Beardsley, J.W.

Bowler, P.A.

Trujillo, E.E.

Proceedings of the Hawaiian Entomological Society

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Vol. XXII, No. 3, December, 1977 451Insect Feeding on Sugarcane Smut in Hawaii1 2P. A. Bowler\ E. E. Trujillch, and J. W. Beardsley, Jr.*The insect fauna associated with sugarcane smut whips is not wellunderstood. Although various insects have been reported (Hayward, 1943),only Phalacrus immarginatus Champion has been well documented as apredator feeding on chlamydospores (Agarwal, 1956). In India this speciesspends its entire life cycle on the host plant; within smut whips duringdevelopment (egg and larva) and on the leaves when mature. Extensiveinsect damage to smut whips on rattoon crops and older stands withsecondary lateral whip formation was observed in experimental plots ofinfected sugarcane in Hawaii. The smut fungus, Ustilago scitaminea Syd., isa recent accidental introduction to the Hawaiian Islands (Byther, Steiner,and Wismer, 1971), and this study was undertaken as one of a series ofinvestigations of dispersal and mechanical vectors of the disease.Materials and MethodsTo assess the extent of insect damage to smut whips, fifty whips in each ofthree approximately one-half acre plots were examined and insect damagewas recorded. Insects captured on whips were dissected after being cleanedwith repeated ethanol wipes, and their viscera were microscopicallyobserved to determine if chlamydospores were present. Representatives ofspecies containing spores were eviscerated and their stomach contents wereplated on the smut selective medium of Anderson and Trujillo (1975). Thesmut selective medium is prepared with 200 ml. V-8 juice (clarified byfiltration or centrifugation), 40 g agar, streptomycin sulfate 500 ppm.,tetracycline hydrochloride 300 ppm., neomycin sulfate 650 ppm.,thiabendazole 10 ppm. and distilled water to make 1000 ml. Viability(percent germination) can be assessed after 24 hours, and species can bedistinguished in culture (incubated at 31°C) after four days.Results and DiscussionFour species in three families have previously been reported feeding onchlamydospores of sugarcane smut (Table 1). Members of the Phalacridaeare known to feed on grass smuts, and Phalacrus spp. have been found on'Research for this investigation was supported in part by ARS Cooperative ResearchAgreement No. 12-14-5001-136.2Published with the approval of the Director of the Hawaii Agricultural Experiment Stationas Journal Series No. 1940.3Formerly Research Associate, Department of Plant Pathology, University of Hawaii atManoa, 3190 Maile Way, Honolulu, Hawaii 96822, presently (Botany Division, Museum ofNatural Sciences, National Museums of Canada, Ottawa, Ontario, Canada).4Plant Pathologist, Department of Plant Pathology, University of Hawaii at Manoa, 3190Maile Way, Honolulu, Hawaii 96822.5Entomologist, Department of Entomology, University of Hawaii at Manoa, 3050 MaileWay, Honolulu, Hawaii 96822.452 Proceedings, Hawaiian Entomological Societywhips in Argentina and India. An unidentified species of Phalacrus occursin Hawaii; however, this black beetle was not collected on smutted plants byus. Insects utilizing chlamydospores as a food source in Hawaii are listed inTable 1.Evidence of insect damage to smut whips was pit-like excavations in thewhip core (Fig. 1A), complete destruction of the whip base (Fig. IB), andareas stripped of chlamydospores (particularly in the basal region where thesilver membrane was intact). Insect damage was observed on whips of allsizes in three categories of sugarcane (Table 2). The basal region exhibitedthe most frequent insect activity, both beneath the leaf sheath and above itwhere the silver membrane had not ruptured. Other damage (pit excavation)occurred above the base where chlamydospores were exposed. Sybraalternans (Wiedemann) and Araecerus sp., both well camouflaged when onthe whip, were found on loose smut and