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To observe the aggregation and dispersal behavior of adult European corn borer, Ostrinia nubilalis (Hubner), males in search of mates, two populations were marked, each with a different dye. One population was continuously reared in the laboratory (>5 yr) and the other was collected annually from the field. From 1986 to 1988, marked adults were released in two release sets per year, with three to five releases per release set, coinciding with the spring and summer flights of European corn borer in central Iowa. Traps for recapture contained lures baited with 40 μg of synthetic 97:3 Z:E-11-tetradecenyl acetate. Traplines extended from 200 m to 48 km. Each trap was assigned a compass direction. Males from the laboratory-reared population dispersed similarly to males just 1 generation from the wild. European corn borer males and females dispersed 23–49 km and some were recovered 14 km from the release site within 100 min after release. Sampling of aggregation sites demonstrated that on the nights of...

Munkvold, G. P., Hellmich, R. L., and Showers, W. B. 1997. Reduced Fusarium ear rot and symptomless infection in kernels of maize genetically engineered for European corn borer resistance. Phytopathology 87: 1071-1077. Field experiments were conducted in 1994, 1995, and 1996 to evaluate the incidence and severity of Fusarium ear rot and the incidence of symptomless Fusarium infection in kernels of maize hybrids genetically engineered with Bacillus thuringiensis genes encoding for the δ-endotoxin CryIA(b). Treatments included manual infestation with European corn borer (ECB) larvae and insecticide applications to limit ECB activity to specific maize growth stages or mimic standard ECB control practices. Fusarium symptoms and infection were affected by the specific cryIA(b) transformation used in each hybrid that determines tissue-specific expression of CryIA(b). In hybrids expressing CryIA(b) in kernels, incidence and severity of Fusarium ear rot and incidence of symptomless kernel infection were reduced compared with near-isogenic hybrids lacking cryIA(b) genes. In plants that were manually infested with ECB, ear rot incidence was reduced by 87, 58, and 68%; severity was reduced by 96, 54, and 64%; and incidence of kernel infection by Fusarium species was reduced by 17, 38, and 38% in 1994, 1995, and 1996, respectively. Results were similar in treatments that were not manually infested, but differences between transgenic and nontransgenic hybrids were smaller. Most kernel infection was due to F. moniliforme, F. proliferatum, and F. subglutinans (section Liseola) collectively, and it was within this group that transgenic hybrids exhibited reduced infection. Expression of CryIA(b) in plant tissues other than kernels did not consistently affect Fusarium symptoms or infection. Disease incidence was positively correlated with ECB damage to kernels. Insecticide applications also reduced Fusarium symptoms and infection when applied to nontransgenic plants.

▪ Abstract The long-range migration of insects in general is briefly discussed here and serves as an introduction for in-depth inquiry into the migratory ecology of Agrotis ipsilon, the black cutworm. Zoogeography, pest status and injury, and seasonal occurrence of the species are reviewed. Circumstantial evidence of long-range movement of A. ipsilon moths within both hemispheres is presented, followed by experimental evidence of long-range movement of A. ipsilon moths in China and North America. Based upon experimental evidence published by several investigators, a theory is proposed of the existence of a thermal range (0–36°C) for A. ipsilon pupae that acts as the precursor for adult (moth) migration. This theory should help explain the circumstantial and empirical evidence gathered upon the annual appearance and disappearance of this species over large geographic areas.

Larval collections of European corn borer, Ostrinia nubilalis (Hubner),were made in and surrounding a seed corn nursery at Johnstown, ND, a year before and each of 3 yr during a test for hybrid resistance to this insect. Johnstown is in an area known to maintain a univoltine population of O. nubilalis . The 30,000 inbred corn plants tested for resistance, however, were infested each year with a bivoltine population of O. nubilalis . Each sample site collection was maintained as a separate population, and the 2nd laboratory-reared generation was tested for diapause frequency in growth chambers programmed to force most univoltine individuals to enter larval diapause and allow a minimum of 50% of bivoltine individuals to continue development. These results illustrate that bivoltine populations dispersed at least 32 km/yr. The results indicate further that light southerly or easterly surface winds (under 8 km/h) were the essential transport mechanisms for this dispersal. It is probable that bivoltine O. nubilalis have been invading the historically univoltine areas of northwestern Minnesota, North Dakota, and the Canadian prairie provinces from the south for years.

Male black cutworm, Agrotis ipsilon (Hufnagel) moths, were attached to laboratory flight mills on the third night after emergence. Individuals were classified according to their longest uninterrupted flight during the night. There were not enough non-fliers or trivial fliers (flight < 1 h) to make meaningful comparisons, so only short-fliers (flight ≥ 1 h but ≤ 5 h) and long-fliers (flights ≥ 5 h) were further tested. After a day of rest, short- and long-fliers were tethered to a stationary pin and forced to fly 0, 10, 20, 30, 60, 120, or 180 min, after which hemolymph was sampled and lipid and carbohydrate concentrations determined. Concentrations in samples taken at intervals after cessation of a 60-min flight indicated that both energy sources were being utilized during flight. Neck-ligation experiments indicated that a handling-induced hyperlipemic response occurs 15 min after the beginning of the sampling procedure, and that the hormone triggering does not come from the head. Resting concentration of lipid in long-fliers is about half that of short-fliers, but it increases threefold in the first 20 min of flight, whereas that of short-fliers remains unchanged. In-flight lipid concentration in controls, which experienced their first and only flight on day 5, was greater than the concentration in both short- and long-fliers. Between 10 and 20 min, carbohydrate concentrations decrease about twofold in long-fliers but drop only slightly in short-fliers. These data suggest that long-fliers may have a lower basal metabolic rate and depend more on carbohydrate when at rest than short-fliers and that long-fliers may utilize more carbohydrate than lipid during the initial period of flight. In addition, previous flight on the flight mills has a greater influence on lipid mobilization and usage in short-fliers than it does on long-fliers. Patterns of lipid mobilization during flight seem to differ between migrant and non-migrant species and to vary among migrants depending on the flight strategy used, but there are no major differences in patterns of carbohydrate usgaeg. © 1995 Wiley-Liss, Inc.

