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Interactions of the parasitoid Lysiphlebus testaceipes (Cresson) and the greenbug, Schizaphis graminum (Rondani), on greenbug-resistant “Cargill 607E’ (antibiosis), “Cargill 797’ (primarily tolerance), and -susceptible “Golden Harvest 510B’ sorghum, Sorghum bicolor (L.) Moench, were tested using three levels of biotype I greenbug infestation. The parasitoid infestation rate was 0.5 female and 1.0 male L. testaceipes per plant. For all three greenbug infestation levels, the parasitoid brought the greenbug under control (i.e., prevented the greenbugs from killing the plants) on both resistant hybrids, but it did not prevent heavy leaf damage at the higher greenbug infestation rates. At the low greenbug infestation rate (50 greenbugs per resistant plant when parasitoids were introduced), greenbugs damaged 5 and 18% of the total leaf area on “Cargill 797’ and “Cargill 607E’, respectively, before greenbugs were eliminated. Leaf damage was higher for the intermediate infestation study (120 greenbugs per plant), 21% and 30% leaf area were damaged on the resistant sorghum hybrids “Cargill 797’ and “Cargill 607E’, respectively. At the high greenbug infestation rate (300 greenbugs per plant), heavy damage occurred: 61% on “Cargill 607E’ and 75% on “Cargill 797’. The parasitoids did not control greenbugs on the susceptible sorghum hybrid “Golden Harvest 510B’. L. testaceipes provided comparable control on both greenbug-resistant hybrids. This study supports previous studies indicating that L. testaceipes is effective in controlling greenbugs on sorghum with antibiosis resistance to greenbugs. Furthermore, new information is provided indicating that L. testaceipes is also effective in controlling greenbugs on a greenbug-tolerant hybrid.

Field cage studies were conducted to describe the relationship between the percentage of Lysiphlebus testaceipes (Cresson) parasitism (as measured by aphid mummies) and densities of green bug, Schizaphis graminum Rondani, on grain sorghum, Sorghum bicolor L. In 1993 and 1994, a biotype E-susceptible grain sorghum hybrid was grown in field cages and L. testaceipes adults were released after each plant was infested with 20 biotype E green bugs. The release rates were 0, 0.5, 1.0 and 2.0 wasps per plant in 1993, and 0, 0.16, 0.33, and 0.5 wasps per plant in 1994. Greenbugs and mummies were counted 1-2 times a week on all leaves of 2-4 randomly selected plants per cage. A release rate of 0.33- 0.5 wasps per plant infested with 20 greenbugs maximized the number of mummies produced and prevented the green bugs from reaching an economic threshold of 1,000 greenbugs per plant. Peak numbers of mummies occurred ≈400-500 DD (10°c base) after the initial wasp release. Regression analyses showed that the greenbug population started decreasing when the percentage of parasitism (as measured by mummies) reached 20-30 %. Greenbugs in the absence of wasps significantly reduced yield in 1994, but not in 1993.

Effect of simulated black cutworm, Agrotis ipsilon (Hufnagel) damage on corn, Zea mays (L.), was studied in Illinois, Indiana, Iowa, Nebraska, and Ohio. The results showed that regrowth of injured corn seedlings varied with plant development (location of the growing tip in relation to the soil surface). Seedlings cut above the growing tip Survived and contributed to the corn yield. Early corn plantings WIth considerable simulated black cutworm damage yielded more than late plantings without damage. A calculated regression line suggests that 10–20% stand loss must be realized before a late May or early June replanting would be justified.

Alary polymorphism of Schizaphis graminum (Rondani) was influenced by the immediate temperatures to which the greenbugs were exposed and by the temperatures at which the ancestral and parental generations were colonized. Higher percentages of alatae were produced when aphids were exposed to 27°C than when they were exposed to 21 or 24°C. Aphids colonized at 4°C produced greater percentages of alatae than those colonized at 21, 24, or 27°C when the progeny were exposed to 21, 24, and 27°C. No significant difference in the production of alatae occurred when nymphs were exposed at 27 and 29°C. Colonizing temperatures of 21, 24, or 27°C did not significantly alter the total reproduction of nymphs though the total reproduction of aphids colonized at 21 °C was significantly higher than that of aphids colonized at 4°C. However, the percentages of alatae produced by nymphs from parents colonized at 21 °C were not significantly different from the percentages from parents colonized at 24 or 27°C.

