Homoeosoma Electellum Research Articles

Vitrification of Lepidopteran Embryos-A Simple Protocol to Cryopreserve the Embryos of the Sunflower Moth, Homoeosoma electellum.

Simple SummarySince originally being described for fruit flies in 1990, insect embryo cryopreservation protocols have been developed for several fly species and have been used to preserve several important fly species and strains. However, the development of similar protocols for other types of insects has not progressed as rapidly. For instance, only three species of moths have been successfully cryopreserved, and the technique has not been widely adopted for any of these species. This is mainly due to complications associated with the outer egg coatings surrounding the developing moth embryo, which are substantially different from what surrounds a fly embryo. To expand the usefulness of this technique for moths, we have developed a cryopreservation protocol for the sunflower moth, a key pest of cultivated sunflower in the southern Great Plains of the United States. Our final protocol resulted in 23% of embryos hatching after cryopreservation, with 60% surviving to the adult stage. While designing this protocol, we also developed a novel method to quantitatively assess the ability of water to leave the egg after treatments, which is critically important to successful cryopreservation.Embryos of the sunflower moth, Homoeosoma electellum (Hulst), were cryopreserved after modification to the method that was previously described for Pectinophora gossipiella. The workflow to develop the protocol consisted of methods to weaken the embryonic chorion followed by the application of various methods to disrupt the sub-chorionic wax layer. These steps were necessary to render the embryos permeable to water and cryoprotectants. Initially, the embryos were incubated at 21° and 24 °C, and the development of the double pigment spots/eyespot and eclosion were tracked every two hours. The embryos at 24 °C showed eyespots as early as 30 h, while in the case of the embryos that were incubated at 21 °C, there was a developmental delay of approximately 20 h. The embryos at 24 °C showed peak eclosion between 55 and 70 h, and the embryos at 21 °C eclosed between 80 and 100 h of development. Estimating this range is crucial for the purposes of stage selection and treatment initiation for cryopreservation protocol development for the embryos. The control hatch percentage at either developmental temperature was >90%, and the sodium hypochloride, 2-propanol and alkane-based treatments reduced the embryo hatchability to <10%. Hence, a modified surfactant—hypochlorite mixture—was used to destabilize the chorion and solubilize the hydrophobic lipid layers. Water permeability assessments using the dye-uptake method show that polysorbate 80 in combination with sodium hypochlorite alone is capable of permeabilizing the embryo as efficiently as sequential hypochlorite—alkane treatments, but with significantly higher hatch rates. A vitrification medium consisting of ethane diol and trehalose was used to dehydrate and load the embryos with the cryoprotective agent. The median hatch rates after vitrification were 10%, and maximum was 23%.

Effects of Field and Landscape Scale Habitat on Insect and Bird Damage to Sunflowers

Agriculture-dominated landscapes harbor significantly diminished biodiversity. Woody vegetation along field margins can provide farmers with ecosystem services and benefit biodiversity. However, when crops are damaged by the biodiversity harbored in such vegetation, farmers are reluctant to incorporate field margin habitat onto their land and may even actively remove such habitats. We investigated how damage by both insect pests (sunflower moth, Homoeosoma electellum) and avian pests to sunflower (Helianthus annuus) seed crops varied as a function of field-margin and landscape-scale habitat, as well as by bird abundance and diversity. Surveys for insect damage, avian abundance, and bird damage were carried out over two years in 30 different fields. The mean percentage of moth-damaged sunflowers sampled was nearly four times higher in fields that had bare or weedy margins (23.5%; $877/ha) compared to fields with woody vegetation (5.9%; $220/ha) and decreased in both field types as landscape-scale habitat complexity declined. Birds damaged significantly fewer sunflower seeds (2.7%) than insects, and bird damage was not affected by field margin habitat type, landscape-scale habitat variables, or avian abundance, but was significantly higher along field edges compared to  50m from the field edge. Avian species richness nearly doubled in fields with woody margin habitat compared to fields with bare/weedy margins in both the breeding season and in fall. These results indicate that the benefits of planting or retaining woody vegetation along sunflower field margins could outweigh the ecosystem disservices related to bird damage, while simultaneously increasing the biodiversity value of intensively farmed agricultural landscapes.

