Isolation and Characterization of an Isaria Fumosorosea Isolate Infecting the Asian Citrus Psyllid in Florida
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Journal of Invertebrate Pathology 99 (2008) 96–102 Contents lists available at ScienceDirect Journal of Invertebrate Pathology journal homepage: www.elsevier.com/locate/yjipa Isolation and characterization of an Isaria fumosorosea isolate infecting the Asian citrus psyllid in Florida Jason M. Meyer *,1, Marjorie A. Hoy, Drion G. Boucias University of Florida, Department of Entomology and Nematology, Institute of Food and Agricultural Sciences, Building 970, P.O. Box 110620, Gainesville, FL 32611-0620, USA article info abstract Article history: A fungal pathogen that killed adult Diaphorina citri Kuwayama (Asian citrus psyllid) (Hemiptera: Psylli- Received 23 January 2008 dae) in Florida citrus groves during the fall of 2005 was identified and characterized. Investigation of this Accepted 11 March 2008 pathogen is important because D. citri vectors citrus greening disease (Huanglongbing), which was Available online 15 March 2008 reported in Florida in 2005. The morphological and genetic data generated herein support identification of the fungus as Isaria fumosorosea Wize (Ifr)(=Paecilomyces fumosoroseus) (Hypocreales: Cordycipita- Keywords: ceae) from the Asian citrus psyllid (Ifr AsCP). Koch’s postulates were fulfilled after the fungus was isolated Asian citrus psyllid in vitro and transmitted to healthy psyllids, which then exhibited a diseased-phenotype similar to that Cordycipitaceae observed in the field. Both in vitro growth characteristics and two Ifr AsCP-specific molecular markers dis- Diaphorina citri Hemiptera criminated the psyllid pathogen from another local Ifr isolate, Ifr 97 Apopka. These molecular markers Huanglongbing will be useful to track the dynamics of this disease in D. citri populations. The potential for utilizing Ifr Hypocreales to complement existing psyllid pest management strategies is discussed. Isaria fumosorosea Ó 2008 Elsevier Inc. All rights reserved. Microbial control Paecilomyces fumosoroseus Psyllidae 1. Introduction rixia radiata Waterston (Hymenoptera: Eulophidae) (Hoy et al., 1999; Hoy and Nguyen, 2000). The maintenance of clean nursery The Asian citrus psyllid, Diaphorina citri Kuwayama, (Hemip- stocks and removal of HLB-infected citrus trees are cultural mea- tera: Psyllidae) was discovered in Florida in 1998 and apparently sures used to retard the spread of HLB. Widespread use of chemical arrived without its natural enemies (Halbert, 1998; Knapp et al., insecticides may result in the development of resistant psyllid pop- 1998; Halbert et al., 2000). Control of D. citri is important because ulations and could negatively affect existing biological control this phloem-feeding pest vectors Candidatus Liberibacter asiaticus agents in citrus that suppress populations of mites, scales, white- (Ca. L. asiaticus), a phloem-residing a–proteobacterium that causes flies, mealybugs, aphids, and the citrus leafminer. Therefore, new citrus greening disease or Huanglongbing (HLB) (Garnier et al., approaches are needed that complement existing management 2000). HLB was discovered in Florida in 2005 and poses a serious strategies for D. citri, such as the potential utilization or augmenta- threat to the citrus industry because Ca. L. asiaticus infections tion of microbial pathogens that attack the psyllid. Worldwide, di- cause fruit damage and ultimately kill citrus trees (Halbert and verse species of pathogenic fungi suppress D. citri populations, Manjunath, 2004; Halbert, 2005; Bouffard, 2006). especially during periods of high relative humidity (Samson, To limit the spread of HLB, suppression of D. citri populations 1974; Rivero-Aragon and Grillo-Ravelo, 2000; Subandiyah et al., will require a multi-tactic integrated pest management (IPM) pro- 2000; Étienne et al., 2001; Xie et al., 1988; Aubert, 1987). gram. Petroleum oil and foliar and systemic insecticides are cur- In the fall of 2005, two fungal pathogens were discovered rently recommended to reduce D. citri populations (Rae et al., attacking D. citri in Florida, and one of these pathogens was identi- 1997; Browning et al., 2006; Rogers and Timmer, 2007), but will fied as Hirsutella citriformis (Meyer, 2007; Meyer et al., 2007). The not likely eliminate HLB transmission. Other control agents include initial goals of this study were to identify the second psyllid path- native predators (Michaud, 2004) and the exotic parasitoid Tama- ogen using both morphological and molecular analyses and then determine if the disease could be propagated in a healthy labora- tory colony of D. citri. For convenience within this manuscript, * Corresponding author. henceforth the psyllid pathogen will be referred to as Isaria fumos- E-mail addresses: [email protected] (J.M. Meyer), [email protected]fl.edu orosea Wize (=Paecilomyces fumosoroseus) from the Asian citrus (M.A. Hoy), pathos@ufl.edu (D.G. Boucias). 1 Present address: Purdue University, Department of Entomology, 901 W. State psyllid or Ifr AsCP (Hypocreales: Cordycipitaceae) (Hodge et al., Street, West Lafayette, IN 47907, USA. 2005; Luangsa-ard et al., 2005). 