mhon Beech Bak Disease: Bidogical Contrd Relationships

~1U)CORUS (COLE0ETEPA:COCCINELLIDAB) AND OTHER

PREDATORS OF BEECB SCALE IN CENTRAL NEW YORK~

Mark Mayer2 and Douglas C. ~llen~

Abstract.--The twice-stabbed lady seigma (Say), was studied in two infestations of beech scale, CrYptoarcus fagisuga Lind., to elucidate predator biology and to determine the predator's effect on scale ppulations. -C. is univoltine in north-central regions of New York and its seasonal occurrence is well synchronized with that of C. faqisuqa. The predator was most abundant in dense scale populations. . and ewhihited a numerical reswnse- at hiqh scale densities. The effectiveness of C. stigma was limited by the Propensity of adults to disperse following eclosion, its apparent fai1;re to feed on all-life stages of the scale, mortality during the beetle's pupal stage and high rate of host reproduction. Four species of mites were also noted as predators of C, fagisuga.

Beecn bark disease first appeared in and makes excellent fuelwood. Spread of the North America during the 1890's when the beech disease south and west from its initial point Scale, Cr~~tococcusfaqisu~ Lind., was of entry in Nova Scotia has encouraged introduced from Europe on a species of research on the ecology (Houston 1975; ornamental beech, sylvatica L. The Bouston et al. 1979) and management of disease results when C, faqisuga initially infested stands (Filip 1978). However, infests the stems of American beech, relatively little information about the grandifolia Ehrh. and a fungus, twice-stabbed lady beetle, coccinea var. faginata Lohman, Watson and (Say), a native coccinellid predator of the Ayers then penetrates the bark through feeding beech scale, is available, and other natural Wounds. kale populations alone widently enemies of & faqisuga have received only have little impact on the health of the tree, Cursory attention. but in conjunction with m,Roderate to heavy scale populations may kill trees within C. stigma was first associated with 3-5 years. Presently, extensive areas of dead popul~ionsof & faqisuqa by Ehrlich (1934) beech pervade northern hardwood forests in the who noted the presence of r, atiqma northeastern United States. (identified as C, bivulnerus Muls.) in beech

scale-infested sample rrlots in Nova Scotia.~~ ~ This disease has generated more concern Ehrlich reviewed the ~iropeanliterature and in recent years because modern kiln drying reported several vague references to other methods have enhanced the value of beech, and arachnids that were thought to be predators of beech scale. Brown (1934) whose wood is used for floorinq,-. -plvwood, - dowels, Shuttles, containers and furnitu;e. suggested that C. stigma was the only Beech is also an important pulproad species predator in New England that had potential to control populations of beech scale.

