BIOLOGICAL CONTROL STRATEGIES FOR INVASIVE WEEDS OF SOUTHWESTERN U.S. WATERSHEDS
Title: Localized autoinoculation and dissemination of Isaria fumosorosea for control of the Asian citrus psyllid in South Texas
Submitted to: Subtropical Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 20, 2011
Publication Date: April 28, 2012
Citation: Moran, P.J., Patt, J.M., Cabanillas, H.E., Adamczyk Jr, J.J., Jackson, M.A., Dunlap, C.A., Hunter, W.B., Avery, P.B. 2011. Localized autoinoculation and dissemination of Isaria fumosorosea for control of the Asian citrus psyllid in South Texas. Subtropical Plant Science. 63:23-35.
Interpretive Summary: The grapefruit and orange citrus industry in the Lower Rio Grande Valley of south Texas is worth $50 million per year. The Asian citrus psyllid, a non-native pest, is a tiny flea-like insect that hops and flies onto new spring and fall growth on shoot tips and feeds on fresh, soft leaves on citrus and on related ornamental plants such as orange jasmine. The psyllid can carry bacterial cells that cause citrus greening or Huanglongbing (“yellow dragon”) disease in citrus trees. The bacteria multiply inside the tree’s plumbing system, depriving it of nutrients, making the fruit taste bad and eventually killing the tree. Citrus greening has killed tens of thousands of citrus trees in Florida, Central and South America, Africa, and Asia. The disease is not currently present in Texas, and so there is a critical need to control psyllids that may be carrying the bacterial cells to prevent the disease from destroying Texas citrus. Insecticides are being used but may not be feasible for controlling psyllids in ornamental citrus and related plants around houses and public buildings, or in abandoned citrus groves. USDA-ARS and University of Florida scientists tested a fungus, originally found killing whiteflies in south Texas, to see if it could kill Asian citrus psyllids. They specifically wanted to determine if the fungus could be placed into a trapping device containing scents and colors to attract psyllids, who would then land on the device, inoculate themselves with the fungus and die. Direct spraying of psyllids with fungal spores and close contact with spore-coated cards in the laboratory led to the death of 75-100% of the psyllids within one week, demonstrating that the fungus can kill this pest. In greenhouse cages, the trapping device killed up to 36% of the psyllids, with the best results found when the device contained an artificial mixture of citrus scents. Up to 25% of psyllids not exposed to fungus died after they were mixed with other psyllids that had been exposed in the lab. Additional work is needed to increase attraction of psyllids to the trapping device, so that it can contribute to control of the Asian citrus psyllid in the field in Texas.
The Asian citrus psyllid, Diaphorina citri Kuwayama, vectors the causal organism of citrus greening disease. Integrated strategies are needed to control D. citri in south Texas. Control approaches involving entomopathogenic fungi may be useful on ornamental and abandoned citrus and other rutaceous hosts, which could act as vector and pathogen reservoirs. A Texas isolate of the fungus, Isaria fumosorosea (Ifr), caused 95% mortality in spray applications to D. citri. In laboratory bioassays at 27 °C, 70% of psyllids died within one week when exposed to cards that had been sprayed with liquid blastospore suspension and allowed to dry. A potentially more practical approach of coating cards with filtered powder containing blastospores did not cause significant mortality, but efficacy was 35% higher when adhesive material used to hold powder on the cards contained citrus volatiles, than on cards with no volatiles. Cards with Ifr, as either dried liquid suspension or powder, were hung in cages containing psyllids under greenhouse conditions (25–37 °C). Mortality was low (less than 40%) in all tests, but the inclusion of citrus volatiles increased mortality by 23%. Psyllids caged with fungal powder-coated cards for one week did not transfer inoculum horizontally to other adults or vertically to offspring. However, when psyllids were exposed to fungal powder cards for 24 hours and then released into cages, 25% of unexposed psyllids died within three weeks. The results provide insight into chemical stimuli and fungal exposure methods for an autodissemination device to aid in control of D. citri.