Very few pests bother prickly pear cactus in our area, and many landscapes are graced with these large, beautifully abstract plants. In fact, there are so many Opuntia species that this plant group can make you a collector in no time. Pad size, color, and spines can vary so much that each prickly pear becomes a living work of art. But just like many things in the landscape, there is an occasional pest that comes out of left field – you do not see it coming! Imagine a caterpillar that secretly bores into the cactus, and as a group hollow it out. Not overly widespread, but it is in our area and prickly pear cactus are specifically on the menu. I really should have titled this article “Cactoblastis in My Cactus” as it is my personal Opuntia cactus that was infested. Let’s take a closer look at this messy pest.
Cactoblastis cactorum, a cactus moth, is originally from several countries in South America. This cactus moth was first recognized as a biological control for prickly pear cactus in Australia where it had originally been planted as cattle fodder but got out of control. Cactoblastis cactorum was also used in other sites around the world as a biological control but has spread and become invasive in various locations including Florida. In places such as Florida, there are also native endangered species of Opuntia that are at risk to this insect pest. As it potentially moves north and west of Florida, the risk could continue. While in its native home there are various natural predators and parasites for suppression, this cactus moth has few natural controls here. The concern continues not only for native Opuntia, but also for commercial operations in the western USA and south into Mexico.
So, what should we look for here? The adult is a small non-descript, grayish-brown, moth – you wouldn’t give it a second glance. The female lays a stack of eggs on the tips of spines eventually forming an “egg-stick”. The caterpillars emerge and bore into the prickly-pear cactus pads. The caterpillars are about one inch long at maturity and are uniquely pigmented being orange red in color with bands of dark spots. These caterpillars hollow-out the pads pushing frass out through bore holes. The pads become discolored and eventually either rot or remain as empty, chewed up husks. The mature larvae emerge from the pads and pupate in nearby protected areas.
What can you do once you have discovered an infestation? Chemical control is difficult at best and is in general impractical. There may be some beneficial natural enemies that could offer a degree of suppression, but don’t count on it. Perhaps the most practical and immediate technique is hand-picking. Remove the infested pads, cut them open and destroy the individual caterpillars – essentially surgically amputating a couple of pads. The sacrifice of a few pads removes the problem – full stop. Hopefully, you caught the infestation early enough that the whole cactus is not ruined. Moving forward, just monitor often for any change in the appearance of the Opuntia pads.
If you have a prickly pear cactus you may want to keep a look out for this cryptic insect. Knowledge is power in this case and mechanical control was a method that worked for me. We may not immediately win the war on Cactoblastis, but we can win a battle or two for now. For more information on all types of insect pests in our area – and how to control them – or to ask a question, please visit https://www.facebook.com/CharlotteCountyExtension. You can also call the Master Gardener Volunteer Helpdesk on Mondays, Wednesdays, and Fridays from 1 to 4 pm at 764-4340 for gardening help and insight into their role as an Extension volunteer. Ralph E. Mitchell is the Director/Horticulture Agent for UF/IFAS Extension Charlotte County. He can be reached at 941-764-4344 or ralph.mitchell@charlottecountyfl.gov. Connect with us on social media. Like us on Facebook @CharlotteCountyExtension and follow us on Instagram @ifascharco.
Resources:
Habeck, D. H., Bennett, F. D. & Miller, C. (2016) Cactus Moth, Cactoblastis cactorum (Berg) (Insecta: Lepidoptera: Pyralidae). The University of Florida, IFAS.
Cactoblastis cactorum (2026) https://en.wikipedia.org/wiki/Cactoblastis_cactorum.
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