The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is a major pest of citrus crops worldwide. A large number of insecticides have been used to manage D. citri in Florida. Therefore, insecticide resistance could become an important problem facing citrus production. Monitoring insecticide susceptibility in populations of D. citri and providing a technique to use as an early warning is needed so citrus producers can modify chemical control strategies for this pest in Florida. The objective of this study was to develop a simple and fast tool to determine insecticide resistance in D. citri and apply it to commercial citrus production in Florida. LC50 and LC95 estimates were determined for 8 commonly used insecticides on a susceptible laboratory population of D. citri 24 h after treatment in a residual contact bottle assay. Five to 7 concentrations of each insecticide were tested. The LC50 values (and 95% fiducial limits) ranged from 0.06 (0.02–0.26) to 0.80 (0.26–2.46) ng/μL for each insecticide tested. Exposure time—mortality indices were determined for 0, 10, 100, 1,000, and 10,000 ng/μL concentrations of each insecticide in a laboratory susceptible strain. Knockdown was assessed after 15, 30, 45, 60, 75, 90, 105, and 120 min. Complete knockdown (100.0%) occurred within 60 min for dimethoate, fenpropathrin, imidacloprid, bifenthrin, and flupyradifurone at the 10,000 ng/μL concentration. For spinetoram, 86.7% knockdown occurred within 120 min at 10,000 ng/μL. For sulfoxaflor and cyantraniliprole, 44.0 and 42.6% knockdown, respectively, occurred within 120 min at 1,000 ng/μL. We also developed a bottle bioassay to survey field populations of D. citri for insecticide resistance in central Florida. Exposure time—mortality indices developed in the laboratory were used to assess susceptibility of 1 laboratory and 4 field populations of D. citri after 15, 30, 50, 75, 90, 105, and 120 min of exposure at the 10,000 ng/μL concentration of various insecticides. Little to no evidence of resistance was detected for bifenthrin, dimethoate, imidacloprid, and fenpropathrin in central Florida. Our investigation demonstrated that a bottle bioassay is suitable for assaying insecticide resistance in D. citri adults under laboratory and field conditions. It should be a flexible tool for rapid testing of insecticide resistance in possible cases of insecticide failure. Its simplicity should allow trained professionals to rapidly monitor for insecticide resistance in commercial settings where “hot spots” of D. citri populations may occur.
The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is one of the most important pests of citrus as it is the vector of the bacteria causing citrus greening, also called huanglongbing (Halbert & Manjunath 2004; Halbert & Núñez 2004; Bové 2006; Pelz-Stelinski et al. 2010; Boina & Bloomquist 2015). Diaphorina citri was first described in Taiwan in 1907 (Kuwayama 1908; Grafton-Cardwell et al. 2013), and the infectious nature of huanglongbing was described in China (Lin 1956). Diaphorina citri was first reported in Brazil in the 1940s (da Costa Lima 1942), Florida in 1998 (Tsai & Liu 2000), and currently, D. citri can be found in most citrus-producing regions of the United States (French et al. 2001; Halbert et al. 2010; Hummel & Ferrin 2010).
Huanglongbing is one of the most economically important diseases of citrus throughout the world (Halbert & Manjunath 2004; Manjunath et al. 2008). Huanglongbing previously occurred in Asia and Africa (Gottwald 2010). It was first found in the western hemisphere in Brazil in 2004 (Texeira et al. 2005; Grafton-Cardwell et al. 2013), and Florida in 2005 (Halbert 2005), and has since spread to Central America and most citrus production areas in the United States. Citrus trees infected by this disease produce misshapen, small, discolored, and reducedquality fruit over a shortened lifespan (Bové 2006; Gottwald et al. 2007; Grafton-Cardwell et al. 2013). In Florida, about 10.8 out of 60 million orange trees have been infected with huanglongbing (Quarles 2014; Boina & Bloomquist 2015). It is estimated that over the last 5 yr in Florida, huanglongbing has caused over US$1.3 billion in lost revenue to the citrus industry and a loss of over US$3.6 billion in total economic activity (Hodges & Spreen 2012). The 2014 citrus harvest may have been the lowest in approximately 50 yr without the impact of a serious weather event. Prevention of disease transmission has proven difficult worldwide (Aubert et al. 1996). There is currently no method of curing diseased trees (Morris et al. 2009; Tiwari et al. 2010, 2011). Currently, the most common practice for managing huanglongbing relies on chemical insecticides for vector suppression (Tiwari et al. 2011).
Insecticides are presently a critical component of D. citri management in Florida, and 8 to 12 treatments are common