Pathogenicity ofMetarhizium anisopliae(Hypocreales: Clavicipitaceae) to Tick Eggs and the Effect of Egg Cuticular Lipids on Conidia Development

Abstract

The ovicidal efficacy of two entomopathogenic hyphomycetes fungi--Metarhizium anisopliae variety acridum (M. an. ac.) Driver and Milner (Hypocreales: Clavicipitaceae) and Metarhizium anisopliae variety anisopliae (M. an. an.) (Metschn.) Sorokin (Hypocreales: Clavicipitaceae)--was evaluated against eggs of three tick species (Acari: Ixodidae)--Hyalomma excavatum (Koch), Rhipicephalus (Boophilus) annulatus (Say), and Rhipicephalus sanguineus (Latereille)--by placing eggs, laid by surface-sterilized females, on conidia-impregnated filter paper. Although M. an. an. strains differed in their virulence to the tested ticks, they reduced the hatching percentages of eggs of all three tick species to 0-32% compared with 80-90% in the control eggs. The M. an. ac. strains were found highly virulent to H. excavatum and R. sanguineus eggs, reducing the hatching percentages to 2-6% but had no influence on hatching of R. annulatus eggs. Older tick eggs were more susceptible to fungal infection than newly laid ones. The effects of polar and nonpolar lipid fractions, extracted from the surface of tick eggs, on the development of conidia were tested. Both germination of M. an. an. conidia and formation of appressoria were stimulated by extracts from egg cuticles of all three tested tick species. However, the stimulating effect was lower when the conidia were exposed to lipids from relatively less susceptible R. annulatus eggs than when exposed to lipids from H. excavatum or R. sanguineus eggs. Unlike those of M. an. an., conidia of M. an. ac. exposed to such lipid extracts did not germinate and did not form appressoria.

The entomopathogen Metarhizium anisopliae can modulate the secretion of lipolytic enzymes in response to different substrates including components of arthropod cuticle

“…Olive oil is a vegetable lipid source that usually induces higher levels of lipolytic activity in fungi (Shirazi et al 1998;Maia et al 1999;Lee et al 2009); however, higher specific activities were found in the medium containing cholesteryl stearate in all incubation times and substrates tested, thus reinforcing our hypothesis of the specificity that M. anisopliae might have for animal lipids. Similar conclusions were reached by Gindin et al (2009) andMent et al (2010), who reported on the specific stimulatory effect of tick cuticular lipids for M. anisopliae development, conidia germination and formation of appressoria.…”

Ovicidal Efficacy of Metarhizium anisopliae (Hypocreales: Clavicipitaceae) towards Rhipicephalus sanguineus (Acari: Ixodidae) Eggs

“…Indeed, M. anisopliae strain HSAH5 containing 10 6 and 10 7 conidia mL -1 were able to cause 100% mortality on local R. sanguineus eggs. This result is also in agreement with the findings by Gindin et al (2009) where the study shows that R. sanguineus eggs are more susceptible to M. anisopliae compared to R. annulatus. Surprisingly, the mortality caused by flumethrin exposure (positive control) was only 8.97%, which was subsided compared to eggs treated with M. anisopliae spore suspension.…”

“…The present study shows, for the first time, that a native strain of M. anisopliae was found highly virulent towards R. sanguineus eggs. Metarhizium anisopliae has long been studied on its efficacy towards different species of soft and hard ticks (Gindin et al, 2009;Ren et al, 2016;Fernandez-Salas et al, 2017;Fischhoff et al, 2017;Prado-Rebolledo et al, 29.57 ± 4.82b 10 6 conidia mL -1 30.22 ± 4.90b 10 7 conidia mL -1 30.22 ± 4.90b…”

“…Infectious conidia can either get into contact with tick eggs indirectly on substrates which are previously treated with the fungus or treated topically (directly) with conidia. Whereas fungal activity against R. sanguineus eggs, larvae, nymphs, and adults is well established (Dantas-Torres, 2008;Fernandes & Bittencourt, 2008;Gindin et al, 2009), the native strains have been shown to be more virulent (Pajar et al, 2013). However, of the few studies available in the literature on the use of entomopathogenic fungi against R. sanguineus, none of the native strains of these fungi were tested against R. sanguineus.…”

Endophytic and entomopathogenic strains of Beauveria sp to control the bovine tick Rhipicephalus (Boophilus) microplus

“…(B.) microplus Bittencourt, 2008;Lubeck et al, 2008;Gindin et al, 2009), being effective against ticks such as Ixodes scapularis, Oligonynchus yothersi, Rhipicephalus appendiculatus, R. sanguineus, Hyalomma excavatum, and Amblyomma variegatum under laboratory and field conditions (Oliveira et al, 2002;Leemon et al, 2008). The entomopathogenic B. bassiana is usually found infecting insects.…”