The white liquid/honeydew looking thing called white beads in red betel plant is mostly a secretion by plants and does not cause any harm to the plant. This white bead has sugar content which attracts fungus and then turns white beads to black powdery stuff. This also doesn't harm plants as it happens in general. But some studies say that it can block the photosynthesis process. Anyways, to get rid of this, you don't need to apply any insecticide. Just wash the leaves. I some other cases, honeydews are caused by either by Aphid or similar insects. For this you need to treat for Aphids. But in case of betel leaf, it's mostly released by the plant itself. Follow me on Instagram: / nimmi_doodle