroides L.; Phaseolus vulgaris L. (snap bean); Rhynchosia minima (L.) (least rhynchosia); and Vigna luteola (Jacq.). Development time, number of instars, pupal weights and foliage consumed were used to evaluate host suitability. Based on the first three categories, I. hirsuta , R. minima , P. lathyroides , V. lutoela , D. lablab , and M. alba were at least as good as soybean for larval development. P. vulagaris was the poorest host.

Beetle Transmission of Cowpea Chlorotic Mottle Virus

HOBBS, H. A., and J. P. FULTON. 1979. Beetle transmission of cowpea, chlorotic mottle virus. Phytopathology 69:255-256. Cowpea chlorotic mottle virus was transmitted by the bean leaf beetle, from and transmitted to beans. Levels were much lower when the virus was Cerotoma trifurcata, and by the spotted cucumber beetle, Diabrotica either acquired from or transmitted to cowpeas. Lespedeza cuneata, which undecimpunctata howardii. Three strains of the virus were transmitted at may be an overwintering host, was a poor source of virus for vectors. low levels. Levels of transmission were highest when virus was acquired Several viruses in the bromovirus group are transmitted by antiserum, using the Ouchterlony gel diffusion technique. Virus in leaffeeding beetles. Cowpea chlorotic mottle virus (CCMV) was beetles that had fed on infected plants was tested by severing one transmitted by the chrysomelid species Cerotoma trifurcata metathoracic leg and collecting in a capillary tube the hemolymph (Forster) and Diabrotica undecimpunctata howardii (Barber) (6); that exuded. Hemolymph was diluted approximately 1:300 in 0.01 the bean yellow stipple strain (BYSV) of CCMV by C. ruficornis M phosphate buffer, pH 7.2, and inoculated to young Monarch Olivier and D. balteata LeConte (2,3); and broad bean mottle virus cowpea plants. (BBMV) by D. undecimpunctata howardii, Acalymma trivittatum (Mannerheim), and Colaspis brunnea (F.) (7). Levels of transmission were moderate to low in all cases. Because CCMV is

Seasonal Sequence of Parasitism of Unaspis yanonensis : (KUWANA) (Homoptera:Diaspididae)

The seasonal sequence of parasitism of Unaspis yanonensis (KUWANA) was investigated in Kagoshima and Fukuoka prefectures in 1970-72. In Kagoshima during the first generation of the scale the parasitism by the dominant parasite, Aspidiotiphagus citrinus (CRAW), was very low but it gradually increased through the second generation and reached the maximum level of parasitism during the third generation of its host. However, parasitism by A. citrinus was again very low in the first generation of the host the following year. Such discontinuity was due to poor adaptability of this indigenous parasite to the invader. A.citrinus could not successfully overwinter in this scale, i.e., the immature parasites died within the over-wintering host during the months of January to March. But it may be able to do so in other diaspine scales such as Aonidiella aurantii (MASKELL), Aonidiella taxus LEONARDI and Quadraspidiotus perniciosus (COMSTOCK). The first generation of U. yanonensis was in the susceptible stage at a time between the first and second appearance of A. citrinus. Thus, the parasite scarcely had a chance to attack the scale. In Fukuoka the parasitism was very low throughout the year because the host scale had only two generations a year.

Arbovirus infections in reptiles: Immunological evidence for a high incidence of japanese encephalitis virus in the cobra Naja naja

The plasma of 80 cobra snakes ( Naja naja) was investigated in the haemagglutination inhibition (HAI) and virus neutralization (NT) tests for evidence of Japanese encephalitis (JE) virus infection. 71% were antibody positive by both tests, 20% by the one or the other and the remaining 9% negative by both. The mean HAI and NT titres of plasma samples collected in spring/summer were considerably higher than those of the autumn/winter seasons. Macroglobulin and 7S antibodies were detected in autumn/winter and only 7S in spring/summer seasons. It is suggested that the cobra could be a host for JE virus throughout the Oriental Region depending on suitable vector distribution. Circumstantial evidence that the cobra may be an overwintering host for JE virus is considered.

