Oviposition preference of Pieris brassicae (L) on different Brassica oleracea var. capitata L. cultivars

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1 Agronomy Reserch 7(Specil issue I), , Oviposition preference of Pieris rssice (L) on different Brssic olerce vr. cpitt L. cultivrs L. Metsplu, K. Hiiesr, K. Jõgr, E. Švilponis, A. Ploomi, I. Kivimägi, A. Luik nd N. Mens hikov Institute of Agriculturl nd Environmentl Sciences, Estonin University of Life Sciences, 1 Kreuzwldi St, 51014, Trtu; e-mil: Luule.Metsplu@emu.ee Astrct Cge White Butterfly, Pieris rssice L. is widely distriuted pest world wide nd cuses severe dmge to white cge (Brssic olerce vr. cpitt f. l L.). We studied oviposition preference of P. rssice on six different cge cultivrs in the field experiment. As in Estoni frmers grow rther numerous cge cultivrs, the determintion of more resistnt cge cultivrs is of gret importnce for frmers. Significntly more eggs were lid on the lte cultivrs 'Krutkizer' (52% of ll of the counted eggs) nd 'Turquoise' (40%). The mid seson cultivrs 'Krutmn', nd 'Lennox' were chosen more or less to the sme extent (2.5 5%). P. rssice dults void the erly cultivrs 'Prel' nd 'Golden Acre'. Key words: white cge cultivrs, Pieris rssice, oviposition preference INTRODUCTION The Lrge White Butterfly (LWB), Pieris rssice L., is cosmopolitn insect, nd is found wherever cruciferous plnts re grown (Hill, 1987). Sometimes mssive outreks of LWB my occur nd injury on cge cultures my e extensive. The first genertion lrve of LWB in Estoni usully feed on vrious cruciferous weeds; the second genertion prefers cge vegetle plnts. Insecticide ppliction ginst the lrvl stge of the LWB is the primry method of control. However, the use of rod spectrum insecticides hs led to well-known prolems, such s development of insect resistnce, the resurgence of secondry insect pests, nd persistence of residues tht re toxic to humns, nimls nd nontrget orgnisms (Hrdin et l., 1995). The insects sensitive olfctory sense cn e exploited y humns in severl wys to reduce dmge to economiclly importnt plnts. Host plnt selection is ehviourl process, which is minly regulted y chemoreception (Jeremy & Szentesi, 2003). Choosing good site for oviposition is chllenging tsk for femle nd her decision hs fr-reching nd profound consequences for the life history of her offspring (Jnz, 2002). The thickness of wx lyer, physiologicl ge, s well s the peculirities nd iochemicl composition of the plnt lef re mong the most significnt fctors when choosing the suitle oviposition plce (Bernys & Chpmn, 1994). Schoonhoven (1972) supposed tht P. rssice dults select sustrtes for oviposition sed on presence of specific group of llelochemicl glucosinoltes, which re common for ll Brssiccee, nd now more thn 120 different structures of those re known (Hopkins et l., 2009). Distriution of individul glucosinoltes s

