Sleeping Beauties: Horizontal Transmission via Resting Spores of Species in the Entomophthoromycotina.

Many of the almost 300 species of arthropod-pathogenic fungi in the Entomophthoromycotina (Zoopagomycota) are known for being quite host-specific and are able to cause epizootics. Most species produce two main types of spores, conidia and resting spores. Here, we present a review of the epizootiology of species of Entomophthoromycotina, focusing on their resting spores, and how this stage leads to horizontal transmission and persistence. Cadavers in which resting spores are produced can often be found in different locations than cadavers of the same host producing conidia. Resting spores generally are dormant directly after production and require specific conditions for germination. Fungal reproduction resulting from infections initiated by Entomophaga maimaiga resting spores can differ from reproduction resulting from conidial infections, although we do not know how commonly this occurs. Reservoirs of resting spores can germinate for variable lengths of time, including up to several months, providing primary infections to initiate secondary cycling based on conidial infections, and not all resting spores germinate every year. Molecular methods have been developed to improve environmental quantification of resting spores, which can exist at high titers after epizootics. Ecological studies of biological communities have demonstrated that this source of these spores providing primary inoculum in the environment can decrease not only because of germination, but also because of the activity of mycopathogens.

Zombie soldier beetles: Epizootics in the goldenrod soldier beetle, Chauliognathus pensylvanicus (Coleoptera: Cantharidae) caused by Eryniopsis lampyridarum (Entomophthoromycotina: Entomophthoraceae).

Adult goldenrod soldier beetles, Chauliognathus pensylvanicus, were found infected by the fungus Eryniopsis lampyridarum (Entomophthoromycotina) in Arkansas during September - October (1996, 2001, 2015 and 2016). Living and dead infected beetles were found on flowering frost aster, Symphyotrichum pilosum, common boneset, Eupatorium perfoliatum, and Canada goldenrod, Solidago canadensis. Live and dead beetles (n=446) were collected in 1996 from S. pilosum flowers and held individually in the laboratory for determination of fungal prevalence. Of the beetles collected, 281 (63%) were males and 165 (37%) were females. A total of 90 beetles were infected with E. lampyridarum, an overall prevalence of 20.2%. Prevalence in males was 19.6% (n=55 infected/281 males total) and prevalence in females was 21.2% (n=35 infected /165 females total). Conidia were produced from 57% of the infected beetles, 23% of the infected beetles produced resting spores, and 20% contained the hyphal body stage. Infected beetles produced either conidia or resting spores but never both in the same host. Post-mortem morphological changes in the hosts due to E. lampyridarum were observed periodically for 24h. Shortly before death, by unknown mechanisms, dying infected beetles tightly clamped their mandibles into flower heads and ca. 15-22h later (between 2400 and 0700h) the fungus caused dead beetles to raise their elytra and expand their metathoracic wings.

The natural occurrence of Pandora heteropterae (Zygomycetes: Entomophthorales) infecting Lygus lineolaris (Hemiptera: Miridae).

An unknown fungal pathogen was recovered from Lygus lineolaris (Palisot de Beauvois) during a survey of parasitic and pathogenic natural enemies conducted in Franklin County, Arkansas. The pathogen was identified as Pandora heteropterae (Balazy) Keller based on characteristics of the morphology, as well as growth and sporulation on hosts. The fungus infected 11 of the 3405 (0.32%) wild L. lineolaris collected. In a laboratory host-range bioassay, five of seven hemipteran species from the families Miridae, Coreidae, Lygaeidae, and Pentatomidae were successfully infected. P. heteropterae was previously reported only once, from an unidentified host species in Poland. Here we describe the morphology and growth of P. heteropterae and discuss its potential impact on L. lineolaris in the field.

Rise and fall of cotton aphid (Hemiptera: Aphididae) populations in southeastern cotton production systems.

The impact of natural enemies on cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), populations in cotton, Gossypium hirsutum L., production systems in the southeastern United States was evaluated over 3 yr in irrigated commercial cotton fields. Fungal epizootics caused by the entomopathogen Neozygites fresenii (Nowakowski) Batko reduced aphid numbers to subthreshold levels in 1999, 2000, and 2001 and occurred consistently in early to mid-July in all 3 yr. Scymnus spp. were the most abundant aphidophagous predators, although other coccinellid species and generalist predators such as spiders, fire ants, heteropterans, and neuropterans also were present. Studies using arthropod exclusion cages demonstrated little impact of predators or parasitoids on aphid populations before fungal epizootics. Arthropod natural enemies were most abundant after epizootics and may have suppressed aphid populations late in the season. Seed cotton yield, and lint quality were not affected by aphicide applications in any year of the study. Implications of these findings for aphid management in the southeastern United States are discussed.

Factors affecting transmission of fungal pathogens of aphids.

