BioControl 48: 503–513, 2003.© 2003 Kluwer Academic Publishers. Printed in the Netherlands.

Parasitism by the mite Acarophenax lacunatus onbeetle pests of stored products

Carlos Romero F. OLIVEIRA1, Leda Rita D’A. FARONI2, Raul Narciso C.GUEDES1,3∗ and Angelo PALLINI1

1Departamento de Biologia Animal, Universidade Federal de Viçosa, Viçosa, MG36571.000, Brasil; 2Departamento de Engenharia Agrícola, Universidade Federal deViçosa, Viçosa, MG 36571.000, Brasil; 3Department of Biology, University of Leicester,Leicester, LE1 7RH, UK∗Author for correspondence; e-mail: guedes@mail.ufv.br

Received 18 January 2002; accepted in revised form 29 January 2003

Abstract. Recent reports of the biocontrol potential of the mite species Acarophenax lacun-atus (Cross & Krantz) (Prostigmata: Acarophenacidae) and the lack of biological studieson this regulatory agent led to the present study carried out under laboratory conditions.The objective of the investigation was to assess the host range of A. lacunatus, so faronly reported as egg parasite of Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae). FourColeoptera species of stored cereals were used: R. dominica, Tribolium castaneum (Herbst)(Tenebrionidae), Cryptolestes ferrugineus (Stephens) (Laemophloeidae) and Oryzaephilussurinamensis (L.) (Cucujidae). The highest rates of egg parasitism were observed on R.dominica and T. castaneum, leading to a significant decrease of populations of both speciesand reduced wheat weight loss. A. lacunatus was also able to parasitize eggs of C. ferrugineus,but not of O. surinamensis. These results indicate a broader host range of A. lacunatus thaninitially suspected and also strengthen its possibility of use in integrated pest managementprograms in storage environments.

Key words: Acarophenax lacunatus, Acarophenacidae, biological control agent, Cryptolestesferrugineus, Oryzaephilus surinamensis, Rhyzopertha dominica, stored product pests, storedwheat, Tribolium castaneum

Introduction

Insecticide use is a widespread tactic for controlling pests of stored products(Harein and Davies, 1992; White and Leesch, 1996). However, the everincreasing problems of insecticide resistance in stored grain insects, therelatively small number of insecticides available for stored product protec-tion, and the increasing environmental and health concerns surroundinginsecticide use have sparked renewed interest in the biological control ofinsect-pests of stored products (Brower et al., 1996; Schöller et al., 1997).This renewed interest led to reports of potential biological control agents

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for use against stored grain insect-pests (Plarre et al., 1999; Steidle et al.,2001), among which the parasitic mite species Acarophenax lacunatus (Cross& Krantz) (Prostigmata: Acarophenacidae) seems promising and deservesfurther attention (Faroni et al., 2000, 2001).

There is little information available about parasitic and predatory mitesof stored product insects (Brower et al., 1996). The mite species Pyemotestritici (Lagreze-Fossat & Montagne) (Prostigmata: Pyemotidae), Blattiso-cius tarsalis (Berlese) (Mesostigmata: Ascidae), Acarophenax mahundaiSteinkraus & Cross and A. lacunatus (Prostigmata: Acarophenacidae) arenatural enemies of stored product insect-pests that have been the focus ofmore attention (Bruce and LeCato, 1979; Haines, 1981; Steinkraus and Cross,1993; Faroni et al., 2000, 2001). P. tritici is the best studied species, butits commercial use has been limited because it can also bite humans, asdo other members of the family Pyemotidae (Moser, 1975; Brower et al.,1996). B. tarsalis, A. mahundai and A. lacunatus do not seem to show thesame inconvenient habit although the genus Acarophenax has been initiallydescribed within the family Pyemotidae and only later transferred to a newfamily – Acarophenacidae (Cross and Krantz, 1964; Haines, 1981; Steinkrausand Cross, 1993; Faroni et al., 2001).

