(excerpt)
The corn leaf aphid (CLA), Rhopalosiphum maidis (Fitch), is found on field corn in the midwest Cnited States each year. Except for infrequent and scattered outbreaks, CLA populations remain at low levels. Injury to corn occurs during tasseling (Snelling et aL 1941) and is caused by CLAs which are the progeny of colonizers that arrived 2-3 weeks earlier when the corn was in the whorl stage (Bryson 1934, Falter 1963)

Ruesink, W. G

Wagner, S. W

English

Valparaiso University

The Great Lakes Entomologist Volume 15 Number 3 - Fall 1982 Number 3 - Fall 1982 Article 2 October 1982 The Distribution of Natural Enemies of the Corn Leaf Aphid (Homoptera: Aphdidae) on Field Corn S. W. Wagner Michigan State University W. G. Ruesink Illinois Natural History Survey Follow this and additional works at: https://scholar.valpo.edu/tgle  Part of the Entomology Commons Recommended Citation Wagner, S. W. and Ruesink, W. G. 1982. "The Distribution of Natural Enemies of the Corn Leaf Aphid (Homoptera: Aphdidae) on Field Corn," The Great Lakes Entomologist, vol 15 (3) Available at: https://scholar.valpo.edu/tgle/vol15/iss3/2 This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. THE DISTRIBUTION OF NATURAL ENEMIES OF THE CORN LEAF APHID (HOMOPTERA: APHIDIDAE) ON FIELD CORN1 S. W. Wagner2 and W. G. Ruesink3 The corn leaf aphid (CLA), Rhopalosiphum maidis (Fitch), is found on field corn in the midwest Cnited States each year. Except for infrequent and scattered outbreaks, CLA populations remain at low levels. Injury to corn occurs during tasseling (Snelling et aL 1941) and is caused by CLAs which are the progeny of colonizers that arrived 2-3 weeks earlier when the corn was in the whorl stage (Bryson 1934, Falter 1963). Yield reductions averaging up to :H'C on heavily infested plants have been reponed {Bigger 1958, Everly 1960, Randell 196-" Various workers have shown that CLA biotype (Painter and Pathak 1%2), corn variety IOemen 1917, Everly 1971, Long et al. 1977) and planting date (McColloch 1921, Falter 1963! can influence CLA popUlation levels. The impact of natural enemies on CLA popUla­tions has usually been assumed to be negligible. This study was undenaken to learn which species of potential natural enemies, especially pre-daIors. were most abundant in corn fields in central Illinois and whether any of these was temporally and spatially synchronized with the CLA. All of the research was done i  Champaign County. illinois. METHODS _~phid and natural enemy populations on field corn were sampled during 1977 by non­destructi',e visual searches. Three groups, each consisting of 20 plants (four sets of five consecutive plants), wer  visually monitored between four and seven times during the whorl and ta..'iseling stages. Each plant was marked and monitored at ca. 4-day intervals from whorl stage until CLA populations declined after tasseling. At each date, data were taken concern­ing selected predator and phytophagous insect species, abundance, location, and field corn maturity. Group I was located in Field I, which tasseled 7 July. Groups 2 and 3 were both in Field 2: Group 1 tasseled 29 July, while Group 3 tasseled 16 August. For data analysis, the corn plant was divided into the upper plant (UP) and lower plant (LP). The UP consisted of eirher the tassel plus the upper two leaves or the whorl. The LP consisted of that ponion of me com plant from the ground to the whorl or to the second leaf from the top of the corn plant. Para.sitoids were reared from aphid mummies collected from corn in the vicinity of the three com groups being monitored. A repesentative collection of parasitoids was identified by E. E. Grissell and Paul M. Marsh of the Systematic Entomology Laboratory, USDA, Agricultural Research Service, Beltsville, Maryland. The remainder of the specimens were identified by comparison and were deposited in the Illinois Natural History Survey insect collection. Whorls cannot be sampled without destroying them, so another sampling procedure was initiated in 1977 to complement the data gathered by visual searches. Until tasseling oc­curred. whorls of five consecutive plants in the vicinity of each group of five marked plants were removed. placed in a plastic bag, and stored at 5°C. The whorl was disassembled into a -()C( ethanol bath. shaken vigorously, and the leaves and tassel were then rinsed with 70% [This pUblication is a contribution of the Illinois Natural History Survey and Illinois Agricultural ExperiIn<:nt Station. CoUege of Agriculture, University of Illinois at Urbana-Champaign, supported in part by Hatch Entomology Project 1-6-53193. :Departmenr of Entomology. Michigan State University. East Lansing. MI48824. ·'Illinois "atural History Survey. 