Host-specificity testing onLeipothrix dipsacivagus (Acari: Eriophyidae), a candidate for biological control of Dipsacus spp. A. Stoeva,1 B.G. Rector2 and V. Harizanova1 Summary Leipothrix dipsacivagus Petanovic & Rector is the first eriophyid mite recorded from hosts in the genus Dipsacus L. and is considered a potential candidate for biological control of invasive teasels (Dipsacaceae). Host-specificity testing onL. dipsacivagus (Acari: Eriophyidae) was carried out under insectary conditions for 4 months, from 19 April until the end of August, 2006. The laboratory colony of L. dipsacivagus was descended from mites collected on Dipsacus laciniatus L. in Klokotnitsa, Bulgaria. They were tested in choice and no-choice tests on Dipsacus fullonum L., Knautia arvensis L., Cephalaria sp. and Scabiosa sp. In the choice experiments, individual D. laciniatus plants in- fested with L. dipsacivagus were placed in cages with one to two plants of each test species. There were four replicates. Data were recorded at 10, 20, 30, 40, 60 and 90 days after infestation of test plants. After 10 days, only D. laciniatus was infested. After 20 days, mites were vagrant on all the plants except Scabiosa, and colonies were established on all Dipsacus plants. Some Cephalaria and Scabiosa plants had vagrant mites at days 20 and 30, respectively, but all of these were dead by days 30 and 40, respectively. By day 60, all Knautia plants were colonized, although these colonies later died. The mite successfully colonized only D. laciniatus and D. fullonum and temporarily colonized K. arvensis. In the no-choice tests, each of four plants of a given test species was infested with five mites/plant in a single cage. There were three replications (cages) for each test-plant species. Mites on plants other than Dipsacus spp. began to die after 10 days. Reproducing populations of L. dipsaciva- gus established only on D. laciniatus and D. fullonum. Keywords: teasel, invasive plants, mites, Dipsacaceae. Introduction USA. According to Petanovic and Rector (2007), the mite occurs on both the upper and lower leaf surfaces Leipothrix dipsacivagus Petanovic & Rector is the first of Dipsacus spp. as a vagrant causing rust-like symp- eriophyid mite recorded from hosts in the genus Dip- toms, wrinkles on the longitudinal folds of the leaves, sacus L. (Petanovic and Rector, 2007). This species was ‘witches broom’ of the plant (i.e. reduced internode first collected in Serbia in 1999 but was misidentified length and deformed leaves), stunting, delayed flow- (Petanovic, 2001). It was subsequently collected during ering and malformation of the flower heads. Analyses surveys conducted in Serbia, Bulgaria and France in of symptomatic plant tissues for presence of microbial 2005, described as a new species (Petanovic and Rec- plant pathogens were negative (Petanovic and Rector, tor, 2007), and is now a candidate for biological control unpublished data). A study of the injuries caused by the of invasive teasels (Dipsacus spp., Dipsacaceae) in the mite (Pecinar et al., 2007) showed that the injury to the leaves is conspicuous at the morphological and physi- ological as well as the anatomical level. 1 Agriculture University, Faculty of Plant Protection, Department of En- Eriophyid mites are frequently considered to be tomology, 12 Mendeleev Street, 4000 Plovdiv, Bulgaria. promising candidates for weed biological control due 2 USDA-ARS, European Biological Control Laboratory, Campus Inter- to their high host specificity, rapid life cycle and se- national de Baillarguet, Montferrier-sur-Lez, France. vere damage to their host plants (Littlefield and Sob- Corresponding author: A. Stoeva <[email protected], vili@au- plovdiv.bg>. hian, 2000; Rancic and Petanovic, 2002; Sobhian et © CAB International 2008 al., 2004). In one study, more than 80% of eriophyid 328 Host-specificity testing onLeipothrix dipsacivagus species occurring on weeds were monophagous (Boc- laciniatus plant was placed together with either three zek and Petanovic, 1996), which is a key criterion for or seven pots of a test plant species, depending on the a successful weed biological control agent. A critical size of the cage. Plants were arranged in a randomized part of any biological control program is to test the design within the test cages (four pots in the small and host range of candidate agents to establish the level of eight pots in the large cages). Pots were arranged such risk posed to non-target plants and ensure that agent that the leaves of adjacent test plants within each cage releases will not do more harm than good (Cullen and were touching to facilitate migration of the mites be- Briese, 2001). tween plants. For each plant species, four replications The purpose of the present paper is to report on ini- were made with each cage representing a replication. tial results concerning