Mites of the family Acarophenacidae (Acari: Prostigmata: Heterostig-mata) are egg parasites on various insect-pests, but relatively little is knownabout their biology (Goldarazena et al., 1999, 2001). A. lacunatus wasfirst reported in colonies of the rusty grain beetle, Cryptolestes ferru-gineus (Stephens) (Coleoptera: Cucujidae), but it has been reported as anegg parasite of only one species – Rhyzopertha dominica (F.) (Coleoptera:Bostrichidae) (Cross and Krantz, 1964; Faroni, 1992). The co-occurrenceof different pest-species of stored products within storage units requires abroader action of control agents to prevent grain losses in stores. The potentialbenefits of a broader host range is counteracted by the higher environmentalrisks usually associated with generalist biocontrol agents and demands theassessment of suitable hosts of potential regulatory agents of stored productpests (Howarth, 1991; Sinha, 1995; Simberloff and Stiling, 1996). Thus, theobjective of the present study was to examine the host range of A. lacunatusby studying its ability to parasitize and control four different species of storedproduct pest beetles.

Material and methods

Mass rearing of stored product pests and the parasitic mite

Laboratory populations of C. ferrugineus, O. surinamensis, R. dominica andT. castaneum were kept on broken wheat grains with 13% moisture content

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(m.c.) inside 1.7 l glass jars maintained at 28 ± 2 ◦C temperature, 65 ± 5%relative humidity (r.h.) and 24 hours scotophase. Insect eggs were collectedfrom colonies that were over seven-days old using sieves with an aperturediameter of 1 mm.

A. lacunatus was obtained from laboratory colonies of R. dominicainfested by this mite species and maintained since its introduction from Spainand eventual clearance for research purposes by the Vegetal Sanitation StateService and the Brazilian Ministry of Agriculture (Faroni et al., 2000, 2001).Colonies of R. dominica infested with A. lacunatus were maintained underthe same environmental conditions as mite-free insect colonies.

Newly-emerged mites were obtained from infested colonies ofR. dominica using sieves and were transferred to Petri dishes (14 cmdiameter) containing host eggs. After 24 hours, females of A. lacunatusattached to host eggs, but not yet in physogastry (i.e., attached to the hostegg but still without significant increase in body volume), were collectedand individually placed in smaller Petri dishes (5 cm diameter) until progenyemergence.

Parasitism potential of A. lacunatus on different hosts

The four host species of Coleoptera pests of stored cereals [R. dominica,Tribolium castaneum (Herbst) (Tenebrionidae), Cryptolestes ferrugineus andOryzaephilus surinamenis (L.) (Cucujidae)], infested or not with A. lacun-atus, constituted the eight treatments of the present study. This was initiallyestablished as a 4 × 2 factorial experiment (four host species × mite pres-ence or absence) in a completely random design with four replicates. Eachreplicate utilised a Petri dish (14 cm diameter) containing 25 g of brokenwheat (13% m.c.), where 25 unsexed adults of the host species were released.Adults were between three and seven days-old. Four female mites in physo-gastry were also released in each Petri dish. Physogastric females havean enlarged body due to the development of progeny within the female.Offspring emerge as sexually mature adults. The Petri dishes were coveredwith a PVC film to prevent arthropod escape, and contamination, and theywere maintained under controlled conditions (28 ± 2 ◦C, 65 ± 5% r.h., 24 hscotophase) for 45 days. This storage period was long enough to includeemergence of offspring of host insects and also enabled detection of grainloss caused by the pest species (Faroni et al., 2000).

After 45 days of storage, the content of each Petri dish was sieved,separating the broken grains and insects from the residual dust, whichcontained mites and host eggs. This procedure allowed the assessment ofgrain loss, enumeration of live adult and larval hosts, and, using a stereo-microscope, the number of parasitized host eggs and the number of living

506 CARLOS ROMERO F. OLIVEIRA ET AL.

physogastric females of A. lacunatus. The instantaneous rate of increase(ri) of the mite and host populations was calculated using the equation ri =[Ln (Nf/No)]/?T, where Nf is the final number of living arthropods, No isthe initial number of living arthropods and ?T is the time interval (days)elapsed between the start and the end of the experiment. The data obtainedwere subjected to single or two-way analysis of variance (ANOVA), usingthe procedure PROC GLM from SAS, and to Tukey’s multiple range test(p < 0.05) whenever appropriate (SAS Institute, 1989). ANOVA assump-tions were checked (PROC UNIVARIATE; SAS Institute, 1989), but no datatransformation was necessary.