607 E. Peabody Drive, Champai n, IL 61820. 153 1Wagner and Ruesink: The Distribution of Natural Enemies of the Corn Leaf Aphid (HomopPublished by ValpoScholar, 1982154 THE GREAT LAKES ENTOMOLOGIST Vol. 15, No.3 ethanol. All 70% ethanol was then filtered through ca. 100 mesh/inch organdy. The organdy was then inspected with a binocular microscope, and the number of CLAs and adult Oriull insidiosus was recorded. In the summer of 1978, plants in three fields of com in the whorl stage of development w e also censused. The whorl was removed and the insects associated with each leaf were noted as the leaf was removed from the whorl. Adult O. insidiosus (Say) (Hemiptera: Anthocoridae) and thrips were collected with an aspirator and preserved. O. insidiosus specimens were sexed and the thrips were identified to species. These data were gathered to determine whether thrips might serve as temporary prey for O. insidiosus prior to the arrival of the CLA. RESULTS The visual census of the three field com groups from whorl through tasseling showed that CLA averaged 0 to 262 per plant depending on the com groups and were located primarily on the UP (Table O. Adult O. insidiosus averaged between 0.95 and 6.13 per UP during the whorl stage. Neuropteran larvae averaged 0 to 0.67 per plant and were located on the LP and larval coccinellids averaged between 0.05 and I.!O per plant and were also found on the LP. Frankliniella tenuieornis Uzel (Thysanoptera: Thripidae) were always present in the whorl and in the leaf sheath. Sehizaphis graminum (Rodani) (Homoptera: Aphididae), the green­bug, averaged from 0.4 to 14.3 per plant and was always located on the LP. Other insect~ species were found infrequently with average densities of at most a few per 20 plants and were also found on the LP. CLA populations peaked within a week of tassel emergence: X(SD) of 128(91),38(79), and 236(479) respectively, for the three groups. CLA popUlations on the lower plant (LP) peaked at the same time as the UP popUlation or a few days later and had peak values of 5.0(7.0), 1.4(2.4). and 25.9(97.7) for the three groups. Populations of adult O. insidiosus on the UP peaked within 5 days of tassel emergence while popUlations  the LP peaked 3-11 days after tassel emergence. The relative distribu­tion of this predator shifted from the UP prior to tasseling to the LP after tasseling. Correla­tions of CLA and adult O. insidiosus numbers on individual plants within a sampling date for the UP were significant once each at both 0.05 and O.OlleveJ and were not significant on 16 dates. Alternately, analysis of the distribution of the CLA, O. insidiosus and F. tcnllicornis from the destructive sampling of whorls indicated that their distribution  random with respect to one another (X2, 2 x 2 contingency table, P > 0.05, n 176,57 plants in 1977 and 119 plants in 1978). O. insidiosus adults were observed feeding on CLAs on four occasions and once on thrips, probably F. tenuicornis. Observations during the summers of 1977 and 1978 indicated that F. tenllicornis colonized plants prior to the whorl stage. Individuals remain under the leaf sheath or in the whorl until tasseling when populations decline and are found in the ear shucks. Coccinellid and neuropteran distributions were almost exclusively limited to the LP for all life stages. The only exception to this was Hippodamia convergens Guerin-Meneville (Coleoptera: Coecinellidae) adults with 63.2% located on the UP. In contrast, 93.2% of the Coleomegilla maelliata (DeGeer) (Coleoptera: Coccinellidae) adults were on the LP which is a significantly different distribution (X' analysis of 2 x 2 contingency table, P < 0.00(5) and in keeping with the results of Ewert and Chiang (1%7). The density of potential predators did not correlate well with aphid density except in one case: chrysopid