Field Efficacy of Cordyceps javanica, White Oil and Spinetoram for the Management of the Asian Citrus Psyllid, Diaphorina citri

Advances in submerged liquid fermentation and formulation of entomopathogenic fungi

Entomopathogenic fungi (EPF) can be defined as beneficial multifunctional eukaryotic microorganisms that display pivotal ecological services in pest management, with some species possessing the special ability to establish mutualistic relationships with plants. Mass production of these fungi is critical to support affordable widespread commercialization and worldwide field application. Among the mass production methods explored mainly by industry, submerged liquid fermentation is a robust and versatile technology that allows the formation of different types of propagules designated for various applications in pest control. Many hypocrealean EPF are easily culturable on artificial substrates by producing single-celled structures (hyphal bodies, blastospores, and submerged conidia) or multicellular structures (mycelium and microsclerotia). Less frequently, some EPF may form environmentally resistant chlamydospores, but these structures have almost always been overlooked. A continued research pipeline encompassing screening fungal strains, media optimization, and proper formulation techniques aligned with the understanding of molecular cues involved in the formation and storage stability of these propagules is imperative to unlock the full potential and to fine-tune the development of robust and effective biocontrol agents against arthropod pests and vectors of diseases. Finally, we envision a bright future for the submerged liquid fermentation technology to supplement or replace the traditional solid substrate fermentation method for the mass production of many important EPF. KEY POINTS: • Submerged liquid fermentation (SLF) allows precise control of nutritional and environmental factors • SLF provides a scalable, robust, and cost-effective platform for mycopesticide production • Enhancing formulation, shelf life, and field efficacy of submerged propagules remain crucial • Understanding the molecular mechanisms behind submerged propagule formation is key to advancing SLF technology.

Association of Non-host Crop Plants with Mandarin in Host Location and Survival of Diaphorina citri Kuwayama (Hemiptera: Psyllidae)

Research efforts have been made to develop novel tactics, such as those targeting behavioral control, for management of the Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera: Psyllidae), vector of the causal agent of citrus Huanglongbing. Here, we investigated whether association of "Ponkan" mandarin (Citrus reticulata) with volatiles from non-host crops: avocado, passion fruit or coffee, alters host location by the Asian citrus psyllid; and whether they can be temporary hosts for the Asian citrus psyllid. In wind tunnel assays, we found that the association of mandarin seedling with avocado plant volatiles reduced in 30% the number of psyllids sitting on host plants compared to the mandarin alone. In contrast, passion fruit plant volatiles facilitated host location by psyllids, which found mandarin seedlings faster than when exposed to mandarin alone. The association with coffee volatiles did not alter the attractiveness of mandarin to the Asian citrus psyllid. Survival and half-lethal time (LT50) of D. citri fed on non-host plants were longer than those insects with water only, but shorter than those fed on mandarin. Among the non-host plants, D. citri performed better in coffee, followed by avocado and passion fruit plants. Our results indicate that the association of mandarin with avocado plant can be beneficial for Asian citrus psyllid management.

Synergism of Adjuvants Mixed With Spinetoram for the Management of Bean Flower Thrips, Megalurothrips usitatus (Thysanoptera: Thripidae) in Cowpeas

The bean flower thrips, Megalurothrips usitatus (Bagnall) is an economically important insect pest of cowpea, Vigna unguiculata (L.) Walp in south China. Spinetoram is a newly available commercial active ingredient in the spinosyn mode of action group of insecticides that has been recommended for thrips management in China. In this study, the toxicity and efficacy of spinetoram for controlling M. usitatus were evaluated and compared to six other conventional insecticides. In addition, the synergistic effects of adjuvants (Silwet 806, Silwet 618, AgroSpred 910, and AgroSpred Prime) mixed with spinetoram for thrips control on cowpea were evaluated in both the laboratory and the field. Results of this study showed that spinetoram had higher toxicity and field efficacy of M. usitatus than other tested insecticides. A significant increase in efficacy was observed when spinetoram was applied at a recommended rate of 0.67 ml/L, mixed with Silwets (806 and 618) at the rate of 0.5 ml/L. Reductions of 50% and 40% in thrips infestation in the field over treatments without adjuvants were observed 3- and 7-days posttreatments, respectively. However, no significant reduction of M. usitatus was recorded when spinetoram was mixed with AgroSpreds (910 and Prime). Furthermore, no significant differences were found in thrips infestation between spinetoram sprayed alone at the rate of 0.67 ml/L and a reduced rate of spinetoram (0.45 ml/L) mixed with Silwets (806 and 618). The current research shows that Silwets mixed with spinetoram has a synergistic effect in the management of thrips.

Silencing of V-ATPase-E gene causes midgut apoptosis of Diaphorina citri and affects its acquisition of Huanglongbing pathogen

The Asian citrus psyllid, Diaphorina citri Kuwayama, is among the most important pests of citrus. It is the main vector of the Huanglongbing (HLB) pathogen Candidatus Liberibacter asiaticus (CLas), which causes severe losses in citrus crops. Control of D. citri is therefore of paramount importance to reduce the spread of HLB. In this regard, using RNA interference (RNAi) to silence target genes is a useful strategy to control psyllids. In this study, using RNAi, we examined the biological functions of the V-ATPase subunit E (V-ATP-E) gene of D. citri, including its effect on acquisition of CLas. The amino acid sequence of V-ATP-E from D. citri had high homology with proteins from other insects. V-ATP-E was expressed at all D. citri life stages analyzed, and the expression level in mature adults was higher than that of teneral adults. Silencing of V-ATP-E resulted in a significant increase in mortality, reduced body weight, and induced cell apoptosis of the D. citri midgut. The reduced expression of V-ATP-E was indicated to inhibit CLas passing through the midgut and into the hemolymph, leading to a majority of CLas being confined to the midgut. In addition, double-stranded RNA of D. citri V-ATP-E was safe to non-target parasitic wasps. These results suggest that V-ATP-E is an effective RNAi target that can be used in D. citri control to block CLas infection.

Screening and Identification of Indigenous Entomopathogenic Fungal Isolates from Agricultural Farmland Soils in Nile Delta, Egypt

The compound negative impact of insect pests attacking agricultural ecosystems includes (i) direct yield losses from damaged crops, (ii) the economic cost of the attempt to prevent these losses and (iii) the negative short- and long-term hazard effects of chemical pesticides on human and environmental health. Entomopathogenic fungi (EMPF) are a group of microorganisms that represent the natural enemies of a number of crop pests, presenting an opportunity to harness their evolutionary fine-tuned relationship with their insect hosts as biocontrol agents in integrated pest management programs. The aim of this study was to establish an indigenous EMPF collection via the Galleria mellonella (greater wax moth) entrapment method from the soils of Nile Delta, Egypt. Obtained insect associated fungal isolates were bio-assayed for pathogenicity against the serious pest Spodoptera litura and Tenebrio molitor, and the seven outperforming isolates were selected for molecular identification and thermotolerance assay. Based on ITS sequence analysis and phylogeny, selected isolates were identified as Beauveria bassiana (four isolates), Metarhizium anisopliae (two isolates) and one isolate of Cordyceps javanica. The obtained results demonstrated (i) the efficacy of using insect baiting coupled with molecular identification and pathogenicity screening to isolate EMPF to control insect pests, and (ii) the availability of indigenous virulent EMPF in Nile Delta's soil, which can be exploited for the development of sustainable crop protection strategies.