The cereal rust , Abacarus hystrix, cannot be used for biological control of quackgrass

A. Skoracka1 and B.G. Rector2

Summary Quackgrass, Elymus repens (L.) Gould, is a perennial grass spreading by vigorous underground rhi- zomes. Because of its capacity for rapid spread and persistence, it is considered as a common weed in many settings worldwide. The cereal rust mite, Abacarus hystrix (Nalepa), is a polyphagous, phy- tophagous mite attacking quackgrass and many other grasses including wheat. Its feeding causes leaf discoloration and inhibition of seed production. This mite can also transmit plant pathogens. Its role as a potential biological control agent for quackgrass control was considered since previous work had suggested that populations of this mite colonizing quackgrass may be specifically adapted to that host. The ability to colonize wheat by these quackgrass population should, however, be first excluded. The aim of this study was to estimate whether the cereal rust mite quackgrass population can colonize wheat. For this purpose, female from quackgrass were transferred and subsequently reared on quackgrass (control, n = 132) and wheat (n = 125). Colonization ability was assessed by comparing the mean oviposition rate, mean female survival and mean number of progeny on each host. Mites had similar success in the colonization of both quackgrass and wheat. The conclusion is that the quackgrass population of cereal rust mite is well adapted to wheat and thus cannot be considered as a potential agent against quackgrass.

Keywords: , , wheat, quackgrass.

Introduction Quackgrass is most effectively and commonly con- trolled by a combination of chemical and cultural meth- Quackgrass, Elymus repens (L.) Gould [ex. Agropyron ods. Herbicides for its control are available for most repens (L.) P. Beauv.], is a common and cosmopoli- crops (e.g. Kells and Wanamarta, 1987; Ivany, 2002; tan species, occurring almost worldwide. It repro- Ivany and Sanderson, 2003). A few that duces vegetatively by vigorous underground rhizomes, live and feed on quackgrass are known, including Hy- which, in turn, develop axillary buds that are capable draecia spp. (Lepidoptera: Noctuidae) (Giebink et al., of developing into new rhizomes and daughter shoots. 2000), Delia coarctata Fallen (Diptera: Anthomyiidae) Quackgrass is a highly aggressive, sod-forming, peren- (Marriot and Evans, 2003) and Abacarus hystrix (Na- nial grass native to Eurasia. Because of its invasive- lepa) (Acari: Eriophyidae) (Frost and Ridland, 1996). ness and persistence, it is considered as a serious weed However, no information on the biological control of of agronomic crops, turfgrass, landscapes, grasslands, this species was found in the literature. gardens, lawns and nurseries in many parts of the The cereal rust mite (CRM), A. hystrix (Nalepa), is world. In the USA, it is listed as a noxious and inva- a phytophagous mite belonging to the family Eriophy- sive weed introduced from Europe (Palmer and Sagar, idae. Eriophyid mites are often considered to be prom- 1963; Hultén and Fries, 1986). ising biological control agents for weeds because they debilitate their hosts by their feeding, they can transmit 1 Adam Mickiewicz University, Department of and diseases to their hosts in certain cases and they tend Ecology, Institute of Environmental Biology, Faculty of Biology, to be highly host-specific (Rosenthal, 1996). Feeding Umultowska 89, 61-614 Poznań, Poland. on A. hystrix causes leaf discoloration and inhibition 2 USDA-ARS, European Biological Control Laboratory, Montpellier, France. of host seed production. The mite is known to transmit Corresponding author: A. Skoracka . plant pathogens, including ryegrass mosaic virus, a se- © CAB International 2008 rious disease of temperate grasslands, and Agropyron

