Diurnal pattern of death and sporulation in Entomophaga maimaiga-infected Lymantria dispar

Entomophaga maimaiga Humber, Shimazu, et Soper (Zygomycotina: Entomophthoraceae) is a naturally occurring obligate fungal pathogen specific to gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae) larvae. This fungus is considered the most important natural enemy of this pest insect in North America and Asia. A critically important step for the development of E. maimaiga epizootics is the transmission of propagules to healthy larvae, a process known to require high humidity. Some pathogens are known to manipulate the time of day that hosts die so that propagules are produced to maximize chances of survival and thus enhance transmission. The objective of this study was to assess whether E. maimaiga manipulates L. dispar to die at a certain time of day. Laboratory bioassays were conducted at 15 and 20 °C to record the 24‐h activity pattern of death and sporulation exhibited under an L14:D10 photoperiod and 100% r.h. by four isolates of E. maimaiga in its host L. dispar. Events were recorded every 4 h. Our results clearly demonstrate that E. maimaiga‐infected L. dispar larvae die mainly in the afternoon and that the fungus sporulates during the night. The rhythm was independent of the fungal isolate tested and type of spores produced after larval death. By raising the temperature from 15 to 20 °C, the peak death time narrowed and sporulation was initiated earlier at night.     

Distribution in time and space of resistance to the pathogenic fungus Erynia neoaphidis in the pea aphid Acyrthosiphon pisum

Two biotypes of pea aphid, Acyrthosiphon pisum, have been recognized in Australia, by their susceptibility (S) or resistance (R) to certain isolates of the fungal pathogen Erynia neoaphidis. The responses of these two biotypes to 40 isolates of the fungus have shown that the R form is largely confined to two States, New South Wales and Victoria, but appears to have recently spread into Queensland and Tasmania. There is no evidence to suggest it occurs outside Australia. Sequential sampling of two field populations of pea aphids during 1981 and 1982 showed that the proportion of R form remained stable at 10.7±3.0 and 14.6±2.6% (mean±standard error) for the two populations. Glasshouse competition experiments run at the comparatively high temperature of 25°C resulted in the R form becoming dominant even when the initial ratio was 4:1 in favour of the S form. The ecological and genetical implications are discussed.

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Résumé Deux types biologiques d'Acyrthosiphon pisum ont été définis, en Australie, suivant leur sensibilité (S) ou leur résistance (R) à certains isolats du champignon pathogène Erynia neoaphidis. Les réponses des deux biotypes à 40 isolats du champignon ont montré que la forme R est essentiellement cantonnée à deux états: Nouvelle Galle due Sud et Victoria, mais a récemment gagné le Queensland et la Tasmanie. Aucun élément ne fait dire qu'elle existe hors d'Australie. Des échantillonnages séquentiels des deux populations de pucerons dans la nature en 1981 et 1982 ont montré que la proportion de la forme R est restée stable à 10,7 et 14,62 dans les deux populations. Des expériences de compétition en serre à la température relativement haute de 25°C ont rendu la forme R dominante, même quand le rapport initial était de 4/1 en faveur de la forme S. La discussion porte sur les conséquences écologiques et génétiques.

     

Infectivity of resting spores of Massospora cicadina (Entomophthorales: Entomophthoraceae), an entomopathogenic fungus of periodical cicadas (Magicicada spp.) (Homoptera: Cicadidae)

Progeny of eastern oyster, Crassostrea virginica, introduced into France in 1992, were reared in IFREMER facilities to test their growth performances. During the summer of 1993, sporadic mass mortalities (80-90%) occurred among C. virginica spat reared in the IFREMER laboratories in La Tremblade (Charente Maritime, France) and Bouin (Vendée, France). Affected oysters presented mantle retraction and deposition of an anomalous conchiolin layer on the inner surface of the shell. The incidence of oysters with gross signs exceeded 80%. No obvious pathogen was identified in soft tissues by histology and transmission electron microscopy (TEM). However, histological examination showed the presence of anomalous basophilic round structures, 0.5-1 microm in diameter, in gill and mantle connective tissues. These extracellular Feulgen-negative structures reacted positively with the von Kossa stain. TEM examination on mantle and gill samples in diseased spat showed that the basophilic bodies consisted of concentric deposits of an amorphous substance interpreted as containing calcium. These observations may indicate that the mineralization process in spat shells was disturbed without exact determination of the cause. Based on the similarities of the gross signs to those reported in juvenile eastern oysters in the United States, we believe that the cause of the mortalities observed in France was probably the Juvenile Oyster Disease. Moreover, we report for the first time the detection of anomalous amorphous structures in gill and mantle connective tissues associated with mortalities and deposition of an anomalous conchioloin layer on the inner shell surface in C. virginica spat.     

