Trichocereus as a Potential Nursery Crop in Southern Arizona, With Discussion of the Opuntia Borer (Cerambycidae: Moneilema gigas) as a Serious Threat to its Cultivation

Southern Arizona and southern California are economically competing regions with regard to production of ornamental cacti and succulents for sale throughout the United States. Economics of field -production vs greenhouse- production are discussed for both regions. Comparatively few cacti and succulents are field -produced in Arizona because few ornamental selections have been located which can economically be produced in the open considering the rigors of the desert environment. The Golden Torch Cactus (Trichocereus spachianus (Lem.) Ricc.) represents a promising nursery crop for field production in southern Arizona but has four seemingly unrelated problems. These problems are all shown to result from damage to Trichocereus by a single species of Cerambycid beetle, with damage to the cactus occurring throughout the life cycle of the beetle. Despite such an intimate relationship between beetle and Trichocereus, and although the beetle seems more destructive to Trichocereus than to native North American cacti, the beetle, far from proving to be an Argentinian introduction like Trichocereus, actually belongs to the genus of native Opuntia Borer (Moneilema), associated with Cholla and Prickly Pear in North America since the classic observations by Thomas Say on Major Long's 1819 -20 expedition to the Rocky Mountains. Although the present article is thought to be the first report of damage to Trichocereus by Moneilema, the degree to which we have found Trichocereus in Arizona to be infested suggests a rather long- standing condition. Specifically, we report Moneilema gigas LeConte to cause the following pathologic conditions in Trichocereus spachianus in Arizona: 1) bacterial and fungal rot of deep internal tissues, 2) external chewing disfiguration by adult beetles, 3) sporadic growth spurts making disfiguring constrictions of the stem, and 4) hollowing out of stems by boring larvae. Possible reasons for the virulence of Moneilema gigas in attacking Trichocereus are discussed. With the knowledge that four major problems associated with Trichocereus cultivation in Arizona actually result from infestation by a single beetle species, and with the possibility of controlling this insect pest, commercial field -production of the cactus in southern Arizona may finally prove economically rewarding.Desert Plants is published by The University of Arizona for the Boyce Thompson Southwestern Arboretum. For more information about this unique botanical journal, please email the College of Agriculture and Life Sciences Publications Office at pubs@cals.arizona.edu