Aphidiid Parasitoids Twenty Years Post-Release in the Mariana Islands
Despite the release of approximately 6,500 Aphidius colemani Vierick and Diaeretiella rapae (McIntosh) parasitoids as biological control agents for a variety of aphids on Guam and Saipan in 1998, no long-term establishment on either island was observed. However, the aphidiid parasitoids Lipolexis oregmae Gahan and Lysiphlebus testaceipes Cresson were found parasitizing Aphis gossypii Glover on a variety of crops in follow-up surveys in the years immediately following the initial aphidiid releases. The presence of L. oregmae is apparently the result of a fortuitous introduction, while the presence of L. testaceipes likely resulted from a previous introduction as an aphid biological control agent. Aphidiid surveys conducted on Guam and Saipan from 2016 through 2018 again found L. oregmae parasitizing A. gossypii, Aphis craccivora Koch and Cerataphis sp, and L. testaceipes infesting A. gossypii, Aphis (Toxoptera) citricidus (Kirkaldy), and Hysteroneura setariae (Thomas) on a variety of host plants. No A. colemani or D. rapae were found in any collections made from any island. The genotype of aphidiid parasitoids has largely been ignored in past biological control studies on aphids and should be considered when matching the natural enemy to the targeted aphid species.