Capitate Glandular Trichomes Fail to Provide Significant Resistance to Banded Sunflower Moth (Lepidoptera: Tortricidae)

Extracts from capitate glandular trichomes (CGT) of wild and cultivated sunflowers, Helianthus spp., have repellent or toxic effects on sunflower specialists and generalist herbivores less closely associated with sunflower. Though CGT have been primarily examined for their potential to provide partial resistance to the sunflower moth, Homoeosoma electellum Hulst (Lepidoptera: Pyralidae), a floret- and seed-feeding pest, the banded sunflower moth (Cochylis hospes Walsingham [Lepidoptera: Tortricidae]) is a similar species more common in the primary sunflower-producing states of North Dakota and South Dakota. Replicated field trials using partially inbred lines with low or high CGT densities were used to evaluate possible reductions to seed damage by C. hospes larvae in 2016-2017. Results failed to support the idea that CGT are a useful defense against larvae of C. hospes; the putative plant defense of high trichome density corresponded to slightly more, rather than less, insect damage. A test of a secondary explanation, that strength of sunflower hulls could help determine patterns of seed damage among tested lines, produced similarly negative results. Though timing of bloom differed between groups of most- and least-damaged lines, prior research and pheromone-trapping data suggest differences in plant maturity also cannot adequately explain the observed results. While the specific mechanisms remain unclear, significant differences in susceptibility to C. hospes exist for cultivated sunflower and limit losses from this primary insect pest.

Concentrations of sunflower phenolics appear insufficient to explain resistance to floret- and seed-feeding caterpillars

Cultivated sunflowers, Helianthus annuus L., show significant variation in susceptibility to insect pests, though specific mechanisms of resistance are not clear. Plant secondary compounds, including phenolics, are often associated with resistance to insects and pathogens. Because several phenolics are present in sunflower florets, wild sunflowers and cultivated inbred lines were sampled to document natural variation in free phenolics and evaluate their potential effects on floret-feeding pests. Four di-O-caffeoylquinic acid isomers were the largest contributors to total phenolic content of disc florets. When identified phenolics were combined with unidentified flavonoid glycosides, total phenolic concentration in inbred lines varied fourfold (≈ 18–72 mg/g), and was significantly greater than that in wild sunflowers. Two lab assays with 50 or 100 mg/g chlorogenic acid showed inconsistent reductions in mass or increases in mortality of sunflower moth (Homoeosoma electellum Hulst) larvae after 9 days, and tests using floret tissue with low or high levels of total phenolics did not show an effect of tissue type on H. electellum development. Tests for correlation between total phenolics and field data on susceptibility of sunflowers to another floret-feeding pest, banded sunflower moth (Cochylis hospes Walsingham), did not show any significant association. Cumulatively, results suggest there may be minor effects of phenolic compounds on floret-feeding insects, but these alone are insufficient for plant defense. However, variation in concentration of phenolic compounds may remain valuable, both as a component of plant defense and a source of oxidative stability in sunflower oil.

Effect of female sunflower moth, Homoeosoma electellum (Hulst) (Lepidoptera : Pyralidae) age at first mating on fecundity, fertility, longevity and egg laying pattern

Knowledge of the reproductive behaviour of a pest species is beneficial to improving pest control strategies, particularly those based on perturbing reproduction, such as sex pheromone-based mating disruption. Following copulation, mated females of the different ages were individually transferred to separate 34 ml, clear plastic containers, with a 10% sugar solution absorbed onto a cotton wick. A 2 x 2 cm long blue felt cloth, dusted evenly with ca. 1 mg of H. annuus (variety RHA 274) pollen over its entire surface, was added to the container as an oviposition substrate. Mean fecundity, fertility and longevity were all analyzed by ANOVA. Data were checked for normality and homogeneity of variance; if non-normally distributed, data were transformed and checked again (arcsine or log). Age of female H. electellum at time of first mating significantly influenced lifetime fecundity (F=7.93, df = 4, 45, P<0.0001, ANOVA) and fertility (F=9.09, df =4, 45, P<0001). In general, younger females had greater fecundity and fertility than did older females. Thus, females that first mated at 1 day were significantly more fecund and had greater fertility than did females that first mated at 3 days or older.

