Blastospores from Metarhizium anisopliae and Metarhizium rileyi Are Not Always as Virulent as Conidia Are towards Spodoptera frugiperda Caterpillars and Use Different Infection Mechanisms.

Infective conidia from entomopathogenic fungi are widely used to control insect pests. Many entomopathogenic fungi also produce yeast-like cells called blastospores under specific liquid culture conditions that can directly infect insects. However, little is known about the biological and genetic factors that allow blastospores to infect insects and make them potentially effective for biological control in the field. Here, we show that while the generalist Metarhizium anisopliae produces a higher number of and smaller blastospores, the Lepidoptera specialist M. rileyi produces fewer propagules with a higher cell volume under high-osmolarity conditions. We compared the virulence of blastospores and conidia of these two Metarhizium species towards the economically important caterpillar pest Spodoptera frugiperda. Conidia and blastospores from M. anisopliae were equally infectious, but acted slower, and killed fewer insects than M. rileyi conidia and blastospores did, where M. rielyi conidia had the highest virulence. Using comparative transcriptomics during propagule penetration of insect cuticles, we show that M. rileyi blastospores express more virulence-related genes towards S. frugiperda than do M. anisopliae blastospores. In contrast, conidia of both fungi express more virulence-related oxidative stress factors than blastospores. Our results highlight that blastospores use a different virulence mechanism than conidia use, which may be explored in new biological control strategies.

Low Virulence of the Fungi Escovopsis and Escovopsioides to a Leaf-Cutting Ant-Fungus Symbiosis.

Eusocial insects interact with a diversity of parasites that can threaten their survival and reproduction. The amount of harm these parasites cause to their hosts (i.e., their virulence) can be influenced by numerous factors, such as the ecological context in which the parasite and its host are inserted. Leaf-cutting ants (genera Atta, Acromyrmex and Amoimyrmex, Attini: Formicidae) are an example of a eusocial insect whose colonies are constantly threatened by parasites. The fungi Escovopsis and Escovopsioides (Ascomycota: Hypocreales) are considered a highly virulent parasite and an antagonist, respectively, to the leaf-cutting ants' fungal cultivar, Leucoagaricus gongylophorus (Basidiomycota: Agaricales). Since Escovopsis and Escovopsioides are common inhabitants of healthy colonies that can live for years, we expect them to have low levels of virulence. However, this virulence could vary depending on ecological context. We therefore tested two hypotheses: (i) Escovopsis and Escovopsioides are of low virulence to colonies; (ii) virulence increases as colony complexity decreases. For this, we used three levels of complexity: queenright colonies (fungus garden with queen and workers), queenless colonies (fungus garden and workers, without queen) and fungus gardens (without any ants). Each was inoculated with extremely high concentrations of conidia of Escovopsis moelleri, Escovopsioides nivea, the mycoparasitic fungus Trichoderma longibrachiatum or a blank control. We found that these fungi were of low virulence to queenright colonies. The survival of queenless colonies was decreased by E. moelleri and fungus gardens were suppressed by all treatments. Moreover, E. nivea and T. longibrachiatum seemed to be less aggressive than E. moelleri, observed both in vivo and in vitro. The results highlight the importance of each element (queen, workers and fungus garden) in the leaf-cutting ant-fungus symbiosis. Most importantly, we showed that Escovopsis may not be virulent to healthy colonies, despite commonly being described as such, with the reported virulence of Escovopsis being due to poor colony conditions in the field or in laboratory experiments.

Agroforestry coffee soils increase the insect-suppressive potential offered by entomopathogenic fungi over full-sun soils: A case proposing a "bait survival technique".

Entomopathogenic fungi are important natural enemies of insects. However, there is little information on the insect-suppressive potential of these fungi and possible effects of farming management on this. Meanwhile, changes in natural landscapes due to agricultural intensification have caused considerable biodiversity loss and consequent decay of ecosystem services. However, the adoption of practices such as agroforestry in agroecosystems can foster abiotic and biotic conditions that conserve biodiversity, consequently restoring the provision of ecosystems services. Here, we assessed the effect of management systems (agroforestry or full-sun) on the pest-suppressive potential of entomopathogenic fungi in Brazilian coffee plantations. We used the insect bait method coupled with survival analyses to assess the speed of kill by entomopathogenic fungi and their presence in soil samples from both farming systems. We found that insects exposed to agroforestry soils died more quickly than insects exposed to full-sun soils. Of the fungi isolated from the bait insects, Metarhizium was found most frequently, followed by Beauveria. Meanwhile, Fusarium was frequently isolated as primary or secondary infections. We propose that the differential survival of insects is indicative of a greater suppressive potential by entomopathogenic fungi in agroforestry, and that this could be promoted by the diversified landscape, microclimatic stability, and reduced soil disturbance in agroforestry systems. Furthermore, our results provide a useful demonstration of the potential use of the insect bait method to investigate pest-suppressive potential through bait insect mortality, and we term this the "bait survival technique."