Results

A. lacunatus was not able to parasitize eggs of O. surinamensis and did notshow any influence on the population of this stored product pest. Thereforethis species was not included in the statistical analysis. In contrast, A. lacun-atus was able to survive and reproduce in the other three beetle speciesinvestigated – C. ferrugineus, R. dominica and T. castaneum. Females ofA. lacunatus did particularly well on R. dominica, but a large number ofphysogastric females mites was also observed on T. castaneum (∼60 per Petridish) (Figure 1).

There was a significant difference among treatments regarding the numberof physogastric females present at the end of 45 days, the largest numbersbeing present on R. dominica and the smallest on C. ferrugineus (dftrt,error =2,9; F = 140.65; p < 0.0001) (Figure 1). A similar trend was observed for theinstantaneous rate of increase of the parasitic mite population (dftrt,error = 2,9;F = 166.26; p < 0.0001) (Figure 2). There were also significant differences inegg parasitism by A. lacunatus on different species of stored product beetles(dftrt,error = 2,9; F = 62.53; p < 0.0001). Egg parasitism on R. dominica andT. castaneum were similar (> 70%), but this was significantly higher than eggparasitism on C. ferrugineus (< 20%) (Figure 3). A. lacunatus was unable toparasitize eggs of O. surinamensis.

There was no significant interaction between host species and mite pres-ence/absence affecting the number of larvae (dftrt,error = 2,18; F = 2.71; p =0.09) and adults (dftrt,error = 2,18; F = 2.64; p = 0.10) of the pest species, ortheir population growth (dftrt,error = 2,18; F = 1.05; p = 0.37). These resultsindicate substantial differences among pest species regardless of mite pres-ence/absence, and also a substantial effect of mites across the different hosts,leading a to similar trend – host suppression.

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Figure 1. Mean number of physogastric females of Acarophenax lacunatus (± SEM)collected from wheat samples infested with three different host species of stored productinsects. Means followed by the same letter are not significantly different at p < 0.05 by Tukey’smultiple range test.

The mite caused a significant reduction of 61% in the larval populationof R. dominica, and reductions of 53% and 26% in the larval populations ofT. castaneum and C. ferrugineus respectively (dftrt,error = 1,18; F = 36.49; p <

0.0001) (Table 1). There was no significant difference in density of the larvaeof different hosts (dftrt,error= 2,18; F = 2.55; p = 0.11), but the adult popula-tion of C. ferrugineus was higher than the adult population of T. castaneum(dftrt,error = 2,18; F = 17.61; p < 0.0001) (Table 2). Mite infestation signifi-cantly reduced the adult population of all three species (dftrt,error = 1,18; F =60.73; p < 0.0001), with reductions being about twice as great on R. dominicaand T. castaneum as on C. ferrugineus (Table 2).

A. lacunatus was able to significantly decrease the instantaneous rate ofincrease of C. ferrugineus, R. dominica and T. castaneum (dftrt,error = 1,18; F =29.40; p < 0.0001). Rates were higher for C. ferrugineus and R. dominica,and lower for T. castaneum (dftrt,error = 2,18; F = 10.05; p = 0.0012) (Table 3).Grain weight loss differed significantly between treatments, showing signifi-cant interaction between host species and mite presence/absence (dftrt,error =2,18; F = 50.26; p < 0.0001) (Table 4). The presence of R. dominicacaused significantly higher grain weight loss, regardless of mite presence,

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Figure 2. Mean instantenous rate of increase (ri) (± SEM) of Acarophenax lacunatus onthree different host species of stored product insects. Means followed by the same letter arenot significantly different at p < 0.05 by Tukey’s multiple range test.

compared to T. castaneum and C. ferrugineus. Grain weight loss was signifi-cantly reduced (∼45%) as a result of parasitism by A. lacunatus only forR. dominica (Table 4). No significant reduction in wheat weight loss wasobserved after inoculation of A. lacunatus into wheat samples infested eitherwith T. castaneum or C. ferrugineus (15 and 8% reduction respectively).

