Smicronyx Fulvus Research Articles

Efficacy of red sunflower seed weevil resistance from inbred line cms HA 488 in single‐cross hybrids

AbstractSunflower line HA 488 (where HA is Helianthus annuus) is resistant to the red sunflower seed weevil, Smicronyx fulvus LeConte, with ≈80% less seed damage compared to susceptible lines. To determine the value of resistance in single‐cross hybrids, six hybrids were created by pollinating weevil‐resistant (cms HA 488, where cms cytoplasmic male sterile) or susceptible (cms HA 412HO) inbred lines with three putatively susceptible restorer lines (RHA 274, RHA 464, or RHA 468) and artificially infesting each with 30 weevils head−1. In 2021–2022, resistant hybrids from cms HA 488 reduced seed damage by ≈40%–50% for hybrids with RHA 274 or RHA 464. However, cms HA 488 did not reduce damage when crossed with RHA 468. Infestation of male‐fertile isogenic lines HA 488 and HA 412HO with 60 weevils head−1 showed resistance remained effective at 12–20 times economic thresholds. Results confirm the value of resistance to S. fulvus for sunflower hybrids but also suggest a need to further examine the role of the male heterotic group in resistance to the red sunflower seed weevil.

Thermal biology and overwintering behavior of the red sunflower seed weevil (Coleoptera: Curculionidae).

Most natural mortality of the red sunflower seed weevil, Smicronyx fulvus LeConte (Coleoptera: Curculionidae), occurs while larvae overwinter in the soil. To test the hypothesis that S. fulvus mortality is related to low temperatures, experiments were used to (i) evaluate the temperature at which larvae freeze (= supercooling point [SCP]), (ii) assess possible vertical movement between entry into the soil in fall and adult emergence in summer, and (iii) determine if realistic soil temperatures could explain patterns of overwintering mortality. Mean SCP for groups of S. fulvus larvae differed between years and months, but only ranged from -20.93 to -22.68 °C. Most overwintering larvae were found within 6 cm of the soil surface, but larvae appeared to move 1-2 cm deeper between pairs of successive sample dates (September to January, January to April). Significant larval mortality that occurred between January and April 2021 was tentatively attributed to a period in February where daily minimum soil temperatures ranged from -8 to -12 °C. When overwintering under control conditions (constant 4 °C) was interrupted with week-long exposure to -4, -8, or -12 °C in a cold bath, significant S. fulvus mortality was seen for temperatures at or below -8 °C. Combined results suggest that mortality of overwintering S. fulvus is likely caused by continuous exposure to low temperatures that may not be cold enough to freeze larvae. Additionally, the shallow overwintering by S. fulvus supports the idea that routine farm management, including tillage and herbicide incorporation, may help limit populations of this sunflower pest.

Fatty Acid Data and Crop Surveys Indicate Sources of Red Sunflower Seed Weevil (Coleoptera: Curculionidae), Populations and Suggest Strategies for Management

The red sunflower seed weevil, Smicronyx fulvus L., is a univoltine seed-feeding pest of cultivated sunflower, Helianthus annuus L. Artificial infestations of S. fulvus onto sunflowers with traditional (<25% oleic acid), mid-oleic (55-75%), or high oleic (>80%) fatty acid profiles were used to test if fatty acids could be used as natural markers to estimate the proportion of weevils developing on oilseed sunflowers rather than wild Helianthus spp. and confection (non-oil) types. Oleic acid (%) in S. fulvus confirmed the fatty acid compositions of mature larvae and weevil adults reflected their diets, making primary (oleic or linoleic) fatty acids feasible as natural markers for this crop-insect combination. Oleic acid in wild S. fulvus populations in North Dakota suggests at least 84 and 90% of adults originated from mid-oleic or high oleic sunflower hybrids in 2017 and 2018, respectively. Surveys in 2017 (n = 156 fields) and 2019 (n = 120 fields) extended information provided by S. fulvus fatty acid data; no significant spatial patterns of S. fulvus damage were detected in samples, damage to oilseed sunflowers was greater than confection (non-oil) types, and the majority of damage occurred in ≈10% of surveyed fields. Combined, data suggest a few unmanaged or mismanaged oilseed sunflower fields are responsible for producing most S. fulvus in an area. Improved management seems possible with a combination of grower education and expanded use of non-insecticidal tactics, including cultural practices and S. fulvus-resistant hybrids.