Sunflower Moth (Lepidoptera: Pyralidae) Biology, Ecology, and Management

AbstractSunflower moth, Homoeosoma electellum (Hulst) is an important insect pest of cultivated sunflower in North America. In this review, we outline sunflower moth life history and biology and describe direct and indirect crop injury to cultivated sunflower. Pest management strategies for sunflower moth are discussed including proper field scouting, pheromone trapping, use of economic thresholds and biological control, cultural control, host plant resistance and chemical control for incorporation into an integrated pest management (IPM) program.

Effect of female and male age on copulation of sunflower moth, Homoeosoma electellum (Hulst) (Lepidoptera : Pyralidae)

In moths, the female generally produces the sex pheromone in a gland, formed from modified epidermal cells, located between the 8th and 9th abdominal segments. A male moth perceives the pheromone through its antennal receptors, which are tuned to the sex pheromone components produced by the female. Typically, following copulation, a female often becomes unreceptive to further mating attempts by males. Several factors have been postulated to be responsible for this, including the physical act of mating, sperm and seminal fluids. Mating is known to cause either a permanent or temporary cessation of sex pheromone production in many species of moths. The effects of female and male age on time of copulation and periodicity of H. electellum were investigated. Individual virgin females of H. electellum, age 1, 2, 3, 4 and 5 days, were placed with a single conspecific virgin male (2–4 days old) in a 20 ml glass vial 3 h prior to the onset of the scotophase, in a room under the same conditions as those of the respective colonies. The percentages of copulations, and percentages of females with spermatophore in their bursa copulatrix, were compared by χ2 analyses; if there were any significant differences, each pair was compared by a χ2 analysis. The distributions of time that copulation started for the different age females and males were compared, respectively, by chi-squared tests. Female age had a significant effect on the proportion of copulations, with a significantly smaller proportion of the youngest females (1 d) copulating than of the older females (2–5 d). High proportions of females that copulated had spermatophores in their bursa copulatrix, regardless of age; there was no significant difference in these proportions among any of the different-aged females.

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).

Variation in the number of capitate glandular trichomes in wild and cultivated sunflower germplasm and its potential for use in host plant resistance

The capitate glandular trichomes of wild sunflowers (Helianthus spp.) are considered to be effective defence components that act against some herbivorous insects, but cultivated sunflowers are reportedly deficient in glandular trichomes. To investigate whether glandular trichomes have a role in the protection of cultivated sunflowers against insects, in the present study, Helianthus annuus L. accessions were grown to quantify glandular trichome density in wild and cultivated germplasm types and assess potential anti-insect effects of terpenoids in the glandular trichomes of cultivated sunflowers. Evaluation revealed that capitate glandular trichomes are often abundant in cultivated sunflowers; relative to wild H. annuus, inbred maintainer (HA) lines have similar numbers of glandular trichomes per floret, while commercial hybrids have only ≈ 20% fewer trichomes when compared with wild sunflowers. In the laboratory assay, it was found that glandular trichome extracts increased the mortality rates of sunflower moth, Homoeosoma electellum (Hulst), larvae exposed from the neonatal stage to 9 d. In the surviving larvae, the extracts significantly reduced larval mass and head capsule width. Though there are limitations to the value of glandular trichomes for host plant resistance, the feeding deterrent or toxic effects of sesquiterpene lactones and diterpenes in sunflower glandular trichomes are not limited to sunflower moth larvae, suggesting a potential for resistance to other sunflower insect pests. Additional research is required to understand the inheritance and value of glandular trichomes in commercial sunflower germplasm and how the composition of terpenoids in the glandular trichomes of wild H. annuus may differ from that in cultivated material.

Pericarp strength of sunflower and its value for plant defense against the sunflower moth, Homoeosoma electellum

Sunflower pericarps provide a barrier against seed feeding by larvae of the sunflower moth, Homoeosoma electellum. Pericarp hardening is thought to be accelerated by a phytomelanin layer beneath the hypodermis, but among germplasm with phytomelanin, broad variation in sunflower pericarp strength exists. To facilitate the use of pericarp strength in sunflower breeding, resistance to mechanical puncture was assessed for diverse sunflower germplasm, and feeding tests were used to evaluate whether differences in pericarp strength prevent H. electellum larvae from penetrating achenes. Test on field-grown sunflowers indicates that public restorer lines have lower pericarp strengths compared with maintainer lines and commercial hybrids at 14 days after the start of anthesis. Interspecific crosses or plant introduction (PI) accessions believed to be resistant to H. electellum, including PI 170415, comprised a group with exceptionally high pericarp strength relative to other germplasm. In subsequent tests on greenhouse-grown sunflowers, overall results were similar, but using field-grown plants provided greater statistical power. In choice tests with achenes that differed in pericarp strength, 7- to 9-day-old sunflower moth larvae fed more often on seed protected by a weaker pericarp, at a more than 5-to-1 ratio, while 10-day-old larvae fed indiscriminately. Pericarp strength data contradict previous published results for individual entries and heterotic groups, but support the generalization that improved physical resistance to the sunflower moth is possible. To use pericarp strength in PI 170415 or similar sources, the inheritance of high pericarp strength and potential trade-offs between pericarp strength and other agronomic traits need to be understood.