Carbofuran, ethoprop, fonofos, fensulfothion, CGA 12223 (O-[5-chloro-l-(l methylethyl)-1 H-1,2,4,-triazol-3-yl]O, O-diethyl phosphorothioate), and SRA 12869 (phosphoroamidothioic acid, N-isopropyl-O-ethyl ester, O-ester with isopropyl salicylate) were applied at planting time (1.2 oz AI/1000 ft of row) as mixtures with starter fertilizer (10-36-0 at 100 lb/acre) in split-boot placement at seed depth for control of larvae of western, Diabrotica virgifera LeConte, and northern, D. longicornis (Say), corn rootworms. When placed at seed depth the starter fertilizer-insecticide mixtures resulted in significantly less (P=0.05) root damage than in the untreated rows. Carbofuran and CCA 1223 were the only mixtures that resulted in control equivalent to the soil insecticide treatment standard (carbofuran 10G in a 7-in. band over the row in front of the press wheel at planting time) every year of the study. Applications of carbofuran or fonofos as mixtures with starter fertilizer resulted in significantly less root protection when applied in split-boot placement 2 in. below the seed rather than at seed depth.

Field and greenhouse experiments were conducted in 1975 and 1976 to evaluate several insecticides as potential controls of larvae of Phyllophaga anxia (LeConte). None of the insecticide treatments in the field tests provided significant white grub control. In the greenhouse studies CGA 12223 15G (0-[5-chloro-1-(1-methylethyl)-1H-l,2,4-triazol-3-yl]O, O-diethyl phosphorothioate) treatments resulted in the highest levels of control. The influence of conventional vs. minimum tillage corn production procedures on white grub populations was compared by planting corn into a grub infested sod field. There were significantly more (P < 0.005) white grubs found in the soil around plants in the conventional tillage as compared to the minimum tillage areas. This probably was due to the grubs preferring to feed on the grass left between the rows in the minimum tillage areas rather than on corn when both were available.

We developed a rating system to predict the mortality of Diabrotica undecimpunctata howardi Barber larvae used to bioassay soil insecticides. Larvae were categorized, following 48 h exposure to insecticide-treated soil, as living, dead, or in one of five intermediate categories based on movement when exposed to bright light. The eventual mortality of larvae within a rating category was determined by returning the larvae to the treated soil for an additional 5 days and establishing the probability of mortality corresponding to each category. Percentage of dead larvae in the five behavioral rating categories was independent of the insecticide used. Compared to the bioassay method in which the test organisms are considered either alive or dead, the rating system was more consistent and more precise with respect to the assumptions underlying conventional parametric statistics. The rating-system approach is a sensitive and rapid bioassay technique that might be adapted to other test organisms and situations where the subject is under continuous exposure to the toxin being tested.

A 4-yr study comparing planting vs. cultivation time applications of soil insecticides for control of larvae of western, Diabrotica virgifera LeConte, and northern, D. longicornis (Say), corn rootworms showed no significant difference between the 2 application methods. There was a significant year X application method (cultivation vs. planting) interaction but not an insecticide X application method interaction. Although the insecticide X application method interaction was not statistically significant, bufencarb 10G and diazinon 14G applications at planting time consistently failed to provide the same degree of root protection as compared to cultivation applications.

Influence of corn plant densities (37,000, 54,600, and 71,300 plants/ha), time of day, and plant growth stage on adult western (WCR) (Diabrotica virgifera virgifera LeConte) and northern (NCR) (D. barheri Smith & Lawrence) corn rootworm population estimates was studied in eastern Nebraska during 1981 and 1982. Populations of both NCR and WCR adults were affected by plant density. Smaller populations of beetles were present in low plant density plantings. Adjusting beetle counts (whole-plant and ear zone) for plant density resulted in better estimates of the beetle population. Beetle counts for both species were significantly correlated with the actual beetle population. However, there were higher correlations between beetle counts and actual beetle population when counts were adjusted for plant density and expressed on an area basis. WCR beetle counts adjusted for plant density were highly and significantly correlated with number of eggs laid. With only one exception, NCR beetle counts adjusted for plant population were also highly correlated with number of eggs laid. Unadjusted counts were not significantly correlated with egg numbers.

