Feeding and oviposition tests refute host–herbivore relationship between Fragaria spp. and Abia sericea, a candidate for biological control of Dipsacus spp. B.G. Rector,1 V. Harizanova2 and A. Stoeva2 Summary Two species of teasels, Dipsacus fullonum L. and Dipsacus laciniatus L. (Dipsacales: Dipsacaceae), have become invasive in the USA and are targets of a classical biological control programme. The sawfly, Abia sericea (L.) (Hymenoptera: Cimbicidae), was identified as a teasel biological control candidate, but reports in the literature raised concerns about the possibility of non-target effects on members of the genus Fragaria L. Oviposition tests and multiple- and no-choice feeding tests were conducted on A. sericea to test the suitability of three Fragaria spp. (Fragaria ´ ananassa Duchesne, Fragaria vesca L. and Fragaria viridis Duchesne) as host plants. In oviposition tests, males were paired with females in cages containing a D. laciniatus plant and plants of the three Fragaria spp. In 16 replicates, all eggs were laid in D. laciniatus leaves, except in one replication in which two eggs were laid in a leaf of F. viridis (vs >100 eggs in D. laciniatus leaves by the same female and >1000 eggs by all females). From these two eggs, one larva hatched, which fed only on D. laciniatus in a choice test and died before pupating. In no-choice feeding tests on the three Fragaria spp., larvae of first, second, third and fourth instars were infested in separate tests, and no feeding, tasting or damage was observed on any Fragaria spp. in any replicate; all larvae died. In multiple-choice feeding tests, first, second, third and fourth instar larvae were reared to pupation. Larvae of all instars fed exclusively on D. laciniatus, while no feeding attempts, tastes or feeding damage was observed on any Fragaria spp. plant. Entomology and agricultural literature were thoroughly reviewed, and the connection between Fragaria and A. sericea was traced to two brief anecdotal mentions that were widely repeated but never supported by collection or bioassay data. The tests and other evidence presented in this paper refute the idea that Fragaria spp. are suitable hosts for A. sericea. Keywords: teasel, invasive plants, strawberry. Introduction as affecting natural areas in 14 states and four national parks (USDI-NPS, 2005). This combined status and Two invasive teasels of European origin, Dipsacus other factors led to the initiation of a US-government- fullonum L. and Dipsacus laciniatus L., are emerging sponsored biological control programme targeting Dip- as problem weeds in various parts of North America, sacus spp. in 2003. particularly in non-agricultural habitats (Sforza, 2004). The genus Dipsacus L. is in the family Dipsacaceae, Either or both species occur in 43 states (Singhurst and an exclusively Old World family with no species native Holmes, 2001; USDA, 2005; Rector et al., 2006) and in to the Western Hemisphere (Verlaque, 1985) and no several Canadian provinces (Werner, 1975). Five states members of significant economic importance (Bailey, (Colorado, Iowa, Missouri, New Mexico and Oregon) 1951). Thus, in selecting biological control candidates have declared teasels noxious (USDA-NRCS, 2005). (BCCs) to combat invasive teasels in North America, They are also listed as invasive by 11 other states and those restricted to feeding on hosts within the family Dipsacaceae should be specific enough to avoid non- 1 USDA-ARS, European Biological Control Laboratory, Campus Inter- target concerns (Wapshere, 1974; Rector et al., 2006). national de Baillarguet, Montferrier-sur-Lez, France. However, for any teasel BCC, the list of plants tested 2 Agricultural University, Faculty of Plant Protection, Department of En- tomology, 12 Mendeleev St., 4000 Plovdiv, Bulgaria. will include many species outside the family Dip- Corresponding author: B.G. Rector <[email protected]>. sacaceae, including economic and rare or threatened © CAB International 2008 species, as well as those occupying similar ecological 311 XII International Symposium on Biological Control of Weeds niches, those sharing similar life histories, plant archi- in northern Bulgaria at two locations in the vicinity tecture and secondary chemistry, and those with pub- of Pleven (43°24.26¢N, 24°28.76¢E and 43°14.16¢N, lished associations with the BCC (Rector et al., 2006). 