Discussion

The parasitic mite A. lacunatus, in common with other members ofAcarophenacidae, shows the phenomenon of female physogastry (Cross andKrantz, 1964; Steinkraus and Cross, 1993; Faroni et al., 2001). This is charac-terized by attachment of the female mite to the host egg and development ofprogeny within the body of the mite. Physogastric females of A. lacunatus areeasily observed and counted due to the substantial enlargement of the femalebody that takes place. Physogastry is also a good indicator of the potential ofthis biological control agent to control different host species since it is closelyrelated to mite fecundity and egg parasitism (Faroni et al., 2000, 2001). In the

PARASITISM BY THE MITE ACAROPHENAX LACUNATUS 509

Figure 3. Mean rate of egg parasitism (%) (± SEM) by Acarophenax lacunatus on threedifferent host species of stored product insects. Means followed by the same letter are notsignificantly different at p < 0.05 by Tukey’s multiple range test.

Table 1. Mean number of larvae of three Coleoptera host species subjected or not to eggparasitism by A. lacunatus for 45 days

Mean number of host larvae (± SEM)

Rhyzopertha Tribolium Cryptolestes Meandominica castaneum ferrugineus

Mite absent 56.00 ± 3.80 42.75 ± 2.82 48.00 ± 4.14 48.92 ± 2.81 a∗Mite present 21.75 ± 2.43 20.25 ± 1.75 35.50 ± 8.05 25.83 ± 3.31 b

Mean 38.87 ± 6.80 a∗ 31.50 ± 4.93 a 41.75 ± 4.81 a

∗Means followed by the same letter are not significantly different by two-way analysis ofvariance (p < 0.05).

present case, no females developed physogastry on O. surinamensis. Togetherwith the complete absence of parasitism of eggs of this beetle species, thisindicates the inability of A. lacunatus to regulate populations of this storedproduct pest.

Colonies of R. dominica sustained large numbers of physogastric femalemites, showed high levels of egg parasitism by A. lacunatus (>80%), andsupported the highest rates of parasite population growth. These findings

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Table 2. Mean number of adults of three Coleoptera host species subjected or not to eggparasitism by A. lacunatus for 45 days

Mean number of host adults (± SEM)

Rhyzopertha Tribolium Cryptolestes Meandominica castaneum ferrugineus

Mite absent 134.48 ± 15.10 93.00 ± 5.50 125.95 ± 3.70 117.83 ± 7.26 a∗Mite present 70.75 ± 4.66 46.50 ± 2.72 96.00 ± 5.88 71.08 ± 6.55 b

Mean 102.62 ± 14.02 ab∗ 69.75 ± 9.09 b 111.00 ± 6.52 a

∗Means followed by the same letter are not significantly different at p < 0.05 by Tukey’smultiple range test.

Table 3. Mean instantaneous rate of population growth (ri) of three Coleoptera host speciessubjected or not to egg parasitism by A. lacunatus for 45 days

Mean ri (± SEM)

Rhyzopertha Tribolium Cryptolestes Meandominica castaneum ferrugineus

Mite absent 0.040 ± 0.004 0.033 ± 0.001 0.040 ± 0.001 0.039 ± 0.001 a∗Mite present 0.028 ± 0.001 0.018 ± 0.002 0.033 ± 0.002 0.026 ± 0.002 b

Mean 0.035 ± 0.003 a∗ 0.026 ± 0.003 b 0.037 ± 0.002 a

∗Means followed by the same letter are not significantly different at p < 0.05 by Tukey’smultiple range test.

Table 4. Mean dry weight (g) of wheat grains damaged by three Coleoptera speciessubjected or not to egg parasitism by A. lacunatus for 45 days

Mean wheat dry weight (± SEM) (g)

Rhyzopertha Tribolium Cryptolestesdominica castaneum ferrugineus

Mite absent 23.97 ± 0.88 aA∗ 2.48 ± 0.53 bA 2.15 ± 0.45 bA

Mite present 13.23 ± 1.07 aB 2.27 ± 0.05 bA 1.83 ± 0.08 bA

∗Means followed by the same low case letter in a row or the same capital letter in a columnare not significantly different at p < 0.05 by Tukey’s multiple range test.

agree with reports on the potential of A. lacunatus to regulate R. dominica(Faroni, 1992; Faroni et al., 2000, 2001). However, the performance ofA. lacunatus on C. ferrugineus, and especially on T. castaneum, was unex-pected, since a rather small host range is currently known. A. lacunatus canoccur on colonies of C. ferrugineus, as initially observed by Cross and Krantz

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(1964), but this occurrence was thought to be fortuitous since no parasitismwas reported on this stored product beetle.