The role of chemical cues in host-plant selection by adult female Homoeosoma electellum (Hulst) (Lepidoptera: Pyralidae) and Cochylis hospes Walsingham (Lepidoptera: Tortricidae)

The sunflower moth, Homoeosoma electellum (Hulst), and banded sunflower moth, Cochylis hospes Walsingham, are important insect pests of cultivated sunflower, Helianthus annuus L., in North America. We tested whether females and larvae of the two species were able to different iate between different phenological stages of sunflower heads, as well as whether females of the two species could detect the presence of conspecific larvae in heads. Sunflower moth adult females laid more eggs on R5-stage than R2-stage sunflower heads, and also on covered R5-stage heads as compared to covered R2-stage heads. In contrast, C. hospes laid more eggs on R2-stage heads than R5-stage heads, but there was no differentiation between the two when the heads were covered. In a bioassay testing, the preferences of neonate larvae of H. electellum and C. hospes to R2-stage and R-5-stage head tissues of both species exhibited preferences to the head stage they typically feed on (that is, H. electellum larvae preferred R5 florets to R2 involucral bracts, whereas, C. hospes larvae preferred R2 involucral bracts to R5 florets). Finally, both H. electellum and C. hospes females exhibited ovipositional preferences to uninfested sunflower heads over heads infested with conspecific larvae, suggesting that females could detect infested heads, possibly by a change in chemical signal. This study demonstrates the importance of chemical stimuli in the preferences of these two species to sunflower phenological stages.

Female preference and larval performance of sunflower moth, Homoeosoma electellum, on sunflower pre‐breeding lines

AbstractThe preference–performance hypothesis for insect herbivores predicts that adult females should preferentially choose hosts on which their offspring perform better. We tested this hypothesis for the sunflower moth, Homoeosoma electellum (Hulst) (Lepidoptera: Pyralidae), using 16 sunflower (pre‐breeding) lines, derived from a number of wild species of Helianthus, including Helianthus annuus L., Helianthus deserticola Heiser, Helianthus paradoxus Heiser, Helianthus praecox Engelm. &amp; Gray ssp. hirtus (Heiser) Heiser, Helianthus praecox Engelm. &amp; Gray ssp. runyonii (Heiser) Heiser, Helianthus petiolaris Nutt., Helianthus resinosus Small, and Helianthus tuberosus L. (Asteraceae), that are suitable for introducing wild sunflower germplasm into commercial cultivars. Female moths showed a range of ovipositional preference measures to the various lines. Combined data for three Helianthus species represented by multiple lines showed significant differences in female preference with respect to the parental species. Larval performance, determined by proportion of infested neonate larvae reaching the pupal stage, or mean pupal weight, varied across the lines and, as for the female preference data, also showed significant differences among the three parental Helianthus species represented by multiple lines. These data suggest that the characteristics in the pre‐breeding lines influencing female sunflower moth preference and larval performance likely originate from the parental species and may be consistently transferred to the derived pre‐breeding lines. Of particular note with regard to potential plant resistance mechanisms, lines derived from H. tuberosus showed consistent low preference–performance measures. Female preference and larval performance (for both measures) were strongly correlated, indicating that females preferred plants and lines on which larvae performed better, in support of the preference–performance hypothesis.

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

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.

