Parasitism of the brown citrus aphid in Dominica by Lysiphlebus testaceipes and Lipolexis oregmae (Hymenoptera: Aphidiinae).
Before importation and release of L. oregmae in Dominica, a survey was conducted during Feb and Apr 2007 at 6 parishes to evaluate the distribution and parasitism rates of brown citrus aphids. Brown citrus aphids and aphids of unknown species were collected in 95% ethyl alcohol and DNA was analyzed for parasitoid DNA with the High-fidelity PCR protocol developed by Persad et al. (2004). Genomic DNA from pooled brown citrus aphids was extracted with Puregene reagents according to the method suggested by the manufacturer (Gentra Systems, Minneapolis, MN) and resuspended in 10 uL of sterile water. The nuclear rRNA ITS2 sequences of L. oregmae were amplified with the specific forward primer LO-ITSF 5'-GGCCAGTTGTCGAGTCC-3' in combination with the 28 SR reverse primer (5'-ATGCTTAAATT-TAGGGGGTA-3'), while the rRNA ITS2 partial sequences of L. testaceipes were amplified with the forward primer LTITSF 5'-CTAGCGATAAATGAATGTTC-3'in combination with the 28 S-R reverse primer (Persad et al. 2004). PCR products were separated by electrophoresis on 2% agarose gel, stained with ethidium bromide, and photographed. The L. oregmae-specific primers produced a 270-bp PCR product, while the ITS2 sequences amplified from L. testaceipes produced a 520-bp PCR product.
Although L. oregmae was not purposefully released in Dominica, the survey indicated that both parasitoids are present throughout the island (Table 1), with L. oregmae found in all 6 parishes at 76% of the locations sampled, and L. testaceipes found in 5 parishes at 53% of the sampling sites. Both L. oregmae and L. testaceipes were detected from aphids of unknown species on weeds within citrus groves in St. George parish at 3 locations. This indicated that both parasitoids parasitize alternative aphid hosts in the presence of the brown citrus aphid. When and by which mechanisms L. oregmae was introduced to Dominica are unknown. The fortuitous introduction of parasitoids of citrus pests into different Caribbean islands indicates that, as in Florida, it is difficult to prevent invasive insect introductions.
Although evaluation of the effectiveness of parasitoids of the brown citrus aphid was beyond the goal of this study, the rate of parasitism on a single date was assessed by selecting randomly 5 aphids from each of 4 parishes and testing them individually with both L. testaceipes- and L. oregmae-specific primers following the protocol described above (Table 2). The percentage of parasitized aphids was remarkably high, ranging from 80 to 100%. None of the brown citrus aphids tested was positive for L. oregmae only, while 20, 20, and 40% of the samples from St. Mark, St. David, and St. Peter, respectively, were positive for L. testaceipes only. Most of samples were positive for both L. oregmae and L. testaceipes, indicating that both parasitoids had parasitized the brown citrus aphid. The oviposition sequence, age of larvae, and larval development time are key factors that affect the development of parasitoids within parasitized brown citrus aphids, so it is impossible to resolve which species would emerge from the brown citrus aphid in these cases (Persad & Hoy 2003). However, the parasitism level estimated for L. oregmae and L. testaceipes ranged from 80 to 100% overall in this limited sample, suggesting that they are common parasitoids of the brown citrus aphid in Dominica. Despite this apparent abundance, natural enemies cannot prevent transmission of diseases such as CTV by aphids, so replanting with citrus on CTV-resistant rootstocks should be considered.
The brown citrus aphid parasitoids Lipolexis oregmae and Lysiphlebus testaceipes are present and widely distributed in Dominica. Lipolexis oregmae was not purposefully released and it is not clear when and by which pathway the parasitoid was introduced to Dominica. The brown citrus aphid samples tested were parasitized by both parasitoids (80-100%), suggesting that both L. oregmae and L. testaceipes might be effective parasitoids of T. citricidus in Dominica.
The authors thank Peter Hill, Naomi Commodore, Ryan Anselm, and Bemitta Serrant of the Ministry of Agriculture, Fisheries and the Environment, Commonwealth of Dominica, for assistance in collecting parasitized aphids. This research was funded by the Autonomous Region of Sardinia (A.C.) and the Davies, Fischer and Eckes Endowment in Biological Control (M.A.H.).
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Arturo Cocco (1), Ayyamperumal Jeyaprakash and Marjorie A. Hoy
Department of Entomology and Nematology, University of Florida, Bldg. 970, Natural Area Drive, Gainesville, FL, 32611-0629, USA
(1) Presently at Dipartimento di Protezione delle Piante, Sezione Entomologia Agraria, Universita di Sassari, Via De Nicola 1, 07100 Sassari, Italy
TABLE 1. SURVEY ON DISTRIBUTION AND ABUNDANCE OF BROWN CITRUS APHID PARASITOIDS IN CITRUS-GROWING AREAS OF DOMINICA DURING 2007 WITH A HIGH-FIDELITY PCR PROTOCOL AND SPECIES-SPECIFIC PRIMERS. No. of pooled aphids Sample date Parish Location Host tested 7 Feb St. Peter Syndicate Citrus 3 7 Feb St. Peter Syndicate Citrus 22 7 Feb St. Peter Syndicate Citrus 15 (2) 2 Feb St. Patrick Grand Bay Citrus 50 6 Feb Unknown Sundalae Citrus 200 16 Feb St. Andrew Melville Hall Citrus 100 15 Feb St. Andrew Wesley Sweet pepper 50 20 Apr St. Mark Soufriere Citrus 50 20 Apr St. Andrew Marigot Citrus 50 20 Apr St. Andrew Hatton Garden Citrus 50 20 Apr St. Andrew Woodford Hill Citrus 50 20 Apr St. Andrew Woodford Hill Citrus 50 20 Apr St. David Castle Bruce Citrus 50 23 Apr St. George Giraudel Composite weed 100 (3) 23 Apr St. George Morne Prosper Composite weed 50 (3) 20 Apr St. George Roseau Citrus 50 (3) 23 Apr St. George Giraudel Colocasia sp. 503 Sample date L. oregmae (1) L. testaceipes (1) 7 Feb + + 7 Feb + - 7 Feb + + 2 Feb + - 6 Feb + + 16 Feb + - 15 Feb - - 20 Apr + + 20 Apr + + 20 Apr + + 20 Apr + - 20 Apr + + 20 Apr + + 23 Apr - - 23 Apr + + 20 Apr - - 23 Apr - - (1) + = positive detection; - = negative detection. (2) Adult wasps collected from a citrus grove. (3) Aphids of unknown species collected from citrus or composite weeds within a citrus grove. TABLE 2. PARASITISM ASSESSMENT OF 5 INDIVIDUAL BROWN CITRUS APHIDS AT EACH SITE BY L. OREGMAE AND L. TESTACEIPES IN DOMINICA DURING 2007 WITH SPECIES-SPECIFIC PRIMERS AND A HIGH-FIDELITY PCR PROTOCOL. Sample date Parish Location Host 19 Apr St. Peter Syndicate Citrus 20 Apr St. Andrew Marigot Citrus 23 Apr St. Mark Soufriere Citrus 20 Apr St. David Castle Bruce Citrus Percentage positive by PCR Sample L. oregmae only L. testaceipes L. oregmae and date only L. testaceipes 19 Apr 0 40 60 20 Apr 0 0 100 23 Apr 0 20 60 20 Apr 0 20 80
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|Title Annotation:||Scientific Notes|
|Author:||Cocco, Arturo; Jeyaprakash, Ayyamperumal; Hoy, Marjorie A.|
|Date:||Sep 1, 2009|
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