Epidemiology of potato leaf roll virus in the Fraser River delta of British Columbia

The spread of potato leaf roll virus (PLRV) and the resulting phloem necrosis in the tubers has been a limiting factor in the production of the Netted Gem (Russet Burbank) variety in southwestern British Columbia, Canada. Steckling sugar beets are an important overwintering host for nymphs and adults of the green peach aphid,Myzus persicae (Sulzer). By June, aphids are widely disseminated to the florets and new leaves of sugar beet and other hosts, including potato. Colonies with alates are produced on summer hosts which are not treated with insecticides. The peak of the flight of alates from the colonies on the summer hosts occurs during the first half of August. Those alates that were produced on PLRV-infected potato and which travel to other potatoes transmit the virus as soon as they feed. By the end of August, the sugar beet seed crops and the early and mid-season potato crops have been defoliated or harvested. Thus many colonies ofM. persicae are destroyed and the threat of PLRV spread diminishes. Crop and weed plants which serve as overwintering hosts become infested during late summer with alate aphids. Their offspring survive the winter in numbers which are determined by the weather and survival of host plants.

Coccidiosis in Wisconsin Cottontail Rabbits in Winter

Since coccidiosis is generally considered a disease of the warm months of the year, little research has been conducted on its importance and incidence in over-wintering hosts. Boughton (1937), in a study of Isospora infection in the English sparrow in Wisconsin, noted 100 per cent incidence of the coccidia in winter, while Fitzgerald (1959) noted in Utah cattle a decline in incidence from 95 per cent in November to 30 per cent in March. Preliminary sampling of fresh feces of the cottontail rabbit (Sylvilagus floridanus) in Wisconsin indicated that occasional large showers of oocysts occurred in the middle of the winter. To clarify the winter status of this disease, a fecal survey was made during the winters of 1959 to 1960, and 1960 to 1961 near Green Bay, Wisconsin. Although comparative data from the summer months are lacking, this short paper will explore the potential importance of winter infection in the epizootiology of this disease in wild cottontails.

Some Abnormalities in the Foxglove Aphid in Northeastern Maine

Unprecedented numbers of alate foxglove aphids, Myzus solani (Kltb.), developed at Presque Isle, Maine, in the late summer and fall of 1956 and 1957 on potato plants not treated with insecticides. Many of the alatae exhibited abnormalities in both the number and and position of the wings. Also atypical venation in the forewings was common in both abnormal and normal alates. Abnormally alate forms were observed in the spring migrant forms maturing on Hieracium spp., hawkweed, an overwintering host. These phenomena may be genetic manifestations due to the crossing of two strains of the aphid or the effects from unusual environmental conditions, including subnormal temperatures.

Spore Release in Peronospora tabacina Adam.

DOWNY mildew or blue mould of tobacco caused by Peronospora tabacina Adam. is destructive in the American and Australian regions and has now been reported for the first time in Europe1. It survives in association with over-wintering or over-summering host plants of which infected N. tabacum is of major importance2,3. Such plants produce conidia that are airborne and can establish infection in distant areas2.

HOST FINDING BY APHIDS IN THE FIELD: GYNOPARAE OF MYZUS PERSICAE (SULZER)