Male migrant black cutworms, Agrotis ipsilon (Hufnagel), were sampled by pheromone trapping in several locations in the central and northern Corn Belt of North America in the spring of 1985 and 1990. Moths were also sampled in the southern United States at several locations suspected or known to be sources of migrant black cutworms. Forewing length, forewing width, prothoracic width, and body length were measured; and relative darkness of thoracic pubescence was scored for each moth. By comparing the morphology of northern moths (migrants, by definition) with that of southern moths (presumably containing mixtures of migrants and nonmigrants), we hoped to determine whether migrant A. ipsilon could be distinguished morphologically from nonmigrants. Principal component analyses extracted two important axes from the raw data. The first was a generalsize axis, and the second was primarily a relative-darkness, or color, axis. All analyses were performed on the factor scores along these axes. There was no difference in mean size of northern and southern moths, nor was there a consistent latitudinal gradient in size between northern locations. There was, however, reduced variation in the migrant populations; i.e., very small and very large moths were underrepresented in the northern compared with the southern populations, Comparisons between northern moths thought to have originated in the Brownsville, Texas, region suggested that migrants tended to have lighter coloration than those in the source population. But light coloration by itself cannot indicate migrant individuals because, in one instance (Columbia, MO 1985), a migrant population was darker than populations from all other locations sampled that year, The data indicate that, at least in the case of males, migrants cannot be distinguished morphologically from nonmigrants. The results are consistent with the hypothesis that A. ipsilon is an obligate migrant and that there is no distinctive migratory phase induced by environmental cues or conditions.

To determine whether an economically important moth species emigrates from the western Corn Belt (Iowa and Missouri) to the gulf coastal areas of Louisiana and Texas each autumn, adult populations of Agrotis ipsilon (Hufnagel) males were monitored with traps baited with female sex pheromone, 16 July to 31 October 1986—1987. Concurrently, to estimate the potential for southward displacement of A. ipsilon, moths marked with a vital dye, Calco Red N—1700, were released at dusk 28 September and 2 October 1986, and 10 and 17 September 1987, from Ankeny, Iowa. Increased nightly moth—capture in Texas was positively related to numbers of nights with near—surface (100—300 m) northerly airflow (southward displacement of air) and decreased moth—capture in the western Corn Belt. Capture in Louisiana was also negatively correlated with capture of moths in the western Corn Belt. The recapture in autumn 1986 of two moths in Missouri, 397 km and 460 km south of the release site, respectively, was possible because of nightly near—surface northerly airflow. Near—surface northerly airflow the night of and subsequent to 17 September 1987 was responsible for a marked moth being recaptured near Neota, Illinois, and another being recaptured near Brownsville, Texas, 276 km southeast and 1900 km southwest of the release site, respectively. We conclude that during late summer and autumn, A. ipsilon, and probably other insect species, respond to deteriorating environmental conditions by using certain weather systems with northerly (southward displacement) near—surface airflow to complete midcontinental migrations to more favorable areas.

Starving fourth-instar Agrotis ipsilon (Hufnagel) for 4 d did not increase the propensity of 3-d-old moths to engage in long-duration (i.e., ≥1 h) continuous flights, or the duration of such flights, on flight mills. Adult diet (nothing, distilled water, or honey–water) did not significantly influence male flight propensity until 2 d of age or female propensity until 3 d of age. Male propensity to fly and flight profiles (flight duration, times of flight initiation and termination) seem to depend more upon the availability of liquids than carbohydrates, whereas female behavior is more dependent on a carbohydrate source. In all instances, the influence of both larval and adult diet stress on flight propensity and duration is negative. One would expect a positive effect if such stress factors act as cues that trigger a behavioral or physiological shift to a migratory phase. Instead, environmental factors that stress individuals seem only to decrease the already high propensity to make prolonged flights and decrease the duration of those flights.

Identifying the pollen attached to black cutworm, Agrotis ipsilon (Hufnagel), and armyworm, Pseudaletia unipuncta (Haworth), moths provided a powerful tool for recognizing food plants used by these noctuids before initiation of long-range movement. Pollen was found primarily on the proboscis and in decreasing frequency on the eyes, legs, and antennae. Fourteen moths collected in Iowa and Missouri were marked with the exotic pollens Pithecellobium spp. or Calliandra spp, or both. These plants are indigenous to southern climes, and the closest site of origin to the capture points is in southern Texas. From the closest plant location in Texas, these moths traveled 1,300km to central Missouri, 1,450 km to northern Missouri, and 1,600 km to central Iowa. Moths captured in March probably originated ≥600 km farther to the south than those captured in late April and May. Known exotic pollen was discovered on moths captured during May in Iowa, but these same pollens were found on moths captured earlier in Missouri. These results provided evidence of moth immigration into Missouri from within Mexico, possibly from the state of Tamaulipas.

Larvae of black cutworm, Agrotis ipsilon (Hufnagel), reared under crowded conditions in the laboratory were darker and developed more slowly than larvae reared singly. Crowding reduced the length and weight of pupae, and the adults were correspondingly smaller than those from uncrowded populations. Rate of reproductive maturation of females was not influenced by larval density. Crowding had no significant effect on the crawling behavior of sixth instars and very little effect on the flight behavior of adults tethered to flight mills. No evidence that crowding leads to a distinct migratory phase or even to an increased propensity to initiate long-duration flight was found. To the contrary, the data suggest that moths from crowded populations may suffer a loss in migratory capacity because of their smaller size (and presumably smaller stores of flight fuel) and lower wing area:body size ratios, which may make flight energetically more expensive.

