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pH level test comparison

Figure on a white background with four rows. At left, the middle two rows begin each with a label and a mealybug specimen, "Paracoccus marginatus" in the second row and "Nipaecoccus viridis" in the third row. Following each mealybug, from left to right, are four small, clear dishes labled A-D in the Paracoccus marginatus row and E-F in the Nipaecoccus viridis row. All dishes have a small horizontal strip in the middle. In the A ane E dishes, labled "KOH (pH=14)," the strip is red; in B and F, labled "HCL (pH=1)," yellow; in C and G, labled "NaOH (pH=14)," pale pink; and in D and H, labled "water (pH=7)," light blue. The top row shows a closeup inset box from each dish in the Paracoccus marginatus row; in all four insets are dark, blotchy smudges, mainly black and white in color. The bottom row shows a closeup inset box from each dish in the Nipaecoccus viridis row; the insets for E and G dishes (pH=14) show green smudges, while the insets for F and H dishes show dark brownish or reddish smudges.

A color test of Nipaecoccus viridis and Paracoccus marginatus in chemical solutions with different acid/base (pH) levels revealed that a high pH of 14, not potassium specifically, is the driver in turning N. viridis hemolymph green—enabling the development of a field diagnostic test using a safer chemical solution, sodium hydroxide (NaOH) with a similar pH. (Image originally published in Ahmed et al 2023, Journal of Applied Entomology)

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