0022-2011/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.jip.2008.03.007 J.M. Meyer et al. / Journal of Invertebrate Pathology 99 (2008) 96–102 97 Once determined, the morphological and molecular characteris- quarter-strength Sabouraud dextrose agar +1% yeast extract tics of Ifr AsCP were compared to a reference strain, Ifr 97 (=Pfr 97), (SDY) or malt extract agar (MEA) media. Another local isolate of which was isolated from Phenacoccus sp. (Hemiptera: Pseudococci- Ifr, Ifr 97 Apopka, was kindly supplied by Dr. L. Osborne and main- dae) in Apopka, FL. Ifr 97 was commercially developed as the tained on psyllids and in vitro according to the methods described microbial insecticide Pre-FeRal W.R. Grace and Co., Columbia above. Transparent tape-mounts of sporulating cultures were MD; Thermo Trilogy/Biobest N.V., Belgium) (Vidal et al., 1998; Far- stained with acid fuchsin and examined under a light microscope ia and Wraight, 2001). These comparisons were conducted to at 400Â to examine the structural characteristics of the fungi determine if Ifr AsCP was the same local strain as the well-charac- grown in vitro (Koneman and Roberts, 1985). terized Ifr 97. If the two fungi were the same strain, then we could The growth rate and conidia yield of Ifr AsCP and Ifr 97 were pursue field trials with a commercially-available microbial formu- compared 1-week post-inoculation on SDY and MEA. Fungal cul- lation. If they were different strains, then Ifr AsCP, the naturally tures were held at 26 °C without light, and conidia were harvested occurring D. citri pathogen, could be formulated and compared as follows: (i) hyphae + conidia were scraped from plates with a with Ifr 97 in laboratory and field trials for psyllid control. Collec- sterilized spatula and suspended in 10 mL sterile water; (ii) the tively, this research contributes the first steps towards evaluating suspension was filtered through Miracloth (Calbiochem, EMD Bio- Ifr for its potential use in an IPM program to suppress D. citri pop- sciences Inc., La Jolla, CA) held in a funnel and collected in a glass ulations in Florida or elsewhere. beaker; (iii) conidia were quantified using a hemocytometer. For Ifr AsCP and Ifr 97, two replicates each consisting of six SDY and MEA plates (6 cm) were spot-inoculated with 5 lL of 4.5 Â 105 con- 2. Materials and methods idia + water to measure growth, and 100 lL of 4.5 Â 107 conidia/ mL to measure conidia production. To test the effect of media on 2.1. Collection of psyllid cadavers and description of the fungus mean growth (diameter) and mean conidia yield for Ifr AsCP and Ifr 97, the data were subjected to a one-way analysis of variance Cadavers of adult D. citri were collected from a single orange with PROC GLM, and the least squares means were separated using 0 00 0 grove in Polk county, FL (28°06 295 N, 81°42.895 W) during Sep- a probability of a significant divergence of P 6 0.05 (SAS Institute, tember and October 2005. The cadavers were placed into sterile 1996). 50-mL centrifuge tubes (USA Scientific, Ocala, FL) and held at Qualitative assays were conducted to determine if the in vitro 4 °C during transit to the Entomology and Nematology Department cultures were infective to D. citri. Adult D. citri from the laboratory at the University of Florida, Gainesville, FL. Mycosed D. citri were colony were grasped with a fine-tipped forceps and touched (20 photographed using a dissecting microscope linked with the individuals) or not touched (20 controls) directly to the surface Auto-Montage Pro system using software ver. 5.02 (Synoptics, of sporulating cultures of Ifr AsCP and Ifr 97 grown on quarter- Frederick, MD) and with scanning electron microscopy (SEM) on strength SDY media. Inoculated psyllids were then maintained a Hitachi 4000 FE-SEM operating at 4–6 kV (Quattlebaum and Car- according to the method used to propagate the pathogen on psyl- ner, 1980). Differential interference contrast (DIC) microscopy lids after exposure to the field-collected cadavers. Mortality due to (360–1000Â) was used to analyze the hemolymph of infected fungal pathogenesis in these assays was recorded three days after adult D. citri and mature conidia isolated from in vitro cultures of treatment. Ifr AsCP. SPOT software 3.4.3 (Diagnostic Instruments, Sterling Heights, MI) was used to measure structures of the psyllid patho- 2.4. Molecular analyses gen captured digitally. DNA was isolated from a single field-collected mycosed adult D. 2.2. Laboratory propagation of the psyllid disease citri, from 1-week-old cultures of Ifr AsCP initiated from that same cadaver, and from Ifr 97 grown on 6-cm plates containing quarter- A laboratory colony of D. citri was maintained according to Skel- strength SDY media. All DNA extractions were conducted using ley and Hoy (2004) in a greenhouse at 20–32 °C with a 16L:8D pho- PUREGENE reagents (Gentra Systems, Minneapolis, MN) according toperiod. Adult D. citri were allowed to oviposit on the tender new to the instructions provided by the manufacturer.