Long-duration flight behavior of the migratory moth Agrotis ipsilon (Hufnagel) was examined using computer-interfaced flight mills. Moths were tested each day for the first 5 d after eclosion. Time of flight initiation, time of flight termination, duration of flight, and flight speed were similar for males and females within each age class. Three-day-old moths began flight earlier in the night (164 min after sunset) and flew significantly longer (391 min) than moths of all other age classes. One-day-old moths initiated flight significantly later (331 min after sunset) than all other age classes. Time of flight termination and flight speed were not significantly affected by age. Although moths of any age could make flights of any length, the percentage of moths making flights of a given duration was consistently greatest for those 3 d old and least for those 1 d old.

The black cutworm, Agrotis ipsilon (Hufnagel), larva is a pest of seedling corn in the Midwest. Adults migrate from the south during the spring. Determination of their arrival date is critical to anticipate accurately the time of appearance of larvae in the field. A simplified and easily applied procedure called the moth influx potential (MIP) system was developed to project black cutworm moth movement. The procedure uses National Weather Service atmospheric trajectory forecasts in a backtracking trajectory strategy that projects moth movement from source regions estimated by soil temperature analysis. The MIP system was tested for its ability to determine nights of introduction of A. ipsilon moths into central Iowa; estimates were compared with numbers of adult males captured in traps baited with synthetic sex pheromone. Pooled data from 5 yr (1978-1981 and 1983) were used for these comparisons. Regression analysis revealed a significant (P < 0.01) but weak correlation ( r = 0.210) between square-root transformations of daily MIPs and trap captures. The correlation of 4-d ( r = 0.292), 5-d ( r = 0.311), 6-d ( r = 0.366), and 7-d averages ( r = 0.369) of MIP and trap captures increased sequentially. Significant linear ( r = 0.400) and quadratic trends ( r = 0.366) were also detected between calendar week and trap captures. Stepwise regression of 7-d MIP and time variables provided a model for predicting trap captures.

Developmental velocities of European corn borer, Ostrinia nubilalis (Hubner), colonies collected at four geographically separate locations (Delaware, Iowa, Missouri, and North Dakota) were compared. Each colony was reared under five or six constant temperature regimes. Mean developmental times and standard deviations about the means were determined. Developmental velocities were used to formulate both linear and sigmoid developmental velocity equations. Because the sigmoid and linear functions exhibited similar fits to the data, the latter were used in a European corn borer phenology model that predicts the period of second generation oviposition. The resulting predicted oviposition periods are reported for model runs using developmental velocity equations generated for the four colonies. The resulting predictions suggest that developmental rates are similar among the four geographically separate European corn borer populations. For European corn borers reared at 32°C, however, developmental times and developmental threshold temperatures during the period of larval eclosion to adult emergence appeared different among the colonies.

Laboratory-reared black cutworm, Agrotis ipsilon (Hufnagel), larvae were used to determine if incorporating fenvalerate and permethrin in the soil to a depth of 8 cm would alter efficacy. Laboratory bioassays were done 0, 7, 14, and 21 d after application. Results of second- and fourth-instar bioassays show that second instars are more sensitive to fenvalerate and permethrin but require 89% more handling time than fourth instars. Incorporation significantly reduced the efficacy of fenvalerate and permethrin. Decreased efficacy from incorporating permethrin was counteracted by increasing the application rate from 0.113 kg(AI)/ha to 0.226 kg(AI)/ha, the maximum labeled rate. Incorporation of fenvalerate reduced efficacy to an unacceptable level even at the maximum labeled rate. Limited data suggest that incorporation also affects cyfluthrin and esfenvalerate adversely.

Survival of reciprocal populations of European corn borer, Ostrinia nubilalis (Hubner), equaled or was intermediate to natural populations and an introduced low-diapause population (exotic), which survived less well. When peak natural second-generation hatch (31 July–3 August) north of 39°00′ N lat. was approximated, most of seven natural populations approached 100% diapause. However, only 0.25–22.95% of the exotic population diapaused. Diapause by progenies of reciprocal crosses was greatly influenced by this exotic parent. At the most northern locations, Ankeny, Iowa, and St. Paul, Minn., influence of the parental male was particularly evident. When peak natural third-generation hatch (13–16 August) south of 39°00′ N lat. was approximated, five reciprocal populations diapaused similarly to their corresponding natural populations (≈85%). Late-season hatch allowed larval diapause of the exotic population to increase to 46%. Under these late-season conditions, influence of the parental male was evident only at the most southern locations, Portageville, Mo., and Tifton, Ga. This apparent contradition of parental male influence between midsummer and late-summer hatch is because heterogeneity for diapause remains in a low-diapause population. Introductions of a low-diapausing population north of 39°00′ N lat. during late July apparently encourage resultant progeny from reciprocal crosses to avoid larval diapause and to perish in late autumn.

A relative sampling method for second flight adult European corn borer, Ostrinia nubilalis (Hubner), was used to predict egg mass levels within hybrid seed cornfields ( Zea mays L.). An aluminum bar (1 m) was swept through adult aggregation areas of giant and green foxtail grass ( Setaria spp.) and adults were counted as they flushed from the grass. Numbers of scouted egg masses in the field were regressed onto numbers of flushed adults during early to late silking stages of corn. Egg masses were dependent on the number of European corn borer adults in aggregation areas (example: predicted 0.5 egg masses per corn plant with an average of 52 moths flushed from 10 m2 grass at 5% silking or an average of 66 moths flushed from 10 m2 grass at 80% silking). This relationship between flushed adults and egg masses can be used to determine the need and timing of field scouting by consultants or seed companies for second-generation egg masses in the Corn Belt.

