|Duval, B - Northern Arizona University|
|Whitford, W - New Mexico State University|
Submitted to: Ecological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2008
Publication Date: 2/1/2008
Citation: Duval, B.D., Whitford, W.G. 2008. Resource regulation by a twig-girdling beetle has implications for desertification. Ecological Entomology. 33:161-166.
Interpretive Summary: Many deserts around the world have experienced an increase in woody species, or brush, in the past century. The reasons for these increases are often seen as a reduction in the occurrence of fire due to fire suppression, overgrazing, and prolong drought in many regions of the world. In the southwestern U.S. many areas have seen an increase in the common shrub, honey mesquite, for many of these same reasons. The purpose of this study was to examine the importance of one other factor, insect damage, as a contributing factor to shrub increases in southern New Mexico. This study examined mesquite responses to bark damage by the twig girdling beetle. This native beetle chews strips from mesquite stems and kills the stem above the girdle. The beetle deposits eggs in the area of the girdle as part of its natural reproductive cycle. This study concluded that girdling by this beetle increases stem density of mesquite below the girdle as a plant response to the insect damage. This response increases the ability of the mesquite to capture blowing sand, and increases the suitability of a site to further support more shrubs. This is an example of a native insect contributing to changes in plants and landscapes over time.
Technical Abstract: 1. Resource regulation by insects is the phenomenon by which herbivory enhances resources for the progeny of the herbivore. This report provides an example of resource regulation with implications for desertification in the Chihuahuan Desert of North America. 2. Female Oncideres rhodosticta beetles chew girdles around mesquite (Prosopis glandulosa ) stems before ovipositing in those stems. The mesquite plants respond by producing compensatory stems below the girdle. Mesquite volume was significantly correlated with the total number of beetle girdles across a suite of low shrub density grassland and high shrub density dune sites, and plants in dune sites had more old and new girdles than mesquite in grasslands. 3. Smaller, younger shrubs in grassland responded more vigorously to girdling than did larger, older shrubs in dune landscapes. Stems on shrubs within grassland produced significantly more and longer compensatory stems per girdle than stems on shrubs in dunes. Soil capture by individual plants positively correlated with stem density, and stem density is increasing in the younger plants as a response to beetle damage. 4. This study suggests that the interaction between O. rhodosticta and mesquite is an example of resource regulation that increases the stem density and soil capture ability of mesquite. Because the conversion of productive grasslands to mesquite dune landscapes is one of the most important drivers of desertification in the Chihuahuan Desert, feedbacks between organisms that promote an increase in the size and soil capture ability of mesquite may exacerbate desertification.