Cycad scales can reach astounding densities on the fronds of sago palms and other cycads.
Last week we visited the west coast of Florida to meet a charismatic colonist to our land, the Green Orchid bee. This week we meet another non-native, but this one is not so pleasant. The cycad scale, a native of Thailand, was first detected in Miami-Dade County in 1996 and has since spread throughout much of Florida. This insect is a member of the Sternorrhyncha gang, an ignoble group of sucking insects that includes aphids, whiteflies, psyllids, and several other scale insects, some of which we met in previous episodes.
What’s up with this sago palm? As we zoom in, we can see thousands of cycad scales lining the leaves. With so many scales destroying plant tissue, the cycad takes a beating and may not survive. Large roundish scales are females and smaller males have parallel sides. Notice small exit holes on several scale covers where tiny lethal parasitic wasps have emerged.
With populations of scales in the myriad thousands, the sago palm on the left may soon meet the fate of its partner on the right.
The dermis of the armored scale is covered with pores that exude a fine white wax which forms a protective cover over the soft body of the insect. This cover, also called a test, is circular or oblong in the female and parallel sided in the much smaller male. After mating, the female lays more than 100 eggs beneath her cover. Eggs hatch into tiny mobile nymphs called crawlers. Crawlers are the dispersal stage of the armored scale insect. They crawl to new areas of the plant before becoming sessile and settling down to feed. Crawlers can also disperse from plant to plant by becoming airborne and surfing the wind or by hitching a ride to a new plant on the foot of an unwitting avian accomplice. After hunkering down, the settled crawler will produce a waxy cover and probe the tissues of the cycad leaf with an elongated beak, bursting cells and removing nutritious cell contents. In the warmth of the Floridian sunshine, several generations are produced each year and tens of thousands of scales can be seen encrusting the fronds of cycads. Local predators and tiny parasitic wasps seem incapable of keeping up with the scale tsunami and after a few seasons cycads can succumb to this dastardly pest.
Tiny lady beetles in the genus Chilocorus consume cycad scales. For obvious reasons some go by the name of twice stabbed lady beetles. This one has a lot of eating ahead to make a dent in this scale infestation.
Thorough inspections of cycads, especially favored species like King and Queen Sago, will help pinpoint incipient damaging populations of this scale before they reach epic proportions. Well-timed applications of horticultural oils and other contact insecticides will help reduce populations, especially when applied to emerging crawlers. Systemic insecticides applied to foliage or soil have also been shown to dramatically reduce populations. If you see a cycad flocked with white, have a closer look and you may discover the cycad scale.
Acknowledgements
“Aulacaspis yasumatsui (Hemiptera: Sternosshyncha: Diaspidae), a scale insect pest of cycads recently introduced into Florida” by Forrest W. Howard, Avas Hamon, Michael McLaughlin, Thomas Weissling, and Si-Lin Yang; “Biological control agents of the cycad scale, Aulacaspis yasumatsui” by Ronald Cave; and “Cycad Aulacaspis Scale (Aulacaspis yasumatsui)” by Catharine Mannion, Adrian Hunsberger, Kim Gabel, Eileen Buss, and Lyle Buss, were consulted for this episode.
To learn more about cycad scale and its management, please visit the following website: https://trec.ifas.ufl.edu/mannion/pdfs/CycadScale.pdf