317 XII International Symposium on Biological Control of Weeds mosaic virus, a minor disease of quackgrass (Oldfield colony was maintained in the laboratory (20°C, 40% ± and Proeseler, 1996). Thus, the mite is able to seriously 1 RH, 16–17:7–8 L/D) for 6 weeks. Afterwards, mites damage its host plants. However, up to now, A. hys- were used for the experiment. trix was not considered as a possible biological control Plants for the experimental were prepared as fol- agent due to its wide host range. The host range of the lows. Laboratory-grown quackgrass shoots were trans- CRM includes records from at least 60 grass species, planted to pots, and wheat shoots were grown from many of which are of economic importance (E. de Lillo seed. There was one grass shoot in each pot. Ten to and J. Amrine, 2007, personal communication). Among fifteen females were transferred from the quackgrass the hosts, the mite is dispersed passively by wind stock colony to grasses grown in pots. Females were currents. transferred under a stereomicroscope using an eyelash High host specificity is an extremely important char- glued to a preparatory needle and put to the leaf of the acteristic in a biological control candidate. Above all, grass. Two combinations were tested: (1) QQ – females a weed biological control agent should not attack non- from quackgrass transferred to quackgrass (control), target plants, especially important crops. Despite many n = 134 and (2) QW – females from quackgrass trans- grass species having been recorded as hosts of A. hys- ferred to wheat, n = 125. Ten replicates were carried trix, its role as an agent of quackgrass control was con- out for each combination. A replicate was defined as sidered since previous work has shown that some CRM a single plant with 10 to15 mites transferred onto it. populations colonizing quackgrass may be specifically Each plot was covered on with nylon taffeta and main- adapted to that host. Previous observations have shown tained at 20°C, 40% ± 1 RH for 14 days. Afterwards, that certain quackgrass and ryegrass populations of the the plants were checked, and mites (number of experi- CRM neither accept nor survive on each other’s hosts mental females and their progeny: eggs, larvae, nymphs (Skoracka and Kuczyński, 2006; Skoracka et al., 2007). and adults) were counted using a stereomicroscope. Moreover, the existence of reproductive barriers among Three components of colonization ability were these populations has been found (A. Skoracka, 2007, measured for each treatment: (1) mean oviposition rate personal communication), suggesting that host popula- (total number of eggs oviposited by all females within tions of A. hystrix may represent a complex of species. the trial/total number of females tested within the trial), If a quackgrass-associated population of the CRM is (2) mean female survival rate (total number of females highly specific and adapted only to this host, it should survived within the trial/total number of females tested be considered as a potential biological control agent of within the trial) and (3) mean number of progeny (eggs, quackgrass control. Because quackgrass often grows larvae, nymphs and adults tallied separately) within near wheat, the potential for wheat colonization by a each trial. Bootstrap (Efron and Tibshirani, 1993) was quackgrass-associated population of A. hystrix should used to compute 95% confidence intervals (CI). Differ- be first excluded. Specifically, the aim of this study ences between means were tested using the criterion was to estimate whether the quackgrass-specific CRM of CI overlapping (i.e. means were regarded as ‘sig- population can colonize wheat. nificantly different’ when their CI did not overlap) and using a Hotelling’s T 2-test and t-test. Methods and materials Results Two grass species were used as host plants in this study: quackgrass and wheat Triticum aestivum L. Quack- No significant differences were shown between the grass rhizomes were collected in September 2006 from ability to colonize quackgrass and wheat by the quack- a study plot in Poznań, Poland (52°24.5¢N, 16°53.0¢E; 2 grass-associated mites (T : F3,16 = 0.49, p < 0.6946). elevation 87 m) and put in boxes with sandy soil. The Specifically, there were no significant differences in plants were kept at room temperature and exposed to mean oviposition rate (t = 0.56, df = 18, p = 0.5865), artificial light for 19 h per day. To protect the plants mean female survival (t = 0.36, df = 18, p = 0.7215) or from infestation by mites, insects or fungi, the boxes mean number of progeny between mites developing on were covered with nylon taffeta fastened to a wooden quackgrass and those developing on wheat (Table 1, frame. When sufficiently grown, plants were used for Fig. 1). the preparation of the stock mite colony and the ex- periment. A stock colony of mites was established with individuals collected from quackgrass from the same Table 1. Mean oviposition rate and mean female survival ° ¢ study plot and from two other study plots (52 25.0 N, with 95% confidence limits (in parentheses) of 16°55.0¢E, elevation 63 m, and 52°23.0¢N, 16°52.0¢E, Abacarus hystrix that developed on quackgrass elevation 79 m.) in October 2006. Females from field- (QQ) and wheat (QW). collected plants were randomly selected and transferred to the un-infested plants in the laboratory. A detailed Trials Oviposition Survival description of the stock colony preparation can be QQ 13.9 (11.7–-16.9) 0.5 (0.4–0.7) found elsewhere (Skoracka and Kuczyński, 2004). The QW 13.1 (11.8–-14.3) 0.5 (0.3–0.6)

