Submitted to: Crop Protection Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/24/2014
Publication Date: 3/1/2014
Citation: Hall, D.G. 2014. Interference by western flower thrips in rearing Asian citrus psyllid: damage to host plants and facultative predation. Crop Protection Journal. 60:66-69. Interpretive Summary: The Asian citrus psyllid is an important pest of citrus primarily because it vectors a bacterium responsible for a serious citrus disease known as huanglongbing (citrus greening disease). Scientists often depend on insectary colonies of the psyllid for research purposes. Recently, an infestation of western flower thrips developed on potted citrus grown openly in a USDA greenhouse for the purpose of propagating large numbers of psyllids infected by the disease bacterium. The thrips caused extensive damage to young flush shoots, on which the psyllid is dependent for reproduction. Further, the thrips also began feeding on young psyllid nymphs, killing hundreds in a short time. This manuscript presents the results of experiments conducted to document the observations of thrips damage to psyllid host plants and facultative predation by the thrips on the psyllid. A minute pirate bug regarded as an effective thrips predator was found to predate heavily on immature psyllids, thus it would be incompatible with a psyllid rearing operation. Neither thrips nor pirate bug had previously been noted as potential predators of the psyllid.
Technical Abstract: The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is an important pest of citrus primarily because it vectors a bacterium responsible for a serious citrus disease known as huanglongbing (HLB) (also known as citrus greening disease). Researchers seeking solutions to HLB often depend on laboratory or greenhouse ACP colonies. USDA in Fort Pierce, Florida routinely maintains a number of ACP colonies. Recently, an infestation of Western flower thrips [Frankliniella occidentalis (Pergande)] developed on potted citrus grown openly in a greenhouse – these plants were being used to propagate large numbers of ACP infected by the HLB bacterium. As this infestation of thrips increased, large numbers of young flush shoots were killed which resulted over a short period of time in an enormous loss of oviposition sites for ACP. The thrips apparently killed so many young flush shoots that not enough remained for the thrips population to maintain itself and thus they began feeding on young ACP nymphs. Hundreds of young nymphs were killed. This prompted two experiments to document the observations of plant damage caused by the thrips. In one experiment, an infestation of ten thrips on a young Murraya exotica L. plant (a favored ACP rearing plant) which had a single newly-developing flush shoot resulted in shoot death 73% of the time. Among shoots that were not killed, these were growth retarded with respect to length and number of leaflets. In a second experiment, an infestation of ten thrips on a young Citrus sinensis L. sweet orange plant (also a favored ACP rearing plant) did not kill any flush shoots or cause enough damage to significantly retard shoot growth. These results suggest that adult WFT may cause more damage to jasmine than sweet orange. However, direct comparisons of WFT damage to the two host plants may not be valid because they were not studied at the same time. Also, the ages of adults used in these experiments were not known, and age might influence feeding activity and consequently how much plant damage an individual WFT might cause. Based on damage observed in the original greenhouse infestation, WFT can cause damage to young flush shoots of at least some Citrus spp. It was possible that the infestation density of WFT in the greenhouse was much higher than 10 WFT per young flush shoot. Insectaries rearing ACP should be aware of the potential for interference by Western flower thrips. An experiment was also conducted to further document observations on facultative predation by the thrips on ACP and to evaluate predation on ACP by the minute pirate bug, Orius insidiosus (Say), a known predator of WFT (five predators per plant infested by ~90 ACP eggs). The percentage of eggs that survived to the adult stage was 13 or 0% for plants infested by thrips or pirate bugs, respectively, compared to 87% for control plants (infested by ACP eggs in the absence of predators). Neither thrips nor pirate bug had previously been noted as potential predators of ACP. The minute pirate bug might be effective against WFT but would be incompatible with an ACP rearing operation.