J. Appl. Entomol. Host range of Secusio extensa (Lepidoptera: Arctiidae), and potential for biological control of Senecio madagascariensis (Asteraceae) M. M. Ramadan1, K. T. Murai1 & T. Johnson2 1 State of Hawaii Department of Agriculture, Plant Pest Control Branch, Honolulu, Hawaii, USA 2 Institute of Pacific Islands Forestry, Pacific Southwest Research Station, USDA Forest Service, Volcano, Hawaii, USA Keywords Abstract Host range, Secusio extensa, Senecio madagascariensis Secusio extensa (Lepidoptera: Arctiidae) was evaluated as a potential bio- logical control agent for Madagascar fireweed, Senecio madagascariensis Correspondence (Asteraceae), which has invaded over 400 000 acres of rangeland in the Mohsen M. Ramadan (corresponding author), Hawaiian Islands and is toxic to cattle and horses. The moth was intro- State of Hawaii Department of Agriculture, duced from southeastern Madagascar into containment facilities in Plant Pest Control Branch, 1428 South King Hawaii, and host specificity tests were conducted on 71 endemic and Street, Honolulu, Hawaii 96814, USA. E-mail: [email protected] naturalized species (52 genera) in 12 tribes of Asteraceae and 17 species of non-Asteraceae including six native shrubs and trees considered key Received: September 15, 2009; accepted: components of Hawaiian ecosystems. No-choice feeding tests indicated April 6, 2010. that plant species of the tribe Senecioneae were suitable hosts with first instars completing development to adult stage on S. madagascariensis doi: 10.1111/j.1439-0418.2010.01536.x (78.3%), Delairea odorata (66.1%), Senecio vulgaris (57.1%), Crassoceph- alum crepidioides (41.2%), and at significantly lower rates on Emilia fos- bergii (1.8%) and Erechtites hieracifolia (1.3%). A low rate of complete larval development also was observed on sunflower, Helianthus annuus (11.6%), in the tribe Heliantheae. However, sunflower was rejected as a potential host in larval-feeding and adult oviposition choice tests involv- ing the primary host S. madagascariensis as control. Although larvae died as first instars on most test species, incomplete development and low levels of feeding were observed on nine species in the tribes Helian- theae, Cardueae and Lactuceae. Larvae did not feed on any non-Astera- ceae tested, including species with similar pyrrolizidene alkaloid chemistry, crops, and six ecologically prominent native species. Because all species of Senecioneae are non-native and weedy in Hawaii, these results indicate that S. extensa is sufficiently host-specific for introduction for biological control. High levels of feeding damage observed on potted plants indicate that S. extensa can severely impact the target fireweed as well as D. odorata, a noxious weed in native Hawaiian forests. The seed heads produce numerous plumed achnes Introduction (as many as 30 000 per plant) that disperse easily Madagascar fireweed, Senecio madagascariensis Poiret by wind, allowing rapid infestation of pastures (Asteraceae, Senecionae), is a daisy-like annual or (Motooka et al. 2004). All parts of fireweed contain biennial branching herb that grows upright to 50 cm pyrrolizidine alkaloids (PAs) which when consumed in height with small (1.5 cm diam) yellow flowers. by animals are converted into toxic compounds that ª 2010 Blackwell Verlag, GmbH 1 Host range assessment and potentials of Secusio extensa M. M. Ramadan, K. T. Murai and T. Johnson cause liver damage (Dale Gardner et al. 2006). Infestations on Oahu and Kauai have been con- Young animals are particularly vulnerable to PAs trolled mechanically, but on Maui and Hawaii, since senecionine may accumulate in milk (Small where more than 400 000 acres of rangelands have et al. 1993). Although unpalatable, fireweed is con- been invaded, chemical and mechanical control is sumed by livestock when other feed is not available not economically practical. Chemical control of fire- (Sindel and Michael 1988; Scott et al. 1998) or weed on the island of Hawaii alone would cost over when small plants are intermixed with desirable for- eleven million dollars per year, estimated as three age. Contaminated hay or silage from invaded fields treatments with the systemic herbicide MCPA @ $11 may also cause poisoning since the toxins are unaf- per acre on 350 000 acres (P. Motooka, University of fected by drying (Dickinson et al. 1976; Sindel Hawaii, CTAHR, 2002 pers. comm.). Generalist her- 1986). bivores (e.g. grasshoppers, weevils, thrips, aphids, Fireweed is native to the southeastern region of scale insects, whiteflies, and mites) that currently Africa, where it is known to occur from coastal areas feed on fireweed in Hawaii cause insignificant dam- to 1500 m above sea level. It is distributed from age (M. Ramadan, pers. obs.). Classical biological Madagascar and the Mascarene Islands through control using host-specific natural enemies from the coastal Mozambique to Kwazulu-Natal and the East- native range was selected as a method for reducing ern and Western Cape provinces of South Africa existing fireweed populations, curbing their spread (Sindel et al. 1998). In Madagascar, fireweed occurs and