Colonies of R. dominica, and T. castaneum to a lesser degree, are ableto sustain large numbers of physogastric female mites, and also high levelsof egg parasitism and population growth of A. lacunatus. C. ferrugineussustained much smaller populations of physogastric mites and far lower ratesof egg parasitism, and led to a slight decrease in the population of A. lacun-atus after a period of 45 days. These findings suggest that R. dominica andT. castaneum are suitable hosts for A. lacunatus, because the parasitic miteis able to survive and reproduce. In contrast, C. ferrugineus appears to beable to sustain the mite population, but mite reproduction seems poor on thishost. O. surinamensis does not appear to be a host of A. lacunatus, since themites fail to survive and reproduce on this species. These findings agree withour results for the number of larvae and adults of the various beetle speciesobtained with and without the parasitic mite, and also the differences betweenhost species in wheat grain loss prevented by inoculation of A. lacunatus.

The host range of A. lacunatus does not seem to be as broad asamong other parasitic mites reported as biocontrol agents of stored productinsects, but it does surpass the initial expectation of a single host. Pyemotestritici, for instance, attacks Plodia interpunctella (Hübner) and Ephestia(= Cadra) cautella (Walker) (Lepidoptera: Pyralidae), Lasioderma serricorne(F.) (Coleoptera: Anobiidae) and even O. surinamensis (Bruce and LeCato,1979). B. tarsalis is also able to feed on T. castaneum in the absence of itsmain host species E. cautella. The host range of other Acarophenax speciesis poorly known, but among Acarophenacidae there are some species, suchas Adactylidium costarricensis Goldarazena, Jordana & Zhang and A. moori-ensis Goldarazena & Jordana, which appear to have broad host ranges as well(Goldarazena et al., 2001).

The host range is a particularly important aspect of biological controlagents of stored product insects due to the common co-occurrence of differentpest-species within a store. T. castaneum, for instance, is referred to as asecondary pest of stored products because of its inability to attack wholegrains and grains at low moisture content (< 9%). In contrast, R. dominica, aprimary pest, attacks whole grains and grains at low moisture content, butis not able to attack flour unlike T. castaneum unless heavily compacted(Guedes, 1991; Subramanyam and Hagstrum, 1996). A secondary infestationof stored wheat by a secondary pest, such as T.‘castaneum, usually followsan initial attack by a primary pest, like R. dominica. Therefore, the ability ofA. lacunatus to successfully parasitize both of these species is a favourabletrait for its potential use in pest management programs of stored cereals. Inaddition, artificial selection for use of T. castaneum and C. ferrugineus as the

512 CARLOS ROMERO F. OLIVEIRA ET AL.

host may further extend and/or improve the performance of A. lacunatus onthese species and add to its versatility as a biological control agent of storedproduct insects.

Acknowledgements

Financial support provided by CAPES, CNPq and FAPEMIG was greatlyappreciated. The comments and suggestions provided by the editor, Dr. K.D.Suderland, and referees were also appreciated.

References

Brower, J.H., L. Smith, P.V. Vail and P.W. Flinn, 1996. Biological control. In: Bh.Subramanyam and D.W. Hagstrum (eds), Integrated Management of Insects in StoredProducts. Marcel Dekker, New York. pp. 223–286.

Bruce, W.A. and G.L. LeCato, 1979. Pyemotes tritici: Potential biological control agent ofstored-product insects. Rec. Adv. Acarol. 1: 213–220.

Cross, E.A. and G.W. Krantz, 1964. Two new species of the genus Acarophenax Newsteadand Duvall 1918 (Acarina: Pyemotidae). Acarologia 6: 287–295.

Faroni, L.R.D’A., 1992. Biologia y Control del Gorgojo de los Granos Rhyzopertha dominica(F.). D.Sc. Thesis, Universidad Politécnica de Valencia, Valencia, Spain.