Field studies were conducted in 1984 and 1985 to evaluate the interaction between black cutworm, Agrotis ipsilon (Hufnagel), damage and weed competition on notill corn (Zea mays L.) growth and yields. Corn seedling damage by A. ipsiLon introduced as third instars 5 d before planting was most severe when weeds were removed at the coleoptile stage and larvae were predicted to be fifth to sixth instars. Delaying weed removal until plants had attained the two-leaf stage significantly decreased the percentage of corn plants damaged by A. ipsiLon larvae. A. ipsiLon larvae introduced as second instars or a combination of neonate, second, and third instars 5 d before planting damaged more corn plants when weed removal was performed at two-leaf stage corn and larvae were predicted to be fifth to sixth instars. A significant relationship between the number of corn seedlings cut and weed population occurred for these introduced smaller instars when weed removal occurred at two-leaf stage corn. Delaying weed removal until four-leaf stage corn resulted in significant grain yield reductions from both weed competition and A. ipsiLon damage in 1984 and only from weed competition in 1985.

Adult activity and ovarian dynamics of the variegated cutworm, Peridroma saucia (Hubner), were studied during 3 yr by using blacklight traps. Initial mating in females coincided with ovarian development, with females continuing to mate up to six times during their lives. Adult catches, ovarian dynamics, and degree-day calculations indicated that P. saucia has three generations each year in Iowa. Very few preovipositional females were collected during the spring flight. This observation and the strong association of adult activity during the spring with weather patterns resulting in southerly winds suggested that P. saucia adults migrate into the state each spring when weather conditions are favorable. Flights during June through November contained a large portion of preovipositional females. Degreeday calculations also revealed that adults collected during June and July were the progeny of spring migrants, but temporally distinct influxes of migrants may produce distinct peaks of adult activity during June and July. Degree-day calculations and the collection of a few preovipositional females during the spring suggested that P. saucia may overwinter as pupae, which may produce adults that contribute to the influx of migrants in the spring.

Differently colored bucket traps were tested to determine if the capture of male moths would be affected. Four colorswere tested: yellow top with white boltom (yellow-white), green top with a white boltom (green-white), all white (white), and all green (green). The traps were baited with sex pheromones of black cutworm, Agrotis ipsilon (Hufnagel), and armyworm, Pseudaletia unipuncta (Haworth). For black cutworms, the yellow/white (mean, 46.1) trap captured significantly more male moths, followed by the white (mean, 23.1) and green-white trap (mean, 21.6). Capture of moths in the green trap was significantly less (mean, 10.9) than for any of the other trap types. For capture of armyworm, the yellow-white and white traps were not significantly different. Similar to capture of A. ipsilon , moth capture of P. unipuncta (mean, 1.2) in the green trap was significantly less than in the white (mean, 6.5) and yellow-white (mean, 4.8) traps. The yellow-white traps caught significantly more bumblebees than did each of the other traps. Where traps are to be used for both noctuid species and capture of bumblebees is undesirable, the white trap is acceptable.

The ability of the modified Missouri cutworm trap to predict cutworm damage in field corn was investigated in Missouri, Illinois, and Iowa from 1979 to 1981. Black cutworms, Agrotis ipsilon (Hufnagel), and claybacked cutworms, Agrotis gladiaria (Morrison), were associated with stand cutting, whereas dingy cutworms, Feltia ducens Walker, had no discernible effect on the plant stand. Most plant damage occurred in the coleoptile (precollar) and the one-collar stage, with population maturity having a significant effect on the relative number of plants cut per leaf stage. The proportion of surface-cut plants (relative to subsurface-cut plants) declined as plants and cutworm populations matured. Survival of surface-cut plants was much greater than that of subsurface-cut plants. A regression model was developed that predicts yield loss by using as inputs the mean number of black and claybacked cutworms in the 2nd-, 3rd- and 4th-, and 5th- and 6th-instar groups, the expected plant population, and the anticipated yield if no cutworms were present.

Field studies were conducted in 1979 and 1980 to determine whether differences exist in feeding behavior between black cutworm, Agrotis ipsilon (Hufnagel), larvae reared 1, 12, and 24 generations. Larvae were released on corn at three developmental stages (coleoptile, two leaf, and four leaf). Damage was more severe during the coleoptile stage. Also, corn seedlings in the two-leaf stage had significantly more damage than corn in the four-leaf stage of development. Irrespective of corn developmental stage, however, more damage occurred on corn after weed seedling removal than on corn adjacent to weed seedlings. The feeding behavior of larval populations of black cutworm reared for one or multi-generations in the laboratory was not significantly different

Black cutworm, Agrotis ipsilon (Hufnagel, attack during the coleoptile to one-leaf stage of corn development caused significant loss of plants (27%) and yield (2,900 kg/ha) if there was just one insect of cutting age (4th instar and older) per m of row (24 insects per 24 m). Essentially, the decrease in percent plant stand and yield was directly proportional to the increase in larval density; however, the yield loss attributed to 2 insects per m (48 insects per 24 m) was similar to that of one insect because of yield compensation by uncut plants. When corn was attacked by black cutworm during the two-leaf to three-leaf stage of development, there was not a significant decrease in potential yield until there were three insects per m of row (72 insects per 24 m). Black cutworm attack during four-leaf to five-leaf stage of corn development usually did not cause declines in plant stand or potential yield. When conditions were dry (9.6 cm of accumulated precipitation)during the period of black cutworm attack, 60% cutting affected the potential yield as much as 87% cutting affected the potential yield when conditions were damp (28 cm of accumulated precipitation).

Under greenhouse conditions, late-instar black cutworm, Agrotis ipsilon (Hufnagel), larvae cut significantly more seedling corn plants and fed on more baits under dark conditions than in light. The feeding behavior followed closely the daily solar cycle except when the larvae were kept under dark conditions for 24 h. In the absence of baits, 5th instars fed significantly more often on corn seedlings than did either 4th or 6th instars. Further, 5th and 6th instars cut more than twice as many plants when baits were absent than when baits were present. Highly significant differences occurred between the numbers of larvae recorded feeding in different baits and apple-grape, grape, and bran pellets were the most attractive of all materials tested. Overall, wet bait was preferred to dry, but there were no significant differences between wet and dry soil conditions.