A reliable method of labeling is needed to study dispersal of the braconid parasitoid, Lysiphlebus testaceipes (Cresson), an important biological control of greenbugs, Schizaphis graminum (Rondani), on grain sorghum, Sorghum bicolor (L.) Moench. The feasibility of using aqueous solutions of rubidium chloride (RbCl) applied as a foliar spray or soil drench to label greenbugs and L. testaceipes developing within greenbugs was studied. Laboratory and field studies were conducted to identify the minimal concentration of RbCl to assure labeling of greenbugs and wasps, persistence of Rb throughout the wasp's life span, mobility of Rb to unsprayed sorghum leaves, and feasibility of studying dispersal using a release–recapture technique with Rb-labeled wasps. Both greenbugs and wasps could be labeled using RbCl at concentrations of 2,500–10,000 ppm. Rubidium content in labeled wasps did not significantly vary during the first 7 d after emergence. Greenbugs feeding on unsprayed leaves were labeled up to 4 wk after leaves were sprayed. Rb-labeled wasps were found at the maximum trap distance from the release site (60 m) within 1 d after release.

The spatial distribution of western (WCR), Diabrotica virgifera virgifera LeConte, and northern (NCR), D. longicornis barberi Smith and Lawrence, corn rootworm eggs in the soil was studied in eastern Nebraska under three types of water management systems for 5 years. Eggs were found deeper in the soil under dry conditions. The upper 10 cm of soil contained ca. 80% of the corn rootworm eggs in irrigated fields and ca. 45% in the dryland fields. Eggs were detected to a depth of 35 cm in nonirrigated fields. Under both irrigated and dryland conditions, WCR tended to oviposit more eggs between corn rows rather than in rows. The NCR oviposited significantly more eggs within the corn row in irrigated fields, but only slightly more were found in the rows of dryland fields. Generally, the WCR oviposited deeper in the soil than the NCR.

Over the past 30 yr the western corn rootworm (WCR) Diabrotica virgifera LeConte, largely displaced the northern corn rootworm (NCR), D. longicornis (Say), as the dominant rootworm species in eastern Nebraska. Only in the northeast cropping district has the NCR exhibited significant persistency. Here a comparative study of the ecology and behavior of the 2 species disclosed specific distributional and behavioral differences. The avg no. and percentage of the 2 species varied according to whether the samples were from “upland” or “lowland” fields. The NCR was significantly more abundant in upland fields. The NCR dispersed more readily from cornfields to weedy oat stubble and soybean fields, whereas the WCR for the most part moved from corn to other cornfields. These behavioral differences, coupled with prevailing farming practices (continuous corn vs corn in short rotations), partially explain the displacement phenomenon and varying degrees of coexistence now observed between the NCR and WCR in different areas of Nebraska. The southern corn rootworm (SCR), D. undecimpunctata howardi Barber is of minor importance as a pest of corn in Nebraska.

Five exotic parasite species of the European corn borer, Ostrinia nubilalis (Hbn.), were introduced into Nebraska in 1948–1950. Only 3 species became established: a tachinid, Lydella thompsoni Herting (=grissescens Robineau-Desvoidy of Authors); an ichneumonid, Eriborus terebrans (Gravenhorst) (=Horogenes punctorius (Roman)); and a eulophid, Sympiesis viridula (Thomson) (=Eulophus viridulus). Population trends for L. thompsoni and E. terebrans are reported for 2 counties for the years 1957–1971. No evidence has been found of L. thompsoni since 1965 but E. terebrans was widespread and present in low numbers in 1975 and 1976.

In a 3-year study from 1974–76, planting dates significantly (P<0.05) influenced the control provided by soil insecticides applied at planting time to control larvae of the western corn root worm, Diabrotica virgifera LeConte, and the northern corn root worm, D. longicornis (Say). With the exception of the June plantings (damage was extremely reduced in all treatments), most of the insecticide treatments provided slightly more root protection when applied to later plantings of corn. When the June plantings were omitted from the analysis, there was still a significant planting date effect in the 1974 and 1975 studies but not in the 1976 test. There was a significant planting date X insecticide interaction each year. Applications of carbofuran and fonofos provided the least variable control and phorate and fensulfothion resulted in the most variable control over the planting dates of the insecticides included in the study.

