G. R. CARNER’s research while affiliated with Clemson University and other places

Five small-plot tests with a nuclear polyhedrosis virus of the velvctbean caterpillar, Anticarsia gemmatalis Hubner, were conducted in soybeans in South Carolina during 1979 and 1980. Virus rates ranging £rom 5 to 40 larval equivalents {LE)/ha were tested and compared with an insecticide standard (carbaryl at 560 g AUha). Control of A. gemmatalis larvae ranged from 59.3 to 86.4% at 14 d post-application with rates of 20 LE/ha. Control levels were not increased by the higher rate of 40 LE/ha. and application rates of less that 20 LE were less effective. After 21 d, control was generally higher in virus treatments than after 14 d. Soil bioassayed from lest areas receiving virus applications indicated that low levels of virus were present in the soil. Levels of virus capable of causing 13% mortality in bioassayed A. gemmalalis larvae were detected from a location 16 months after application. However, naturally-occurring A. gemmatolis larvae collected rrom these locations the year after virus applications showed no symptoms or mortality due to virus infections.

Larvae of Heliothis spp. collected from cotton, soybean, and peanut fields in South Carolina were found to be infected with virus-like particles (VLPs). Infected larvae became pale and swollen, stopped feeding, and remained alive for 2–3 weeks. Hemolymph from these larvae was milky and contained numerous spherical bodies ranging in diameter from 2 to 10 μm. The hemolymph also contained VLPs which were oval and measured 375 × 125 nm. Infectivity tests with crude saline extracts of infected larvae demonstrated that the pathogen could be transmitted by injection but not per os. The spherical bodies contained VLPs (387 × 149 nm) surrounded by two envelopes and packed together in clusters. These VLPs were also found in fat body cells, cuticular epithelial cells, tracheal cells, and connective tissue associated with the body wall and the gut. They were not found in muscle tissue or in midgut epithelial cells. Similar VLPs have been found in Heliothis zea from Mississippi and Trichoplusia ni from California, but a positive identification of the VLPs has not been made in any of these studies. Morphologically they appear to be distinct from any other previously described insect viruses.

In 1974 and 1979 in Clemson, South Carolina, adults of the common soldier beetle, Chauliognathus pennsylvanicus, were found to be infected by the fungal pathogen, Entomophthora lampyridarum. After infected beetles died they remained attached by their mandibles to foliage and flowers. The wings of infected beetles remained open, allowing conidiophores to develop on the upper surface of the abdomen. Primary conidia were elongate and measured 36.5 × 17.1 μm. Two types of secondary spores were formed: Type I spores were similar in form to primary conidia, but were somewhat smaller; Type II spores were formed at the apex of slender stalks and measured 37.7 × 15.3 μm. Resting spores were spherical, hyaline, and 22.3 μm in diameter.

Two applications of the fungicides Benlate®, Du Ter®, and Bravo®, and Benlate in combination with carbaryl were made to soybean. Infection of lepidopterous larvae by the entomogenous fungus Nomuraea rileyi (Farlow) Samson was inhibited to some degree by application of Benlate ®, Du Ter®, and Bravo®. Bravo caused the most inhibition followed by Bentlate and Du Ter respectively. In one instance the combination of Benlate + carbaryl was more disruptive to N. rileyi than either chemical alone. Inhibition was greatest when pesticide application coincided with the early stages of N. rileyi epizootics.

Eight species of noctuid larvae were tested for susceptibility to a nuclear polyhedrosis virus of the velvetbean caterpillar, Anticarsia gemmatalis. Velvetbean caterpillar larvae were highly susceptible to crude preparations of polyhedral inclusion bodies (PIBs; LD50 = 4.7 PIBs/larva), but preparations of purified polyhedra were much less effective against these larvae (LD50 = 319.7 PIBs/larva). Of seven other noctuid species tested, only Heliothis virescens was as susceptible to the virus as A. gemmatalis. High dosages were required to kill Heliothis zea, Trichoplusia ni, Pseudoplusia includens, and Spodoptera ornithogalli. Plathypena scabra and Spodoptera frugiperda were not susceptible.

During a study of the ultrastructure of a nuclear polyhedrosis virus of the velvetbean caterpillar, Anticarsia gemmatalis, various types of nuclear and cytoplasmic inclusions were found in fat body tissue heavily infected with the virus. Virogenic stroma was present in the nuclei of most infected cells. Bundles of fibrous material were observed in the nuclei and cytoplasm of cells containing polyhedral bodies. Other nuclear inclusions included concentric multilayered material, vacuoles, and membrane structures.

In the laboratory, Heliothis zea (Boddie) larvae that were fed foliage of ED73–371, a genotype resistant to the Mexican bean beetle, Epilachna varivestis Mulsant, weighed less and were more susceptible to methomyl and Bacillus thuringiensis Berliner compared to larvae fed foliage of the ‘Bragg’ variety. No difference was detected in the LD50, of methyl parathion when H.zea larvae were reared on Bragg and ED73–371. Larvae of Pseudoplusia includens (Walker) weighed less and were significantly more susceptible to methyl parathion when fed ED73–371 foliage than when fed Bragg foliage, whereas LD60’s of methomyl and B. thuringiensis were similar on the 2 genotypes. Percent control of field populations of H. zea was greater in ED73–371 than in Bragg soybeans when plots of each genotype were treated with similar rates of methyl parathion or B. thuringiensis. Fewer larvae were found in untreated plots of ED73–371 than in Bragg, indicating a lower natural population in the resistant soybeans.

A nuclear polyhedrosis virus was isolated from larvae of Anticarsia gemmatalis Hübner, collected from Chapec6, Santa Catarina in southern Brazil. Electron microscope studies revealed that the virus was multiply embedded with 1-11 virions/envelope. Average size of polyhedral bodies was 1.31 µm and virions, 195×25 nm. Infectivity studies revealed the virus was an effective pathogen at dosages as low as 17 PIB's/larva. Mortality occurred in 8-12 days at 26.7°C. In small plot field tests, the virus at 49 LE/ha significantly reduced populations of A. gemmatalis.

Treatment of soybean with methyl parathion and methomyl caused resurgence of populations of Plathypena scabra F., Heliothis spp., Pseudoplusia includens (Walker), Anticarsia gemmatalis Hübner, and Epilachna varivestis Mulsant. Less resurgence occurred when monocrotophos was applied. Removal of the natural biotic agents by the insecticides was probably the major reason for the resurgence. Newly-established soybean fields in isolated situations were more susceptible to outbreaks of these pests than fields which were cultivated annually.

Entomophthora sp. killed its host, Tetranychus urticae, in 3.38 days at 25°C and in 11.02 days at 15°C. Development of hyphal bodies within the mite was studied with a light microscope, and a scanning electron microscope was used to examine spore development and structure. A comparison of this fungus with other mite-infecting fungi revealed that it is more closely related to E. floridana than to E. tetranychi, and should be called Entomophthora sp. near floridana until a more detailed study of E. floridana can be made.