The North Central Regional Project relating to the European corn borer, Ostrinia nubilalis (Hubner). has progressed through 4 stages: 1954–62, 1963–65 under NC-20, 1966–70 under NC-87, and 1971-present under NC-105. How and why this project is still in existence after 24 years can be condensed into one word, “cooperation.”

Hourly captures of male black cutworms, Agrotis ipsilon (Hufnagel), in traps baited with different ages of virgin females (2, 4, 6, and 8 d) were examined during three phases of phenology in Iowa: migration–infestation, early postinfestation, and mid-postinfestation. Six-d-old virgin females captured the most males during migration-infestation, whereas traps using 4-d-old females, although not statistically significant, captured the most males during early postinfestation. Two factors, greater capture rate and longer capture period, were responsible for the enhanced attractiveness of 6-d-old females during migration–infestation. Only capture rate contributed to increased attractiveness of 4-d-old females during early postinfestation. Trap captures during mid-postinfestation were extremely low despite active calling by females and possibly reflected the beginning of reproductive diapause in males. Nocturnal rhythms of capture were similar across virgin female ages and seasons. Likewise, comparisons with a trap baited with synthetic pheromone revealed similarities that suggest that the nightly rhythm of mating activities is mediated primarily by the male.

Meteorological influences on long-distance and local black cutworm (BCW), Agrotis ipsilon Hufnagel, flight were analyzed. Male BCW capture was compared with ratings describing the favorability of meteorological conditions for the suspected transport. The meteorological ratings (SET Rating System) were based on reported influences of environmental factors on BCW flight. Fluctuations of the ratings and of BCW capture coincided in early spring, indicating that the early-spring Iowa and northern Missouri BCW moth populations are composed only of introduced individuals, probably originating in the south-central United States. Moths may be carried several hundred kilometers to Iowa in one to three nights at considerable height by strong southerly winds. Northern Missouri seems more subject to BCW invasion than Iowa because of more numerous southerly wind events.

Field studies were conducted to examine whether vision and odor are factors used by black cutworm (BCW) larvae when orienting to the modified Missouri larva bait trap (Story and Keaster 1983). The wheat bran treatments were from 52 to 121% more effective in attracting larvae than similar treatments without bran during 1981 and 1982. These results indicate that BCW larvae use odor to discriminate between attractive and unattractive hosts. In 1982, treatments with wheat seedlings and with simulated seedlings (sticks) showed that 93% more BCW larvae were captured with the wheat seedlings than with simulated wheat seedlings. The wheat seedlings attracted BCW larvae by olfactory rather than visual cues. However, the addition of vertical screens to the larva trap significantly enhanced larval BCW captures by from 30 to 82%. Therefore, the attractiveness of the modified Missouri larva trap was due to a visual response (vertical screen) and an olfactory response (wheat seedlings and wheat bran).

Cutworm populations in field corn were sampled from 1979 to 1981 in Missouri, Illinois, and Iowa. The black cutworm (BCW), Agrotis ipsilon (Hufnagel), and the dingy cutworm (DCW), Feltia ducens Walker, were the most abundant species, followed by the claybacked cutworm (CBCW), Agrotis gladaria (Morrison), and the bristly cutworm (BRCW), Lacinipolia renigera (Stephens). Variegated cutworms, Peridromia saucia (Hubner), spotted cutworms, Xestia spp., sandhill cutworms, Euoxa detersa (Walker), and Euoxa spp. were also captured. The relationship between larval cutworm population maturity of DCW, CBCW, BRCW, and BCW and cumulative degree-days from 1 January was quantified. Both BCW and DCW were slightly aggregated in distribution. The coefficient of association for pairs of BCW, DCW, CBCW, and BRCW were all positive, although only DCW and CBCW, and CBCW and BRCW, were significantly associated.

The association of strong southerly winds with first spring captures of black cutworm (BCW), Agrotis ipsilon (Hufnagel), adults in blacklight traps and captures of male BCW in traps baited with 40 μg of synthetic pheromone (3:1 ratio of Z-7-dodecanyl acetate:Z-9-tetradecanyl acetate) indicates that the first flight of BCW moths immigrate to central Iowa. This hypothesis is supported by the fact that all captured first-flight females are mated, a condition often associated with immigrating females. Additionally, a BCW development simulation model demonstrated the potential existence of two separate BCW populations, i.e., (1) immigrants and progeny, and (2) natives and progeny. We attribute low pheromone trap captures of BCW males and blacklight trap captures of mostly unmated females during the autumn flight to reproductive diapause in one or both sexes. We hypothesize further that a reproductive diapause might portend an autumnal southward migratory flight of BCW from Iowa.

Surface synoptic weather maps, atmospheric trajectory forecasts, and observational upper-air reports (radiosonde data) were used to estimate the relative displacement of black cutworm, Agrotis ipsilon (Hufnagel), moths dyed with Calco Red N-1700 from two release sites. Among significant ( P < 0.05) average capture of natural males on 13–15 June 1984, were two marked by Calco Red (Passaic Color and Chemical Company, Paterson, N.J.), one near Elkhart, Iowa (41°30'N latitude), and the other near Centerville, Iowa (40°45'N latitude), 1,142 and 1,043 air km, respectively, from Crowley, La., where 6,928 males were released 4–11 June 1984. A release of 9,799 males (capable of flight) on 16–28 May 1985 resulted in captures of three males marked by Calco Red, among significant ( P < 0.05) captures of natural moths, one observed near Bates City, Mo. (39°00'N latitude), one near Sac City, Iowa (42°30'N latitude), and a third near Shawnee Mission, Kans. (39°00'N latitude). These marked moths were recovered 960, 1,175, and 921 air km, respectively, from the release site (College Station, Tex.). A release of 3,520 males (capable of flight) on 17–21 July 1985 resulted in a single marked male being observed 24 July near Rock Rapids, Iowa, 1,266 air km north of College Station. Seemingly, many of the captured natural and all of the recaptured marked moths were capable of arriving in the trapping zones in two to four nights. The atmospheric low-level jet (300–900-m elevation) and a surface synoptic system of low pressure over the Plains states (that induces air flow northward) are theorized as being necessary for moth transport.