Susceptibility of sunflower inbred lines and putative resistance sources to Smicronyx fulvus LeConte (Coleoptera: Curculionidae)

AbstractThe red sunflower seed weevil, Smicronyx fulvus LeConte (Coleoptera: Curculionidae), is a primary seed‐feeding pest of cultivated sunflowers, Helianthus annuus L., in North America. Host plant resistance is one tool available to complement insecticide‐based management of S. fulvus. Artificial infestations of 30 adult weevils per head were used to determine whether variation for susceptibility to S. fulvus exists in previously released inbred lines, and how a new weevil‐resistant line, HA 488, compares with other putative sources of resistance. Correcting for the number of seeds per head, 13 older inbred lines showed variation in per cent seed damage from 20% to 38%, with two lines (HA 412 HO, HA 821) being more damaged than most of the tested lines. Among four putative resistance sources, HA 488 was significantly less damaged (5%) than two previously identified open‐pollinated varieties (PI 170424, PI 253417, with 13%–14% seed damage), while the source of the resistance in HA 488, PI 431542, was statistically intermediate (12%). The resistance available in HA 488 is a marked improvement, potentially reducing damage per weevil by two thirds or more, but additional work on genetic markers for resistance, economic thresholds and basic weevil biology (e.g. degree‐day models for adult emergence) is needed to support implementation of integrated pest management for this key sunflower pest.

Effects from Early Planting of Late-Maturing Sunflowers on Damage from Primary Insect Pests in the United States

AbstractDelayed planting is recommended to reduce damage from sunflower insect pests in the United States, including the sunflower moth, Homoeosoma electellum (Hulst) and banded sunflower moth, Cochylis hospes Walsingham. However, in some locations, planting earlier or growing later-maturing hybrids could improve yield or oil content of sunflowers which would partially offset any added costs from insect pests or their management. Because the abundance and distribution of some sunflower insects have changed since recommendations for delayed planting were developed, experimental plots were grown in 2012 and 2013 at sites in North Dakota, Nebraska, Iowa, and Illinois. Sunflowers were planted two to four weeks earlier than normal, including hybrids that flower two to three weeks later than elite commercial hybrids. The sum of seed damaged by sunflower moth, banded sunflower moth, and red sunflower seed weevil, Smicronyx fulvus LeConte, (i. e., total percentage) was influenced by location, but not the relative maturity of tested entries. However, when damage attributed solely to the red sunflower seed weevil was analyzed, more damaged seed were found for late-maturing entries in North Dakota and Nebraska. In addition to the trial data, current pest populations are lower than when delayed planting was first recommended and insecticide use during sunflower bloom is both common and effective. Together, these observations suggest factoring insect pests into planting time decisions may be unnecessary, except for areas with a history of problems with severe pests that cannot be managed using insecticides (e. g., sunflower midge, Contarinia schulzi Gagné).

Nonconstant Thermal Regimes Enhance Overwintering Success and Accelerate Diapause Development for Smicronyx fulvus (Coleoptera: Curculionidae).

Recent populations of the red sunflower seed weevil, Smicronyx fulvus LeConte (Coleoptera: Curculionidae), have been inconsistent or declining, particularly in North Dakota. Consequently, research on weevil biology, including development of resistant germplasm, has been limited. To determine whether cold storage of diapausing larvae could be improved, nonconstant temperature treatments (fluctuating thermal regime [FTR] and thermoperiod [TP]) were tested versus a constant 6°C for storage up to 365 d. Both alternate temperature treatments produced more adult weevils than constant 6°C for short (42, 91 d) storage, while all temperature treatments were good (≥60% adult emergence) at moderate term (182 d) cold storage, and FTR was best for long (365 d) periods. Excluding the 14-d storage period, which produced too few weevils for comparison, each doubling of cold storage time (e.g., from 42 to 91 d, 91 to 182 d), usually decreased the number of days to 50% relative emergence by ∼10 d. After 365 d of larval storage, emerged S. fulvus adults successfully infested sunflowers in a plant growth chamber, with damage per female similar to that observed in field trials. Compared with previous efforts to store weevil larvae, the method of collection and FTR storage is either more effective (greater adult emergence and reduced parasitism) or more time-efficient, and should permit year-round research using S. fulvus adults. Because successful emergence under FTR was >75% after 365 d, additional research would be required to determine the maximum effective duration of cold storage for S. fulvus.

