Chemical insecticides have been commonly used to control agricultural pests, termites, and biological vectors such as mosquitoes and ticks. However, the harmful impacts of toxic chemical insecticides on the environment, the development of resistance in pests and vectors towards chemical insecticides, and public concern have driven extensive research for alternatives, especially biological control agents such as fungus and bacteria. In this review, the mode of infection of Metarhizium fungus on both terrestrial and aquatic insect larvae and how these interactions have been widely employed will be outlined. The potential uses of Metarhizium anisopliae and Metarhizium acridum biological control agents and molecular approaches to increase their virulence will be discussed.

https://www.mdpi.com/2309-608X/3/2/30/pdf

Mode of Infection of Metarhizium spp. Fungus and Their Potential as Biological Control Agents.

Stress-free microbes lack vitality.

The olive fly, Bactrocera oleae, is the key pest on olives in the Mediterranean area. The pest can destroy, in some cases, up to 70% of the olive production. Its control relies mainly on chemical treatments, sometimes applied by aircraft over vast areas, with their subsequent ecological and toxicological side effects. Bacillus thuringiensis is a spore-forming soil bacterium which produces a protein crystal toxic to some insects, including the orders of Lepidoptera, Diptera, and Coleoptera and other invertebrates. The aim of this study was to search for isolates toxic to B. oleae. Several hundred B. thuringiensis isolates were obtained from olive groves and olive presses in different areas of Greece, Sardinia (Italy), and Spain and from cooperating scientists throughout the world. Some isolates were found toxic only to adults or larvae and some to both stages of the olive fly. In addition, the most toxic isolates were assayed on Opius concolor Szepl. (Hym. Braconidae), the most important parasitoid of the olive fruit fly. Only 3 isolates out of 14 gave significant mortality against this parasitoid. Several of the most toxic crystalliferous isolates may contain novel toxins since they gave no PCR products when probed with primers specified for 39 known toxin genes.

Insecticidal activity of isolates of Bacillus thuringiensis on larvae and adults of Bactrocera oleae Gmelin (Dipt. Tephritidae)

A new approach for single cell microencapsulation in an oil-in-water (o/w) Pickering emulsion is presented. The water/paraffin emulsions were stabilized by amine-functionalized silica nanoparticles. The droplet size of the emulsions was highly tunable, and ranged from 1 to 30 μm in diameter. The controllable droplet size along with the high colloidal stability of the Pickering emulsionswas harnessed to obtain single cell microencapsulation. Successful encapsulation of the conidia entomopathogenic fungus Metarhizium brunneum by the studied Pickering emulsions was confirmed via confocal laser scanning microscopy. The resulting systems were implemented to develop a novel biopesticide formulation for arthropod pest control. The conidia incorporated in the emulsions were applied to Ricinus communis leaves by spray assay. After drying of the emulsion, a silica-based honeycomb-like structure with an ordered hierarchical porosity is formed. This structure preserves the individual cell encapsulation. The successful single cell encapsulation has led to a high distribution of conidia cells on the leaves. The Pickering emulsion-based formulation exhibited significantly higher pest control activity against Spodoptera littoralis larvae compared to the control systems, thus making it a promising, cost-effective, innovative approach for tackling the pest control challenge.

Single Cell Encapsulation via Pickering Emulsion for Biopesticide Applications

This study aimed to evaluate Metarhizium anisopliae (Metschn.) Sorokin (Hypocreales: Clavicipitaceae) persistence in the soil and its impact on Rhipicephalus microplus Canestrini (Acari: Ixodidae) larval recovery in a semifield trial after the treatment of female ticks. Nine strains from the genus Metarhizium Sorokin were isolated from the soil in Brazil and taxonomically classified using the ef1-α gene. The thermotolerance of the strains and their in vitro virulence to tick larvae were tested. One M. anisopliae strain was selected and formulated for the semifield test. The presence of M. anisopliae in the soil ranged from 0.4 × 105 to 1.4 × 105 colony forming units per gram of soil after the treatment during the five months of the survey. The fungus-treated grass pots had significantly fewer larvae than did the control pots. Evidence was gathered about the soil persistence of a native M. anisopliae strain and its efficacy in the biological control of ticks.

Efficacy of a native isolate of the entomopathogenic fungus Metarhizium anisopliae against larval tick outbreaks under semifield conditions

The chemical composition of tick cuticles acts as a barrier to pathogens and may limit infection by entomopathogenic fungi. This study characterized the cuticular neutral lipids (NL) and hydrocarbons (HCs) of four ixodid ticks that are widely distributed in Brazil. HC extracts were analyzed by gas chromatography-mass spectrometry and used to challenge Beauveria bassiana IP361 and Metarhizium robertsii IP146; the effect of cuticular extracts in fungal growth were evaluated by disk diffusion and conidial viability assays. In addition, conidial germination on the tick cuticle was evaluated by scanning electron microscopy, and NL from ticks treated with fungi were assessed by thin layer chromatography. Six HCs were exclusively identified in Amblyomma sculptum. Additionally, cuticle extracts from Dermacentor nitens and A. sculptum inhibited the growth of M. robertsii IP146 and reduced conidial germination of B. bassiana IP361 to 70% and 49%, respectively; the same extracts also produced cytotoxic effects, with conidial death above 30% and 60%. Electron micrographs showed a delayed germination of conidia incubated for 48 h or 72 h on D. nitens and A. sculptum. The lipid profile of A. sculptum treated with fungi was not significantly altered; triacylglycerol was not detected in the cuticle extracts of any other tick species. Finally, A. sculptum and D. nitens cuticles have lipid components that may limit the development of M. robertsii.

/pdf/cuticular-lipids-as-a-first-barrier-defending-ixodid-ticks-txh6orn5.pdf

Elen Regozino Muniz

Papers

Cuticular Lipids as a First Barrier Defending Ixodid Ticks against Fungal Infection

Microsclerotial pellets of Metarhizium spp.: thermotolerance and bioefficacy against the cattle tick