Species composition and seasonal abundance of the insect fauna were identified from the foliage of mating and resting sites of European corn borer (ECB), Ostrinia nubilalis (Hubner). A total of 99,519 foliage-dwelling insects was collected during 1983 and 1984. Homoptera, Hemiptera, Hymenoptera, and Diptera accounted for 89% of the total fauna captured. The Chalcididae were the most abundant insects captured from the foliage of action sites. The major herbivores identified from ECB adult action sites were Athysanus argentarium Metcalf, Draeculacephala anticox (Walker), and Leptopterna spp. Coleomegilla maculata (De Geer) and Hippodamia convergens (Guerin-Meneville) were the most abundant predators inhabiting the grassy canopy of ECB adult action sites. Peak predator abundance coincided with early season population peaks of the foliage herbivores. The role of ECB adult action sites as a possible source of predators for Iowa cornfields is discussed. The effects of carbaryl and fen valerate applied for spring- and summer-generation adult ECB control were tested on the foliage-dwelling insects in action sites. Only one species, A. argentarium , was significantly reduced by spring applications of carbaryl and fenvalerate to the foliage of ECB adult action sites. A. argentarium was significantly reduced for 28 d post treatment during 1983 and for 7 d in 1984. Summer adult control had minimal impact on the foliage insects. Foliage predator populations were not negatively affected by the application of insecticides. Therefore, application of carbaryl and fenvalerate for controlling ECB adults in action sites resulted in minimal disruption of the foliage-dwelling insect community.

Survival of 10 populations of Ostrinia nubilalis (Hubner) was progressive from north (Morris, Minn.) to south (Portageville, Mo.) except that survival decreased again at Tifton, Ga., because of the stunted condition of the corn and the density of the test insect populations. In the south, increasing temperature overrode photoperiod (shorter photophase, longer scotophase) and reduced the number of borers that diapaused. Conversely, in the north, photoperiod (longer photophase, shorter scotophase) overrode decreasing temperature, but again the result was a reduction in diapause. The highest percentage diapause occurred at the latitude where the photoperiod-temperature interaction was most severe. From the diapause response, populations of European corn borers in North America fit 3 ecotypes: a northern one represented by the Minnesota and Quebec populations; a central one represented by the Iowa, Nebraska, Ohio, and Frederick Co., Md., populations; and a southern one represented by the Alabama, Georgia, Missouri, and Somerset Co., Md., populations.

Results of field studies during the summer of 1973, 1974, and 1978 indicated that sampling the population European corn borer moths (ECB), Ostrinia nubilalis (Hubner), in dense vegetation (action sites), predominately giant and green foxtailgrass, Setaria faberi Herrm. and S. viridis (L.) Beauv., respectively, could predict the potential 2nd-generation ECB populations in adjacent corn fields. Numbers of ECB egg masses on corn plants were highly correlated (r = 0.94, 1973; r = 0.91, 1974; r = 0.92, 1978) with numbers of female ECB moths/1-m2 (min of 20, one-m2 samples/sample date) in dense grass in waterways and near borders of corn fields. Treatment of these areas bordering corn fields with 2.26 kg AI/ha carbaryl killed ECB moths, significantly reduced numbers of egg masses deposited per plant in the corn fields (untreated borders, 3.3 egg masses/corn plant; treated borders, 0.2 egg masses/corn plant), significantly reduced ECB cavities per plant (untreated borders, 40.8 cm; treated borders, 14.3 cm), and significantly increased grain yield per plant (untreated borders, 192.1 g; treated borders, 210.0 g). A regression equation, based on numbers of female ECB moths per 1-m2 of action site was developed for predicting potential 2nd-generation ECB populations in corn fields.

A flight mill system developed for large, heavy, and strong flying moths such as the black cutworm, Agrotis ipsilon (Hufnagel), is described. Flight mills have specially constructed pivots and bearings that effectively control flight direction of tethered moths. The system uses infrared sensors interfaced with a microcomputer to monitor and record flight mill operation. Parameters recorded include distance flown and flight duration used to calculate speed, resting time, and number of flights. Two types of tethers are compared. The semirigid tether provides a limited amount of flexibility such that the moth supports its own weight and is free to adjust to its posture during flight. The rigid tether fixes the orientation of the moth to a horizontal posture. Results of flight tests indicate that laboratory-reared black cutworms are comfortable in a horizontal posture and energy utilization of moths attached to the two tethers are comparable.

Field studies were conducted to determine the relationship between low-altitude (< 3 m) flight and sexual activity of the European corn borer, Ostrinia nubialis (Hubner), and to delineate the effect of environmental factors on these activities. ECB moths flew out of tall, dense foxtailgrass ( Setaria spp.) at 2000–2200 h and moved over short grass where dew had formed. The number of males flying under 3 m was not synchronized with the number of males captured in traps baited with virgin ECB females or the synthetic pheromone, Z:E -11-tetradecenyl acetate (96:4 Z:E -11-tda) until after dew or raindrops were deposited on the grass leaves. Free water contributed to the aggregation of ECB adults in patches of tall, dense foxtail grass. Multivariate regressions showed that dew (dewpoint temperature, dewpoint depression, and temperature interaction with dewpoint depression) significantly affected the sexual activity of feral males. And even though the caged females (baits) were kept close to water, there was a suggestion of a natural dependence on free water from dew or rain to stimulate the sexual activity of females. The presence of free water, however, is only a condition required for the initiation of sexual activity. Whether this potential is expressed depends on the availability of both sexes (competition) combined with several physical parameters (temperature, relative humidity, illumination). These studies also suggest that low illumination and a slight wind is necessary to provide guidance to the ECB male in mate seeking.

