134 DIAllRQTlgA .·..(JRl$.TA·.·rA,.·..A·...CHR¥SQ~E.l.I·I) (C()LEO·PTERA)/()F'.R.ELICTMIDWESTERN PRAIRIES DlSCQVEREl)i/IN.· .•EASTERN SERPENTINE BARRENS· A.d. Wheeler, Jr.2 ABSTRACT:Diabroticacristata. agalerucinechrysomelidcharacteristicof relictprairie ecosystemsin the GreatPlainsbut seldom collected on the eastern seaboard, is reported from fourserp.entinebarrens insoutheastemPennsylvania and one in adjacentMaI')'land. Large populations were presentintwoofthe barrens, with adults collected frominflorescences of two grasses and from17species offorbs in? families. The larval host was not determined but is suggested to be tittle bluestem,Sch£wchyriul11 scoparium, aperennialgrassdominant on serpentine soils, or theless abundant big bluestem,Alldropogoll gerardii.e: known host orD. cristata in midwestern prairies. Diabrotica cristata (Harris)beIongstothechrysomeHd subfamily Galerucinae and tribe Luperini. It isamemberofthe virgifera group of the large N ewWorld genusD iabrotica, which in the United States includes the northern corn rootworm, D. barberi Smith and Lawrence; western com rootworm; D. l'irgiferavirgiferaLeConteiand .Mexican cornrootworm, D. l'. zeae Krysan and Smith (Branson and Krysan, 1981 ; Krysan and Srhith,·.1987). Smith (1966)notedthe association ofD.cristalawithwiId grassesin the United States eastof the Rocky Mountains and south onto the Mexican Plateau.ButuntilrecentlybioJogicalinformation on this rather incon- spicuousinhabitant of relict prairie ecosystems was scant, and the use of grasses as larval hosts remained unconfirmed, Problems in developing corn linesresistantto rootworms, however.focused attention on the noneconomic D, .cristata. ,. It was.hopedthatan increased. knowledge of its habits might elucidate-the evolution of hostrelationships among pestiferous species of thevirgifera group and lead tobetter methods ofmanaging their populations. Wiesenbornand Krysan (l980) observed adults oiD. cristata on flowers of various forbs.iwhere they. apparently feed on pollen .. In their survey -of. relict prairies in. eastern South Dakota and southwestern Minnesota, they found that.big bluestern, AndropogongerardHVitman, usuallywas agoodindicator.plant forD~cristata. but that its presence did not always providefora beetlepopulation. Krysan (1982}hypothesized a tropical origin oftheegg dormancy mechanism inthis group ofD iabrotica, which enabled the. species to invade temperate North America and to specialize on perennialgrasses.tapredictabie food resource but one of J Received November 28. 1987. Accepted January 5. 1988. 2Burcau of Plant Industry. Pa. Dept. of Agriculture, Harrisburg, PA. 17110-9408. ENT. NEWS99(3YI34~142.May&June. 1988 VoL.99. No.3, May & June 1988 135 restricted~vailability.F6r Il. cris fa ta,col11P Iexity ofpra irie sod ands maU larvalpopulatio~s precludedth~verificationof grasses as host-plants; thus. gra~s~sh~dpeen.ofll)'inferred ashostsuntilXaro and Krysan (1986 )found larvae feeding on roots of A. gerardiiinSouthDakota.ln the laboratory, this ·specieshasbeenrearedo.0roots of corn (Krysan and .Smith,. 1987). Although o. qristata was origin~lIydescrihed froB1Northarnpton. Massachusetts{seeSmith .and Eawrenee,1967J.and is known from New Hampshire south toG~orgiaandAlabama (Krysan. and SI11ith. 1987). specimens from eastern Ul1ited States are generally scarce in .coHections q.L Krysan, pers. comrrl')'>J(rysanand Smith {1987Jremarked that ..populations: ofnonp~stspe~i(!s8fthe.virgifera group are "highly localized within theif9veraU ranges." Large numbers of D. crist ata apparently have not .been recorded along the eastern seaboard .: and habitat preferences outside.relict midwestern.prairiesare unknown. The presenceofi).cristalLlin eastern serpentinebarrens. including large populations at two localitirs.is here reported. Serpentinebarrens are unique habita.ts thatharborasharacteristicflora associated with nutrient- poor, rocky soils and . are .•only .•.beginning 10 be .appreciated. for their interestinginsect fauna. Thc./humber of adults collected in inflorescences of various forbs and grasses on several sample dates.is also given. METHODS AND STUDY SITES Following the discovery of D...cristata. in aPennsylvaniaserpentine barren,s~veral eastern barrens were surveyed during late July to early SeptemberI987 to determine the beptle's relativeabundance and plant speciesused.for adult feeding. Inflorescences of forbs .and grasses were t~ppedinto.a small beating net and .plarit species harboring adults were recorded. ()n 8Aug. thenumbersofD.cristatataken in inflorescences of various plants during approximately 7;' minutes ofcoHectingat each of 3 serpentine barrens fCioatHitl,Nottinghal11 Park. and .Soldicrs Delight) w~rerecorded.Simiiar surveys of some of the same and additional