egg density was significantly correlated with non-CLA populations on the LP (P < 0.01, r 0.60, n = 18). Otherwise, neither eggs nor larvae of either coccinellids or neuropterans could be related to LP aphid density. On the premise that predator populations should lag behind prey popUlations, the analysis was repeated comparing predator density with the number of aphids found on the preceding sampling date, but in this case none of the correlation coefficients was significantly greater than zero. Eight species of parasitoids emerged from the aphid mummies that were collected and returned to the laboratory (Table 2). Known primary parasitoids composed 18.7% of those 2The Great Lakes Entomologist, Vol. 15, No. 3 [1982], Art. 2https://scholar.valpo.edu/tgle/vol15/iss3/2Tahle I. Average ropulation levels on three IolIUUPS of rlants IIwnitol'ed perimlieally, ami n whorls of plnnts locllted Ileal' the Io l'OlIpS. during Ihe slimmer of 11)77. ~ Samplingb Orlus '.I Other'russel Method and Adults CLA (J roonbug' Aphids N cur0t?terun CoccinoLlld Date Emergence Number UP LI) UP LP LP LP Eggs Larvae Eggs Lal'vao 1 7-02 Before W 23 1.04 54.80 7-10 After E 21 0.95 0.62 89.14 3.50 3.52 0040 0.24 0. 0 0.90 0.48 7-14 7-18 7-22 7-26 After After After After E E E E 20 20 20 20 0.75 0.75 0.40 0.00 0.25 127.90 1.65 48.80 0.75 14.25 0.75 1.80 5.00 0.05 1.60 1.35 14.30 8.15 3.20 2.50 2.70 1.10 0.20 0.50 1.80 1045 1.00 0.60 0.25 0.00 0.05 0.10 4.95 3.70 0.00 0.00 0.70 1.10 0.55 0.15 ..., :I: tTl a :;:Q 2 7-12 Before E 20 1.15 0.05 10.00 1.10 11.8 1.10 0.95 0.20 2.40 0.15 tTl>­..., 7-16 7-17 7-20 7-20 Before Before Before Before W 20 E 20 E 20 W 14 1.05 1. 95 1.10 2.14 0.10 0.25 0.60 0.00 0.20 4.30 0.00 0.00 11. 25 4.00 2.6  0.9  0.90 0.55 0.00 0.25 3.45 0.95 0.20 0.05 !;: ;:-:: tTl CIl 7-24 7-25 Before Before E 20 W 16 1.10 4.31 0.35 27.35 24.94 0.05 2.85 0.70 0.85 0.10 1.30 0.10 tTl Z..., 7-28 Before E 20 2.85 3.35 37.75 0.05 2.15 0.25 0.55 0.00 0.60 0.10 0 8-01 After E 20 5.90 7.05 24.40 lAO 1.45 0.10 0.95 0.05 2.05 0.10 ~ 0 8-06 After E 20 2.95 2.70 0.00 0.65 0.50 0.05 0.85 0.00 8.65 0.25 r 0 a-3 8-8 & 10 Before E 20 5.90 2.80 234.90 0.00 1. 20 0.20 0.40 0.00 1.15 0.25 CIl..., 8-13 Before E 15 6.13 4.07 236.27 25.87 0.67 0.07 0.33 0.67 5.27 0.07 8-19 & 20 After E 20 4.60 4.35 187.45 13.95 0.90 3.00 0.00 0.00 6.35 0.25 8-24 After E 20 1.65 3.55 87.15 5.30 0.40 0.40 0.10 0.05 4.60 0.35 field 1, tasseled 7-7; 2 field 2, tasseled 7-29; 3 field 2, delayed germination tasseled 8-16. entire plant was visually sampled (see Methods); W, only whorl was sampled (see Methods). V; Vl 3Wagner and Ruesink: The Distribution of Natural Enemies of the Corn Leaf Aphid (HomopPublished by ValpoScholar, 1982156 THE GREAT LAKES ENTOMOLOGIST Vol. 15, No.3 Table 2. Hymenopterous paras ito ids reared from unidentified aphid mummies collected from corn at Urbana, Illinois, in 1977. Number Percent Trophic Parasitoid of mummies of total affinitya Braconidae Aphidius sp. 17 IS.7 1° Eulophidae Tetrastichlls minutus (Howard) 14 15.4 Ie Encrytidae Aphidencyrtus aphidivorus (Mary) 3 3.3 IIe Genus sp. I 1.1 ? Pteromalidae Asaphes sp. 11 12.1 ? PachneurOI1 siphOl1ophorae (Ashmead) 42 46.2 lIO P. altisclltum (Cook) I 1.1 ? Megaspilidae Dendrocerus niger (Howard) 2 2.2 ? a1° = primary parasite of aphid, n° secondary parasite of aphid. emergmg, while three species composing 64.9% of those emerging were secondary para­sitoids. The trophic relationships of the remaining 16.5% are not known. Mummies on the monitored plants were located on the LP, often in clusters of greenbug. The number of mummies/plant were similar both between the different fields (2 miles apat1) and on com of differing age within the same field. While no data were gathered on percent parasitism, based on the low number of mummies found, it would appear that far less than 1% of the aphids were parasitized. Aphid flights were very low in 1977. DISCUSSION The results of these field observations indicate that potential CLA natural enemies other than O. insidiosus were generally restricted to the LP and thus could have little effect on CLA populations colonizing com. The only exception to this was H. collvergens adults, but any significant impact on CLA dynamics by this species was precluded by low numbers (maximum