24°18.24¢E) and one location near Lovech (43°04.12¢N, Abia sericea (L.) (Hymenoptera: Cimbicidae) is a 14°44.09¢E). All larvae from these three sites were sawfly that is native to Europe and is a candidate for grouped together and reared to pupation under ambient biological control of invasive teasels in the USA. The climatic conditions near Plovdiv, Bulgaria (42°08.64¢N, most recent, comprehensive host-range records for A. 24°43.81¢E). On 29 June 2006, adult females were col- sericea (Liston, 1995, 1997; Taeger et al., 1998) list lected from D. laciniatus plants in the field near Sofia two host species in the family Dipsacaceae [Knautia ar- (42°3757 N, 23°303427 E). Oviposition tests and feed- vensis (L.) Coult. and Succisa pratensis Moench], plus ing tests were conducted using all of these insects and the genus Fragaria L., which is in the family Rosaceae their progeny. and includes cultivated and wild strawberries. In assessing A. sericea as a BCC of teasels, it was nec- Test plants essary to start by testing the suitability of Fragaria as a host, to either confirm or refute the existing herbivore– The D. laciniatus plants used in host-specificity host records. Any amount of A. sericea larval feeding on testing were either grown from seed gathered from Fragaria plants, particularly on cultivated strawberry wild plants in Bulgaria or were transplanted from fal- (Fragaria ´ ananassa Duchesne), would immediately low fields near Plovdiv (42°08.64¢N, 24°43.81¢E). disqualify it as a BCC of teasel. It was also necessary The test plants of the wild Fragaria spp. (Fragaria vesca from the start to confirm the use of D. laciniatus as L. and Fragaria viridis Duchesne) were dug up from a host plant suitable for complete development by A. the wild on a mountainside near Plovdiv (41°53.80¢N, sericea, as this relationship had only previously been 25°20.07¢E), transferred to pots and identified to spe- observed in the field without further testing (Rector et cies with a key (Markova, 1973). Cultivated strawberry al., 2006; Rector et al., unpublished data). (F. ´ ananassa) plants were vegetatively propagated The purpose of this paper is to report the successful from 6-year-old plants. rearing of A. sericea on D. laciniatus and to refute the published herbivore–host relationship between A. seri- Oviposition tests cea and Fragaria spp. Test 1: On 11 Oct 2005, a male and three female A. sericea adults were put in a large cage (40 ´ 20 ´ 40 cm, made from clear, plastic panels with fine nylon mesh Materials and methods tops) with two D. laciniatus and two F. ´ ananassa plants. At 8:30 A.M. on 12 October, the teasel plants Literature survey were removed from the cages, leaving only the straw- An intensive literature search was conducted to berry plants. At 4:30 P.M. on the same day, the teasel determine the origin(s) of reports of a herbivore–host plants were returned to the cages. The insects were then relationship between A. sericea and Fragaria spp. An left in the cage with both plant species until they died. attempt was made to identify the original source lit- A 5% sugar solution was provided for the insects with erature behind this alleged association and to gauge a cotton wick from which to feed. its plausibility. Literature surveyed included various Test 2: Pairs of newly emerged adults were released entomological texts, articles and monographs. Most of into small plastic cages (20 ´ 20 ´ 30cm) with one pot- these were on the subject of basic sawfly (Hymenop- ted plant each of D. laciniatus, F. ´ ananassa, F. vesca tera: Symphyta) biology and taxonomy (e.g. André, and F. viridis. Cages were kept in an insectary at ap- 1879; Stein, 1883; Cameron, 1890; Dalla Torre, 1894; proximately 22/15°C, day/night, and 16 h daylight. Konow, 1901; Enslin, 1917; Berland, 1947; Lorenz and The adults were kept in the cages until they died, af- Kraus, 1957; Ermolenko, 1972; Vasilev, 1978; Wright, ter which the plants were removed from the cages and 1990; Magis, 2001). Other sources included sawfly examined with a magnifying glass for eggs laid, and host-range compendia (Liston, 1995, 1997; Taeger et this number was recorded for each plant species. A total al., 1998), work specific to Abia spp. (Kangas, 1946) of 16 replications were conducted during the period 1 and a general entomology text (Krishtal, 1959). In ad- April to 1 Aug 2006. dition, pest management literature for cultivated straw- berries was surveyed to determine whether A. sericea is No-choice larval feeding tests considered a pest to commercial strawberry growers in its native range in Europe. No-choice feeding tests were conducted in small plastic cages. In each cage, one plant of each of the three Fragaria spp.—F. vesca, F. viridis and F. ´ anan- Insect material assa—were exposed to six larvae of first instar of A. On 4 September 2005, 29 late-instar larvae of A. sericea. Four replications were carried out, while one sericea were collected from the wild on D. laciniatus cage with only D. laciniatus plants and six larvae of the 312 Feeding and oviposition tests refute host–herbivore relationship between Fragaria spp. and Abia sericea same instar from the same cohort was set up as a con- host–plants list for A. sericea. The Krishtal (1959) in- trol. Larvae were checked every 48 h whereupon the formation in particular has been characterized as ‘unre- number of dead larvae was recorded.