Insight into Biological Control Potential of Hirsutella citriformis against Asian Citrus Psyllid as a Vector of Citrus Huanglongbing Disease in America

Abstract

Studies on Hirsutella citriformis Speare are scarce. Among these, some reports have focused on phenotypic identification, based on its morphological structure and morphometric characteristics. This fungus is known to control economically important citrus crop pests. In recent years, H. citriformis has received increased attention as a control agent for the Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera: Liviidae), which causes the Huanglongbing (HLB) disease. Unfortunately, formal H. citriformis strains characterization is marginal, which mainly involves the role of biologically active exudates (metabolites) produced during their growth. Information regarding their mode of action and biocontrol potential is limited. However, epizootics reports of this fungus, under suitable environmental conditions for its development (25 °C to 28 °C and ~80% relative humidity), have demonstrated its parasitization efficacy. Therefore, it becomes challenging to determine whether H. citriformis strains may be developed as commercial products. In this review, we showed relevant information on isolation and bioassay strategies of H. citriformis to evaluate potential biocontrol strains under laboratory and field conditions in America.

Improved Diaphorina citri (Hemiptera: Liviidae) Adults Biocontrol in Citrus by Hirsutella citriformis (Hypocreales: Ophiocordycipitaceae) Gum-Enhanced Conidia Formulation

“…Gum analysis revealed proteins with a molecular weight of ~14 and ~20 kDa, which may be related to oosporins (also reported by Hirsutella spp. ), whose activity is associated with female’s egg reduction [ 33 ] and hirsutellin [ 20 ], respectively.…”

“…Once inside, mycelium develops from insect tissues, which leads to the insect’s death. After the insect dies, mycelium protrudes [ 19 , 20 ]. Hirsutella citriformis produces a mucilaginous conidium envelope (gum), which facilitates its adherence and provides protective potential to temperatures above or below the optimum, ultraviolet radiation, cold stress, or high osmotic pressure exposure [ 20 , 21 ].…”

“…After the insect dies, mycelium protrudes [ 19 , 20 ]. Hirsutella citriformis produces a mucilaginous conidium envelope (gum), which facilitates its adherence and provides protective potential to temperatures above or below the optimum, ultraviolet radiation, cold stress, or high osmotic pressure exposure [ 20 , 21 ]. During developing, most fungi produce secondary metabolites, some of which may act as insect toxins.…”

“…The aim of the present study was to evaluate different protein sources as supplements to stimulate Hirsutella citriformis growth and improve conidiation and gum production on solid culture media [ 24 ]. In addition, the toxins present in the gum produced by Hirsutella may increase this fungus virulence against target insects [ 20 , 25 ]. Thus, formulation of Hirsutella citriformis gum and conidia may increase Diaphorina citri adults´ biocontrol as applied.…”

Adult Diaphorina citri Biocontrol Using Hirsutella citriformis Strains and Gum Formulations

“…Epizootics are often caused by pathogenic fungi that naturally control Hemipteran insect populations through horizontal transmission, including Diaphorina citri , whose epizootics are mainly due to the fungus Hirsutella citriformis Speare [ 18 ]. However, few studies, particularly related to this fungus’s distribution, pathogenicity, and biocontrol of D. citri , have been reported.…”