Field studies show that, if tillage operations occur 2 days before planting or on planting day and herbicide applications occur 2 days before planting, on planting day, or 2 days after planting, black cutworm, Agrotis ipsilon (Hufnagel), larvae present at the time of tillage or herbicide application can survive and produce significant damage to seedling corn. The number of herbicide- or tillage-killed plants per square meter did not seem to affect the survival of black cutworm unless the plant mortality occurred 8 or 14 days before corn planting (15 or 21 days before corn emergence). Black cutworm that presumably fed only on surface plant debris for 11 days survived and significantly affected the corn crop. On the basis of accumulated centigrade degree-days necessary for black cutworm to shift to subsequent stadia, survivors feeding on plant debris will develop as quickly as survivors feeding on weed seedlings, and both populations can achieve cutting stadia (fourth to sixth) by the time corn emerges.

In central and eastern Iowa, adults of the European corn borer (ECB), Ostrinia nubilalis (Hubner), were captured hourly with blacklight traps (BLT) in and away from action sites (dense vegetation where ECB adults mate and rest) for 14 nights during the second flights of 1980 and 1981. Also, samples of moths in the grass at the action sites were taken hourly. Peak capture of females in the BLT occurred immediately after dusk, whereas peak male capture occurred during the period of greatest mating activity (ca. 2400 to 0100 h). Captures of males remained much greater than those of females throughout the rest of the night, indicating that, during this period, males are captured while seeking less mobile females. This difference in mobility explains the tendency of males to outnumber females in BLT. Males tended to outnumber females in captures obtained daily in action sites with a drop-net. The drop-net data suggest that, after oviposition in cornfields, not all mated females return to the action site each night, but that males usually remain in the action sites because of the pheromone released by the unmated females.

Spider fauna was sampled in 1983 and 1984 from action sites of adult European corn borer (ECB), Ostrinia nubilalis (Hubner). The ground-dwelling spider community was best characterized as a hunting guild and consisted primarily of Lycosidae, Thomisidae, and Gnaphosidae. A gnaphosid species, Gnaphosa parvula Banks, is a new state record for Iowa. Total ground spiders reached greatest numbers by June and declined thereafter. The foliage-dwelling spider community was characterized as both an orb-web guild and a hunting guild. Tetragnathidae, Araneidae, Salticidae, Thomisidae, and Oxyopidae accounted for 89% of the foliage-inhabiting spiders. Effects of carbaryl and fenvalerate applied for adult ECB control were tested on the spider fauna in action sites. Spider populations were generally not affected, except for the foliage spider family, Tetragnathidae, whose numbers were significantly reduced for 28 d in 1984 in treated action sites. It is suggested that beneficial spider populations, particularly ground-dwellers, could be protected from adverse effects of insecticide treatments if treatment was timed to miss peak densities and the application was primarily directed at the upper foliage canopy

Two relative methods of sampling Ostrinia nubilalis (Hubner) adults, blacklight trap (BLT) and flush bar (FB), were compared with the more absolute drop-net (DN) method over four flights in central and eastern Iowa (1980–1981). Although light traps showed similar population trends regardless of proximity to cornfields or action sites (aggregations of adults in dense grass), the trends were not the same as those shown by the DN. The FB method, however, showed trends similar to those of the DN, and this sampling procedure can replace the DN during the critical period (first 12 to 17 days) of a moderate to heavy flight. An average of 61 European corn borer adults per 10 m2, indicated by the new FB sampling method, was equivalent to the DN threshold average of 3 European corn borer females per 1 m2 of action site (dense grass) previously established and reported in the literature.

Inheritance of the diapause trait in the European corn borer, Ostrinia nubilalis (Hubner), followed a pattern substantially consistent with that of a sex-linked system. Lacking an understanding of the sex-linked inheritance of diapause, interpretation of research data on physiological and environmental responses has been difficult. Where feral or unselected populations are studied, results will be an average response of insects with different diapause capabilities. When European corn borer strains with known histories of diapause induction were exposed to varying photoperiods, we found high mortality in larvae normally destined to diapause, with the highest mortality in females. There is an urgent need for genetics research on insects which are used in intensive research programs and on insects of economic importance where the potential for genetic mechanisms for population management remain a vast, untapped resource.

Several field trials were conducted in likely activity sites in Iowa to determine how chronological age and laboratory propagation affect the ability of black cutworm (BCW), Agrotis ipsilon (Hufnagel), females to attract male BCW moths. The effects of seasonality also were studied. In 1978, initial experiments were conducted to ascertain the factors that might contribute to variability in trap catches. Trap location and night of capture were identified as highly variable factors. In experiments conducted from 6 July to 13 July 1978, there were no significant differences in the attractancy of BCW female moths reared for one or multigenerations in the laboratory. In 1979, only the seasonal trends in reproductive behavior for 2-, 4-, 6-, and 8-d-old virgin female BCW were analyzed. In general, neither 4- nor 6-d-old virgin female BCW were significantly more attractive at any time during the year; however, a trend favoring the attractancy of older females (up to 6 d) early in the season seems evident. A reduction in sexual responsiveness of male BCW was noted during late July and early August in Iowa.

The percentage of recovery and yields of corn plants damaged by black cutworm, Agrotis ipsilon (Hufnagel), larvae were compared with manual damage. Significant losses in yield generally occurred before the four-leaf stage (84%of all damaged plants). The recovery of corn seedlings from actual damage and manual damage differed; 1982, 50 and 67%; 1983, 34 and 45%; 1984, 54 and 45%. Often seedlings damaged by black cutworm produced greater yields than did manually damaged plants. The degree of yield reduction depended on the position of the growing point within the plant relative to where the plant had been severed (i.e., above, at, or below the soil surface). Corn plants were much less likely to recover if cut by black cutworm below the soil surface. The possible use of manual cutting in screening corn genotypes for their ability to recover from black cutworm damage is discussed.

