Ditribution, pest status and fungal associates of Euwallacea nr. fornicatus in Florda avocado groves

Authors: CARRILLO, DANIEL - University Of Florida; CRUZ, LUISA - University Of Florida; Kendra, Paul; Narvaez, Teresa; Montgomery, Wayne; MONTERROSO, ARMANDO - Brooks Tropicals, Llc; DEGRAVE, CHARLOTTE - University Of Liege; COOPERBAND, MIRIAM - Animal And Plant Health Inspection Service (APHIS)

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2016
Publication Date: 10/14/2016
Citation: Carrillo, D., Cruz, L.F., Kendra, P.E., Narvaez, T.I., Montgomery, W.S., Monterroso, A., Degrave, C., Cooperband, M.F. 2016. Ditribution, pest status and fungal associates of Euwallacea nr. fornicatus in Florda avocado groves. Insects. 7(4):55.

Interpretive Summary: Over the past few years, avocado production in California has been reduced due to establishment of two new ambrosia beetles similar to Euwallacea fornicatus, a pest of tea in India. Female Euwallacea beetles carry Fusarium fungi that cause branch dieback disease in host plants. In early Spring 2016, similar Euwallacea beetles were discovered in a commercial avocado grove in Miami-Dade County, Florida. In response, research was initiated by the USDA-ARS (Miami, FL), University of Florida (Homestead) USDA-APHIS PPQ, and Brooks Tropicals LLC to (1) identify the beetle species, (2) determine its abundance in Florida avocado groves, and (3) identify its fungal symbionts. Results indicated that the beetle was widely distributed in Florida groves, found in 31 of 33 sites surveyed, but typically found in low numbers. Initial inspections showed limited damage to trees in all orchards except for two. Genetic analysis and identification of fungal symbionts indicated that the Euwallacea species in Florida is different than the two species found in California. This report will alert action agencies of the presence of this new pest in Florida, and the need for monitoring its levels in commercial avocado groves. I also identifies a need for additional research on this new Euwallacea-Fusarium complex established in south Florida.

Technical Abstract: Members of a complex of cryptic species, that correspond morphologically to the Asian ambrosia beetle Euwallacea fornicatus (Eichhoff) (Coleoptera: Curculionidae: Scolytinae), were recently found attacking avocado (Persea americana Mill) in Israel and California. Also, early in 2016 an outbreak of another member of this species complex was detected infesting approximately 1,500 avocado trees in an avocado orchard at Homestead, Florida. An industry-wide survey was conducted in the avocado production region of Miami-Dade County, Florida to determine the distribution and abundance of E. nr. fornicatus in commercial avocado groves, to characterize different populations of E. nr. fornicatus and their fungal associates, and to assess the extent of damage caused to avocado trees. Ewallacea nr. fornicatus individuals were captured in 31 of the 33 sampled sites distributed throughout the avocado growing region in south Florida. A sub sample of 35 beetles were identified as E. nr. fornicatus sp # 2, which is genetically distinct from the species causing damage in California and Israel. In addition, the following eight fungal associates were identified: an unknown Fusarium sp., AF-8, AF-6, Graphium euwallaceae Acremonium sp. Acremonium morum, Acrimonium masseei and Elaphocordyceps sp. The unknown Fusarium isolates were the most abundant and frequently found fungus species associated with adult beetles and lesions surrounding the beetle galleries. In addition to fungal associates, three bacteria and three yeast species were found associated with adult E. nr. fornicatus. Visual inspections of the 33 orchards showed limited damage caused by E. nr. fornicatus in all orchards except two. A large number of beetles were captured in locations with no apparent damage on the avocado trees suggesting that E. nr. fornicatus are associated with other host(s) outside the groves or with dead trees or branches inside the grove. More research is needed to determine the potential threat that E. nr. fornicatus and its fungal associates pose to the avocado industry and other agricultural and natural ecosystems in Florida.