decreasing reliance on costly chemicals. The in small isolated populations in the low elevation potential for classical biological control of fireweed southeast and the semi-arid southwest of the island in Hawaii appears good because, unlike in Australia, (Marohasy 1989). In its native region, fireweed is there are no native species in the same tribe as fire- not perceived as an invasive species and is only com- weed (Senecioneae) and none of the naturalized mon on vacant lands, sand dunes, lands cleared for species is economically important. agriculture, and along roadsides (M. Ramadan, pers. The Hawaii Department of Agriculture (HDOA) obs.). initiated a survey for potential biological control Fireweed has variable growth habits and leaf agents in South Africa (Kwazulu-Natal province) shapes dependant on the type of soil and habitat, and Madagascar (southeastern Toliara province) dur- (Le Roux et al. 2006). Genetic analyses of fireweed ing August and September of 1999. During this sur- in Australia showed a close match with the S. mad- vey, eleven insects and two pathogens were shipped agascariensis complex from South Africa and a slight to the HDOA Insect Containment Facility for evalua- difference from S. madagascariensis from Madagascar tion and host range testing (M. Ramadan, unpub- (Scott et al. 1998). Molecular analysis of Hawaiian lished data). A yellow rust fungus identified as fireweed populations showed that they also match Puccinia lagenophorae Cooke (Basidiomycetes: Uredi- populations from South Africa more closely than nales) from fireweed in Australia, South Africa, and populations from Madagascar and Swaziland (Le Madagascar was tested on 42 species in eight tribes Roux et al. 2006). Hawaiian populations are thought of Asteraceae. The rust severely infected fireweed, to have arrived in carpet grass seed shipments from but tests were discontinued when two Hawaiian Australia (Motooka et al. 2004). endemic species were found to be susceptible (Killg- A significant weed of agricultural grasslands in ore et al. 2001). The insect agents included five Australia, fireweed has spread through many parts flower-head feeders, three stem borers, two root of coastal New South Wales and southeastern feeders, and a defoliating arctiid moth. Host testing Queensland, as well as southeastern Buenos Aires on seven of these species and a white rust were ter- province in Argentina (Sindel et al. 1998). It also minated because of rearing problems or minimal has been recognized as a noxious weed in Colombia, impact on fireweed. One insect, the arctiid moth Sec- Venezuela, Uruguay, and Japan (Satoru et al. 1999). usio extensa (Lepidoptera: Arctiidae), showed poten- Efforts to control fireweed by mechanical, chemical tial as an agent and was therefore studied further. and biological means, using herbivores already pres- This report summarizes results of detailed studies ent, failed against well-established populations in on the host range of the Madagascan fireweed moth, Australia, and a previous biological control project S. extensa. A cohort of this species was introduced in against fireweed was halted because of lack of funds October 1999 to the HDOA Insect Containment (Marohasy 1989; MacFadyen and Sparks 1996). Facility, where host-specificity tests were conducted Fireweed has been spreading widely in the Hawai- to address its potential as a biological control agent ian Islands since its first appearance around 1980. and its possible impact on non-target species. 2 ª 2010 Blackwell Verlag, GmbH M. M. Ramadan, K. T. Murai and T. Johnson Host range assessment and potentials of Secusio extensa deposition. Moths were provided with honey on the Materials and Methods lid netting and a water container with a cotton wick. Eggs were collected daily and placed in Petri dishes. Origin and identity of agent population Newly hatched larvae were used in host range tests Caterpillars of the fireweed moth, S. extensa (But- and colony maintenance. ler), (Lepidoptera: Arctiidae) were collected from Colonies were continuously propagated on potted the southern region of Toliara Province, Madagas- fireweed for about eight generations per year. car. Young and mature larvae were collected from Fireweed was propagated on Oahu from field col- fireweed infested plants at three localities along the lected plants shipped from the island of Hawaii. In sand dunes of the Indian Ocean: Saint Luce case of a shortage of fireweed, Crassocephalum crepid- (24°.46¢S, 47°.10¢E), Evatra (24°.58¢S, 47°.05¢E), ioides (Benth.) was added to the cages mainly dur- and Fort Dauphin (25°.02¢S, 46°.56¢E). Larvae were ing the intense feeding periods of the final instar. reared to the pupal stage on field collected fire- This plant has been shown in previous experiments weed cuttings immersed in water. The initial to be a secondary host for S. extensa. However, lar- cohort produced from this collection was 606 vae in control cages for host-specificity tests were pupae, out of which 398 developed into adults reared exclusively on the primary host, S. madaga- (34% pupal mortality) with a sex ratio of approxi- scariensis.