News 19N Host-specificity tests were conducted involving two reproductive compatibility and the impact of hybrid- provenances of D. tomentosus: one collected from C. ization on host specificity. The two biotypes cross- imbricata in South Africa (henceforth called the bred freely in the laboratory producing viable off- imbricata provenance) and one collected from C. spring that had similar or greater potential to cause rosea in Mexico (henceforth called the rosea prove- damage to Cff and C. imbricata than their parents. nance). These provenances were reared on both C. The hybrid offspring were less host specific than imbricata and the target weed, Cff. On the target their parents, implying that hybridization would not weed, the imbricata provenance survived poorly and have a negative impact on biological control of either insects of the rosea provenance did not complete weed. their life cycle. However, both populations thrived on C. imbricata. This remarkable finding led to a reas- During this part of the study, a bias in hybrid per- sessment of the target weed which was subsequently formance towards their maternal parent host was identified as Cylindropuntia fulgida var. fulgida, observed indicating that host specificity may be whose native range is the Sonoran desert of Arizona genetically based. Genetic diversity among the bio- and Mexico. types was assessed by sequencing part of the mitochondrial cytochrome c oxidase subunit 1 gene. With the correct identification of the weed, the Sequences within a biotype were identical and bio- project undertook the first study of the biology of D. types from the same host species clustered together tomentosus revealing that this species exhibited irrespective of place of origin. This provides further some biological and morphological aspects that dif- evidence for the existence of host-adapted biotypes in fered from those of its congeners1. The next task was D. tomentosus. to search for a D. tomentosus provenance with the potential to cause severe damage to, and successfully These studies on D. tomentosus highlight the impor- control Cff. Further exploration by Helmuth Zim- tance of considering the existence of biotypes when mermann led to the collection and importation of D. selecting insects for biological control, as the selec- tomentosus provenances from a number of Cylindro- tion of an inappropriate biotype may lead to its puntia taxa in the New World: Cff and C. f. var. failure in the field. mamillata in the Sonoran desert, C. rosea and C. tunicata from different localities in Mexico, and C. 1Mathenge, C.W., Holford, P., Hoffmann, J., cholla from different localities in Baja California. Spooner-Hart, R., Beattie, G.A.C. & Zimmermann, Experiments were conducted in South Africa, at the H.G. (2009) The biology of Dactylopius tomentosus Plant Protection Research Institute, Pretoria, to (Hemiptera: Dactylopiidae). Bulletin of Entomolog- assess survival and performance of the provenances ical Research (online 10 February 2009; doi: 10.1017/ on Cff. These studies revealed significant differences S0007485308006597). between provenances in their performance on and damage to Cff 2. A provenance (collected from C. 2Mathenge, C.W., Holford, P., Hoffmann, J., Zim- cholla, the cholla provenance) with great potential to mermann, H.G., Spooner-Hart, R. & Beattie, G.A.C. control Cff was identified and is the insect used for (2009) Distinguishing suitable biotypes of Dactylo- biocontrol as described in the article above by Klein pius tomentosus (Hemiptera: Dactylopiidae) for and Zimmermann. The most surprising aspect of this biological control of Cylindropuntia fulgida var. provenance was that it came from C. cholla from fulgida (Caryophyllales: Cactaceae) in South Africa. Baja California, Mexico whereas provenances from Bulletin of Entomological Research (online 23 March the weed’s native range performed poorly. This may 2009; doi: 10.1017/S0007485309006671). be explained in terms of the ‘new association’ phe- nomenon in which insect populations that have not By: Catherine Mathenge & Paul Holford, co-evolved with a target weed perform better than Centre for Plant and Food Science, old associations. University of Western Sydney, Locked Bag 1797, Penrith South DC, NSW 1797, Australia. Based on the observed subspecific differentiation in Email: [email protected] host specificity among D. tomentosus provenances [email protected] towards Cff and C. imbricata, the research further explored the hypothesis of the occurrence of biotypes of this insect in relation to host plant species. The Can Manipulations of Amphibians’ Mutualistic results of these studies showed that the provenances Skin Bacteria Control a Lethal Skin Disease? fell into three categories on any host: some thrived on a