'paper presented at the IUFRO Beech Bark The general biology of C. stigma was Disease Working Party Conference, Hamden, CT. first investigated by Girault (1907). who USA, 27 Sep to 7 Oct 1982. determined that the beetle wiposited in bark cracks, crevices, and under loosened bark on -est Entonologist, New Jersey Dept. of scale-infested apple trees. Marlatt (1902) Agriculture. and Deband Weidhaas (1976), on the other hand. reported that the beetle oviposited 3Professor of Forest Entamlogy, State beneath scale secretions and predominantly fed University of New York, College of Environmental Science and Forestry, Syracuse, NY. on immature scales. M uma (1955) indicated height. Two strings, one meter long and that oviposition occurred on the leaves, subdivided into 10 em units, were vertically trunk, fruit and t wigs of Flor ida attached to the 10 em marks around the trees. Be found that adults and all four circumference of the tree. A ladder and tree instars voraciously fed on adult scales. ~ trimmer's apparatus were used to climb each stiqaaa has been re<:orded as a predator of 18 tree and sample 3600 around the bole. species of scales, 7 species of , and one species of coccinellid (Thompson and The number and posit ion of Chilocorus Si1111110nds 1965) • were determined within each 10 em sq. Populations of ~ faqisuqa in each sq were DeBoo and Weidhaas (1976) examined ~ arbitrarily classified as light, medium , and stigma in central New Yor k as a predat or of heavy (DeBoo and Weidhaas 1976) , based on five pine needle scal e, Phenacaspis pinifoliae subsamples that were obtained by placing the (Fitch). The coccinell id colonized moderately mouth of a vial (2 em dia . ) o n an ink pad and and severely infested Scotch pine (Pinus then prossing tho ink-coated rim onto the sylvestris L.) in nat urally regenerated tree. Counts were made of the number of adult stands, but was absent on sparsely infested scales within the circle. The sample unit was trees. Lady aggregated on trees that 3. 14 sq. em of bark, and an average of 1-10 harbored the greatest number of scales, but scales, 11-25 scales and 25+ scales per sample only in stands that had a large number of were regarded as light, medium and heavy infested trees. In areas with small isolated populations, respectively. infestations, the beetles did not remain (or reproduce) on scale- infested trees and did not Adults and pupae of ~ ~ were easy significantly reduce scale density. DeBoo and to recognize. The last three instars were Weidhaas hypothesized that alternate prey on distinguished by size; color was used to nearby plants prevent ed ~ stigma from identify first instars. The dorsal midline of congregating on trees i nfested with pine t he thoracic and abdominal regions and much of needle scale. MOnocul t ures (plantations) of the dorsum of the first abdomi nal segment of Scotch pine resulted i n high numbers of pine instars II-IV are light cream to white (Muma needle scale, which subsequently supported 1955). First instars are unif ormly dark gray abundant natural enemies that eventually and approximately 1 mm long. Second instars controlled this host. are 2.5 to 3.5 mm long, the third instar is 4.0 to 5 . 0 mm long, and fourth instars are 6.0 The objectives of the present study were mm or longer. Whenever identification of to (1) determine the biology of ~ ~. instars was questionable, setaceous dorsal and (2) to evaluate the effe<:t of ~ ~ on lateral processes, the senti (sic Gage 1920), populations of ~ faqisuga, and (3) to were examined. identify other predators of ~ faqisuqa. RESULTS AND DISCUSSION MATERIALS AND METHODS Periodic examination of beech boles made The study sites at Wanakena, New York it possible to (1) determine t emporal changes (St. Lawrence County) and Tully, New Yor k in populations of ~ ~ ; (2) estimate (Cor tland County) consisted of mature beech, population density by mapping the scale eastern hemlock, Tsuqa canadensis (L.) Carr, infestation; (3) examine the relationship sugar maple, ~ saccharum Mar sh, red maple, between changes in the scale and predator Acer rubrum L., and yellow birch, Betula populations and; (4) observe the effect of il'i'le9~sis Britton. To deter11ine the physical variables on the scale and beetle response of ~ ~ to different densities populations. Also, this approach enhanced the of ~ fagisuqa at Wanakena, as well as to probability of finding other predators and/or facilitate observations, 12 beech trees 10-20 parasites of ~ faqisuqa, because a large m tall that represented a range of ~ total area of tree bOle was systematically faqisuqa densities were selected for examined throughout several 24 hr periods. population measurements. The four most heavily infested trees were sampled weekly from June through October, 1979 (n • 17-19 Effect of C. fagisuqa density ~ populations obs./tree) and the remainder were examined of c. stigma biweekly (n = 8-9 obs. /tree). There was a significant positive Sample trees were divided into 1 11 correlation between the density of ~ stigma vertical segments and each meter was and that of its prey. While the correlation subsectioned into 10 em x 10 em squares. This (r = 0.75, p • .05) between scale density and was accomplished by marking every 10 em around predator density is encouraging from a natural the circumference of the tree at each meter control standpoint, it is important to examine

