Biology of Diorhabda elongata deserticola (Coleoptera: Chrysomelidae), an Asian leaf beetle for biological control of saltcedars (Tamarix spp.) in the United States

Adults and larvae of Diorhabda elongata Brulle subspecies deserticola Chen feed on the foliage of saltcedars (Tamarix spp.). All three instars are black, the 2nd with an indistinct, and the 3rd with a distinct yellowish lateral stripe; full-grown larvae reach ca. 9 mm in length and pupate in cells in litter on the ground or a few cm below the soil surface. Adults are yellowish with two dark brown stripes on each elytron. Duration of the egg averaged 5 days, 1st instar 4.9 days, 2nd instar 4.8 days, 3rd instar 7.4 days, prepupa 4.8 days, and pupa 7.1 days at 24.1 degreesC. Preoviposition averaged 3.9 days and an average female oviposited over a 12-day period and laid 194 eggs. Degree-day accumulations for development were 234.2 for the three larval instars and 91.3 for the pupa above a developmental threshold of 12.5degreesC. Net reproductive rate (R-0) in the laboratory at 28.6degreesC and on the best Tamarix accession was calculated at 88, generation time at 37 days, and innate capacity of increase (r(m)) at 0.112, giving a population doubling time of 6.2 days. In field cages in Colorado, Wyoming, Utah, Nevada, and California, overwintering adults emerged from late April to early May. Adults of the first generation emerged in early to mid-July, and 2nd generation adults emerged from mid-August to early September and overwintered. High populations of larvae developing in field cages caused defoliation, dieback, and sometimes death of the Tamarty trees. At the three study sites in Texas, maximum daylength was 14h 21 min and larvae exposed to these conditions produced adults in reproductive diapause early in the season and subsequently failed to overwinter. North of 38degrees latitude in the United States, populations of D. e. deserticola originating from Fukang, China and Chilik, Kazakhstan are active throughout the growing season, successfully overwinter, and are potentially a highly effective control agent for saltcedar. Published by Elsevier Science (USA).