Ecological and evolutionary research on lepidoptera migration has tradi- tionally concentrated on the long-range dispersal of day-flying butterflies. Nocturnal flights at high altitudes and the difficulty in species identification have resulted in a paucity of evidence supporting long-range dispersal of moth species attacking economic crops. Black cutworm (Agrotis ipsilon (Hufnagel)), moths were reared on diet containing a marker dye and were released at Crowley, Louisiana, and College Station, Texas. Traps baited with A. ipsilon sex pheromone were stationed in a line east to west over 618 km. There were six trap lines 108 km apart north to south and two more trap lines 720 km further south. Following release, six male moths were captured after two to four nights in Missouri, Kansas, and Iowa. The climatological conditions that allow this rapid long-range movement were quantified and the data suggest that the moths were traveling at altitudes of < 1500 m. These results may provide information on the mechanism for long-range migration of many moth species into the north central United States. These findings also strengthen the compatibility of other components of A. ipsilon physiology and behavior with "oogenesis- flight syndrome" (sexual maturity after long-range flight).

Survival of European corn borer, Ostrinia nubilalis (Hubner) in a single corn field was studied over 2 yr by introducing the insect at ca. the time natural infestations occur. Several climatic variables were measured and incorporated into multivariate analyses. Maximum daily temperature, moisture-stress, and atmospheric evaporation proved to be the parameters that accounted for 81–93% of the variation of ECB mortality. The data for the 4 generations of ECB were extrapolated to predict ECB per ha in adjacent Boone Co., Iowa. The expected number of 1st-generation ECB accurately reflected the observed number of ECB in Boone Co., but the expected number of 2nd-generation ECB was much larger than the observed number of ECB in Boone Co. Nevertheless, the predicted trend for larger 2nd-generation populations of ECB was correct. In central Iowa, the results of the study suggest survivorship of ECB is independent of egg laying and dependent on available feeding sites in the host. But, temperature-related climatic factors determine whether ECB will fill these feeding sites.

A black cutworm, Agrotis ipsilon (Hufnagel), developmental model was evaluated in Iowa field trials. The model's simulations deviated from the biological data. In all but one case, actual black cutworm development was faster than the simulation. Consequently, two areas of potential model refinement were identified. First, incorporation of the variable development times within a population would allow the model to accurately simulate individuals that develop either faster or slower than usual. Second, accounting for accelerated black cutworm development under natural, fluctuating temperatures would enhance the model's predictive capabilities. Interestingly, the model's simulations were similar when soil temperature inputs were compared with air temperature inputs. During the field studies, it was determined that black cutworm field development was unaffected by the natural photophases of Iowa spring, summer, or autumn. Further, it was hypothesized that soil moisture may have influenced black cutworm developmental rates during the field trials.

A study was undertaken to determine species composition and seasonal abundance of ground-dwelling insects associated with European corn borer (ECB), Ostrinia nubilalis (Hubner), adult action sites and to determine impact of adult ECB control on nontarget insects in these sites. A total of 24,497 ground-dwelling insects was collected during the 2-yr study. Coleoptera, Orthoptera, and Homoptera accounted for 98% of the total insect fauna. Three predator species were abundant in ECB action sites: Evarthrus alterans Casey, Pterostichus chalcites (Say), and Harpalus pennsylvanicus DeGeer. Carbaryl (2.26 kg [AI]/ha) or fenvalerate (0.1 kg [AI]/ha) applied for adult ECB control had minimal impact on the ground-dwelling insect community. Predator populations were not affected. Role of action sites as a source of predators for Iowa cornfields is also discussed.

Although the European corn borer, Ostrinia nubilalis (Hubner), began flight shortly after dusk, capture of feral males in traps baited with virgin females or feral males and females captured in light traps and studies of released insects in cultivated and uncultivated corn showed that this early evening activity is not oriented toward mating. Sexual activity peaked between 2400 and 0100 h, and most of it took place in tall (57.5–117.5 cm), dense foxtailgrass ( Setaria faberii Herrn. and S. viridis (L.) Beaur.), where large numbers of both sexes aggregated. Aggregation and sexual activity occurred as much as 100 m from the nearest cornfield. The grass habitat is of major importance in the aggregating phenomenon though pheromone emission by females may also have a part. Techniques employed to disrupt pheromone communication between the sexes in cornfields might be futile because mating could occur in dense vegetation outside the cornfield.

Survival and diapause of F1 progeny of the European corn borer, Ostrinia nubilalis (Hubner), from reciprocal matings of populations from the southern fringe (Alabama), east coast (Maryland), and northern fringe (Minnesota) of the species' distribution in the United States were studied in field cages during the summers of 1968–69 in the heart (Ankeny, Iowa) and on the northern fringe (Morris, Minnesota) of the Corn Belt. A microsporidian, Perezia pyraustae Paillot, affects survival, particularly of F1 populations with Minnesota parentage. Also, at Morris, the development of the plant hosts relative to the development of the insects affected the survival of populations with Maryland parentage. A direct relationship existed between the number of tunnels produced in corn stalks and the survival of all populations of European corn borer. However, the tunnels per borer tended to increase with decreased survival or with increased incidence of diapause among survivors. Thus, the feeding habits of survivors or of that portion of the survivors that had been in diapause may have changed. The data on incidence of diapause suggest a genetic difference in degree of sensitivity to photophase and temperatures between the Alabama and Maryland populations and the Minnesota population. The greatest sensitivity was expressed by the progenies from reciprocal matings of Minnesota with Alabama and Maryland populations.