90 the within-tree distribution of the predator a higher predator density than the medium population at different host densities. In infestations (M) , which in turn supported more other words, predator abundance should be predators than did the liqht infestation (I). viewed in terms of the proportion of total This relationship is typical of a predator bark surface area occupied by an infestation with well developed searching behavior and level (i.e., light, medium or heavy) (Fig. host finding capabilities. & stigma was 1 Initially, as the proportion of bole area able to locate prey colonies even when a small occupied by each infestation level increased, proportion of the bole was infeated. The data the proportion of predators found in that area indicate that the density and distribution of also increased. However, the data indicate -C. on beech boles was influenced by that beetles do not readily establish the density and distribution of C, fagisuqa. themselves on trees that are lightly infested. Bven though a light infestation occupied a This may account, in part, for the fact that relatively large total bark area, the beetle sparse scale colonies are capable of rapid density in that category was usually lower numerical increases over a relatively short than that in the next highest infestation Period. Apparently, the predator concentrates category. on trees, or portions of trees, where the host is easily found (i.e., dense populations). The decrease in predator densitv when 15%of -Life history of C. stigma the infested area contained a medium scale density, and the increase in predator density C. stigma overwintered as an adult in where 30% of the bark area was lightly the dzf. Adults at Tully, New York were infested (Pig. 11 probably are a result of first observed feeding on beech scale on a sampling error. Also, there could be a limit warm day (ma. 13'~) in early March. For to the number of predators that will occur on example, during one day of observation they an infested area of bark at a given time. remained on the lower bole until the This limit may have little to do with the temperature increased (max. 13-14°C1 at which carrying capacity of the food base. but rather time they moved up the tree several meters. with ~hilowrusitself. Predator density may In late afternoon adults descended and be determined by other mechanisms, eventually dropped into the duff. Adults irrespective of the fact that roore than enough often congregated on the lower boles of trees, prey are available. and mated during mid-April and early May at Tully and Wanakena, respectively. The relationship between the density of -C. stigraa and Wtal bark area occupied by !& Oviposition by C, stiqna was first fagisuqa infestation categories (Figs. 2-5) observed at Tully in late April. The scale further support the hypothesis that high oviposited in bark fissures, some of which beetle density is associated with high host were caused by another scale, Xylococculus density. The figures indicate that heavy Pergande. The last first instar was infestations (8) were usually associated with observed on 15 August (first instars were - difficult to see because they were camouflaged 0.6 on the gray beech boles) ano second instars were observed four weeks later. The last second instar was noted on 13 October. Most third- and fourth-instars disappeared the 4 first week in October, and larvae that did not pupate by October did not survive. Adults were most nmerous on 20 June and 9 August. During this period only 8 of 21 median weekly temperatures were above 16.7 C. At median e 4r temperatures below this, C. stiqma larvae - llc.vu require 12 weeks or longer to ccnplete one @ - ndtm generation (Muma 1955). 0 - Light Bvidence for one generation a year was strengthened by the temporal distribution of -C. life stages in the more northerly Wanakena (Fig. 6). indicating only one peak abundance for each stage. If there were two generations a year atwanakena, there should Pig. 1. Distribution of total 5. be two peaks. mittedly, the data do not population in relation to propor- cover early spring, but pupae would have been tion of scale-infested bark in 3 present prior to July if there were two infestation categories (n = 4 generations a year. DeBoo and Weidhaas trees). (19761, who also worked in central New York, recorded two distinct populations for all life population of stimpa. On the other hand. stages. The first generation occurred from in New York, P, pinifoliae and C. stigma late July through August. No pupae were each had two generations a year (DeBw and observed at Wanakena until July and large. Weidhaas 1976). Hemlock scale, Fiorinia numbers of them did not appear until August. externa (Ferris), in Connecticut is Climatological records from Oswego, NY, the univoltine, as is the local population of C, weather station closest to where DeBoo and (Wlure 1979). This association Weidhaas did their study, indicated that 16 of between the voltinism of predator and prey is 24 median weekly temperatures approximated most likely related to temperature, rather 16.7OC. This lends further support to the than to the number of prey generations. hypothesis that their population of C, stiqma However, it is highly probable that & stigma was hivoltine. is able to synchronize its develowent with that of the most suitable (=abundant) host. Interestingly, the hosts in Muma's study, Coccinellids display close synchrony with Florida red scale, Chrvsomphalus a (L.) their prey, especially on sedentary hosts (=- Ashmead), and purple scale, (Hagen 1962). The coccinellids reproduce kpidosaphes beckii (Newman) have three when populations of their prey are increasing generations a year, as did the local and hibernate when the prey is dormant.

= 5 5

3

0 1 0 1

20 ; , @ 4 0 ;j0 10 20 30 4 50 M 70 0 405064 mm- TOTAL BARK AREA OCCUPIED; :::BY 2: FAGISUGA INFESTATION CATEGORIES (X1,0WCR2)

Figs. 2-5. Mean density of C. stigma in relation to total bark area infested by 2. fagisuga. Each Fig. represents a single tree (H = >25 scales; M = 11- 25 scales and L = 1-10 scales/sample unit. Biology and behavior of C. stiqma beetle was sated. Hourly observations of Adult Chilworus (Fig. 7C) moved from marked beetles for a 24 hr. period indicated tree to tree in search of prey which that adults were dirunal and relatively apparently were located tactilely or visually. quiescent at night. Some coccinellids locate their prey by means of prey odor (Eodek 1967). but this has never First instars searched for fwd soon been established for the Chilocorini; other after eclosion. Searching appeared random and species apparently rely on visual cues (Allen feeding occurred only when the prey were et al. 1970; Stubbs 1980). Approximately contacted with the maxillary palpi. half of the beetles' time was spent apparently Thereafter, the larvae slowed down and resting (and possibly digesting prey) and the conducted a more thorough search of the remaining time was spent searching for prey surrounding area by moving in a circular and feeding. Adults rested for a few minutes pattern and frequently changing direction. snall ta hours, probably in respnse to temperature The size of first instars allowed them and hunger level. As long as the maxillary to search bark fissures that were inaccessible palpi remained in contact with the prey, the to later instars. Beech scales within the beetles fed until the prey was conswed or the fissures were utilized with little conpetition from later instars. Larvae in bark openings