Virulence of entomopathogenic nematodes (Rhabditida: Steinernematidae and Heterorhabditidae) for the control of Diabrotica speciosa germar (coleoptera: chrysomelidae) / Virulência de nematoides entomopatogênicos (Rhabditida: Steinernematidae e Heterorhabditidae) para o controle de Diabrotica speciosa germar (coleoptera: chrysomelidae)

Entomopathogenic nematodes (EPNs) are used in biological control of soil insects and show promise in the control of D. speciosa. The objective of this work was to evaluate the potential of native and exotic entomopathogenic nematode isolates in the control of D. speciosa under laboratory and greenhouse conditions. Results showed that all of EPNs caused larval mortality. The most virulent were Heterorhabditis sp. RSC01 (94 percent), Steinernema glaseri (84 percent), Heterorhabditis sp. JPM04 (82 percent) and Heterorhabditis amazonensis RSC05 (78 percent). There was no effect of the Heterorhabditis sp. RSC01 and S. glaseri isolates on eggs. The maximum mortality of D. speciosa larvae by Heterorhabditis sp. RSC01 was observed at a concentration of 300 IJ/ insect, while by S. glaseri observed the highest mortality at the concentration of 200 IJ/ insect. The Heterorhabditis sp. RSC01 isolate caused over 80 percent pupal mortality at a concentration of 250 IJ/insect. The virulence of Heterorhabditis sp. RSC01 and S. glaseri was affected by temperature. The Heterorhabditis sp. RSC01 isolate caused reduction in larva survival under greenhouse conditions at all of the tested concentrations and there was no difference in mortality among different concentrations of infectid juveniles.

Os nematóides entomopatogênicos são utilizados no controle biológico de pragas de solo, e são promissores para o controle de D. speciosa. Neste trabalho, objetivou-se avaliar o potencial de espécies nativas e exóticas de isolados de nematóides entomopatogênicos para o controle de D. speciosa, em condições de laboratório e de casa de vegetação. Verificou-se que todos os nematóides causaram mortalidade larval. Os mais virulentos foram Heterorhabditis sp. RSC01 (94 por cento), Steinernema glaseri (84 por cento), Heterorhabditis sp. JPM04 (82 por cento) e Heterorhabditis amazonensis RSC05 (78 por cento). Não houve efeito dos isolados Heterorhabditis sp. RSC01 e S. glaseri em ovos. A mortalidade máxima de larvas de D. speciosa por Heterorhabditis sp. RSC01 foi observada na concentração de 300 JI / inseto, enquanto para S. glaseri a maior mortalidade foi obervada na concentração de 200 JI/ inseto. O isolado Heterorhabditis sp. RSC01 causou mais de 80 por cento de mortalidade de pupas na concentração de 250 IJ/ inseto. A virulência de Heterorhabditis sp. RSC01 e S. glaseri foi afetada pela temperatura. O isolado Heterorhabditis sp. RSC01 causou redução na sobrevivência da larvas em casa de vegetação em todas as concentrações de juvenis infectantes testadas e não houve diferença na mortalidade entre os diferentes tratamentos.

Evaluation of entomopathogenic nematodes under laboratory and greenhouses conditions for the control of Spodoptera frugiperda / Avaliação de nematoides entomopatogênicos em condições de laboratório e casa-de-vegetação visando ao controle de Spodoptera frugiperda

The increased corn planting grown in the late season crop and the use of a notillage planting system benefits the development of Spodoptera frugiperda, the main pest of corn crop. Thus, this study aimed to select entomopathogenic nematodes based on the mortality of S. frugiperda, and to adjust the nematode concentrations in the laboratory and evaluate the action of these organisms in greenhouse conditions. Seventeen nematode populations were tested at concentrations of 100, 250, and 500 infective juveniles (IJ)/larvae. The obtained data were submitted to the polynomial regression test. In the greenhouse, corn sowing was performed in plastic buckets with soil, corn straw, and water. After 7 days, Steinernema arenarium or Heterorhabditis sp. RSC02, and the larvae were added (40 larvae, one larvae/repetition). The data were submitted to the variance analysis and the Scott-Knott test (P<0.05). In the laboratory, tests with S. arenarium and Heterorhabditis sp. RSC02 caused mortality of 85 and 90 percent, respectively, being selected for the concentrations test. Concentrations of 150, 200, 250, 300, and 350IJ larvae-1 were tested. At a concentration of 200IJ larvae-1, S. arenarium and Heterorhabditis sp. RSC02 caused 100 and 97.6 percent mortality in laboratory, respectively, and in the greenhouse caused 77.5 and 87.5 percent mortality, respectively, when compared to the control (7.5 percent).

O aumento no plantio do milho "safrinha" e o uso do sistema de plantio direto favorecem o desenvolvimento de Spodoptera frugiperda, principal praga da cultura. Dessa forma, os objetivos deste trabalho foram selecionar nematoides entomopatogênicos, de acordo com a mortalidade causada sobre S. frugiperda, adequar as concentrações em laboratório e avaliar a ação desses organismos em condições de casa-de-vegetação. Foram testadas 17 populações de nematoides nas concentrações de 100, 250 e 500 juvenis infectantes (JI) lagarta-1. Os dados obtidos foram submetidos ao teste de regressão polinomial. Em casa-de-vegetação, a semeadura do milho foi realizada em vasos de plástico contendo solo, palhada de milho e água. Após sete dias, foram adicionados Steinernema arenarium ou Heterorhabditis sp. RSC02 e as lagartas (40 lagartas, uma lagarta/repetição). Os dados obtidos foram submetidos à análise de variância e ao teste de médias Scott-Knott (P<0,05). Nos testes de laboratório, S. arenarium e Heterorhabditis sp. RSC02 causaram mortalidade de 85 e 90 por cento, respectivamente, sendo selecionados para o teste de concentrações. Foram testadas as concentrações de 150, 200, 250, 300 e 350JI lagarta-1. Na concentração de 200JI lagarta-1, S. arenarium e Heterorhabditis sp. RSC02 causaram 100 e 97,6 por cento de mortalidade, respectivamente, e em casa-de-vegetação causaram 77,5 e 87,5 por cento, respectivamente, diferindo da testemunha (7,5 por cento).