Fungal pathogens are the most important pathogens of aphids (Homoptera: Aphididae), and epizootics, particularly those caused by Entomophthorales (Zygomycota), are frequently observed and often rapidly reduce aphid populations. Fungi in the Hypocreales (Ascomycota) are less commonly found infecting aphids but can be important. The transmission of aphid fungal pathogens is affected by many factors, including: host biology and structure, pathogen characteristics, host-plant characteristics, and environmental factors. This paper is an overview of selected factors affecting transmission of aphid pathogens.

Mass harvesting of the entomopathogenic fungus, Neozygites fresenii, from natural field epizootics in the cotton aphid, Aphis gossypii.

Epizootics caused by insect pathogens sometimes occur over wide areas and result in millions of infected insects. Naturally infected insects can be considered a natural resource for harvesting insect pathogens. We developed methods to mass harvest the fungal pathogen Neozygites fresenii (Entomophthorales: Neozygitaceae) from epizootics in Aphis gossypii (Homoptera: Aphididae) in a commercial cotton field in Arkansas. A total of 30,722 aphids infected with N. fresenii in the mature hyphal body or early conidiophore stages were harvested, dried, and frozen. Three desiccants were compared: silica gel, dry rock salt, and wet rock salt. Silica gel was the superior material because it more rapidly and thoroughly dried cotton leaves and aphids. Using this method a mean of 193.4 infected aphids could be harvested per hour from cotton leaves dried over silica gel. The quality of harvested infected aphids was high and resulted in a mean of 70.4% sporulation from infected aphids harvested from the silica gel desiccant.

Evaluation of three formulations of Beauveria bassiana for control of lesser mealworm and hide beetle in Georgia poultry houses.

Initial screening of 12 Beauveria bassiana (Balsamo) Vuillemin isolates against larvae of the lesser mealworm (Alphitobius diaperinus [Panzer]) resulted in the selection of two isolates, GHA and 707, for further testing under field conditions. Three formulations of each strain were prepared: an EC, a ground corn granular formulation, and waste product of fungal propagation containing spent media, mycelia, and unharvested conidia ("residue" formulation). Two field trials were conducted in commercial caged-layer houses in Georgia with 5-6 mo of manure accumulation and established populations of A. diaperinus and hide beetles (Dermestes maculatus DeGeer). In the first trial field, B. bassiana was applied a single time to the manure surface at either 10(9) (EC and granular cornmeal bait formulations) or 10(8) (residue formulation) fungal spores per square meter. In the second trial, two successive weekly treatments were applied, using a total of 6x the rate of application used in the first trial, Significant treatment effects were short-lived and only detected 2 wk after treatment in both trials. The granular formulations of both strains and the residue formulation of the GHA strain provided the greatest degree of suppression (60-90%) of beetle larvae. A laboratory bioassay confirmed that the granular bait was the most effective formulation. More frequent applications made earlier in the manure accumulation cycle may be necessary to achieve satisfactory control of these beetles.

Effects of long-term storage at -14 degrees C on the survival of Neozygites fresenii (Entomophthorales: Neozygitaceae) in cotton aphids (Homoptera: Aphididae).

Neozygites fresenii-infected Aphis gossypii cadavers, containing dormant hyphal bodies of N. fresenii, were stored in 4 ml glass vials at -14 degrees C in a standard consumer-type refrigerator/freezer for 1, 21, 30, 43, 51, and 68 months to determine the effect of storage on fungal survival. When the cadavers were removed from the freezer and placed in 25+/-1 degrees C, 100% relative humidity, and 12:12 (L:D) conditions, N. fresenii survival, as shown by fungal sporulation from the cadavers, was high at all storage periods. The average percentage of cadavers from which the fungus sporulated were 93, 47, 100, 100, 80, and 60% from 1, 21, 30, 43, 51, and 68 months storage periods, respectively. The number of primary conidia discharged from each sporulating cadaver was estimated using a scale of 1 (low, ca. 1000 primary conidia), 2 (medium, ca. 2000 primary conidia) and 3 (high, ca. 3000 primary conidia). The median scores for the number of primary conidia produced per sporulating cadaver were 3, 2, 3, 3, 2.5, and 1 for 1, 21, 30, 43, 51, and 68 months, respectively. Therefore, except for the longest storage period, most cadavers produced medium to high numbers of primary conidia. Mean germination of primary conidia produced from N. fresenii-infected-aphid cadavers from each time period varied significantly from 66.3 to 86.1% in the 21 and 43 months categories, respectively. Infectivity of capilliconidia, produced from frozen N. fresenii, to live healthy cotton aphids varied significantly from 16.7 to 68.7% from cadavers stored 68 months and 1 month, respectively. Overall N. fresenii survived well in dried frozen cotton aphid cadavers for up to 6 years with little reduction in sporulation, numbers of spores produced, germination of primary conidia, or infectivity.