A larval damage prediction method for Diabrotica virgifera virgifera LeConte was evaluated in west central and northeastern Nebraska from 1978–1980. Cornfields averaging < 1 beetle per plant during every weekly count in August were considered to have little chance of being economically damaged by larvae the next year and treatments with soil insecticide were not recommended. Fields averaging > 1 beetle per plant on any sampling date were considered to be indeterminant with respect to a damage prediction; the growers were advised to use a soil insecticide as a precautionary measure. With the possible exception of a few fields in northeastern Nebraska, in which yield difference probably was not due to D. virgifera virgifera larval feeding, the prediction method was reliable >80% of the time. The study indicated that lowering the treatment threshold to 0.75 or 0.90 beetles per plant increased the prediction accuracy to >90% (root damage ratings <2.75), with none of the fields with prediction errors being seriously damaged (root damage ratings <3.1). As a result of this study, only 158 and 263 of ca. 3,050 ha of field corn in the west central study area were treated with soil insecticide for D. virgifera virgifera in 1981 and 1982, respectively. No serious problems were reported in the untreated fields by the field scouts. Before the IPM program, ca. 90%of the fields were treated with corn rootworm larvicides.

A bioassay procedure using southern corn rootworm larvae (Diabrotica undecimpunctata howardi Barber) was used to study the effects of different soils and soil factors on the relative decline in biological activity of six soil insecticides. Larval mortality was used as an index of the effect of various soil factors on the persistence of carbofuran, chlorpyrifos, fonofos, isofenphos, phorate, and terbufos. The range in LC90’s across all soils was least for terbufos and greatest for carbofuran. LC90’s increased as the percentage of organic matter increased. Temperature had very little effect on the change in mortality. Mortality was least depressed at the high moisture level for chlorpyrifos, isofenphos, and to some extent, carbofuran. Phorate response was variable. Mortality from fonofosand terbufos was appreciably decreased at the high moisture level. Mortality in carbofuran treatments declined as soil pH increased. Chlorpyrifos and terbufos activity decreased in soils with a higher percentage of clay. Carbofuran and isofenphos consistently maintained biological activity the longest.

Emergency postplanting applications on June 25, 1975, of granular and liquid formulations of carbofuran, diazinon, and fensulfothion and liquid Dyfonate® (O-ethyl S-phenyl ethylphos-phonodithioate) applied to irrigated and dryland plots already severely damaged by larvae of western corn rootworm, Diabrotica virgifera LeConte, and northern corn rootworm, D. longicornis (Say) (root damage rating = 3.95) did not provide control comparable to a carbofuran 10G treatment applied at planting time (application rate = 1.2 oz AI/1000 ft of row). Application of each liquid insecticide in either 16 or 32 gal of water/acre had no significant (P=0.05) effect on the control provided by carbofuran and fensulfothion treatments bnt the 32 gal rate of diazinon and the 16 gal rate of Dyfonate under dryland conditions resulted in significantly (P=0.05) greater root protection than their alternate rates. A significant (P=0.05) insecticide treatment by irrigalion-dryland interaction was detected for root damage ratings adjusted for regrowth with more root regrowth occurring in the irrigated area. Results indicate that emergency treatments after one node of roots has been destroyed by rootworms may be economically beneficial but major damage already has occurred.

A western corn root worm, Diabrotica virgifera virgifera LeConte, adult bioassay technique using insecticide-treated corn leaves was used to determine the influence of moisture on the residual activity of several insecticides. Results of the studies indicated that moisture (rainfall or sprinkler irrigation) was a major factor influencing the decline in residual activity of carbaryl, carbaryl-oil, phosmet, and Penncap-M. Residual activity of dlazmon and malathIOnwas neghgible at 7 days, regardless of the amount of moisture. In tests comparing dry land and sprinkler-irrigated treatments, there was a significant negative correlation (r = −0.91) between percent control and the amount of water applied. Both linear and quadratic effects were highly significant (P <0.005). There were no significant linear or quadratic effects detected between percent control and days post application. Carbaryl-oil, diluted with ¼ part diesel fuel, and carbaryl-XLR provided slightly shorter residual activity than undiluted carbaryl-oil treatments. However, all three treatments provided considerably longer residual activity than other insecticides tested.

