Probing behavior of the corn leafhopper Dalbulus maidis on susceptible and resistant maize hybrids

DC-electrical penetration graph waveforms for Dalbulus maidis (Hemiptera: Cicadellidae) and the effects of entomopathogenic fungi on its probing behavior

The corn leafhopper Dalbulus maidis is an important transmitter of viruses and bacteria to maize plants. Data on the stylet probing and ingestion behavior of D. maidis, gathered using the DC-electrical penetration graph (DC-EPG) technique, are limited. The increasing prevalence of this pest and the diseases that it transmits in maize crops heighten the importance of studying how control tools affect the probing behavior of these insects, to reduce or prevent the chances of pathogen transmission and the damage from feeding. Our study recorded stylet activities of D. maidis, using a DC-EPG system and compared the appearances of waveforms with those from published AC and AC-DC EPG studies. All types of systems produced similar waveform appearances; therefore, we used the waveform nomenclature previously published. We also determined the effects of the entomopathogenic fungus Cordyceps javanica on the probing behavior of D. maidis at different time points after the fungus was applied by spraying. Forty-eight hours after the insects were sprayed, the effects were pronounced, with significant disruption of the stylet activities in phloem and non-phloem phases. Our study indicated that this commercial microbiological product, with the active ingredient C. javanica, can alter the probing behavior of D. maidis and may be helpful in management of the vector.

Knockdown of double-stranded RNases (dsRNases) enhances oral RNA interference (RNAi) in the corn leafhopper, Dalbulus maidis

The leafhopper Dalbulus maidis is a harmful pest that causes severe damage to corn crops. Conventional chemical pesticides have negative environmental impacts, emphasizing the need for alternative solutions. RNA interference (RNAi) is a more specific and environmentally friendly method for controlling pests and reducing the negative impacts of current pest management practices. Previous studies have shown that orally administered double-stranded RNA (dsRNA) is less effective than injection protocols in silencing genes. This study focuses on identifying and understanding the role of double-stranded ribonucleases (dsRNases) in limiting the efficiency of oral RNAi in D. maidis. Three dsRNases were identified and characterized, with Dmai-dsRNase-2 being highly expressed in the midgut and salivary glands. An ex vivo degradation assay revealed significant nuclease activity, resulting in high instability of dsRNA when exposed to tissue homogenates. Silencing Dmai-dsRNase-2 improved the insects' response to the dsRNA targeting the gene of interest, providing evidence of dsRNases involvement in oral RNAi efficiency. Therefore, administering both dsRNase-specific and target gene-specific-dsRNAs simultaneously is a promising approach to increase the efficiency of oral RNAi and should be considered in future control strategies.