Faroni, L.R.D’A., R.N.C. Guedes and A.L. Matioli, 2000. Potential of Acarophenax lacunatus(Prostigmata: Acarophenacidae) as a biological control agent of Rhyzopertha dominica(Coleoptera: Bostrichidae). J. Stored Prod. Res. 36: 55–63.

Faroni, L.R.D’A., R.N.C. Guedes and A.L. Matioli, 2001. Effect of temperature on develop-ment and population growth of Acarophenax lacunatus (Cross & Krantz) (Prostigmata:Acarophenacidae) on Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae). BiocontrolSci. Technol. 11: 5–12.

Goldarazena, A., R. Ochoa and R. Jordana, 1999. Revision of the genus ParadactyliumMahunka (Acari: Heterostigmata). Internat. J. Acarol. 25: 91–99.

Goldarazena, A., R. Ochoa, R. Jordana and B.M. OConnor, 2001. Revision of the genusAdactylium Cross (Acari: Heterostigmata: Acarophenacidae), mites associated with thrips(Thysanoptera). Proc. Entomol. Soc. Wash. 103: 473–516.

Guedes, R.N.C., 1991. Manejo integrado para a proteção de grãos armazenados contra insetos.Rev. Bras. Armaz. 15: 3–48.

Haines, C.P., 1981. Laboratory studies on the role of an egg predator, Blattisocius tarsalis(Berlese) (Acari: Ascidae), in relation to the natural control of Ephestia cautella (Walter)(Lepidoptera: Pyralidae) in warehouses. Bull. Entomol. Res. 71: 555–574.

Harein, P.K.M. and R. Davies, 1992. Control of stored-grain insects. In: D.B. Sauer (ed),Storage of Cereal Grains and Their Products. American Association of Cereal Chemists,St. Paul, MN, USA. pp. 491–534.

Howarth, F.G., 1991. Environmental impacts of classical biological control. Annu. Rev.Entomol. 36: 485–509.

Moser, J.C., 1975. Biosystematics of the straw icth mite with special reference to nomenclatureand dermatology. Trans. Royal Entomol. Soc. London 122: 185–191.

PARASITISM BY THE MITE ACAROPHENAX LACUNATUS 513

Plarre, R., K. Lieber, W. Burkholder and J. Phillips, 1999. Host and host instar preference ofApanteles carpatus (Say) (Hymenoptera: Braconidae) a possible parasitoid for biologicalcontrol of clothes moths (Lepidoptera: Tineidae). J. Stored Prod. Res. 35: 197–213.

SAS Institute, 1989. SAS/STAT User’s Guide, Version 6. SAS Institute, Cary, NC, USA.Schöller, M., S. Prozell, A.G. Al-Kirshi and C. Reichmuth, 1997. Towards biological control

as a major component of integrated pest management in stored product protection. J.Stored Prod. Res. 33: 81–97.

Simberloff, D. and P. Stiling, 1996. How risky is biological control? Ecology 77: 1965–1974.Sinha, R.N., 1995. The stored grain ecosystem. In: D.S. Jayas, N.D.G. White and W.E. Muir

(eds), Stored Grain Ecosystem. Marcel Dekker, New York. pp. 1–33.Steidle, J.L.M., D. Rees and E.J. Wright, 2001. Assessment of Australian Trichogramma

species (Hymenoptera: Trichogrammatidae) as control agents of stored product moths.J. Stored Prod. Res. 37: 263–275.

Steinkraus, D.C. and E.A. Cross, 1993. Description and life history of AcarophenaxMahundai, n.sp. (Acari: Tarsonemina: Acarophenacidae), an egg parasite of the lessermealworm (Coleoptera: Tenebrionidae). An. Entomol. Soc. Am. 86: 239–244.

Subramanyam, Bh. and D.W. Hagstrum, 1996. Integrated Management of Insects in StoredProducts. Marcel Dekker, New York.

White, N.D.G. and J.G. Leesch, 1996. Chemical control. In: Bh. Subramanyam and D.W.Hagstrum (eds), Integrated Management of Insects in Stored Products. Marcel Dekker,New York. pp. 287–330.