Chelinidea vittiger are “true” bugs, belonging to the order Hemiptera, They have piercing / sucking mouthparts for drinking sap (phloem) and you will find them drilling the vulnerable parts of a wide variety of our outdoor cold hardy cacti: flower buds, new cholla growth, immature opuntia pads but also older pads and cactus parts. Don’t ignore them: in sufficient numbers, they will kill the cactus. On opuntia their feeding pattern leaves ugly circular blemishes on the pads (image at right). Cactus bug eggs are laid on cactus spines and are not easy to find.
Treatment: Insecticidal soaps or horticultural oils can work on nymphs, but the adults are tough to control. For a systemic treatment and prevention a product that contains the neonicotinoid imidacloprid works well as a foliar spray or soil drench. This will provide systemic control and some contact mortality. Do not apply to a plant before or during bloom as imidacloprid can move into the nectar and will harm pollinators! More information on imidacloprid may be found at this UCDavis Integrated Pest Management page on Imidacloprid . Acetamiprid (another neonicotinoid) can be applied as a foliar spray and more environmentally benign than imidacloprid. It is not labeled as a soil drench. You will also want to pluck off and kill any bugs that you see on the plants. Hunting them down can be extremely challenging and frustrating as cactus bugs, especially the adults, are wary and agile movers and are great at hiding in inaccessible parts of the plant and in plant litter. On spiny plants try using spoon-type barbecue tongs to grab, envelope and sweep them into something like a kitchen storage container where you can crush them. They give off a vile odor. If you know that cactus bugs are present on an individual but can’t find them, try giving the plant a light spray with water. The bugs will tend to crawl up to the top of the plant.