|Chinese tallowtree (Triadica sebifera)|
Chinese tallowtree (Triadica sebifera), is an invasive weed of the Southeastern USA. Impacting 185,000 ha of coastal wetlands forests, stranded swamps, flatwoods, ruderal communities and other natural areas. This invasion impacts endangered whooping cranes and Attwater’s prairie chicken recovery efforts. Tallowtree is a prohibited and noxious weed in Florida, Louisiana, Mississippi, and Texas. The projected economic cost of controlling this weed in forest lands of Texas, Louisiana, and Mississippi during the next 20 years ranges from $200 to $400 million. Chinese tallowtree invasions affect the honeybee industry by replacing native vegetation. Invasions by this weed result in monospecific stands, creating pollen deserts where other pollen sources are unavailable during prolonged periods of the year. Classical biological control can provide an ecologically sound, cost effective, and sustainable management solution to protect these diverse agricultural, forest, and natural habitats.
Biological control screening of potential agents for tallowtree began in 2006 with foreign surveys, in collaboration the Wuhan Botanical Garden, Chinese Academy of Sciences (Wuhan, China). These surveys discovered several insect species feeding on Chinese tallowtree that might be suitable for biological control. Several species were not pursued for release as their host range was deemed too broad. These rejected species included Heterapoderopsis bicallosicollis, Sauris nr. purpurotincta, and Dichomeris cymatodes. However, after several years of overseas and quarantine testing two species, Bikasha collaris and Gadirtha fusca, showed narrow host ranges and damaging impacts on the weed. Both species should be released to assist in the sustainable control of Chinese tallowtree.
Chinese tallowtree growing for insects in quarantine. (Photo: E.Pokorny)
Invaded distribution of tallow in the southeastern USA. Not shown here is a small infestation in Butte, Los Angeles, Sacramento, and Yolo counties, California.
Bikasha collaris (Baly) (Coleoptera Chrysomelidae) is a small beetle with adults about 2 mm long. In its native range, this flea beetle has a temperate to subtropical distribution and was collected in Hubei, Ghizhou, Guangsi, and Hunan provinces of China ranging from 31.6° to 24.8 ° north latitude. Adults feed on tallow leaves, young stems, and even woody stems. Eggs are usually oviposited in groups on leaves and the larvae tunnel in roots of the weed. The general life cycle of B. collaris under laboratory conditions fed T. sebifera was about 45 days from egg to adult. Adult females lived on average 156.8 (± 12.1, n=30; range 49-272) days.
Life history stages of the flea beetle, Bikasha collaris reared on roots and leaves of Triadica sebifera in quarantine USDA/ARS/IPRL. Eggs are usually laid in clusters in soil at base of plant. Early and late instar larvae tunnel in roots. Horizontal black bar = 1 mm in length
Research publications on Bikasha collaris:
The defoliating caterpillar, Gadirtha fusca Pogue (Lepidoptera: Nolidae) is a specialist herbivore species found on the host in its native range. Originally assigned to a different species, Gadirtha inexacta, further molecular and morphological study indicated this was a new species. Individuals of G. fusca were collected in its native range at 14 sites in south, central, and eastern China. Collections occurred in several regions from Jiangxi, Hunan, Guangxi, Anhui and Guangdong provinces. Complete G. fusca development from egg hatch to adult emergence required an average (± SE) of 25.8 (± 0.1) days. Populations of the moth G. fusca is multivoltine, possibly passing through 4-5 generations each year in Hubei Province, China. The G. fusca individuals are thought to pass the winter months as eggs.
Life history stages of the defoliating moth, Gadirtha fusca reared on leaves of Triadica sebifera in quarantine USDA/ARS/IPRL. Eggs are usually laid individually on leaves. Early and late instar larvae feed externally on leaves. Scale bar for early instar larva = 1 mm; all others = 1 cm in length.
Research publications on Gadirtha fusca: