Location: Invasive Species and Pollinator HealthTitle: Post-establishment assessment of host plant specificity of Arytainilla spartiophila (Hemiptera: Psyllidae), an adventive biological control agent of Scotch broom, Cytisus scoparius
Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/2016
Publication Date: 5/1/2016
Citation: Hogg, B.N., Smith, L., Moran, P.J., Daane, K.M. 2016. Post-establishment assessment of host plant specificity of Arytainilla spartiophila (Hemiptera: Psyllidae), an adventive biological control agent of Scotch broom, Cytisus scoparius. Biocontrol Science and Technology. 26(7):995-1008. doi: 10.1080/09583157.2016.1178707.
Interpretive Summary: Scotch broom, Cytisus scoparius, is a shrub from northern and central Europe that is invasive in the USA, New Zealand and Australia. This shrub produces pods that look a little like bean pods, but are not edible. The pods produce thousands of seeds that help the weed spread. The weed is unpalatable to most livestock, outgrows native plant species, and increases the risk of wild fire. It currently infests >280,000 hectares, or about 1 million acres in California. One of the most abundant and widespread insects on Scotch broom in California is the broom psyllid, Arytainilla spartiophila, which arrived accidentally. This psyllid is a natural enemy of Scotch broom, as it pierces the plant tissue and feeds on plant fluids. The psyllid reaches high numbers in Europe, where it appears to significantly damage plants, and it was purposely introduced to New Zealand as a biological control agent for Scotch broom. Lupines (Lupinus spp.) are the closest native relatives of Scotch broom in North America, and are therefore at risk of being attacked by the broom psyllid. However, little is known about potential risk to North American lupines, including species native to California, where lupines are abundant and diverse. We conducted a laboratory experiment, a field experiment and a field survey to assess risk to three widespread California native lupine species (Lupinus albifrons, L. bicolor and L. formosus) that often occur near Scotch broom infestations. In the laboratory, the broom psyllid was able to develop to adulthood on one lupine species (L. formosus) but not on the other lupine species. In the field experiment, where potted Scotch broom plants and lupines were placed near large psyllid-infested Scotch broom plants, broom psyllid eggs appeared on all the potted Scotch broom plants but on none of the lupines. In the field survey, no broom psyllid eggs or nymphs were found on naturally occurring lupines growing adjacent to infested Scotch broom. The results indicate that the broom psyllid is unlikely to damage or reproduce on lupines in the field in California.
Technical Abstract: Scotch broom, Cytisus scoparius (Fabaceae), is a shrub native to Europe that is invasive in the USA, New Zealand and Australia. The psyllid Arytainilla spartiophila has been purposely introduced to Australia and New Zealand as a biological control agent of C. scoparius, but is an accidental introduction to California. Lupines (Lupinus spp.) are the closest native taxon to Cytisus in North America, and are therefore considered to be at the highest risk for non-target damage. However, because no lupines are native to Australia or New Zealand, only one imported forage species was evaluated during prior host specificity testing. We conducted a laboratory nymphal transfer experiment, a field choice experiment and a field survey to assess risk to three lupine species (Lupinus albifrons, L. bicolor and L. formosus). In the laboratory, 20% of third instar nymphs were able to develop to adulthood on L. formosus but not on the other lupine species, while 40% completed development on C. scoparius. In the field experiment in which potted lupine and C. scoparius plants were placed beside large infested C. scoparius plants, oviposition occurred on all the potted C. scoparius plants, but on none of the lupines. In the field survey, no A. spartiophila eggs or nymphs were found on naturally occurring lupines growing adjacent to infested C. scoparius. The results indicate that A. spartiophila is not likely to damage or reproduce on lupines, and this study provides an example of how field studies can help clarify the host specificity of biological control agents.