Ms. Ghislaine Cortat is the lead biocontrol researcher at CABI working on the hawkweed insects. CABI researchers and MSU research Dr. Jeff Littlefield have collected and tested eight insect species for three invasive hawkweeds. The three invasive hawkweeds targeted for biocontrol are:
- mouse-ear hawkweed (P. officinarum, H. pilosella)
- orange hawkweed (P. aurantiaca, H. aurantiacum)
- meadow hawkweed (P. caespitosa, H. caespitosum, H. pratense)
The biocontrol insects damage the stolons, roots, and stems of the plant impacting seed production and limited spread. Three of the initial eight insects were found to feed on native species in host-specific testing so now the testing is limited to five remaining insects.
Hawkweed plants used for biocontrol open field insect testing.
The parthenogentic gall wasp (Aulacidea subterminalis) ovipositions into the stolons of orange and mouse-ear hawkweeds in host range testing. The gall wasp screening was completed at Montana State University (MSU) by Dr. Jeff LIttlefield. MSU submitted the petition for release of this insect to the Technical Advisory Group (TAG) in 2009 and USDA APHIS PPQ approved field release in 2010. MSU and CABI have been mass rearing the insects in quarantine since 2008 for release.
The Gall wasp (Aulacidea subterminalis) ovipositing on hawkweed.
Insect galls on mouse-ear hawkweed.
The two hover flies (Cheilosia urbana, Cheilosa psilophthalma) impact different parts of of the hawkweed plant. C. urbana impacts the roots while C. psilophthalma eats the above-ground plant parts. A petition to the Technical Advisory Group (TAG) is currently being compiled by former project scientist, Dr. Gitta Grosskopf-Lachat, for Cheilosia urbana in 2012.
Larvae of C. psilophthalma survived on three native North American hawkweed species in no-choice larval transfer tests. Since the hoverfly does not mate in captivity we were not able to carry out multiple-choice oviposition tests in field cages. For this reason, open-field tests are needed to describe its realized host range. However, testing for Cheilosa psilophthalma was discontinued due to its low occurrence in the field.
Hover fly (Cheilosa urbana) impacts hawkweed roots.
Hover fly (Cheilosa psilophthalma) eats above-ground plant parts.
stem gall wasps
Two different species of stem gall wasps (Aulacidea hieracii and Aulacidea pilosellae) are being investigated. These gall wasps reduce the number of flower heads and inhibit flowering of hawkweed plants. Research still continues on Aulacidea pilosellae but it has been discontinued on Aulacidea hieracii (see below).
Aulacidea pilosellae ovipositing into a stolon.
Aulacidea pilosellae is a small gall wasp which induces galls on the midrib of leaves, flower stalks and stolons. The wasp overwinters in the larval stage. A. pilosellae collected in eastern Germany, Poland, and the Czech Republic is univoltine and prefers orange and meadow hawkweed while the population from southern Germany and Switzerland is bivoltine and showed a preference for mouse-ear hawkweed. Host-range tests are ongoing. So far, the univoltine population attacked four native North American hawkweed species and the bivoltine population attacked one native species under no-choice conditions. None of the native North American hawkweeds exposed in multiple choice tests were attacked.
Aulacidea pilosellae galls on a flower stalk.
Aulacidea hieracii galls on meadow hawkweed.
Unfortunately, extensive host rang testing showed the gall formation of A. hieracii on the target weeds appears to be a rare event and work with this species was therefore discontinued.
new Zealand insects
There are also many insects released on hawkweeds in New Zealand where they too are invasive. There are four invasive hawkweed species in New Zealand with the most troublesome being mouse-ear hawkweed (Hieracium pilosella). Five insects have already been approved for release in New Zealand. New Zealand does not have any native hawkweeds so the biocontrol approval process has progressed more quickly than in North America.
The gall midge (Macrolabis pilosellae) has been released for biocontrol on invasive hawkweeds in New Zealand and is now established in the field. The multivoltine gall midge galls the rosette center, flower heads, and stolen tips of hawkweeds. Larval feeding on the leaf tissue prevents the unfolding of the leaves. In no-choice tests the gall midge did develop on most native North American Hieracium spp. so this agent was removed from the list of potential North American agents.
Female gall midge (Macrolabis pilosellae) ovipositing.
For more information on hawkweed biocontrol research, contact Ghislaine Cortat.