Western corn rootworm, Diabrotica virgifera virgifera LeConte, sex pheromone, racemic 8-methyl-2-decyl-propanoate (MDP) was successfully encapsulated in a starch borate (SB) matrix creating a controlled release granular formulation. The release rate of MDP from starch borate granules was attractive to male D. virgifera at high and low D. virgifera population levels in field corn. Male D. virgifera were attracted to the SB-MDP granules throughout the growing season, but efficacy declined during the period of peak female D. virgifera emergence and corn pollination. The SB-MDP delivery system was as effective as a septa-MDP delivery system, and SB-MDP formulations had a shelf life of at least 2 yr. Data suggest that the starch matrix concept may be useful as a delivery system for semiochemicals and may have potential as a tool that can be used in the development of new, more environmentally sound insect management system.

Second and 3rd stage white grubs, Phyllophaga anxia (LeConte), were collected from timothy grass hay meadows in north central Nebraska and assayed for susceptibility to selected insecticides in the laboratory. The results are presented in terms of lethal dosage values (LD30, LD50, LD70 and LD90) and expressed in µg insecticide/g of insect tissue. Insects treated with carbamate and phosphate insecticides showed higher susceptibility levels than those treated with 2 chlorinated hydrocarbons, aldrin and chlordane, or a new experimental synthetic pyrethrin, FMC 33297 (3-phenoxybenzyl (±) cis-trans-3-2-(2,2-dichlorovinyl)-2,2-dimethyl cyclopropane carboxylate). Carbofuran was the most toxic of the insecticides tested, whereas aldrin, chlordane, and FMC 33297 were either not lethal or notably less toxic than all other insecticides evaluated. The best time to determine dosagemortality relationships was 3–4 days posttreatment.

A study was conducted in Nebraska during 1972 and 1973 to determine whether a small area of late-planted “trap-corn” would attract females of the western corn rootworm, Diabrotica virgifera LeConte, and the northern corn rootworm, D. longicornis (Say), from a larger area of corn planted at the normal time (early-corn) and thus concentrate egg deposition and reduce the injury potential the following year to corn planted in the same field. Except for a 2.4-acre center strip, a 24.5-acre experimental field was planted to corn on May 22, 1972. On June 15, the center strip was planted to serve as “trap-corn.” On May 16, 1973, the entire field was planted to corn and ½ was strip-treated with a soil insecticide. In 1973, beetle populations, root ratings, lodging, and yields were determined for corn growing in the 1972 trap and early-corn areas. In the early-corn area, beetle populations were 21% lower, root ratings 47% higher, lodging 64% less, and corn yielded 26 bu/acre more than in the trap-corn area. These results suggest the injury potential in the early-corn area was reduced through the presence of trap-corn.

Chromosome-length measurements from five greenbug, Schizaphis graminum (Rondani), biotypes (B, C, E, F, and Maryland) were compared by discriminant analyses procedures. There were highly significant (P = 0.0001) differences in total lengths of chromosome sets among biotypes. In individual paired comparisons, where each biotype was compared with only one other biotype at a time, chromosome measurements correctly classified aphids to their respective biotype in 45–85% of the cases. Degree of correct classification was dependent on the two biotypes being compared and the discriminant function used in the analysis. Results indicate that there are two groups of biotypes that can be correctly distinguished from each other most of the time. Chromosome lengths of biotypes C and E were closely related. They could be distinguished from those of biotype B and F in 75–85% of the cases. The Maryland biotype appeared to be more closely related to C than to the other biotypes. There was considerable variation in the lengths of biotype C chromosomes, which suggests that biotype C may comprise several population variants, perhaps separate biotypes. The ranges of variability in length of chromosomes in biotype C overlapped the ranges of biotype E, which suggests that biotype E may be a selection from biotype C. Conclusions drawn from these data regarding relationships among biotypes are similar to those suggested by biological and plant-damage studies.

Experiments were conducted on colonies of 3 selected ant species that are abundant in corn fields in the Nebraska Sandhills to determine their predatory potential on eggs of western corn rootworms (WCR) Diabrotica virgifera LeConte. Lasius neoniger Emery was not found to be a predator on WCR eggs under test conditions. Myrmica americana Weber and Pheidole bicarinata longula Emery did remove WCR eggs from filter paper placed upon the surface of their colonies. M. americana did not locate and remove eggs placed beneath the soil in the colonies. Location of WCR eggs in soil appears to be due to chance; thus significant reduction of WCR egg populations in the field is questionable.

