Zoophthora Radicans (Zygomycetes: Entomophthorales) Conidia Production From Empoasca Kraemeri and Dry-formulated Mycelium Under Laboratory and Field Conditions.

Laboratory and field studies were conducted to assess the effects of temperature on sporulation of a dried-mycelium formulation of the entomophthoralean fungus Zoophthora radicans and to compare sporulation of laboratory-produced/formulated fungus versus fungus occurring on cadavers of naturally infected Empoasca leafhoppers. Conidia production by the formulation increased from 3.1×104 to a maximum of 13.7×104 conidia/mg (dry weight) over the temperature range from 5 to 20 °C and decreased to 10.7×104 conidia/mg at 25 °C and to nearly zero at 31 °C. A temperature-dependent development model estimated a sporulation optimum of 23.6 °C. Pieces of formulated mycelium (2×2×0.5 mm) placed on bean and cowpea foliage in the field showed a temporal pattern of nightly conidial discharge similar to the fungus on leafhopper cadavers; both fungi initiated sporulation within a few hours following dewset and ceased with the return of dry conditions after 08:00 h. However, sporulation of the fungus on cadavers peaked between 00:00 and 03:00 h, while peak sporulation of the formulated fungus usually occurred shortly after dawn. Fungus on adult leafhopper cadavers and the pieces of formulated fungus underwent multiple daytime desiccation/nighttime rehydration cycles, producing conidia for up to eight consecutive nights. Second-, third-, fourth-, and fifth-instar cadavers supported sporulation for only 5–6 nights. On a dry weight basis, the fungus on cadavers produced substantially more conidia than the formulated fungus; however, differences were less pronounced based on the surface area of the hymenium. In general, the dried-mycelium pieces generated conidia in a manner similar (both temporally and quantitatively) to the fungus on leafhopper cadavers. These results indicate that the dried-mycelium formulation is well suited as an inoculum source for initiation or augmentation of epizootics in leafhopper populations

Description of a Zoophthora Radicans (Zygomycetes: Entomophthorales) Epizootic in a Population of Empoasca Kraemeri (Homoptera: Cicadellidae) on Beans in Central Brazil

Development of a natural epizootic of Zoophthora radicans in an Empoasca kraemeri population on beans near Goiânia, Goiás, Brazil, was monitored over a 6-week period. At the initiation of monitoring on 23 April 1985, disease prevalence in the leafhopper population was 12.8%. Over the course of the epizootic, infection of second-, third-, fourth-, and fifth-instar nymphs was similar and reached a peak of approximately 55% on 13 May, while infection of adult leafhoppers never exceeded 19%. Fungal inoculum expressed as the number of host cadavers with active (sporulating) fungus attached to the bean foliage was the variable most closely correlated to disease prevalence. Variables quantifying moisture or moisture combined with temperature (degree hours under moist conditions) were the most important abiotic predictors. A moisture variable incorporating a quantitative measure of moisture (level of wetness of a leaf wetness sensor) and a variable based only on the presence or absence of free moisture (dew) were equivalent predictors of disease prevalence. Epizootic development appeared to be inhibited when foliage was wet for less than 9 hr during the night. Infection trends in relation to fungus inoculum levels indicated an inoculum density threshold for epizootic development of approximately 0.8 leafhopper cadavers per plant

Germination and Infection Processes of the Entomopthoralean Fungus Erynia Radicans on the Potato Leafhopper, Empoasca Fabae

The germination and penetration processes of Erynia radicans on fifth instar Empoasca fabae nymphs at 20°C, 100% relative humidity, were investigated by scanning electron and fluorescence microscopy. Oval primary and secondary conidia attached to the host cuticle and germinated rapidly (60% within 2 hr). While percentage germination did not differ on the three body regions of the host, significant differences were observed in the modes of germination. The percentage of spores that produced germ tubes increased from 10% on the leafhopper head to 13% on the thorax and 22% on the abdomen, while capilliconidiophore production decreased from 88 to 84 to 71% on the respective body regions. Hyphae from spores deposited on sclerites displayed strong directional growth toward interscleral membranes, especially on the host abdomen. Penetration of the cuticle was effected by formation of appressoria. Small, globular appressoria were formed immediately adjacent to spores or on short, nonseptate germ tubes, while large, elongate appressoria were produced usually on long, but occasionally on short, septate hyphae. Approximately 3% of penetrations occurred on the leafhopper head, 16% on the thorax, and 74% on the abdomen; ca. 61% of all penetrations occurred through membranes, especially in the intersegmental folds of the abdomen. Earliest penetrations were observed 3–4 hr after inoculation, but significant numbers of penetrations were not observed until after 6 hr. The number of penetrations on individual leafhoppers was largely independent of dose (mean r2 = 0.174), indicating substantial variability in susceptibility of individual leafhoppers. The percentage of viable oval conidia which ultimately gave rise to penetrations (either directly or indirectly via secondary spore production) was ca. 5% after 10–12 hr and 20% after 48 hr. The percentage of leafhoppers infected (percentage penetrated by one or more hyphae from a mean dose of 41 spores per insect) increased rapidly from only 2.4% at 4 hr postinoculation to ca. 60% after 8 hr. The LD50 was estimated at 4.1 spores per leafhopper

Humoral Encapsulatinon of the Fungus Erynia Radicans (Entomophthorales) by the Potato Leafhopper Empoasca Fabae (Hemiptera)

The immune response of the potato leafhopper, Empoasca fabae, to fungal infection is humoral encapsulation. Noncellular, melanotic capsules were formed around invading hyphae of Erynia radicans, Metarhizium anisopliae, and Hirsutella guyana. Melanization of E. radicans hyphae was observed in the cuticle, epidermis, and hemolymph of infected leafhoppers, in some cases within 4-6 hr post-inoculation. The encapsulation response was nearly always ineffective in preventing fungal infection. Rarely, hyphae in the hemolymph were completely encased in thick melanotic capsules. Thin sections of melanized hyphae showed the melanin to be a granular, electron-opaque substance. A few hyphae were observed coated with a filamentous, electron-opaque substance which also may be melanin