in excavations near the moist basalregion or in the mid-whip zone. Schistocerca nitens nitens (Thunberg), arelatively recent New World introduction, was common in infected fieldsand contained large quantities of spores. Larval stages of tineid moths andPsammoecus desjardinsi Guerin were abundant beneath the supporting leafsheath, particularly during the early stages of decomposition. Chelisochesmorio (Fabricius), the black earwig, was common beneath the basal leavesfeeding on moist unexposed chlamydospores. Amphicerus cornutus(Pallas), frequently found boring in dead cane, was observed skeletonizingwhips.Since other smut species occur in Hawaii, notably Ustilago cynodontisand U. maydis, the stomach contents of the larger insects captured werestreaked out on the smut selective medium, and were compared withcultures of these species. The smut selective medium is a valuable diagnostictool in distinguishing smut species from mixed spore samples. On thismedium both chlamydospore and sporidial cultures of U. scitaminea can berecognized from other species of Ustilago (Anderson and Trujillo, 1975).Cultures of U. scitaminea were identified from viscera samples of S. nitens,Araecerus sp., S. alternans, Euconocephalus nasutus (Thunberg), and Cmorio. Since all of the insects sampled contained only sugarcane smut, twoindividuals of Araecerus and S. alternans were allowed to feed on bermudagrass inflourescences infected with U. cynodontis for 48 hours. Teliosporecultures taken from fore-gut samples were easily recognized as bermudagrass smut. The best results in culture were obtained when the insect viscerawere removed and plated out immediately after capture. This uniqueapplication of the smut selective medium could prove useful toentomologists in interpreting host-specificity among smut eating species.In addition to insects utilizing smut chlamydospores as a food source,numerous insects common in uninfected cane fields or indigenous to thestudy site were seen on diseased plants. Ants, wasps, moths, honey bees,cockroaches, and flies were probably casual in occurrence on host plants.Other species, such as Stator pruininus (Horn), Scymnus sp., Ceresiumunicolor (Fabricius), and unidentified mites, are known to consume pollenand fungi, and may occasionally feed on chlamydospores. EuconocephalusVol. XXII, No. 3, December, 1977 453nasutus was seen feeding on whip material; however, other specimenssampled contained only leaf matter. It seems probable that many otherspecies may opportunistically utilize smut.The wings and body parts of all of the insects examined werecontaminated with chlamydospores lodged on the minute hairs covering thebody and wings of many insects. Inoculum contamination could arise fromdirect contact with whips or leaves of infected plants, or from the highconcentration of air-borne inoculum inside crop canopies. Weatherconditions favorable to diurnal insect activity correspond with thoseenhancing spore removal. Contaminated insects could transport smutinoculum to local uninfected plants; however, for the pathogen to initiateinfection inoculum must be introduced through the bud scale or establishedthrough a wound (Antoine, 1961). Although other members of the genusSchistocerca are migratory, there is no evidence of S. nitens nitens beingmigratory in Hawaii. Similarly, other insects discussed here are notmigratory, but could be displaced considerable distances by strong windsduring trivial flight activity (Johnson, 1969). In the area of greatest infectionon Oahu, for example, northeasterly trade winds frequently reach velocitiesof 25 mph. Destruction of habitat during harvest could force displacedinsects to invade new regions. Insects serve as mechanical vectors forinflourescence infecting Ustilago species, notably U. violaceae and probablyU. succisae (Ingold, 1971).Although insect damage to smut whips is extensive and in many cases killsthem, it seems unlikely that insect predation