particular host, others survived poorly, whereas The current extinction crisis is not sparing amphib- others died before completing their life cycles. These ians. While habitat loss and destruction are the observations demonstrated the occurrence of host- major causes of amphibian extinction, disease is also affiliated biotypes. causing population declines. Chytridiomycosis is a skin disease of amphibians caused by the fungus Although the occurrence of biotypes had now been Batrachochytrium dendrobatidis (Bd), and is the determined, the extent of their differentiation was causal agent of population declines and extinctions still an outstanding issue. This warranted some in relatively pristine areas, such as national parks. attention: as C. imbricata and Cff occur in sympatry This species was only described in 1999, yet we have in some areas in South Africa, it is likely that the learned quite a bit about its biology and ecology. Bd ranges of the two insect biotypes may overlap. There- seems to have originated in South Africa and spread fore, cross-breeding studies were conducted between to other parts of the world on Xenopus laevis, the the cholla and imbricata biotypes to assess their African clawed frog, which was exported for use in 20N Biocontrol News and Information 30(2) pregnancy tests1. Despite the pathogen’s role in An important component of amphibian conservation many amphibian species’ decline and extinction, rel- efforts is the creation of survival-assurance colonies. atively little research has focused on how to control Many species are being kept from going extinct in the disease in nature. Our research has focused on these breeding colonies, but they cannot be released the ecology of amphibian skin in an attempt to limit into nature because Bd is endemic and persisting on the disease. resistant amphibian species. Treating susceptible species with anti-Bd bacteria before introduction When Bd colonizes amphibian skin, it encounters into the field may allow successful re-introductions. transient and resident skin microbiota. We have One important open question asks how long bacteria found that many of the resident bacterial species stay on amphibians. Our research with J. lividum inhibit Bd in laboratory challenge assays. Three of suggests that it stays on frogs at least 20 weeks3. In the inhibitory metabolites, 2,4-diacetylphloroglu- the future, we may be able to facilitate the re-intro- cinol from Lysobacter gummosus and violacein and duction of amphibians from survival-assurance indole-3-carboxaldehyde from Janthinobacterium colonies. Population declines and extinctions due to lividum, have been identified from pure bacterial Bd are ongoing and more research is urgently needed cultures2. In addition, these metabolites are found on into the efficacy of a bioaugmentation strategy for some amphibians in nature in concentrations high amphibians. enough to inhibit Bd. To our knowledge, amphibians do not produce these metabolites themselves, so it 1Weldon, C., du Preez, L.H., Hyatt, A.D., et al. (2004) appears that their symbiotic skin bacteria are Origin of the amphibian chytrid fungus. Emerging responsible. Infectious Diseases 10, 2100–2105. We have shown through a ‘bacterial removal’ experi- 2Brucker, R.M., Harris, R.N., Schwantes, C.R., et al. ment that the resident microbes on the skins of (2008) Amphibian chemical defense: antifungal Plethodon cinerus, red-backed salamanders, amelio- metabolites of the microsymbiont Janthinobacte- rate the symptoms of chytridiomycosis. Individuals rium lividum on the salamander Plethodon cinereus. with their skin bacteria reduced by exposure to anti- Journal of Chemical Ecology 34, 1422–1429. biotics had greater morbidity than those salamanders left with their skin bacteria unmanipu- 3Harris, R. N., Brucker, R.M., Walke, J.B., et al. lated. Bioaugmentation is a strategy whereby we (2009 in press) Skin microbes on frogs prevent mor- increase the proportion of individuals with a species bidity and mortality caused by a lethal skin fungus. of anti-Bd bacteria already found on other members ISME Journal, doi:10.1038/ismej.2009.27. of the population. In a laboratory experiment, we added J. lividum to skins of the mountain yellow- By: Reid N. Harris & Kevin P. C. Minbiole, legged frog, Rana muscosa, before exposure to Bd3. Department of Biology (RNH) & Department Those treated with J. lividum suffered no mortality of Chemistry and Biochemistry (KPCM), James or morbidity, whereas frogs exposed to Bd alone lost Madison University, Harrisonburg, VA 22807, USA. weight and died. Frogs that had J. lividum added to Email: [email protected] / [email protected] their skins had much higher concentrations of viola- cein on their skins, suggesting that this bacterial- produced metabolite