L 0 . I"... I

.,*>t.T 1, . - ,"$tar Ill - 19,t.r

Add 11/21 8/29 919 9/13 9/22 911) 1016 10113 10120 DATE (MONTHIDAY) 1979

Fig. 6. Temporal distribution of C. stiw life stages, Nanakena, New York. were difficult to detect and are probably Behavior of fourth instars (Fig. 7A) better protected from the weather. and conformed to that of the third except the predators than are older larvae. Larvae spent former were more mobile and searched a larger more time moving and feeding than the adults area. As fourth instars approached pupation, and rested 10-259 of the time. It took longer their zigzag search pattern became for a first instar to consume prey than it did disorganized. hrce an appropriate spot was other instars, because prey size was large found the Larvae became quiescent for one to relative to the predator. The first instars three days before papation. fed by working their way through the waxy secretion of the scale. When contacted, a The gregarious pupae of C. stigma (Fig. scale was pierced by the predator's mandibles 78) were found on the main bole, under and the scale's body fluids were withdrawn. branches, and in other sheltered areas. The Gnce first instars located an area with reason why larvae selected particular areas abundant prey, they rarely left. for pupation was hot revealed until trees were climbed durin~a rainstorm. Puwe beneath Second instars behaved much like first tree limbs and other protected Leas on the instara except the former were more mobile main bole were not exposed to stem flow. when not feeding. Rain, especially a heavy downpour, is usually intercepted by the tree crown and then flows Because of their larger size, third down the main branchesi thence down the bole. instars covered more area as they searched for In almost all cases, pupae were found in island-like refugia that were protected from prey. During this stage, prey seeking was more involved: larvae moved 10-20 cm over the tree bole in a limited zigzag pattern. If no prey were encountered within this distance the larvae turned around and sometimes retraced Population fluctuations and prer consumption their original trail. Why larvae stopped going in one direction and proceeded in Although larval populations were not another is not known. They did this on all readily estimated, abundance of sedentary bark types, oftentimes walking wer scale pupae was easily determined. The number of colonies in the process. Feeding did not new pupae and the dead or missing pupae on commence until the maxillary palpi contacted a four sample trees were tallied weekly. The scale, at which time larvae masticated prey greatest number of new pupae were found on 5 with the mandibles and did not use their August, 9 August and 15 August (Fig. 6). mouthparts in a piercing-sucking manner. The Pupal mortality (number dead or missing pupae eggs of C, were occasionally eaten. total number of pupae) ranged from 18%to Msia 299. *times only part of a scale was consumed The average for the combined samples is 24.19. Cause of mortality was attributed to before another one was attacked. The larvae two factors: (1) the nymph of a predaceous were not observed feeding on the scale bug, sp. and (2) the fact that some crawlers and seemed to prefer more sedentary Pupae, even though sheltered, were still hosts. exposed to the elements and enough pressure may have been placed on the sucking disc to detach the .

Big. 7. Life stages of g. srilpna: A, fourth instar; B, pupa; C, adult.

