|Deloach Jr, Culver|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/24/2007
Publication Date: N/A
Technical Abstract: Biological control of saltcedar (Tamarix spp.) has involved releases of exotic saltcedar leaf beetles, Diorhabda elongata Brullé sensu lato, in the western U.S. Adults in field cages feed, oviposit, and produce larvae on athel (Tamarix aphylla), an evergreen tree used in the southwestern U.S. and northern Mexico for shade and as a windbreak. The ability of two ecotypes of D. elongata expected to be suitable for release in South and central Texas to alight, oviposit, and produce larvae on athel was investigated in the field. Saltcedar beetles from Crete and Tunisia confined on bagged branches for two weeks produced 30–45% as many egg masses, and 40–60% as many larvae, on athel as on saltcedar. Adults and larvae of a hybrid Tunisia x Crete beetle line were released at a field site near Kingsville, TX., onto mature saltcedar bushes adjacent to 4-year-old planted athel saplings. Two weeks after release, egg mass, larval and adult densities, while low on all plants (approximately 1 egg mass, larva, and adult per m green foliage length) were 10-fold higher or more on both the saltcedar beetle release trees, and on neighboring saltcedar bushes, than on athel saplings. Damage caused by the beetles was 2–10-fold greater on saltcedar than on athel in the first eight weeks. However, Tunisia x Crete beetles did not establish on saltcedar at the Kingsville site in 2006, similar to prior failures in 2004-2005 with pure Crete beetles. At a site on Higgins Ranch/Beals Creek, near Big Spring, TX, which contained an established, defoliating beetle population, egg mass and 1st and 2nd instar larval densities were 3–8 fold higher on potted saltcedar grouped with potted athel than on athel alone in 2006. At two sites in South Texas containing mature athel trees and no saltcedar (Encino and Sarita, TX), Crete beetles released from bagged branches failed to establish, while hybrid Tunisia x Crete adults established on 1 of 8 trees onto which they were released, and small numbers (2-5) of adults were found on this one tree in October and December of 2006 and February of 2007. Aside from light (10-15% estimated leaf area), transient damage to a few branches, saltcedar beetles had no negative impacts on these athel trees. Formerly-bagged, defoliated athel, and saltcedar branches at all South Texas sites recovered 60-80% of their visually-estimated green leaf material. Overall saltcedar foliage quality declined by 50%-60% at the Kingsville site in 2006, due mostly to damage by adventive Opsius stactogalus leafhoppers and Chionapsis etrusca scales. O. stactogalus densities were significantly higher on saltcedar than on athel. Leafhoppers may have attracted assassin bug predators (Zelus spp and Sinea spp.), which were observed feeding on D. elongata adults and larvae on 12 occasions in 2006. The results suggest that episodic damage to athel will occur during biological control of adjacent saltcedar. However, D. elongata beetles are not likely to establish independent, damaging populations on athel. Competitive herbivory and predation are key obstacles to D. elongata establishment on saltcedar in South Texas; releasing beetles as early as possible in the field season may avoid these obstacles.