Laurence D. Charlet

Isolation of the diterpenoids, Ent-Kauran-16α-OL and Ent-Atisan-16α-OL, from sunflowers, as oviposition stimulants for the banded sunflower moth, Cochylis hospes

Two diterpenoid alcohols, ent-kauran-16α-ol (1) and ent-atisan-16α-ol (2), were isolated from pre bloom (R3-R4 stage) sunflower heads as oviposition stimulants for the banded sunflower moth, Cochylis hospes. Fractionation of a sunflower head extract, by normal-phase flash column chromatography, resulted in an early eluting fraction exhibiting significant activity in an egg-laying bioassay. Compounds 1 and 2, along with ent-trachyloban- 19-oic acid (3) and ent-kaur-16-en-19-oic acid (4), were isolated as the major components of this fraction and identified by their NMR and mass spectra. The purified compounds were individually tested for ovipositional activity in dose-response bioassays. In these bioassays, compounds 1 and 2 gave linear dose responses, with increasing numbers of eggs laid as the dosage of either increased. Compounds 3 and 4 failed to stimulate significant egg-laying at any of the dosages tested. A factorial design bioassay, using compounds 1 and 2, showed that 1 was relatively more stimulatory than 2, and that there was no synergistic effect on oviposition when the two compounds were combined.

Cuticular hydrocarbons of the sunflower beetle, Zygogramma exclamationis.

Hydrocarbons were the major lipid class on the cuticular surface of adults, nymphs, and eggs of the sunflower beetle, Zygogramma exclamationis, characterized by gas chromatography-mass spectrometry. Minor amounts of wax ester from 40 to 48 carbon atoms in size were only detected in larvae. The hydrocarbons ranged in size from 23 carbons (tricosene) to 56 carbons (trimethyltripentacontane) and were largely methylalkanes. The major components from females were 13,17,21-trimethylnonatriacontane (19%) and from larvae was n-nonacosane (17%). Males had 11,15- and 9,15-dimethylheptacosane (11%) and 13,17,21-trimethylnonatriacontane (11%) as the major components. In a sample of eggs, 13,17,21-nonatriacontane (16%) was the major component which was approximately 3 to 4-fold greater than the next most abundant hydrocarbons, dimethylheptacosanes, 2-methyloctacosane, methylnonacosanes, dimethyl- and trimethylheptatriacontanes and dimethylnonatriacontanes.

Isolation of three diterpenoid acids from sunflowers, as oviposition stimulants for the banded sunflower moth, Cochylis hospes.

The banded sunflower moth (BSFM), Cochylis hospes Walshingham (Lepidoptera: Cochylidae) is a specialist insect, the larvae of which feed on sunflowers, Helianthus spp., and a few other species of Compositae. It is one of the most important pests of sunflower in the USA. Previous work on H. annuus, the cultivated sunflower, revealed two diterpenoids that function as oviposition stimulants for female BSFM, and that other, more polar compounds also stimulated oviposition. Using a bioassay-guided approach, we isolated three additional diterpenoids, grandifloric acid (1), 15β-hydroxy-ent-trachyloban-19-oic acid (2), and 17-hydroxy-16α-ent-kauran-19-oic acid (3), from polar fractions of pre-bloom sunflower head extracts. In laboratory bioassays, purified natural samples of each of these compounds stimulated oviposition by female BSFM. Structure–activity relationships of the five diterpenoids known to stimulate oviposition by female BSFM are discussed.

Biochemistry and physiology of overwintering in the mature larva of the red sunflower seed weevil, Smicronyx fulvus LeConte (Coleoptera: Curculionidae)

Abstract The red sunflower seed weevil, Smicronyx fulvus LeConte, overwinters in the soil as a mature fifth-instar larva. A strong correlation exists between minimum daily soil temperatures and trehalose accumulation. Larvae buried in the field in September 1988 showed a two-fold increase in whole-body trehalose levels by January (21.0±0.6 vs 40.1 ± 0.6 μg/mg wet wt). During this period of trehalose accumulation, glycogen levels fell from 17.9 ± 1.4 to 2.7 ± 0.6 μg/mg wet wt. There is a partial reconversion of trehalose to glycogen with the onset of spring; trehalose levels dropped while glycogen levels increased. Trehalose accumulation does not affect the supercooling capacity of the larvae. The mean temperature of crystallization of the larvae remained constant at about −24°C from September to June and was also unchanged with temperature acclimation. Respiratory rates fell from 0.65 μl/h/mg in September to 0.29 μl/h/mg in January. Larvae collected in September 1989 and acclimated to 0°C for 7 days also had increased trehalose levels with a concomitant reduction in glycogen. Early autumn larvae subjected to −5°C for 7 days had a survival of 96%. However, only 28% of the larvae collected from containers buried in the field in November survived 1 day at −15°C and none survived 1 day at −20°C. Under the conditions tested the larvae do not appear to be freeze-tolerant.

