Opuntia Pests: (hopefully) a dying memory

By Michael J. Green

In the last Open Gates a “new”, at least to me, pest was supposed to be proposed for this month’s installment. Chelinidea vittiger was suggested as the identity of an insect I found on Ferocactus. Identifying this pest was difficult, researching it was worse due to the scarcity of information. Since the Chelinidea is more typically a pest of Opuntia, I have expanded this month’s “Pest” to include a more generalized “Opuntia Pests: (hopefully) a dying memory”.

Mealybug and scale are known to infest Opuntias. The Florida Entomologist, December 2001 issue, contained an article entitled “PRICKLY PEAR CACTI PESTS AND THEIR CONTROL IN MEXICO” which listed 12 species not including mealybug. A Spanish language only Argentinean website listed 6 additional pests. (http://www.colpos.mx/entomologia/plagas4.htm) Internet searches found 3 more, so far. Correlating common names and scientific names with insects is worse than with plants. Several of the published, named species apparently aren’t correct / current under either the common or scientific name.

The infesting army includes:

Metamasius spinolae (Opuntia Borer)

Cylindrocopturus biradiatus (Spine Borer)

Chelinidea tabulatus (Gray Chinch Bug)

Hesperolabops gelastops (Red Chinch Bug)

Melitara nephelepasa (Zebra Worm)

Laniifera cyclades (White Grub)

Diabrotica sp. (Wireworms)

Phyllophaga sp. (Blind June Beetle)

Dactylopius indicus (one of the Cochineal Insects aka scale)

Neohydatothrips opuntie (Opuntia Thrips)

Moneilema variolaris (Cactus Longhorn Beetle)

Cryptomphalus asperses (Brown Garden Snail)

Platynota n sp. (moth)

Dactylopius opuntiae (scale)

Hyperaspis trifurcate (ladybird beetle)

Laetillia species (protozoan larva)

Bacha species (flies)

All is not eaten, yet. According to the “Mexican” article, these insects seem to prefer just 6 species: Opuntia megacantha, Opuntia tomentosa, Opuntia ficus-indica, Opuntia robusta, Opuntia streptacantha, and Opuntia stenopetala. But that is just prefer; they will probably eat any Opuntia unfortunate enough to be in the dining hall.

In the home of nopales (Mexico), control methods are much different than in California. With California’s protective environmental attitudes, most pesticides see very limited use and then only by “professional” applicators. Cultural and biological controls are generally always preferred over chemical methods just about everywhere they are practical. Most of the pesticide information contained herein is applicable to Mexico or other non-California areas.

Cultural control measures for the Metamasius spinolae include the extraction of the larvae from the damaged areas of the pads using horticultural knives. Slow-moving adults are hand removed from the surface of the pads from May through September. Chemical insecticides used to control this pest include azinphosmethyl, endosulfan, malathion, and folidol.

Another cultural measure universally available is just disposing of the plant. Biological controls are also used. For the Zebra worm (Melitara (now Olycella) nephelepasa), two parasites are used in the Valley of Mexico. One is a tachinid fly (Phorocera texana) that attacks the mature larvae and kills them after they transform to pupae. The other parasitoid is a braconid wasp (Apanteles mimoristae) that attacks the younger larvae. Carbaryl (aka Sevin) and endrin are chemical insecticides for the Zebra Worm and are applied during January.

For those that enjoy the cactus jellys, salads, salsas etc. be aware that White Grub (Laniifera cyclades) larvae throw their feces out of the openings that they make in the pads. Opuntia growers use these holes and visual traces of feces to find and mechanically destroy the larvae (imagine hand held portable smashers?). The same pesticides used against the opuntia borer (Metamasius spinolae) are also used for white grub.

The insecticides carbofuran, chlordane, diazinon, fonofos, heptachlor, and trichlorfon are applied against both the Wireworms(Diabrotica sp.) and Blind June Beetle(Phyllophaga sp) among others. None are California legal.

In Mexico, the only listed biological controls used for scale is the Chilocorus cacti or Twice Stabbed Ladybug. One of the photos shows a Chilocorus voraciously devouring the available Dactylopius varieties. Mexican growers use malathion, methyl parathion, and trichlorfon to kill scale also. Malathion is still readily available in California (last month’s scale article has more).

According to the article, the other pests listed above are destroyed there with (hopefully, judicious applications of) malathion, ethyl parathion, methyl parathion, heptachlor and endrin. Again, for home use, only malathion is California approved.

Another Opuntia pest is the four species of the “Cactus Coreid”, genus Chelinidea. They seem to like Opuntia where ever and however found. The two most common are the C. vittiger and C. tabulatus. They have also been exported to several countries where Opuntia was considered a weed to act as a biological control, but were considered ineffective at destroying the invasive Opuntias. The California Department of Pesticide Regulation does not list Chelinidea as a pest. Of the pesticides listed earlier, California would only allow malathion. However, other systemics such as imidriclopid should also work.

A major geopolitical issue is developing wherein the Cactoblastis cactorum moth is destroying ever growing areas of Opuntia. Originally a South American moth, it was exported to Australia in the 1800’s, then to the West Indies in 1957 to control / eliminate Opuntia itself. Now it is in Florida and Georgia and working its way west. Mexico is desperately trying to stop it as it encroaches on Opuntias being used as a breeding host for the Cochineal scale (Dactylopius sp.) which produces a multi-million dollar dye component, red carminic acid. For more info, see this site:

http://www.desertmuseum.org/invaders/invaders_cactusmoth.htm

Research into control methods is being conducted, looking at chemical, biological and sterile insect techniques (SIT).

Control by available insecticides MAY be appropriate in nursery and small landscape settings, but not in widespread landscapes or agriculture. Specific Biological Control agents (predators) have not been identified and study is continuing.

The song is deafening, but the Cacama valvata aka Cactus dodger does little, if any, injury while feeding on plants. Adults can cause injury when they insert eggs into twigs, producing splintering wounds. Cacama’s are part of the cicada family.

Another pest for this month was the one found on my Ferocactus in the nymph stage, but was not the initial specie identified. The Narnia snowii, and it’s seven genus siblings coachellea, femorata, inornata, marquezi, pallidicornis and wilsoni, typically prefer Platyopuntia and Cylindropuntia species for feasting. Obviously, they are not overly picky eaters. The genus was Not named for the magical land in C.S. Lewis' books; the name was published by Stâl in 1862 before C.S. Lewis was born.

And then there are the thrips. Several species are cited for cactus: Frankliniella fusca, Heliothrips haemorrhoidalis, Rhopalothrips bicolor, and Scopaeothrips bicolor. Narrow-range oil, azadirachtin, neem oil, pyrethrins combined with piperonyl butoxide and insecticidal soaps, can be temporarily effective for thrips if applied when thrips are present and damage first appears. The most effective insecticides against this pest were found to be spinosad and imidacloprid. Licensed pesticide applicators can use abamectin (Avid) which is derived from beneficial microbes and has low to moderate adverse impact on natural enemies. Biological controls have not been proven yet.

In addition to the insects, there are also virus and disease vectors that are beyond the scope of this article. Following are pictures of a number of the pests with “searchable” names.