INSECT PESTS OF CACTI AND SUCCULENTS:  XERISCAPE AND NATIVE PLANTS IN TEXAS

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Cacti, succulents and other native plants that require little moisture make excellent landscape ornamentals (Appendix 1). They are generally thought of as low-maintenance plants because few have had insect pests that commonly attack them. However, certain species and varieties can be pest prone in certain Texas landscapes. When considering planting succulents, examine nearby similar plants for pests. If pests are obvious or plants look unsightly, the pests will likely move to new host plants planted nearby. Even if they are pest-free, however, new pests can

arrive over time. One exotic pest,  the cactus moth, Cactoblastis cactorium, is expected to spread into Texas from the southeastern U. S. When established, this pest will further complicate growing cacti as landscape plants.

Many insects can be observed on succulents that do not harm the plants. Beetles, bees and wasps frequent open flowers and help pollinate plants. Occasionally, small bagworms can be observed on agave, but these likely wandered off of their host plant and may not be feeding. Sharpshooters (Cicadellidae) often occur on agave or Century plants, although they do not appear to cause plant damage. Spiders  nest among the cactus pads and use the plants’ structure to anchor their webs. Some insects, however, utilize succulent plants for food. They use their mouthparts and saliva to damage plants. Understanding how they feed can help diagnose pest problems even when the insects are not present. 

Sucking insects have long, slender mouthparts they insert into plant tissue like a hypodermic needle. They suck out plant sap and inject saliva that further digests plant tissue. Symptoms include spotting and discolored blotching of the leaf surface or cactus pads (Note: the spines on cacti are the leaves). Several species of true bugs (Hemiptera) commonly infest landscape prickly pear cactus, including "leaf-footed" bugs (Hemiptera: Coreidae): 1) Leptoglossis species (Fig. 1); 2) Narnia species (Fig. 2) which look similar to Leptoglossis but lack the widened leg segment (tarsus) on the hind legs of adults. Narnia are common in western Texas on prickly pear fruit; and, 3) Chelinidae vittiger (Fig. 3) have antennae that are triangular in cross section and are common on prickly pear in central Texas.

Adult "leaf-footed" bugs are about 3/4-inch long and tan-colored. Only adult stages have fully-developed wings and can fly to nearby hosts. The winter months are spent as adults that hide among plant debris or in cracks and crevices. There are several generations per year. Young (nymphs) aggregate and feed together as they develop through stages (instars). Both nymphal developmental stages and adults can produce large (1/4 to 1/2-inch diameter) pale blotches on cactus pads and.

Another true bug, Hesperolabops gelastop (Fig. 4), may also be present. Adults are small, fast-moving bugs with reddish heads, gray-colored wings with white stripes along the sides. The eyes look like they are on projections or stalks on each side of the head. Blotches caused by their feeding are smaller than those of the other sucking insects mentioned.

On yucca, particularly"soft yucca," there are several species of the true bug  Haticotoma (Hemiptera: Miridae) in Texas (Fig. 5). Adults are small (less than 1/4 -inch), oval shaped when viewed from the top but flattened. The head and segment behind the head (pronotum) is reddish and the wings are gray-black. They can be found in groups (aggregates) on the upper leaf surface and move rapidly when disturbed. Immature stages, lacking fully-developed wings, can also be present. Like other true bugs, their feeding produces small pale spots or blotches on leaf surfaces where the green chlorophyll has been removed.

Texas sage in the landscape can be damaged by the lantana lace bug, Teleonemia scrupulosa (Tingidae) (Fig. 6). Damaged leaves appear speckled with pale (chlorotic) spots. Adult and developing stages reside on the under surface of leaves and leave dark fecal specs. Adults are less than 1/4 -inch long, brown and have fully-developed wings while immature stages (nymphs) have spines projecting from their bodies. Heavily-infested shrubs may be defoliated and in declining health.

Scale insects have six legs and appear insect-like only in the"crawler" stage that hatches from the egg. It is the crawler stage that spreads the infestation to the new growth and nearby host plants by"hitching a ride" of animals like birds or on peoples’ clothing - or even by being blown by the wind! Once they settle down, they insert their sucking mouthparts and begin feeding. They generally no longer move and slowly develop to the adult stage. In some species, winged six-legged male stages emerge to mate with females.