Resistance in Cultivated Sunflower Germplasm to the Red Sunflower Seed Weevil (Coleoptera: Curculionidae) in the Northern Great Plains

A 5 yr field study evaluated 49 sunflower, Helianthus annuus L., accessions, and 5 interspecific crosses for resistance to infestation by naturally occurring populations of the red sunflower seed weevil, Smicronyx fulvus LeConte (Coleoptera: Curculionidae). Germplasm with potential sources of resistance to attack was identified. The accession PI 162453 averaged only 8% damaged seed per head in 3 yr of testing and PI 431545 averaged 8% damaged seed per head in 4 yr of trials. The accessions PI 431542 and PI 650375, which were tested for five years, averaged 5% and 10% damaged seed per head, respectively over the study. PI 431542 averaged less than 6% in all but one year of testing. Additional accessions that appeared promising in two consecutive years of trials included PI 195573, PI 219649, PI 250085, and PI 432516. Hybrid 894 consistently had high seed damage from S. fulvus feeding. Results revealed potential for developing resistant genotypes for decreasing seed feeding injury by the red sunflower seed weevil. Research is in progress to introgress resistance genes from the identified lines into cultivated sunflower through conventional breeding facilitated by the use of marker-assisted selection.

Phylogenetic Analyses and a Method for Rapid Molecular Diagnosis of Two Sunflower Seed Weevils (Coleoptera: Curculionidae)

The red sunflower seed weevil, Smicronyx fulvus LeConte, and gray sunflower seed weevil, Smicronyx sordidus LeConte (Coleoptera: Curculionidae), are among the most important seed pests of cultivated sunflowers, Helianthus annuus L., in the northern Great Plains. A portion of 18S ribosomal DNA (18S rDNA) sequence from specimens of 31 populations of the morphologically similar species that were collected across a wide geographic region of the United States showed a consistent separation of the two species. The restriction endonuclease HaeII digests the piece of 18S rDNA in only one of the two species, and this restriction fragment-length polymorphism can be used for species diagnosis. Phylogenetic analysis for species of four tribes of the weevil subfamily Erirhininae showed that the sunflower seed weevil tribe, Smicronychini, is monophyletic.

Parasitization of the Red Sunflower Seed Weevil (Coleoptera: Curculionidae) by its Larval ParasitoidTriaspis aequoris(Hymenoptera: Braconidae) in Cultivated Sunflower

The red sunflower seed weevil, Smicronyx fulvus LeConte, is a pest of sunflower in the northern and central Plains sunflower production regions. Weevil larvae feed and develop in the sunflower achene dropping to the soil to overwinter. A total of 630 parasitoids emerging from seed weevil larvae recovered from North and South Dakota and Minnesota from 1991 to 1995 was identified as Triaspis aequoris Martin, a solitary koinobiont endoparasitoid. The mean parasitization rate for the red sunflower seed weevil by T. aequoris ranged from 2.5 to 24.2% per year. There was an increase in the percentage parasitization as overall weevil populations decreased over years. In Nebraska, percent parasitization by T. aequoris, the only species recovered, increased with increasing densities of S. fulvus between 1993 and 1995. Patterns of emergence for both red sunflower seed weevil and T. aequoris were similar in two locations in North Dakota. Oviposition pattern in seeds in the sunflower head showed decreasing density toward the center, but T. aequoris parasitization was equal throughout the head. Triaspis aequoris, an egg-larval parasitoid, effectively searched for and attacked weevil eggs as soon as weevil oviposition had begun in the field. Date of planting studies showed that damage from weevils increased as seeding of fields was delayed, but parasitization of weevil larvae was similar among all dates. Activity by T. aequoris may have contributed to the decline of the red sunflower seed weevil from North and South Dakota and Minnesota. Lower densities of weevils also may account for the reduction in the diversity of parasitoid species of this weevil. The parasitoid appears to be well adapted to its host, efficiently parasitizes the red sunflower seed weevil and is amenable for use with some pest management strategies in cultivated sunflower.

Herbivory and natural selection on flowering phenology in wild sunflower, Helianthus annuus.