significantly reduces thenumber of chlamydospores on a whip or the inoculum load in the air.Agarwal (1956) concluded his discussion of Phalacrus immarginatus bysuggesting that "although this insect may be somewhat beneficial by itsconsuming some of the smut spores, it is more likely to assist in theirdispersal." Francis (1938) observed spores adhering to the bodies ofendomychid beetles, and suggested that they could be vectors in the spreadof the disease. Displaced or migratory insects would be apt to transportinoculum to a potential host plant directly, while air-borne inoculum couldonly make chance contact. The inoculum potential for aerial infection hasnot been established, and the possible role of insects as mechanical vectorsmust remain speculative.AbstractSchistocerca nitens nitens (Acrididae), Araecerus sp. (Anthribidae),Sybra alternans (Cerambycidae), Chelisoches morio (Chelisochidae),Scymnus sp. (Coccinellidae), Euconocephalus nasutus (Tettigoniidae), andlarval stages of Psammoecus desjardinsi (Cucujidae) and an unidentifiedtineid moth feed on chlamydospores of sugarcane smut {Ustilago scitamineaSyd.) in Hawaii. Evidence of insect damage on smut whips includedexcavations in the whip core, severed whip scions, and areas stripped ofchlamydospores. Insect damage was evident on up to 70% of the whipsexamined in three size classes of infected sugarcane. Identification of thesmut species was verified by culturing insect stomach contents on the smutselective medium of Anderson and Trujillo.454 Proceedings, Hawaiian Entomofogicaf SocietyAcknowledgmentsWe gratefully acknowledge the Hawaiian Sugar Planters' Association forthe use of its Experimental Station at Waianae.Figure l.A, Pit-like excavations in the whip core caused by insects eating through thechlamydospore layer. B, Insect damage to a whip base.Vol. XXII, No. 3, December, 1977 455Table 1. Insects reported feeding on sugarcane smut chlamydosporeswith the locality and reference.Family andSpeciesAcrididaeSchistocerca nitens nitensAnthicidaeAnthicus albifasciatusAnthribidaeAraecerus sp.Brachytarsus zeaeCerambycidaeSybra alternansChelisochidaeChelisoches morioCoccinellidaeScymnus sp.CucujidaePsammoecus desjardinsi(larval stages)PhalacridaePhalacrus immarginatusPhalacrus sp.TettigoniidaeEuconocephalus nasutusTineidaeunidentified larvaeHawaiiArgentinaHawaiiArgentinaHawaiiHawaiiHawaiiHawaiiIndiaArgentinaHawaiiHawaiiLocality ReferenceHayward, 1943Hayward, 1943Agarwal, 1956Hayward, 1943Table 2. Results of an examination of 50 whips in each of three sizeclasses of infected sugarcane.Cane heightin meters3 - 3.61.2 - 11% Insect Damaged(N = 50 each)701832Mean length ofdamaged whips in cm44.790.357.4Mean whiplength in cm74.246.756.6456 Proceedings, Hawaiian Entomological SocietyLITERATURE CITEDAgarwal, R. A. 1956. Phalacrus immarginatus Champ. A beetle feeding on sugarcane smut.Indian Journal of Entomology 18: 267-272.Anderson, T. and E. E. Trujillo. 1975. The development of a selective medium for the study ofVstilago scitaminea Syd. in field soil and the effects of moisture, temperature andamendments on its soil survival. (In preparation.)Antoine, R. 1961. Smut, (in) Sugarcane Diseases of the World, ed. J. P. Martin, E. V. Abbottand C. G. Hughes. Elsevier, N. Y. pp. 327-345.Byther, R. S., G. W. Steiner, and C. A. Wismer. 1971. New sugarcane diseases reported inHawaii. Sugarcane Path. News 1(7): 18-21.Francis, C. B. 1938. Sugarcane smut. Madras Agric. Journal 26: 468-474.Hayward, K. J. 1943. El "Carbon" del la cana y los insectos. Estacion Experimental Agricola deTucuman. Circular No. 123.Ingold, C. T. 1971. Fungal Spores. Oxford University Press, London.Johnson, C. G. 1969. Migration and Dispersal of Insects by Flight. Methuen and Co., Ltd.,London.

Insect Feeding on Sugarcane Smut in Hawaii

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Insect Feeding on Sugarcane Smut in Hawaii

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