Greenbug, Schizaphis graminum (Rondani), biotypes were studied by comparing biological data to total esterase activity levels measured by fluorescent microscopy. Also, total esterase activity was evaluated in relation to host plants and insecticide resistance. The intensity of fluorescence was measured from tarsi of large embryos after staining with fluorescein diacetate. Biotypes on susceptible ‘Wheatland’ sorghum produced significantly more and larger progeny than those on resistant KS 30 or PI 264453. Furthermore, there was a carryover effect of the previous host plant on progeny production. Greenbugs reared on resistant plants had a higher level of fluorescence compared with those on susceptible plants. Increased fluorescence was also found in separate insecticide-resistant colonies of greenbugs. However, no significant differences in esterase activity as measured by fluorescence were found among biotypes reared on the same cultivar.

A corn root worm larval sampling technique was evaluated for 5 years in eastern Nebraska. The percentage of larvae of Diabrotica spp. detected in field samples by an experienced scout ranged from 3 to 6% for 1st instars, 6 to 18% for 2nd instars, and 18 to 21% for 3rd instars. High correlations were found between field and absolute counts for all 5 years. Scout experience apparently influenced the number of larvae detected in the field. The number of days from hatch until the first larva was detected in the field ranged from 3 to 11 days. The time frame from field detection to potentially serious root damage is apparently too small for this technique to be used to make control decisions to minimize damage. However, it may be of some value in making emergency treatment recommendations.

A 2-yr study was initiated in 1975 in the North Central States of Illinois, Indiana, Minnesota, Nebraska and Ohio to evaluate the effect of planting date of field corn (Zea mays L.) on beetle emergence and damage by the western, Diabrotica virgifera LeConte, (WCR) and northern, D. longicornis (Say), (NCR) corn rootworms. It was observed consistently that adult emergence for both the NCR and WCR peaked relatively rapidly and declined at an equally rapid rate from corn planted in late Apr. or early May. Emergence from corn planted in late May peaked later in the season, occurred over a longer time period, and declined at a slower rate than for the earlier plantings. All of these trends were even more evident for early and mid-June plantings. Peak emergence averaged ca. 3 wk later for the late May and early June plantings and averaged 5.5 wk later for mid-June plantings than for the late Apr. and early May plantings. Initial and peak beetle emergence of the NCR were 1 and 2 wk later, respectively over those for WCR. The highly significant relationships (P < 0.01) between planting date and root damage was strongly linear for all states. These data indicate that for each 10 day delay in corn planting after Apr. 1, the average root damage rating would decrease 0.48, 0.71, 0.77, 1.05, and 1.08 units for Ohio, Minnesota, Missouri, Illinois, Indiana and Nebraska, respectively.

Greenbug sexuales occurred in the greenhouse from November to the middle of April and were found only in Biotype C greenbugs, Schizaphis graminum (Rondani). Males were found periodically throughout this period, averaging about 17% of the alate population when present. Spermatozoa were observed in testes squashes. Oviparae were found consistently throughout the sexual season and averaged 15 to 25% of the apterous population. An average of 6.6 ova per female was observed by dissections, but on the basis of oviposition studies there were only about 2.5 to 3.5 ova per female. Small populations oviposited equally well on the plants and cages but heavy populations appeared to oviposit to a greater degree on the cages. Mating was observed but no premating behavior was detected. Some oviparae were found to reproduce both viviparously and oviparously. Squashes of ova detected rapidly dividing chromosome sets in ⅓ of the ova examined. None of the ova incubated at 2, 4, 18, 21, or 27°C hatched; however, 2 ova were found with developing embryos.

Aceto-orcein-stained squashes of young embryos of the greenbug, Schizaphis graminum (Rondani), proved to be an expedient staining technique for aphid chromosome studies. Embryos averaging about 0.25 mm long provided the best material for study and were found in the greatest quantities from 5-day-old aphids reared at 24°C. Comparison of chromosome sets of 3 biotypes of the greenbug with one another and to those of the corn leaf aphid, Rhopalosiphum maidis (Fitch); the oat bird-cherry aphid, R. padi (L.); and the yellow sugarcane aphid, Sipha flava (Forbes); revealed a different karotype for each genus studied. Total chromosome length comparisons indicated that Biotype A differed statistically from B and C, but Biotypes B and C did not differ. Corn leaf aphid chromosome lengths were significantly different from those of all other aphids studied. Both the oat birdcherry aphid and yellow sugarcane aphid were significantly different from the corn leaf aphid and Biotype C greenbug. The analysis of total chromosome lengths proved unreliable for comparing species with different karyotypes.