Assessment of risk to native Frankenia shrubs from an Asian leaf beetle, Diorhabda elongata deserticola (Coleoptera: Chrysomelidae), introduced for biological control of saltcedars (Tamarix spp.) in the western United States

Exotic saltcedars, Tamarix spp. (Tamaricaceae: Tamaricales) from Central Asia and the Mediterranean area, have invaded much of the western United States, where they degrade natural riparian areas, reduce water supplies, and interfere with agriculture and recreation. The major taxa are Tamarix ramosissima Ledeb., Tamarix chinensis Lour., and hybrids with these and Tamarix canariensis Willd. throughout much of the West, and Tamarix parviflora DC. in parts of California. The biology and host range of the leaf beetle, Diorhabda elongata Brullé subspecies deserticola Chen from Central Asia, indicate that it is a safe and potentially effective biological control agent. Here we report that species of the somewhat related native North American shrubs, Frankenia spp. (Frankeniaceae: Tamaricales), appear to be at little risk from the introduction of Diorhabda elongata deserticola. In laboratory, greenhouse, and outdoor cages at Temple, Texas and Albany, California, 0–27% of larvae were able to complete their development on four North American species of Frankenia compared to 53–56% on Tamarix host species, depending on the species tested and the growing conditions of the plants. However, adults were not attracted to, did not feed upon, and rarely laid eggs on Frankenia spp. Forced closer contact with Frankenia in smaller cages and even removing all Tamarix host plants did not increase adult selection of Frankenia plants nor oviposition on them. Adults from larvae reared on Frankenia did not show adaptation to nor increased utilization of the plant, compared to those reared on Tamarix. D. e. deserticola, therefore, appears sufficiently host-specific for field release in North America.