host-specificity testing of the The plants were checked regularly under a stereomi- new eriophyoid mite L. dipsacivagus, a potential can- croscope to monitor the migration of the mites. At 10, didate for biological control of Dipsacus spp., in the 20, 30, 40, 60 and 90 days, the number of test plants USA. with mites present was recorded. The infestation was recorded as the number of infested plants in each cage Methods and the percentage of infestation was calculated. No-choice test – Potted plants of D. fullonum, K. Origin and maintenance of test population arvensis, Scabiosa sp. and Cephalaria sp., were tested. D. laciniatus plants were tested in separate cages as a L. dipsacivagus individuals were collected from control. Five adult mites were transferred under a ste- cutleaf teasel, Dipsacus laciniatus L., plants in a field reo microscope to the leaves of each test plant, using near Klokotnitsa, Bulgaria (42°00.43¢N, 25°27.41¢E) a fine brush. For each replicate, four plants of one test and brought to the insectary of the Department of En- species were arranged in a small cage with three rep- tomology, Agricultural University in Plovdiv, Bulgaria. lications per species. The plants were checked under a Species identification was made by R. Petanovic, De- stereomicroscope regularly. At 10, 20, 30, 40, 60 and partment of Entomology, Faculty of Agriculture, Uni- 90 days, the infestation of test plants was recorded. versity of Belgrade, Serbia. The original mite colony In both, the choice and no-choice tests migration, was set up in August 2005 and maintained under insec- reproduction and feeding damage were recorded in ad- tary conditions on potted D. laciniatus plants. dition to the presence of mites. Test plants Results and discussion Several closely related plant species from the fam- ily Dipsacaceae were chosen: Dipsacus fullonum L., Choice test Knautia arvensis L., Scabiosa sp. and Cephalaria sp. Plants of D. laciniatus, the original host of the colony, The initial results from the choice tests are presented were used as a control. The test plants were grown in in Table 1 and Fig. 1. By the tenth day after the begin- plastic pots 8 cm in diameter from field-collected seed. ning of the experiment, migration was observed only Plants were used in tests after they had formed their on D. laciniatus plants. After 20 days, migration was first two foliar leaves. Test plants were inspected to en- observed to all test species, except for Scabiosa sp. At sure that they were in healthy condition at the time of that time, all plants in all control cages were 100% in- testing. fested, while in the test cages, infestation varied from 0% on Scabiosa sp. to 50% on D. fullonum plants. After 30 days, 100% of the D. fullonum plants were Host-specificity testing infested, and after 60 days, 100% of the K. arvensis The host-specificity tests were conducted under lab- plants were infested. Migration to the other two spe- oratory conditions from 19 April until the end of Au- cies, Cephalaria sp. and Scabiosa sp., was observed at gust, 2006. Two types of cages made from clear, plastic 20 and 30 days, respectively. panels with fine nylon mesh tops were used for the ex- Soon after migrating, most of the mites on plants other periments: small (20 ´ 20 ´ 40 cm) and large (20 ´ 40 than Dipsacus spp. died. By the 30th day on Cephalaria ´ 40 cm). During the tests, there was approximately 16 sp. and by the 40th day on Scabiosa sp., all the mites h of light per day in the insectary with temperatures of on these plants were dead. No further migration was approximately 22°C during the day and 15° C at night. observed to any of the test plants of these two species. Relative humidity was 50% to 60% in the insectary Besides the differences in the duration of dispersal, and 70% to 80% within the plastic cages. Two different differences in the development of the mite depending tests were designed for studying the host-specificity: on the host plant species were also noted. On the con- choice tests and no-choice tests. trol (D. laciniatus), the mite began reproducing after Choice test – Free migration was allowed from 10 days, while on D. fullonum and K. arvensis plants, any infested D. laciniatus plant to other plants in the mites were reproducing after 20 days and 30 days, re- same cage. In each cage, one pot with an infested D. spectively. After 30 days, there were no differences in 329 XII International Symposium on Biological Control of Weeds Table 1. Results of host-specificity testing with Leipothrix dipsacivagus at lab conditions at the Agricultural University-Plovdiv in 2006. Test plant species No of plants No of infested plants (days after infestation) Feeding tested 10 days 20 days 30 days 40 days 60 days 90 days damage Test 1. Choice test Dipsacaceae D. laciniatus L. (control) 20 17 20 20 20 20 20 Yes Dipsacus fullonum L.