Plant fitness is strongly affected by flowering phenology, and there are several ecological factors that are thought to shape the distribution of flowering times. One relatively underexamined factor is the timing and intensity of attack by herbivores that feed on flowers or developing seeds. This study tests the hypothesis that herbivores that feed on developing seeds of wild sunflower, Helianthus annuus (Asteraceae), impose selection on flowering phenology. First, the study population was found to contain genetic variation for mean date of flowering, so this trait could evolve if natural selection were operating. Next, the phenological pattern of abundance of five seed-feeding herbivores was documented. Damage by three herbivores, Haplorhynchites aeneus (Cucurlionidae), the head-clipping weevil, Homoeosoma electellum (Lepidoptera: Pyralidae), the sunflower moth, and Suleima helianthana (Lepidoptera: Tortricidae), the sunflower bud moth, was highest early in the flowering season, and declined as the season progressed. Damage by one herbivore, the seed fly Gymnocarena diffusa (Diptera: Tephrididae), was lowest early in the flowering season and increased as the season progressed. Finally, damage by two seed weevils, Smicronyx fulvus and S. sordidus (Curculionidae), whose damage was not distinguished, was constant through the flowering period. Third, damage by Haplorhynchites, Homoeosoma, and Suleima was found to be detrimental to plant fitness, suggesting that plants that flower when these herbivores are not abundant should have higher fitness. Finally, two phenotypic selection analyses were performed. The first included damage by Homoeosoma and Suleima, as well as flowering date, leaf area, and inflorescence diameter, as characters predicting plant fitness. In this analysis directional selection was found to act to decrease damage by the two herbivores, but did not act on flowering date. The second selection analysis was identical except that damage by the two herbivores was not included. In this analysis significant directional selection was found to favor later-flowering plants. Comparison of these two analyses suggests that all selection on flowering phenology is attributable to damage by Homoeosoma and Suleima: plants that flower later avoid damage by these two herbivores. While other influences on flowering phenology, such as pollination, mate availability, and seasonality, have been well documented, this study is one of few to demonstrate natural selection on flowering phenology that is a direct consequence of insect attack.

Sunflower Resistance to the Red Sunflower Seed Weevil (Coleoptera: Curculionidae)

The red sunflower seed weevil, Smicronyx fulvus LeConte (Coleoptera: Curculionidae), Is a major in sect pest of sunflower in North Dakota, South Dakota, and Minnesota. Economic damage is caused by the larvae which are internal seed feeders. During the 1992-1995 growing seasons, sunflower accessions were artificially infested and evaluated for resistance to the red sunflower seed weevil. Accessions 170411, 253417,and 170424 were resistant to the red sunflower seed weevil. Morphological types within accessions 170411 and 170424 varied for seed and pollen color and resistance to the red sunflower seed weevil. The resistant variant of accession 170424 had 45% of the seed damage of the susceptible type. In accession 170411, damage in the resistant type Was 55% of the susceptible. Antixenosis was the major resistance mechanism detected in accessions 170411 and 170424.

Feeding Behavior and Egg Maturation of the Red and Gray Sunflower Seed Weevils (Coleoptera: Curculionidae) on Cultivated Sunflower

Adult gray and red sunflower seed weevils, Smicronyx sordidus LeConte and Smicronyx fulvus LeConte, respectively, are pests of sunflower, Helianthus annum L., and use the plant as food and an oviposition site. The evolved behavior of these weevils minimizes competition for food and oviposition sites on the sunflower plant. Both male and female S. sordidus fed more on leaves of sunflower hybrid ‘894’ than on disk flowers. Mature eggs developed when females were given access to prebloom R1-R3 stage sunflower plants. Females feeding only on blooming capitula did not develop mature eggs even after 12d. S. fulvus females fed more on sunflower hybrid ‘894’ disk flowers than on leaves or bracts; males fed more on disk flowers and leaves than on bracts. Females exposed to prebloom stages (R1-R4) did not produce mature eggs, but did so when access was prolonged until bloom stage (R5.1). Females confined in blooming capitula developed mature eggs after 4d. Pollen stimulated egg maturation only when mixed with other foods such as ground sunflower seed, sucrose, or water. The preference of each weevil species for a particular sunflower plant tissue, organ, or structure, and growth stage for feeding and reproduction may be useful in developing efficient management strategies for these sunflower pests.

Mechanisms of resistance to the red sunflower seed weevil in sunflower accessions

In the northern Great Plains of North America, internal seed feeding by larvae of the red sunflower seed weevil, Smicronyx fulvus LeConte, causes economic damage to sunflower, Helianthus annuus L. Our purpose was to identify sunflower germplasm with resistance to the red sunflower seed weevil and to determine mechanisms of resistance. In 1986, 300 sunflower accessions were evaluated for the percentage of seed damaged by red sunflower seed weevil larvae. In 1987, six accessions selected on the basis of the 1986 results were evaluated for resistance to the red sunflower seed weevil. The selected accessions had flowering dates comparable to the susceptible check. The percentage of seeds with exit holes (emerged and successfully developed larvae), with larvae (unemerged larvae remaining in the seed), with inclusive damage (total percentage of seeds with exit holes or larvae), and with adult feeding or oviposition scars was used to test for larval antibiosis and adult preference. Larval antibiosis was detected in accessions 251465, 175730, 170407 and 170408 which had significantly higher percentages of seeds with larvae than did the susceptible check. The percentages of seeds with larvae and with inclusive damage were positively correlated with adult feeding or oviposition scars. Therefore, in the accessions tested, larval infestations appeared to be at least partially determined by adult red sunflower seed weevil preference.

