Comparison of electropenetrography waveform libraries for Nipaecoccus viridis (Hemiptera: Pseudococcidae) using...

The hibiscus mealybug, Nipaecoccus viridis (Newstead) is a phloem-feeding pest that was first documented in Florida citrus orchards in 2019. Feeding causes fruit and leaf deformation due to cellular changes in host plant tissues. Field assays suggest that systemic insecticides can disrupt the probing behavior of this phloem feeder. However, the mechanisms involved are poorly understood. The objective of this study was to investigate the feeding interactions of second-third instar N. viridis on Volkamer lemon trees (Citrus volkameriana) using AC-DC Electropenetrography. Since preliminary recordings failed to distinguish phloem salivation from phloem ingestion waveforms, the effects of 3 tethering materials to improve waveform resolution were tested: thick gold wire (25 µm diameter), fine gold wire (12.5 µm diameter), and Wollaston platinum wire (2.5 µm diameter). In addition, a combination of 3 different input resistances (Ri) (amplifier sensitivities) and substrate voltages; 109 Ω with 250 mV; 1010 Ω with 100 mV; and 1013 Ω with 0 mV were compared to create a waveform library. The best-quality signal was obtained with the thick gold wire (25 µm diameter) at Ri 1010 Ω using the loop method of wiring. Wollaston platinum wire impeded nymphal movement, causing increased nonprobing duration and increased time from the start of the recording to the first phloem salivation. Biological interpretations of waveforms are discussed in light of fruit and leaf distortion. Results from this study will allow future work to compare effectiveness of insecticides to prevent such damage.