Biochemistry and physiology of overwintering in the mature larva of the sunflower stem weevil, Cylindrocopturus adspersus (Coleoptera: Curculionidae) in the Northern Great Plains

Abstract The sunflower stem weevil, Cylindrocopturus adspersus (LeConte), overwinters as a mature larva at the base of the stalk and in the root crown of cultivated sunflower plants. Sunflower stalks from fields known to be infested with C. adspersus larvae were collected in southeastern North Dakota in October 1991. Larvae from stalks kept outdoors accumulated a high whole-body concentration of trehalose (up to 69 μg/mg wet wt) at the expense of glycogen with the onset of winter followed by a partial reconversion of trehalose to glycogen with the onset of spring. Larvae from stalks acclimated to 0°C also accumulated a high level of trehalose (∼69 μg/mg wet wt) with a concomitant decrease in glycogen. Those larvae from stalks kept at 20°C showed an initial sharp increase in whole-body trehalose that then stabilized but at a concentration well below that of larvae acclimated to 0°C. This indicates that there exists in the larva an underlying developmental component to trehalose accumulation which is further enhanced by low temperature (0°C) exposure. The mean temperature of crystallization ( T c ) of larvae exposed to outdoor conditions showed an abrupt drop from October (−25.0 ± 1.3°C) to November (−28.2 ± 0.6°C) with a minimum in February (−29.1 ± 0.3°C). The level of trehalose accumulated by the sunflower stem weevil larva is to our knowledge the highest reported in an overwintering insect.

Resistance in Cultivated Sunflower to the Sunflower Moth (Lepidoptera: Pyralidae)

Abstract A five-year field study evaluated 42 sunflower (Helianthus annuus L.) accessions, 25 breeding lines, and 40 interspecific crosses for resistance to infestation and damage from larval feeding by naturally occurring populations of the sunflower moth, Homoeosoma electellum (Hulst) (Lepidoptera: Pyralidae). Accessions PI 175728 and PI 307946 had less than 3% feeding damage per head in all three years they were tested. Some interspecific crosses showed evidence of resistance; PAR 1673-1 had less than 2% seed damage in 2002 and 2003 and less than 3% in 2005. PRA PRA 1142 sustained less than 3% seed damage and STR 1622-1 had less than 2% seed damage in three years of trials. Breeding lines with potential resistance included 01-4068-2, which had the least amount of seed damage per head in 2002 (<1%) and in 2003 averaged only 2% damage. Line 01-4080-1, with less than 1% damage in 2002 and in 2003, was the least damaged entry in these evaluations. Hybrid ‘894’ was included as a standard check; however, it consistently had among the lowest average seed damage from H. electellum feeding. Our investigation showed the potential for developing resistant genotypes for the sunflower moth to reduce seed feeding injury and to prevent yield losses for sunflower producers. The development of germplasm with host plant resistance would provide another tool in an integrated pest management approach for H. electellum. Additional effort is in progress to use the identified lines to introgress resistance genes into cultivated sunflower through conventional breeding facilitated by marker-assisted selection.

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

Abstract 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.

Resistance Among Cultivated Sunflower Germplasm to Stem-Infesting Pests in the Central Great Plains