Attempts to test experimentally the theory of olfactory attraction to host plants gave negative results, and more conclusive evidence was sought by recording the behaviour of host‐finding migrants in the field. The first of three occasions when the natural alighting rate was high enough for comparative purposes was an autumn migration dominated by Myzus persicae returning to its specific overwintering host, the peach tree.The proportion of M. persicae gynoparae among all aphids caught alighting on a spindle tree, where persicae does not overwinter, was as high as on peach. The much heavier accumulation of migrants on the peach was evidently due, not to their differential alightment, but to their differential rate of departure, with a longer average stay on the peach. The proportion of persicae gynoparae was smaller in catches on transparent sticky traps than among alighters on the trees, and they avoided alighting on brussels sprout plants more often than on peach. Only a fraction of those that approached the plants alighted, even on peach; and only a small fraction of those that did alight, stayed, even on peach.There was appreciable colonization of spindle and sprouts by the M. persicae gynoparae and some ‘wasted’ oviposition by their progeny on spindle. After the migration was over the peach leaves entered the last stages of senescence before the spindle leaves, and persicae gynoparae (no longer able to fly) that were given access to both at that time, settled preferentially on spindle. The distribution of males created the impression that they were less host‐specific than gynoparae.

FACTORS AFFECTING THE SPREAD OF APHID‐BORNE VIRUSES IN POTATO IN EASTERN SCOTLAND: I. OVERWINTERING OF POTATO APHIDS, PARTICULARLY MYZUS PERSICAE (SULZER)

Three species of potato aphids, Myzus persicae (Sulzer), Macrosiphum euphorbiae (Thomas) and Aulacorthum solani (Kltb.), overwinter in eastern Scotland, primarily as apterae on perennial, glasshouse, frame and brassica crops. Brassica crops are the commonest hosts of overwintering Myzus persicae, the principal vector of potato leaf roll and Y viruses, and these crops are concentrated in the market‐gardening areas of the Lothians and Moray. Although crops of savoy cabbage and brussels sprout often carried numerous M.persicae during the winter, spring cabbage, cabbage for seed and broccoli seem the most important overwintering hosts because they usually persist until mid‐May, long enough to allow the development and dispersal of alatae to spring‐planted crops. Many alatae dispersed during July and August from crops colonized in spring. Although M. persicae overwintered as eggs on peach and viviparously on plants in glasshouses, the influence of such sites, which are generally distributed throughout the main seed‐potato growing areas of Angus, Perth and Fife, was local and unless numerous M. persicae survive the winter on weeds, the market‐garden area of the Lothians is probably the most important source from which this aphid disperses in spring and early summer to colonize potato crops in eastern Scotland.

STUDIES ON THE BIOLOGY OF ERYSIPHE GRAMINIS DC.

A study has been made of various aspects of the biology of Erysiphe graminis DC., including its distribution and prevalence in Canada, method of overwintering, physiologic specialization, and the effects of various environmental factors on the development of different stages of the organism. The fungus causes the powdery mildew of cereals and certain grasses. It occurs in every province of Canada, but is more prevalent in British Columbia and the five eastern provinces. The evidence indicates that the fungus overwinters as mycelial mats on dead straw and as mycelial infections on overwintering hosts. Three new physiologic races of barley mildew have been identified, making a total of seven races isolated in Canada. In wheat mildew only Race 1 was isolated. A study of the stability of six races of barley mildew showed that they are distinct biologic entities comparable to physiologic races in cereal rusts. No evidence was obtained by cross inoculations that any variety of E. graminis, except possibly E. graminis Agropyri, can attack a non-suscept, or an immune variety of its host, or that injury of such hosts renders them susceptible. Conidia of E. graminis germinate on immune hosts and penetration proceeds as far as the papilla stage. Physiologic resistance manifests itself in some hosts by the death of the infected cells and in others by the distortion of the haustoria. The evidence indicates that the organism is homothallic. The cardinal temperatures for the germination of conidia are 0°, 10°, and 35 °C., while the best development of mildew occurs between 15° and 20 °C. Alternating temperatures induce perithecial development. Light is not an important factor, except indirectly, in the development of E. graminis. Alternate drying and wetting of perithecia is necessary to induce the formation of ascospores, but other stages are favoured by relatively dry conditions. Conidia germinate well even at zero humidity. Sprinkling infected seedlings with water checked the development of the disease. The addition to the soil of certain fertilizers and other chemicals commonly claimed to increase host resistance to powdery mildew did not increase the resistance of susceptible seedlings of wheat and barley.