318 The cereal rust mite, Abacarus hystrix

80 QQ QW 60 r

40 Numbe

20

0 egg larva nymph adult

Figure 1. Mean number of progeny of Abacarus hystrix obtained on quackgrass (QQ) and wheat (QW ). Bars represent 95% confident limits around means.

Discussion Among the eriophyid mites causing notable dam- age to their grass hosts, A. hystrix is regarded as one of The idea of using eriophyoid mites for biological con- the most common and important. The mite has a great trol of weeds has been of great interest since the 1970s. capacity for rapid population increase achieving high The characteristics that make eriophyids promising population densities (Skoracka and Kuczyński, 2004). candidates for biological control are their frequent mo- At very high densities, the feeding of this mite causes nophagy (or frequent specificity directed to one host), plant wilting and delayed growth (Frost and Ridland, ability to suppress plant growth and reproduction, abil- 1996). However, this study shows that the quack- ity to destroy whole plant populations under favour- grass-associated CRM had high fecundity, survival able conditions, attack on all plant organs, particularly and development on wheat. It clearly appears that this the inflorescences, and seed suppression (Rosenthal, quackgrass-associated population has great coloniza- 1996). A few eriophyid species have been used in bio- tion ability and is well adapted to wheat and cannot logical control programs targeting weeds, e.g. Aceria be considered as a potential biological control agent chondrillae (Canestrini) to control Chondrilla juncea against quackgrass. introduced to Australia and USA (Anders, 1983) and Aceria malherbae Nuzzaci to control Convolvulus ar- vensis in USA (Boldt and Sobhian, 1993). Many other Acknowledgements species have been investigated and recommended for biological control, e.g. Aceria tamaricis (Trotter) (De We thank Dr Lechosław Kuczyński (AMU, Poznań) for Lillo and Sobhian, 1994), Aceria centaureae (Nalepa) remarks regarding the manuscript. The study was finan- (Sobhian et al., 1989), A. salsolae De Lillo & Sobhian cially supported by Polish MNiSW grant 3P04C03825. (Sobhian et al., 1999), rouhollahi Crae- mer (Sobhian et al., 2004), Epitrimerus taraxaci Liro (Petanovic, 1990), Phyllocoptes nevadensis Roivainen References (Littlefield and Sobhian, 2000) and Floracarus perre- Anders, L.A. (1983) Considerations on the use of phytopha- pae Khinicki et Boczek (Freeman et al., 2005). Sev- gous mites for the biological control of weeds. In: Hoy, eral European eriophyoids were suggested by Boczek M.A., Cunningham, G.L. and Knutson, L. (eds) Biologi- and Petanovic (1996) for the control of weeds in North cal control of pests by mites. University of California, America in the genera Cirsium, Lythrum, Convolvu- Berkeley, CA, pp. 53–56. lus and Galium. In addition, Boczek and Chyczewski Boczek, J. and Chyczewski, J. (1977) Eriophyid mites (Aca- (1977) found eriophyid mites in Poland associated with rina: Eriophyoidea) occurring on weedy plants in Poland. 56 weedy species. Roczniki Nauk Rolniczych 7, 109–113.

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