Huanglongbing (HLB) is a serious and devastating disease of citrus caused by Candidatus Liberibacter spp. and vectored by the Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Psyllidae). The disease has the potential to greatly limit the production of citrus in Florida and other citrus growing regions worldwide. Current control of ACP and HLB is inadequate, but identifying and incorporating traits from uncultivated Citrus spp. and Citrus relatives that confer resistance to ACP is a potential strategy to manage the disease. In a study by USDA-ARS, 87 genotypes primarily in the Rutaceae orange subfamily Aurantioideae, were assessed in the field in South Florida for resistance to natural populations of ACP. The majority of genotypes hosted all three life stages of ACP, however there were differences among genotypes in the mean ranks for eggs (F = 3.13, df = 86, P < 0.001), nymphs (F = 9.01, df = 86, P < 0.001), and adults (F = 4.21, df = 86, P < 0.001). Very low levels of ACP were found on two genotypes of Poncirus trifoliata, 'Simmon's trifoliate' and 'little-leaf'. Poncirus trifoliata, the trifoliate orange, readily forms hybrids with Citrus spp. and is commonly incorporated into rootstock varieties. The field experiment was followed by no-choice tests in which female ACP had the opportunity to lay eggs for six days on five genotypes of Poncirus trifoliata, three genotypes from the Citrus genera that were not represented in the field, and a control (Citrus macrophylla) to determine whether any genotypes were resistant to ACP. Numbers of eggs on the five genotypes of P. trifoliata (means between 7-60) were lower than on the control (mean = 281.3; .2= 59.5, P < 0.001), which indicates that genotypes of P. trifoliata show some resistance to ACP. Numbers of eggs laid on the three genotypes of Citrus (means 129-200) were not significantly lower than on the control (.2= 4.37, P = 0.23). An additional 107 genotypes, including 81 genotypes of P. trifoliata and trifoliate hybrids, were planted mid-January and will be screened for resistance to oviposition by ACP in the coming months. Studies have been initiated to compare plant volatiles associated with plant genotypes that are readily colonized by the psyllid to those less colonized by the psyllid. Collaborators with the Fujian Academy of Agricultural Sciences in Fuzhou, China, initiated two experiments on resistance to ACP within the Rutaceae. Forty genotypes were evaluated in a free-choice experiment conducted in a screen house. Citrus tankan Hort. (cultivar Fuyouxuan Jiagan) was completely avoided by adults, and no eggs or nymphs were ever observed on this cultivar. No eggs or nymphs were observed on the following: C. reticulata Blanco (cultivars Bayueju, Xiang Ponkan, and Mashuiju); C. mitis (cultivars Chengshi Calamondin and Variegated Calamondin); C. sinensis (cultivars Navelia Navel orange and Skaggs Bonanza Navel Orange); C. grandis (cultivar Chandler Pummelo), and Fortunella hindsii var Chintou. The most heavily colonized genotypes included: C. reticulata Blanco (cultivar Fina Sodea Clementine); C. sinsensis (cultivar Fengcai anliucheng); and C. grandis Osbeck (cultivar HB Pummelo). A free-choice field experiment was established comparing 31 genotypes. Due to prolonged cool weather, no results have yet been obtained from this experiment. A delegation from FAAS will be visiting USDA-ARS during April or May to coordinate research efforts.