ECONOMIC INJURY LEVELS FOR THE RED SUNFLOWER SEED WEEVIL (COLEOPTERA: CURCULIONIDAE) INFESTING OILSEED SUNFLOWER

AbstractThe control of the red sunflower seed weevil, Smicronyx fulvus LeConte, relies on the use of insecticides. An economic injury level is essential to the judicious deployment of insecticidal control. Field studies were conducted in 1992 and 1993 to quantify the weight loss and oil content loss of damaged kernels as a result of larval infestation and the relationship between the adult weevil population and the subsequent number of damaged achenes. We found that for each weevil sampled in plant stages R5.0–5.3, 26.88 damaged achenes resulted. Damaged kernels lost an average of 9.86 ± 2.36 mg (mean ± SD) per kernel, approximately equal to the amount consumed by a single larva. The oil content loss in damaged kernels was 3.34%. Economic injury levels were calculated as a function of the cost of controls, the market value, and the plant population density. Use of adult weevil counts when most plants in the fields are in plant stages R5.0–5.3 are recommended for calculating economic status.

SAMPLING PLANS FOR ESTIMATING ACHENE DAMAGE BY THE RED SUNFLOWER SEED WEEVIL (COLEOPTERA: CURCULIONIDAE)

AbstractA sampling plan for the estimation of the number of achenes damaged by the red sunflower seed weevil,Smicronyx fulvusLeConte, is useful in evaluating the efficiency of weevil management strategies. The objective of this study was to determine the distribution pattern of the damaged achenes that would allow the development of a fixed-sample-size plan for estimation of the damaged achenes. Taylor’s power law and Iwao’s patchiness regression were used to analyze the distribution pattern of the damaged achenes. Slopes from both models were &gt;1, indicating an aggregated spatial pattern. The intercepts and slopes from both models were used to calculate the minimal mean number of damaged achenes per sunflower head that can be estimated for a given sample size and precision level. If the mean number of damaged achenes per head is low (&lt;20), the plan developed using the parameters of Taylor’s power law requires significantly more samples than the plan using the parameters of Iwao’s patchiness regression to estimate the same density of damaged achenes. If the mean number of damaged achenes per head is high (&gt;30), the two plans give similar results. If both low and high damage situations are considered, Taylor’s plan is preferred to Iwao’s plan. At the 0.10 precision level, Taylor’s plan requires approximately 40 samples (heads) to estimate a mean of about 200 damaged achenes per head (≈ current economic injury level).

Sunflower Seed Weevils (Coleoptera: Curculionidae) and Their Parasitoids from Native Sunflowers (Helianthus) in the Northern Great Plains

Seed weevils and their associated parasitoids were collected from sunflower heads of eight Helianthus spp. in seven states of the northern Great Plains. Native Helianthus annuus L. constituted the majority of the populations. Weevil larvae collected included both the red and gray sunflower seed weevils, Smicronyx fulvus LeConte and S. sordidus LeConte, respectively. The gray sunflower seed weevils represented 92.4% of the adults collected. Weevil larvae occurred in most samples of sunflower heads; usually more than one-half of the samples contained one or both weevil species. Density of weevil larvae was low, usually less than one larva per sunflower head. Each native species of sunflower, except H. annuus , had a lower incidence of the red sunflower seed weevil than gray sunflower seed weevil. Populations of some sunflower species may possess genes offering resistance to the red sunflower seed weevil and should be evaluated further for resistance to the species. We identified five species of endoparasitic Hymenoptera from the two weevil species, Eutrichosoma mirabile Ashmead (Pteromalidae) and four species of Braconidae; Urosigalphus femoratus Crawford, Nealiolus rufus (Riley), N. curculionis (Fitch), and Triaspis aequoris Martin. U. femoratus was the most prevalent parasitoid species, representing ≈45% of the adults reared from the weevil larvae. These parasitoid species, except N. curculionis , represent new host records from the red and gray sunflower seed weevils. Parasitization rates averaged 0-18.0%. Weevil larvae in seeds of native sunflowers were parasitized more heavily than others have reported for larvae from seeds of cultivated sunflower.