94 Feeding studies were undertaken with & red spot on each elytra. The spots on C- stigna to determine haw many faqisuga each stigma, however, are round and smaller than life stage of the predator consumed per day the squarish spots characteristic of and over a period of 72 hr (Table 1). The quatourdecirnguttata. feeding capacity of each stage was significantly (p = .05) greater than that of the preceeding stage, except for adults, which Acacine predators consumed the same number of prey as fourth instars. All stages, except adults, consumed Mites were the only other organisms that less on the first day than they did on were observed feeding on beech scale. The succeeding days. Possibly the larvae required most frequently encountered mite, Anystis sp. an adjustment period before they settled down nr. Oudemans (Fig. 8A) was very mobile to feed, and adults probably located the bat and preyed on all stages of the scale, more quickly than did larvae. espacially eggs and crawlers. Eaker (1965) characterized Anystis spp. as general Table 1.--kwh scale mnrunptiar by mjlomrur stIm. predators with nan-specific prey preference, and he observed a species of Anystis preying upon another mite, m: we observed the Lverae No. PRY Eatlo (t SDI latter preying on 5 faqisuga eggs. Several Anystis molting chambers, craters in the bark covered with white papery silk, were exwined and usually one large Anystis was found with several smaller protonymphs. Anystis appeared in late June and was present until the end of August. The silken chambers, which can be easily mistaken for beech scales, were first observed in early July. This species may be bivoltine because the mites were not noticed until June, and this would allow time for an earlier generation. Adults tended to disperse after eclosion and this behavior may prevent a buildup of C, A second acarine predator, Tydeus sp., stigma in areas where there are few prey. was difficult to observe because it was De- and Weidhaas (1976) observed natural usually colorless, except after it fed when control by C, in populations of pine the gut turned gray. Tydeids were first needle scale in a monoculture of Scotch pine. observed on a section of infested bark that When C- stigma dispersed under these was placed under a dissecting microscope to conditions, the probability of finding lwk for scale parasites. Several tydeids alternative prey was low. Therefore, the were observed feeding on eggs of C- beetle had a significant impact on scale me populations in the monoculture due to lack of fagisuga, but not on crawlers or adults. alternative prey and low dispersal losses. The northern hardwood forest is a relatively Two erythraeid mites were encountered, diverse community, however, and it probably Abrolovhus sp. (Fig. 8B) and Leptua sp. offers a variety of prey, which may dilute the (Fig. 8C). A few instances of scale influence of C. stiqma on beech scale predation were noted when attempts were made populations. men though C, exhibited to study what were thought to be anystids, but good host-predator synchronization and were Abrolophus ep. instead. Brythraeids are displayed an apparent numerical response to Predators in the adult, trito-, deuto- and high prey density, the hosts' parthenogenetic protonymphal stages, and feed on a wide mode of reproduction, apparent failure of the variety of Prey. Rowever, their larval stages predator to feed on all host life stages, the are ectoparasitic. The larva of Leptu. sp. tendency for adult C. stimna to disperse was noted as an ectoparasite on Anystia sp. after eclosion and mortality during the plpal Of 37 anystids collected. 9 were parasitized stage suggest that (1) this predator is an by Leptus. No adult Leptus or nymphal opportunist and (2) it has little potential Abrolo~huswere encountered. for controlling populations of C, fagisuqa. One bdellid mite (Fig. 8D) was observed Another coccinellid, Preying on C, faqisuqa crawlers, but it could (=Anisocalvia) guatuordecirnguttata var. not be identified to genus because the palps similis Randall, purportedly feeds on C, were accidentally removed during mwnting. fagisuga in New York and Pennsylvania, but we did not observe it on our study trees. C- and auatuordecimguttata closely resemble each other: both are black with a Fig. 8. Mite predators of :fagisuga: A, Anystis sp. ; B, Abralophus sp. ; C, sp. ; D, a bdellid. 96 stimt. Die Marienkafer treten in dichten Laus- populationen - als zahlenmjiBige Reaktion auf hohe Lausdichten am zahlreichsten auf. Die The Occurrence of extensive beech - Wirksamkeit von C. a gegeniiber L. fagisuga mortality and flourishing populations of beech ist begrenzt, da-die Tiere affenbar nici-t alle scale in North America are cogent evidence of Frtvicklungsstadien der l..?cs fressen, wegen der the fact that indigenous natural enemies are MortalitSr der KEfer irn Puppenstadium und wegen not able to control this exotic pest. C, der hohen ~emoduktionsrateder LZuse. -was the most abundant, and usually the Fiinf verschikdene Milhenarten wurden ebenfalls only, insect predator of beech scale that we als FraBfeinde von c. fagisu~afefegestellt. observed in two forest stands in central New York. Parasitic and predaceous mites were frequently associated with inmature scales, but apparently are not able to hold scale CITED populations below damaging levels. Allen, D.C., F.B. Knight and J.L. Foltz. 1970. Invertebrate predators of the jaak pine hudvorm, Qloristoneura We thank Mr. A.T. Drooz, U.S.D.A., inus in Michigan. Ann. Entomol. Am. 63259-64. Forest Service, Olustee, Florida and Dr. G.F. k Fedde, U.S.D.A., Fosest Service, Athens, Baker, W.V. 1965. Meobservations on Georgia for their review of this manuscript, predation in an anystid mite. Wt. and Dr. Roy A. Norton, College of Wviron. mg. 103:58-5s. Sci. and Forestry, Syracuse, New York for mn. identifying and photographing the mites. Brown, R.C. 1934. Notes on the beech scale, CrvPtococcus && (Baer.) Dougl., in New England. J. Econ. Ent. 27:327-333.