barrens weremadeon 12and19 Aug. and 2 SepLI987. VoucherspecimensofD, cristata have been deposited inthe inscct collccticnsof.Corriell University and. Pennsylvania Department'ofAgriculture, In addition, inflorescences-of plants growing just outside (1-2 krn) the well-defined limits of the Goat Hill.and Nottingham Park barrens .wcrc surveyed forD.criSiaul. During. studi~sofother insects; similarmethods were used from late July to early Septemb~r to try to detect populations in nonserpentine .habitars.in eastern Pennsylvania. The serpentine barrens surveyed are OHtcrOPS of serpentinite. an ultramafic. often ·ycUowish-green rock containing at least 509f> 'hydrous 136 ENTOMOLOGICAL NEWS magnesium silicate. In eastern North Amencathese barrens belong to a broken chain of isolated areas stretching from western Newfoundland and the Gaspe Peninsula to east-central Alabama: the best developed formations lie in the hilly, eroded easterrimost portion of the Piedmont Upland in southeastern Pennsylvania and northern Maryland (Pennell, 1930: Miller, 1977: Reed. (986). Serpentine soils, although varying in chemical and physical properties from site to site. tend to be low in calcium (and often other nutrients), high in iron and magnesium. and sometimes also high in chromium, cobalt, and nickel. Soils usually are shallow. excessively dry. rocky and, owing mainly to toxic concentrations of heavy metals, low calcium levels, and to other adverse chemical and physical features, are unfavorable for agriculture. Vegetation developing on nutrient-poor serpentine soils is sparse, often stunted, and nearly always coritrasts sharply from that of surrounding areas (Proctor and Woodell, 1975: Miller, 1977: Mansberg and Wentworth, 1984). Serpentine plant communities are thus characterized by endemism, disjunct ranges.· ecotypic differentiation, and morphological variants (Proctor and Woodell, 1975: Mansberg and Wentworth, 1984). Recent work by Knox (1984) suggested that recruitment of forest communities is episodic rather than continuous and reflects regular disturbance of stands by fire or drought, which maintains the open habitat supporting a characteristic flora. The following are brief descriptions of the serpentine areas surveyed. Additional information on plant communities of these and other eastern serpentine barrens is available in Harshberger (1903. 1904), Pennell (1910.1930). Wherry(l963), Miller (1977},and Reed (1986). Goat Hill Serpentine Barrens: southeastern Chester Co .. Pennsylvania, along the Octoraro Creek southwest of Nottingham near the Maryland State line; one of the largest of the eastern serpentines, encompassing 700 acres (283 ha) of pitch pine (Pinus rigida Mill.) - scrub oak (Querclls ilicifolia Wang. and Q. prinoides Willd.) forest; thickets of greenbrier iSmilax spp.); localized blackjack and post oak (Q.mari/andica Muenchh. and Q. stella/a Wang.); parklike openings dominated by little bluestem or prairie beardgrass (Schizachyrium scoparium (Michx.) Nash) and other bunch grasses; and xeric rock and gravel outcrops characterized by the presence of serpentine aster (Asl er depa uperatus (Port.) Fern.) (Asterceae), fame flower i'Talinum teretifolium Pursh (Portulacaceae), and sandwort iArenaria stricta Michx.) (Caryophyllaccac) (Pennell, 1910). Nottingham Park Barrens: 645 acres (261 ha) west of Nottingham; like Goat Hill. belonging to the state line barrens and having diverse plant communities dominated by pine-smilax thickets. bare exposures with various "indicator" plants, and grassy openings. some with nearly pure stands of little bluestem. 137 N e\\,!~){as{LyIys)llarrens:anotherof.th~ .•st~te}ine g;roup,<255..as.•res ( 103 ··.ha) Jying,.•.sPll. thof'Yak~fieldin sout~ern ..Lan.. caster Co~.near ··C:on()\\fiJ1g?()feek~characterizedbyVirginiapine (~ill.uS virg(ni ana¥i IL), Il1ixed()ak.~;east~rnred-cedar(tulliper[lsl!irgin iaiui L.),and large. open areas gfIittlebluestem and oth~rgrasses; .....•.•......•.•• ·.~?ckSpfiI1gs.Barr~ns:176acres(71ha)?outh.ofi'Jew'fexasatJenkins C(}rtl~rjustnor-t~.oftl:t~Marylandline; .•the?ite()f1v. [iHer'§.(..1~77}·ecological study,consistinwofyjrg!ni~pin~-oakfote~t.open. areas ..of little bIuestern ·andotljergrasses,.andotherplaJ1tc0rnrn.unitiestypicalof easternserpentines. Pink. Hill (MiddletoWIl) Barrens; Tyler Arboretum: ah?ut20-acres(8 ha}(Godfrey, ..1980}11~ar• •.l·..im~ ••·I)elaware.Co., ..and. a member ·.ofth(! Philadelphia Districtbarr~n~ (l{eed,1986 );.arela~ively undisturbedarea ..(Brooks,J98]) •.doItlinatedby carpets of Cerastill 111 <arvense L.( Cary~ phynace~e)andPhI9Xs.ubul~.taiL.fPolemoniac~ae}. standspfSch izaclzy~ ··riu lnscopariufntandscatteredc()lol1ies .•oLPycnantltem uni tenu ifol ill III Schrad( LaIJliaceae). ...•..•.•..•. Unionville13arrens:a mernber'of the Chester