2 well s their reltive mounts in plnts vries considerly. Cge cultivrs hve different glucosinolte profiles tht only prtly overlp, ut the predominnt glucosinoltes re sinigrin (2-propenyl-glucosinolte) nd glucorssicin (Poelmn et l., 2008). This reserch ddresses the need for finding effective options for mnging the cruciferous insect pest LWB in Estoni in the fce of the declining vilility nd populrity of conventionl chemicl insecticides. Dmge cused y LWB could e reduced y growing resistnt plnts nd could e recommended to e incorported in the reeding progrmmes so s to reduce the losses to this crop y P. rssice. We studied P. rssice oviposition preference nd the dynmics of their egg numers on six cultivrs of white cge in the field. MATERIALS AND METHODS Studies on the preference of P. rssice on different white cge (Brssic olerce vr. cpitt f. l L.) cultivrs were crried out in the experimentl grden of the Estonin University of Life Sciences in summer, The experiment ws conducted in rndomized complex lock design with three replictions. The host plnts used in this study included six cultivrs of white cge: erly cultivrs 'Prel' nd 'Golden Acre', mid seson cultivrs 'Krutmn' nd 'Lennox', lte cultivrs 'Krutkizer' nd 'Turquoise' were grown in seprte 2 x 2 m plots. In mid-my the seedling were trnsplnted in the plots with plnt to plnt distnce of 70 cm, 9 plnts per plot in totl. All the gronomic prctices were kept norml nd uniform in ll plots. The inter-plot uffer zones were plnted with eet (Bet vulgris L). The experiment strted in mid July. P. rssice egg-lying ws monitored weekly; eggs in ll experimentl plots were counted nd removed from plnts to void repeted counting. The dt were not suitle for nlysis with prmetric sttistics nd were insted compred using the Kruskl-Wllis test. Significnt differences mong cultivrs were determined using the Duncn s multiple test (P < 0.05). RESULTS The oviposition choice of LWB ws significntly ffected y the cge cultivrs (Kruskl-Wllis test: H 5;18 =13,73; P = ; Fig. 1). Significntly more eggs (P < 0.05, Duncn test) thn on ny other cultivrs were lid on lte cultivrs 'Krutkizer' (52%) nd 'Turquoise' (40%). Comprison of those two vrieties did not revel ny significnt difference etween 'Krutkizer' nd 'Turquoise' (P = 0.307) (Fig. 1). No eggs were lid y LWB on erly cultivr 'Prel', while only few eggs were found on the other erly cultivr 'Golden Acre' during the whole oservtion period. Likewise, the mid-seson cultivrs 'Krutmn' nd 'Lennox' were chosen for oviposition poorly, with 2.5% nd 5% respectively. Sttisticlly significnt difference could not e oserved (P = 0.8) in comprison of the four cultivrs, ut neither in comprison of erly nd mid-seson vrieties (P = 0.8). LBW infesttion strted t the lst week of July nd increse grdully (Fig. 2). It remined t the pek during first week of August nd declined grdully till the lst decde of August. First eggs were found on the July 28 only on lte cultivrs 'Krutkizer' nd 'Turquoise'. 407

3 Men Men±SE Men numer of eggs per plnt Prel dys Golden Acre 65 dys Krutmn dys Lennox 105 dys Turquoise 140 dys Krutkizer dys Cultivrs nd growing period (dys) Fig. 1. Oviposition of Pieris rssice on different white cge (Brssic olerce vr. cpitt f. l L.) cultivrs. Brs denoted with different letters re significntly different (P < 0.05, Duncn multiple rnge test). 140 Men; Whisker: Men±SE 120 Prel Lennox Men numer of eggs per plnt c c Krutmn Krutkise r Turquoise Golden Acre n.s Jul-08 5-Aug Aug Aug-08 Fig. 2. Dynmics of oviposition of Pieris rssice on different white cge cultivrs. Mens within columns followed y the sme letter re not significntly different sed on Duncn s test (P < 0.05). Dte 408

4 A comprison of those vrieties in first ssessment proved certin prevlence of 'Krutkizer', however, no sttisticlly significnt difference ws present (P = 0.059). In the next ssessment on August 05 'Krutkizer' nd 'Turquoise' were gin determined to e the preferred oviposition sites. As the first time, mjority of eggs were counted on 'Krutkizer', lthough difference etween 'Turquoise' ws not sttisticlly significnt (P = 0.26). The sme dy, eggs were found on 'Lennox' nd 'Krutmn', ut former counted significntly less thn 'Krutkizer' (P = ) or 'Turquoise' (P = 0.03) nd the ltter, significntly less thn 'Krutkizer' (P = 0.006) or 'Turquoise' (P = 0.04). It ws the only time during the whole oservtion period when few eggs were found on 'Golden Acrelt'. Similrly, more eggs were found on 'Krutkizer' nd 'Turquoise' in the next ssessment, on August 11. This time, 'Turquoise' ws the preferred cultivr, ut when compred with 'Krutkizer' significnt difference ws sent (P>0.05). Eggs could e found lso on 'Lennox', ut significntly less thn on 'Turquoise' (P = 0.04), wheres sttisticlly significnt difference ws not oserved when compred to 'Krutkizer' (P = 0.45). Lst ssessment on August 18 reveled eggs only on 'Krutkizer'; no other cultivrs were used for oviposition. DISCUSSION The results confirm tht selection of cultivrs cn significntly influence the oviposition of LWB femles. Significntly more eggs were lid on lte cultivrs 'Turqouise' nd 'Krutkizer'. Severl plnt-specific fctors ffect the oviposition choice, most importnt of which re physiologicl ge of plnts nd secondry metolites present. Decline in egg production with lef ge hs een reported in mny insect species. On the sis of our experiment we my conclude tht physiologicl ge of cultivrs is the most significnt fctor in finding suitle oviposition site. By the time of flight of LWB, erly cultivrs 'Prel' nd 'Golden Acre' (growth periods up to 50 nd 65 dys respectively) hd lredy stopped growing with outer leves senescing nd vegetle ripened. Such plnts were neglected for oviposition y LWB. We oserved the sme trend in mid-seson vrieties: the shorter the growth period, the fewer eggs were lid. Lte cultivrs were clerly preferred for oviposition. These results concur with the dt y Dickson & Eckenrode (1980) nd Hoy & Shelton (1987), who hve noted tht plnt physiologicl ge ffects the oviposition of LWB in Brssic crops. LWB usully selects sustrte for oviposition sed on the presence of glucosinoltes nd their rekdown products isothiocyntes (Schoonhoven, 1972; Renwick & Lopes, 1999; Jnkowsk, 2006). Rhmn et l. (1986) detected tht totl nd individul glucosinolte contents vry mong cultivrs, physiologicl ge, etc. Glucosinoltes re more concentrted in young plnts thn in mture plnts nd decline with plnt ge (Ros et l., 1997; Velsco et l., 2007; Crte et l., 2008). Another fctor possily ffecting ehviour of LWB is plnt colour. Though, glycosinoltes re short distnce cues, colour nd plnt size re long distnce cues. Erly cultivrs 'Prel' nd 'Golden Acre' were yellowish green, notly lighter coloured thn ny other cultivrs in the experiment. This could hve een mjor considertion for voiding y LWB. Lte cultivrs were drk green coloured, which my hve cused the oviposition preference. Rdcliffe nd Chpmn (1966) detected tht colour fctor ppered to e importnt in determintion of host preference for P. 409