ABSTRACT A 7-yr field study evaluated 61 oilseed sunflower, Helianthus annuus L, accessions and 31 interspecific crosses for resistance to attack by naturally occurring populations of three stem-infesting pests, the sunflower stem weevil, Cylindrocopturus adspersus (LeConte) (Coleoptera: Curculionidae); a longhorned beetle, Dectes texanus LeConte (Coleoptera: Cerambycidae); and a root boring moth, Pelochrista womonana (Kearfott) (Lepidoptera: Tortricidae), at two locations in the central Great Plains. Germplasm with potential sources of resistance to attack from all three stem-infesting species were revealed. Accessions PI 650558, PI 386230, and PI 431516 were consistent in averaging low densities of stem weevil larvae per stalk among lines tested, and PI 497939 exceeded 25 weevil larvae per stalk in only 1 yr of 5 yr of trials. Several interspecific crosses also had consistently low densities of C. adspersus larvae per stalk. Populations of both D. texanus and P. womonana were variable over years, but differences among the lines tested were evident in many trials, revealing potential for developing resistant germplasm. Four accessions (PI 386230, PI 431542, PI 650497, and PI 650558) had low larval densities of C. adspersus and P. womonana in addition to reduced percentage infestation by D. texanus. Results showed potential for developing resistant genotypes for these pests. The prospect of adding host plant resistance as an integrated pest management (IPM) tactic would provide another tool for reducing economic losses from stem-infesting insect pests of sunflower in the central Great Plains.

Impact of Combining Planting Date and Chemical Control to Reduce Larval Densities of Stem-Infesting Pests of Sunflower in the Central Plains

Abstract The guild of stem-infesting insect pests of sunflower, Helianthus annuus L., within the central Plains is a concern to producers chiefly due to losses caused by plant lodging from the sunflower stem weevil, Cylindrocopturus adspersus (LeConte) (Coleoptera: Curculionidae), and Dectes texanus texanus LeConte (Coleoptera: Cerambycidae). The incidence of a root boring moth, Pelochrista womonana (Kearfott) (Lepidoptera: Tortricidae), also has increased. Experiments were conducted in three locations in Colorado and Kansas during 2001–2003 to investigate the potential of combining planting date and foliar and seed treatment insecticide applications to lower insect stalk densities of these three pests. The impact of these strategies on weevil larval parasitoids also was studied. Eight sunflower stem weevil larval parasitoid species were identified. All were Hymenoptera and included the following (relative composition in parentheses): Nealiolus curculionis (Fitch) (42.6%), Nealiolus collaris (Brues) (3.2%) (Braconidae), Quadrastichus ainsliei Gahan (4.2%) (Eulophidae), Eurytoma tylodermatis Ashmead (13.1%) (Eurytomidae), Neocatolaccus tylodermae (Ashmead) (33.7%), Chlorocytus sp. (1.6%), Pteromalus sp. (0.5%) (Pteromalidae), and Eupelmus sp. (1.0%) (Eupelmidae). The results from this 3-yr study revealed that chemical control was often reliable in protecting the sunflower crop from stem pests and was relatively insensitive to application timing. Although results in some cases were mixed, overall, delayed planting can be a reliable and effective management tool for growers in the central Plains to use in reducing stem-infesting pest densities in sunflower stalks. Chemical control and planting date were compatible with natural mortality contributed by C. adspersus larval parasitoids.

Impact of Planting Date on Sunflower Beetle (Coleoptera: Chrysomelidae) Infestation, Damage, and Parasitism in Cultivated Sunflower

The sunflower beetle, Zygogramma exclamationis (F.), is the major defoliating pest of sunflower (Helianthus annuus L.). Planting date was evaluated as a potential management tool in a variety of production regions throughout North Dakota from 1997 to 1999, for its impact on sunflower beetle population density of both adults and larvae, defoliation caused by both feeding stages, seed yield, oil content, and larval parasitism in cultivated sunflower. Results from this 3-yr study revealed that sunflower beetle adult and larval populations decreased as planting date was delayed. Delayed planting also reduced defoliation from adult and larval feeding, which is consistent with the lower numbers of the beetles present in the later seeded plots. Even a planting delay of only 1 wk was sufficient to significantly reduce feeding damage to the sunflower plant. Yield reduction caused by leaf destruction of the sunflower beetle adults and larvae was clearly evident in the first year of the study. The other component of sunflower yield, oil content, did not appear to be influenced by beetle feeding. The tachinid parasitoid, Myiopharus macellus (Rheinhard), appeared to be a significant mortality factor of sunflower beetle larvae at most locations regardless of the dates of planting, and was able to attack and parasitize the beetle at various larval densities. The results of this investigation showed the potential of delayed planting date as an effective integrated pest management tactic to reduce sunflower beetle adults, larvae, and their resulting defoliation. In addition, altering planting dates was compatible with biological control of the beetle, because delaying the planting date did not reduce the effectiveness of the parasitic fly, M. macellus, which attacks the sunflower beetle larvae.