population O.2/plant). Ewert and Chiang (1967) and Havnvik nd Frye (1%9) noted associations between CLAs and both H. convergells and H. tridecimpllnctata, but neither indicated that these species control CLAs. Between-plant distribution of O. illsidiosus is only slightly affected, if at all, by the between-plant distribution of CLA according to our analysis. This distribution f O. insidiosus adults is consistent with Isenhour'S (1977) description of a floating adult Or lls population. He argued that adults constantly sample the environment, moving from plant to plant within the com and soybean fields under study. This behavior would tend to bring the predator into contact with newly arrived CLAs. when aphid populations are small and predation would have its greatest impact. The pre-tasseling adult O. insidiosus density of ca. l/plant found in this study and by others (Barber 1936, Dicke and Jarvis 1%2) indicates that this predator is often present in com fields in the eastern U.S. at levels which could impact CLA populations. While Dicke and Jarvis (1962) and Havnvik and Frye (1969) suggested that O. insidiosus may have controlled CLA populations in their studies, the actual impact remains uncertain because feeding studies have not been conducted. 4The Great Lakes Entomologist, Vol. 15, No. 3 [1982], Art. 2https://scholar.valpo.edu/tgle/vol15/iss3/21982 THE GREAT LAKES ENTOMOLOGIST 157 LITERATURE CITED Ba.rber. G. W. 1936. Drills illsidiosus (Say), an important natural enemy of the corn ear­worm. CSD.-\. Tech. Bull. 504. Bigger. J. H. 1958. Damage to the corn crop by the corn leaf aphid. Proc. North-Central Br. EnLOmol. Soc. Arner. 13:19-20. Bryson. H. R. 1934. Observations on the summer activities of Aphis maidis Fitch. J. Econ. Entomol. 27:827-S32. Dicke. F. F. and J. L. Jarvis. 1%2. The habits and seasonal abundance of Drills insidiosllS ,Say, (Hemiptera-Homoptera: Anthocoridae) on corn. J. Kansas. Entomol. Soc. 35:339­3-14. E \erl)". R. T. 1%0. Loss in corn yield associated with the abundance of the corn leaf aphid, Rhopalosiphllm maidis, in Indiana. 1. Econ. Entomol. 53:924-932. ----. 1971. Corn leaf aphid populations on singlecrosses from resistant and susceptible dent corn inbred lines. Proc. North-Central Br. EntomoL Soc. Amer. 26:46-52. Ewert. ~L A. and H. C. Chiang. 1967. Effects of some environmental factors on the distri­bution of three Coccinellidae in their microhabitat. in L Hodek (ed.). Ecology of aphidophagous insects. Proc. Symp. Liblice near Prague. Academia, Prague. Falter. 1. ~L 1%3. The bionomics and control of Rhopalosiphllm maidis (Fitch) in Wiscon­sin. Ph.D. thesis. Univ. Wisconsin, Madison. Gernert. W. B. 1917. Aphis immunity of teosinte-corn hybrids. Science 46:390-392. Ha\n\ik. J. L and R. D. Frye. 1%9. Predaceous insects and their prey on corn in south­eastern :Sorth Dakota. Proc. North-Central Br. Entomol. Soc. Amer. 24:87-92. Isenhour. D.J. 1977. Seasonal fluctuations f DrillS insidioslls (Say) and Thysanoptera in adjacent soybeans and corn i  Missouri. M.S. thesis. Univ. Missouri, Columbia. Long. B. 1.. G. ':\f. Dunn, J. S. Bowman, and D. G. Routley. 1977. Relationship of nydroxamic acid content in corn and resistance to the corn leaf aphid. Crop Sci. 17:55-58. ~fcColloch. J. W. 192!. The corn leaf aphid (Aphis maidis Fitch) in Kansas. J. Econ. Emomol. 14:89-94. Painter. R. H. and M. E. Pathak. 1962. The distinguishing features and significance of the four biotypes of the com leaf aphid Rhopalosiphum maidis (Fitch). Proc. XI Intern. Congr. Entomol. 2:110-115. Randell. R. 1967. Evaluating gross yield losses caused by severe com leaf aphid infestations. Illinois Custom Spray Operators Training School Manual 19:34-36. Snelling. R. 0 .. R. A. Blanchard, and J. H. Bigger, 1940. Resistance of corn strains to the leaf aphid. A.phis maidis (Fitch). Amer. Soc. Agron. J. 32:371-381. 5Wagner and Ruesink: The Distribution of Natural Enemies of the Corn Leaf Aphid (HomopPublished by ValpoScholar, 1982

The Distribution of Natural Enemies of the Corn Leaf Aphid (Homoptera: Aphdidae) on Field Corn

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The Distribution of Natural Enemies of the Corn Leaf Aphid (Homoptera: Aphdidae) on Field Corn

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