Several species of scale insects commonly infest prickly pear cacti. The most famous is the cochineal scale, Dactylopius coccus (Fig. 7). This scale was used by Native Americans to make a crimson dye that was used to paint missionary buildings, particularly in the San Antonio area, and exported by early settlers (Drees and Jackman 1998). Cochineal scales are coated by white wax filament that can make cacti look unsightly. When crushed, a red-colored fluid exudes from their bodies."Oyster shell" or"nipple" scales (Fig. 8) are armored scales (Hemiptera: Diaspididae). Adult females appear as round or oval white spots with raised areas on or off the centers. Males can be elongate and white. Their presence is unsightly and high numbers can cause plant stress. Even when killed, however, dead scales will remain on the cactus pads. 

Chewing insects have mouthparts that physically remove tissue from their host plant. Native to Texas are several"long-horned" beetles (Cerambycidae) that feed on pads of prickly pear cactus. Damaged pads appear ragged and irregular in shape. Adults of the most common Texas species,  Moneilema probably armatum, are flightless, large (about 1-inch long) and black (Fig. 9).  It has spines on the first segment behind the head (the pronotum). A mottled species from the sand dunes in the Rio Grande Valley is M. blapsides.

The agave or Sisal weevil, Scyphophorus acupunctatus (Curculionidae) (Fig. 10), can kill landscape yucca and agave (Bogran and Ludwig 2006). Although native to the southwest, it has been introduced into the plant trade and shipped to locations out of its native range to Hawaii, Australia, east Africa and throughout Texas. Adults are solid black, about an -inch long, and have the"snout" typical of weevils. Adults can be found at certain times of the year and feed on leaves and stems. Females bore tunnels into the plants in which they lay eggs. The larvae, or grubs, (Fig. 11) bore into the base of the plant and feed on the roots and crown before leaving the plant to pupate. Larval infestations are associated with bacterial plant diseases (pathogens) such as Erwinia sp., that are carried by the insect. Infested plants die from the bottom up, with the lowest leaves turning brown and dying and dead leaves progressing slowly up the plant so that the top leaves die last.

There are currently no species of moths or butterflies (Lepidoptera) known to be major pests of succulents. One may even be considered to be economically beneficial! In Mexico where Yucca tequilan plants are grown to make tequilla, a species of skipper butterfly, Aegiale hesperiatus, also called the Maguey-worm, feeds on this host plant. These caterpillars have traditionally been harvested and put in bottles of Mescal or Mezcal.

However, this situation may change dramatically over the years to come as the invading species, the cactus moth (Cactoblastis cactorium) (Fig. 12, 13 )found in Australia, South Africa, Dominican Republic, and Puerto Rico and recently found in Florida and Alabama migrates into Texas (see The Cactus Moth Detection and Monitoring Network (CMDMN). Caterpillar bodies have alternating bands of orange and black. They feed together while mining through cactus pads causing blotchy areas filled with excrement. If suspected specimens are observed, please notify your local County Extension office or Department of Agriculture official.

Management

While selecting new succulent plants for the landscape, inspect them carefully for insects or insect damage. Pests can often be transplanted to areas outside of their normal range by hitching a ride on or in host plants. Keep an eye on newly planted succulents over the first two years for pests such as agave weevils which can be internal and slower to develop.

Practice proper horticultural methods to keep landscape plants healthy. Any plant grown under conditions unsuitable to plant health can become vulnerable to pests such as insects or diseases. Over-watering and improper soil or soil conditions can contribute to plant stress. Monitor plants regularly and inspect them for signs of pest damage. Larger landscape plantings of cacti or yucca have a higher probability of infestation over time. Once an infestation begins, eliminating it totally can be challenging. Smaller plantings or individual plants that have chronic pest problems can simply be removed and destroyed to eliminate the problem.

Insecticides are not an option for some insect pests of succulents. Certainly, they would be inappropriate for large native stands of cacti harboring long-horned beetles. Insecticides will not effectively eliminate Sisal weevil larvae inside infested plants and are only used to protect healthy ones. Furthermore, in areas with wide-spread infestations of scale insects or the mobile true bug species, insecticides only offer temporary suppression before the insects return from surrounding areas. Thus, either eliminating host plants, at least temporarily where feasible, or having more tolerance for insects in the landscape become sound options.