DeBoo. R.F. and J.A. Fieidhaas Jr. 1976. La coccinelle stigma, Chilocorus & Plantation Research) XN. (Say), fut itudiie durant deux infestations Studies on the predation of pine de la cochenille du h€tre, Crrptococcus needle scale, Phenacasvis faRisuga Lind., pour en dlucider sa biologie pinifoliae (Pitch), by the et determiner son effet sur les populations coccinellid, Qlilocorus stigma de la cochenille. Dans la r€gion centre-nard (Say). Chemical Control Research de New York, le C. stigma est univoltin et sa Institute Report CC-X-119. prBsence saisonnare est bien synchroniske Canadian Forestry Service, Depart- avec celle du C. fagisuga. Le prkdateur ment of Emrirornnent, Ottawa, Canada. ktait le plus abondant dans les populations klevkes de cochenilles et montrait une Ehrlich, J. 1934. The beech bark disease, corr6lation nm6riaue. oositive.~ aux hautes a disease of densit6s de celles-ci. ~'efficacit6du C. following Crmtococcus a 6cait limicke par la progression des (saer.). Can. J. Res. 10:593-692. adultes 3 se dis~ersera~r>s l'6clasion. son attitude apparente 3 ne pas se nourrir de Filip, S.M. 1978. Impact of beech bark tous les stades de la cochenille, la mortal- disease on unevenage management iti observge durant le stsde nymphal de la of a northern hardwood forest (1952 coccinelle et le taux Blev6 de reproduction to 1976). USDA-FS, General Tech. de l'hste. Quatre esp>ces d'acariens furent Rep. NE-45, 7 p. aussi not6es come pr6dateurs du C. fagisuga. Gage, J.E. 1920. The larvae of the Coc- cinellidae. Ill. Biol. Monogr. V. 6, No. 4, Oct. 1920.

Girault, A.A. 1907. The oviposition of XarienkZfer (Chilocorus (Say.)) wurden Chilocorus bivulnerus Huls. in zwei Vorkommen der Buchenwollschildlaus J. Econ. Ent. 1~300-302. (Cryotococcus fagisuaa Lind.) hinsichtlich ih- res Beuteverhaltens und der Auswirkung auf die Hagen, K.S. 1962. Biology and ecology of Lauspopulationen untersucht. Chilocorus predacious . Ann. bildet in den n8rdlichen Teilen Zentral-New Rev. Bnt. 7:289-326. Yorks eine Generation im Jahr. Sein jahreszeit- liches Auftreten ist gut eufL fagisuaa abge- Bodek, I. 1967. Bionomics and ecology of predacious Coccinellidae. Ann. Rev. Ent. 12:79-104.

Bouston, D.R. 1975. Beech bark disease - the aftermath forests are struc- tured for a new outbreak. J. For. 73:660-663.

Houston, D.R., E.J Parker, R. Perrin and K.J. Lang. 1979. Beech bark disease: a comparison of the dis- ease in North America, Great Britain, Prance and Germany. Eur. J. For. Path. 9:199-211.

Marlatt, C.L. 1902. Proc. 14th ann. meet. Am. Assoc. of Econ. Ent. Bull. No. 37. N. Series. Div. Ent. USDA, wash., D.C.

McClure, M.S. 1979. Spatial and seasonal distribution of disseminating stages of Fiornia externa (Bornoptera: Diaspididae) gnd natural enemies in a hemlock forest (mcanaden- -sis) . Environ. Ent. 8:869-873. h,M.H. 1955. Some ecological studies on the twice stabbed lady beetle, Chilocorus stiqma (Say). Ann. Ent. Soc. Amer. 48:493-498.

Stubbs, M. 1980. Another look at prey de- tection by coccinellids. Bcol. Entomol. 5:179-182.

Thompson, J.R. and F.J. Simonds. 1965. A catalogue of the parasites and predators of insect pests, Section N. Bost-predator catalogue. Can- monwealtb Agr. Bur., Commonwealth Inst. Biol. Control., Ottawa, Ontario.