Zygospore overwintering and sporulative germination in Triplosporium fresenii (Entomophthoraceae) attacking Aphis spiraecola on citrus in Israel

Triplosporium (Entomophthora) fresenii overwinters on citrus trees in Israel as zygospores which germinate in March and April by means of capillary conidiophores bearing capillispores (anadhesive conidia) in synchronization with spring buildup of Aphis spiraecola populations on citrus. The minimum temperature for zygospore germination in Israel is about 9–10°C. In the zygospore population there is variability regarding time needed to break dormancy and temperature needed for germination, which is gradual, its cumulative curve being sigmoidally shaped. Some evidence suggests that dormancy is of the endogenous type. The variability and the ability to overwinter on trees as resting spores are assumed to give T. fresenii an advantage over other Entomophthoraceae present on the same host in spring.     

Natural occurrence of the entomopathogenic genus Pandora on spittlebug pests of crops and pastures in Argentina

The natural occurrence of entomophathogenic fungi infecting spittlebugs (Hemiptera: Cercopidae) considered serious pests to pasture grasses and crops in Argentina was investigated during summer?autumn (December to May) from 2013 to 2016. Adults and nymphs of spittlebugs were collected from Sorghum halepense and Setaria parviflora var. parviflora in San Miguel de Tucumán, Tucumán province. The entomopathogenic fungal species were characterized on the basis of morphological keys and molecular techniques. Microscopic characters were described from material mounted in lactophenol/aceto‐orcein (1% w/v), and the amplification of the fungal SSU rDNA was carried out using the universal primers nu‐SSU‐0021‐5′ and nu‐SSU‐1780‐3′. Summarized information about occurrence of fungal infections on spittlebugs populations is provided. This study reports for the first time the occurrence of the genus Pandora infecting adults of the economically important spittlebugs Deois (Deois) mourei, D. (D.) knoblauchii, Isozulia christenseni christenseni and Notozulia entreriana from Argentina expanding the host range and geographical distribution of entomophthoralean fungi.     

Persistence of conidia of Entomophthora muscae in relation to age, temperature, and humidity

In this paper, the effect of age, humidity, and temperature on the conidial survival of Entomophthora muscae was evaluated. E. muscae was obtained from Musca domestica in a dairy in Itatiba (São Paulo, Brazil) and maintained in the laboratory by continuous passage through flies. Furthermore, the ability of conidia to infect flies at three temperatures (17, 21, and 27 °C), four ages of conidia (12, 72, 96, and 154 hours) and two humidities (100 and 60% RH) was evaluated. The temperature of 21 °C was the most favorable for the infection of house flies. Humidity was a cause of variation at 27 °C when the conidia were up to 12 hours old, but had no effect at lower temperatures. Conidia held at 100% RH and aged 72 hours caused no infection at 17 °C, but were infective at 21 °C. In the present study, conidia retained viability much longer than previously observed. Finally, the effect of humidity, temperature, and conidial age is discussed.     

Effects of 20 fungicides on the infectivity of conidia of the aphid entomopathogenic fungus Erynia neoaphidis

The effect of 20 fungicides on theinfectivity of conidia of the entomopathogenicfungus, Erynia neoaphidis, were assessedin the laboratory. After projection on broadbean leaves, conidia were treated withfungicides applied at their recommended fieldrate. Afterwards, the infectivity of theseinocula was assessed using an aphid bioassay.Four fungicides, carbendazim, kresoxym-methyl, nuarimol and thiophanate-methyl reduced the infectivity of the conidia by less than 25% and can be considered harmless for this aphid pathogen. Propiconazole was a little more toxic, with 37% reduction. Other products reducedinfectivity by between 50% and 100%. These are, from the least to the most toxic:flutriafol, prochloraz, epoxyconazole,iprodione, hexaconazole, triadimenol,azoxystrobine, cyproconazole, cyprodynil,flusilazole and tridemorph. Chlorothalonil,fenpropimorph, spiroxamine and tebuconazoletotally inhibited infectivity of the fungi. Analysis of the results according to chemicalclass showed that the benzimidazoles were theleast toxic for E. neoaphidis and themorpholines the most toxic. Effects oftriazoles and strobilurines were variable, withreduction ranging from 37% to 100% fortriazoles and from 17% to 68% forstrobilurines.