Although insecticide products may not specifically list cactus, yucca or succulents on the directions for use on the label, those listing"ornamental plants" or similar descriptor can be used in the landscape containing ingredients such as acephate, carbaryl, dimethoate, horticultural oil, insecticidal soap, dinotefuran, imidacloprid, or pyrethroids (bifenthrin, cypermethrin, fluvalinate, permethrin, lambda-cyhalothrin and others). Few, if any will list specific insect pests discussed herein, but may list "beetles," "bugs," "caterpillars" or "scale insects," which are more general terms for these pests. However, whenever using a new insecticide product for the first time, spray only a few plants or a part of a larger plant to make sure the insecticide is not itself toxic to the plant causing symptoms of phytotoxicity that include burned edges or tips of leaves and growing points. Few result demonstrations have been conducted to demonstrate"best practices" for insecticidal use on Texas landscape succulents. Thus, the Texas AgriLife Extension Service can not ensure the effects or effectiveness of any treatments applied.

Systemic insecticide products, such as those containing dinotefuran or imidacloprid, can be applied prior to the seasonal occurrence of true bugs or crawler stages of scale insects (Hemiptera) to help reduce damage caused by high numbers of these pests See publication L-5479, "Florida Wax Scales: Control Measures in Texas for Hollies" at the Texas AgriLife Extension Service bookstore.

Acknowledgments

The author wishes to thank Joseph C. Schaffner with assistance in identifying the Hemiptera and Marlin E. Rice for providing information about Cerambycidae. Review comments from Elizabeth "Wizzie" Brown, Kim Schofiled, Carlos Bogran and Laura Nelson are much appreciated.

Literature Cited

anon. Best of Texas Landscape Guide. Texas Nursery and Landscape Association, 7730 South IH-35, Austin, Texas 78745-6698, 97 pp.

Bogran, C. And S. Ludwig. 2006. The agave weevil, a pest of ornamental yucca and agave. TNLA Green Magazine8(7):42.

Drees, B. M., and J. A. Jackman. 1998. A Field Guide to Common Texas Insects. Gulf Publishers, Houston, Texas. 359 pp.

Linsley,  E. G. and J. A. Chemsak. 1984. The Cerambycidae of N. A., Part VII, No. 1. Univ. Calif. Publ. Ent. Vol. 102. (page 20)

Tull, D., and G. O. Miller. 1991. Texas Monthly Field Guide Series A Field Guide to Wildflowers, Trees, and Shrubs of Texas. Gulf Publishing Company, Houston, TX 344 pp.

Wasowski, S. And A. Wasowski. 1991. Native Texas Plants Landscaping Region by Region. Gulf Publishing Company, Houston, TX. 406 pp.

Appendix 1. Cacti and succulents native to Texas used in landscapes
 Best of Texas Landscape Guide List of Landscape WaterWise Xeriscape Plants
Red yucca, Hesperaloe parviflora
Texas mountain laurel, Sophora secundiflora
Adam’s needle yucca, Yucca filamentosa
Soft-tip yucca, Yucca gloriosa
Pendula yucca, Yucca recurviflora
Texas sage, Leucophylum frutescens

Native Texas Plants Landscaping List of Cacti
Prickly pear, Opuntia sp.
Wild variety in southern Texas, O. lindheimeri
Wild variety in Trans-Pecos and northern Texas, O. phaeacantha
"Cow-tongue" variety  
Purple prickly pear, O. violacea

Cacti, Agaves, Yuccas and Other Succulents (Tull and Miller 1991)
Cactaceae, Cactus family
Texas prickly pear, Opuntia lindheimeri, (some varieties spineless)
Agavaceae, Agave family (Agave, Century Plant, Agave Species)
Sotol, Dasylirion sp.
Red yucca, Hesperaloë parviflora
Yucca, Spanish dagger, Izote, Soyate, Yucca sp. (Soaptree yucca - Y. elata; Pale-leaf yucca - Y. pallida; Twisted-leaf yucca - Y. rupicola; Trecul yucca - Y. treculeana)
Century plant, Agave havardiana
Lechuguilla, Agave lecheguilla

Related

USDA Plant Pest Information - Cactus moth