Spatial Distribution of the Red Sunflower Seed Weevil (Coleoptera: Curculionidae) on Sunflower

Knowledge of the distribution of counts of an insect is an essential element for development of a sequential sampling plan. The objectives of this study were to determine the spatial distribution of red sunflower seed weevil, Smicronyx fulvus Le-Conte, counts in sunflower, and to determine the effect of plant stage on the density. Taylor's power law, Iwao's patchiness regression, and the negative binomial probability model were used to analyze the data. All three indices ( b , β, and k ) indicated an aggregated distribution of the weevil. Taylor's power law provided a better description than Iwao's patchiness regression. The negative binomial distribution parameter k was not dependent with mean density, indicating the presence of a common k ( kc ). The estimates of kc ranged from 0.4587 to 0.5255. Plant growth stage had a significant effect on the density of the weevil. When most plants were in the bud stages, more weevils were always found in the blooming sunflower heads (>R5.0 stage). When plants were in the anthesis stage (R5.0–6.0), the adult weevils preferred plants of stage R5.4–6.0, which were suitable for oviposition.

Comparison of glycosylated and deglycosylated vitellins from four species of weevil (Coleoptera: Curculionidae)

1. 1. The vitellins or yolk proteins of four species of weevil (Coleoptera: Curculionidae) consist of two size classes with molecular weights of 150–170 and 42–47 kilo daltons (kDa). 2. 2. The boll weevil, Anthonomus grandis, has one large vitellin while Smicronyx fulvus, S. sordidus, and Cylindrocopturus adspersus each have two large vitellins. 3. 3. All four weevils have a single small vitellin whose size differs with genera. 4. 4. In all four species both large and small vitellins contain N-linked glycosyl groups. 5. 5. Enzymatic removal of the N-linked glycosyl chains lowers the molecular weight of the vitellins 9–17%.

Insect Fauna of the Heads and Stems of Native Sunflowers (Asterales: Asteraceae) in Eastern North Dakota

Insect fauna from the heads (capitula) and stems of six native sunflower species in eastern North Dakota and western Minnesota are reported. Eight insect species in six families of Coleoptera, Diptera, and Lepidoptera were recovered from the heads of six species of Helianthus . Heads of Helianthus annuus L. contained the greatest diversity of insect species. Insect species collected were also commonly found as pests of cultivated sunflower heads. Two major pests of commercial sunflower in the Great Plains—the red sunflower seed weevil, Smicronyx fulvus LeConte; and the banded sunflower moth, Cochylis hospes Walsingham—were collected from the heads of all six native Helianthus species, although they were most common in H. annuus . Neotephritis finalis (Loew) also occurred in the heads of all Helianthus spp. examined. Insects from seven overwintering species were recovered from the stems of all six Helianthus spp. Insect stem fauna diversity was greatest in H. maximiliani Schrader, and least in H. rigidus subrhomboideus (Rydberg). The sunflower stem weevil, Cylindrocopturus adspersus (LeConte), was the only major insect pest of cultivated sunflower that was recovered from sunflower stems. It was most abundant in H. annuus . A single species of parasitoid, Nealiolus curculionis (Fitch), was reared from sunflower stem weevil larvae. Results suggest that some species of Helianthus have high potential as sources of insect resistance for incorporation into commercial sunflower.

Discrimination of sunflower volatiles by the red sunflower seed weevil

AbstractFive principle monoterpenoid and other constituent volatile chemicals of sunflower heads were combined to resemble two lines of sunflower (Helianthus annuus L.): one U.S.D.A. standard line and one French line which was ‘poorly visited by insects’ (Etievant et al., 1984). Field trials of attraction to red sunflower seed weevils (Smicronyx fulvus Le Conte, Coleoptera: Curculionidae) showed that one was clearly preferred over the other. The more attractive mixture contained α‐pinene, β‐pinene, limonene, camphene and bornyl acetate in a ratio resembling that of Flath et al. (1985) rather than that described by Etievant et al. (1984). One or two volatiles were deleted from the optimal blend but only mixtures of five volatiles showed the highest attraction. Substitution of sabinene, another volatile prominent in sunflower, for one of the five in the optimal blend also decreased attraction of seed weevils. When the monoterpenoid components and ‘green leaf volatiles’ in the traps resembled the ratios of most of the prominent volatiles of sunflower, attraction was significantly greater than controls.