5 rssice nd Pieris rpe L. Terfol (1965) showed tht perception of colour from distnce ws n importnt lnding stimulus for LWB. Myers (1985) found, tht femles of Artogei rpe L. (=P. rpe) re more likely to pproch greener plnts. Plnt size my influence utterfly oviposition choice, nd lrge plnts my receive more eggs thn smll plnts ecuse they re visully conspicuous (Tlsm et l., 2008). The iggest leves in our experiment were displyed y lte 'Krutkizer', which ws overwhelmingly preferred. Lef re of erlier cultivrs ws remrkly smller. The cge plnts contin coting of wx on the surfce on the cuticles. Our experiments lso indicted tht the thickness of the wx lyer on the leves cn ply n importnt prt in choosing the lte cge cultivrs. By visul nd tctile exmintions we ssumed tht compring to the second lte cultivr 'Krutkizer' 'Turquoise' hd the thickest wx lyer nd LWB chose 'Turquoise' less. Wx coting mkes it difficult for femles of LWB to otin informtion on the chemicl composition of leves since it prevents the dischrge of specific odours from the lef. Oviously oth the chemistry of lef wxes nd their physicl ttriutes ct together with some plnt-specific fetures. Eigenrode et l. (1991) studied oviposition preferences of Plutell xylostell L. on different cge cultivrs nd found tht the wx of more resistnt cultivrs contined much greter proportion of primry lcohols thn the susceptile cultivrs. The resistnt cge cultivrs hd thicker wx lyer, nd their chemicl composition differed from tht of non-resistnt cultivrs. Resistnce of the cultivrs tht we exmined is likely to e function of severl fctors. A comprehensive study of cultivr differences would complement the more specific studies descried here. ACKNOWLEDGEMENTS. This study ws supported y grnts no 6722 nd 7130 of the Estonin Science Foundtion, nd Estonin Ministry of Eduction nd Reserch trgeted finncing project no SF s REFERENCES Bernys, E.A. & Chpmn, R.F Host-Plnt Selection y Phytophgous Insects. Chpmn nd Hll, New-York, 312 pp. Crte, M.E., Soengs, P., Ords, A. & Velsco, P Resistnce of kle vrieties to ttck y Mmestr rssice. Agric. Forest Entomol. DOI: /j x Dickson, M.H. & Eckenrode, C.J Breeding for resistnce in cge nd culiflower to cge looper, imported cgeworm, nd dimondck moth. J. Am. Soc. Hort. Sci. 105, Doles, J.L Host plnt selection nd cceptnce ehviour. From we site: 001/doles.htm Eigenrode, S.D., Espelie, K.E. & Shelton, A.M Behviour of neonte dimondck moth lrve (Plutell xylostell L.) on leves nd on extrcted lef wxes of resistnt nd susceptile cge. J. Chem. Ecol. 17, Hrdin, M.R., Benrey, B., Coll, M., Lmp, W.O., Roderick, G.K & Bros, P Arthropod pest resurgence: n overview of potentil mechnisms. Crop Protect. 14, Hill, D.S Agriculturl insect pests of temperte regions nd their control. Oxford, 659 pp.

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