Crop domestication creates a refuge from parasitism for a native moth

Summary Insect herbivores are generally more abundant in agro‐ecosystems than in natural ecosystems. One possible cause is that artificial selection of crop plants may have disrupted parasitoid–herbivore interactions. We studied a native tritrophic system to determine if crop domestication has created a refuge for the sunflower moth Homoeosoma electellum from its major parasitoid Dolichogenidea homoeosomae. Parasitoid foraging behaviour on infested wild and agricultural sunflowers was studied using event‐recording software. We used detailed observations on larval feeding location and parasitoid probing behaviour to determine if the lower parasitism on agricultural sunflowers was the result of a structural refuge or a change in parasitoid foraging behaviour. Greater than 20 times more larvae fed on seeds of agricultural sunflowers than on seeds of wild sunflowers. Seed‐feeding enabled larvae to escape parasitoids because their ovipositors were too weak to penetrate the seed. As a consequence, larvae were more likely to be parasitized on wild sunflowers than on agricultural sunflowers, and floret‐feeding larvae were more likely to be parasitized than seed‐feeding larvae. Parasitoids were more stimulated to probe for larvae on wild sunflowers than on agricultural sunflowers. However, they responded to larval feeding location rather than plant genotype. Thus lower parasitism on agricultural sunflowers was due to a structural refuge for larvae rather than a change in parasitoid foraging behaviour. Synthesis and applications. Crop domestication has created a structural refuge from parasitism. The presence of refuges on agricultural plants helps explain why some insects are difficult to regulate using biological control. Studying parasitoid activity on wild relatives of agricultural plants can identify how plant variation contributes to the creation of a refuge. Beneficial plant traits can then potentially be bred back into the crop germplasm in order to enhance the biological control of insect pests in agroecosystems.

Crop domestication disrupts a native tritrophic interaction associated with the sunflower, Helianthus annuus (Asterales: Asteraceae)

Abstract. 1. Crop domestication has been a largely overlooked factor that may explain why insect herbivores tend to be more abundant and less attacked in agricultural habitats than in native habitats. This study explores how domestication of the sunflower, Helianthus annuus L., affects the sunflower moth, Homoeosoma electellum (Lepidoptera: Pyralidae), and its parasitoids.2. Common garden experiments were used to assess the effect of domestication on larval abundance in an agricultural and a native habitat. The effect of domestication on parasitism was determined using two studies: one study that manipulated nitrogen according to levels found in agricultural and native habitats, and a second common garden study in the native habitat.3. At peak infestation in the agricultural common garden, larval abundance was 10 times higher on agricultural plants than on wild plants. In contrast, larval abundance did not differ between plant genotypes in the native habitat.4. Larvae were four times more likely to be parasitised on wild sunflowers than on agricultural sunflowers, and three times more likely to be parasitised on low nitrogen plants than on high nitrogen plants. Parasitism did not differ between agricultural and wild plants in the native habitat, where flowers were more similar in size.5. Sunflower domestication has increased larval abundance, accelerated larval development, and lowered parasitism. The magnitude of the effect appears to depend upon nutrient availability. Thus, domestication can disrupt tritrophic interactions, and may help explain why some insect pests are more abundant and less attacked in agro‐ecosystems.

Confused by domestication: incongruent behavioral responses of the sunflower moth, Homoeosoma electellum (Lepidoptera: Pyralidae) and its parasitoid, Dolichogenidea homoeosomae (Hymenoptera: Braconidae), towards wild and domesticated sunflowers

Abstract Due to domestication, agricultural plants and their wild ancestors encompass a wide range of variation, which is useful for identifying promising plant attributes that promote parasitoid activity. We examined the behavioral responses of the sunflower moth, Homoeosoma electellum Hulst and its major parasitoid, Dolichogenidea homoeosomae Muesebeck to agricultural and wild sunflowers. We found that female moths preferred to land on, and lay more eggs on agricultural plants. While female parasitoids preferred to land on infested agricultural sunflowers, they foraged poorly on them. Parasitoids spent 74% more time foraging on wild flowers than on agricultural flowers, and they probed for a significantly longer period of time for host larvae on wild flowers. As a result, each individual female parasitized 25.7% ± 0.06 more larvae on wild flowers than on agricultural flowers with the same larval density. Also, parasitoids probed for hosts four times longer on wild flowers than on agricultural flowers, while resulting parasitism levels were 19 times higher, indicating that parasitoids were more efficient on wild flowers. Agricultural flowers are about four times larger than wild flowers, and the increase in flower size correlated with higher moth oviposition but lower parasitoid efficiency. Our results show that changes to plant attributes through domestication can disrupt host–parasitoid interactions and limit the ability of parasitoids to control insect pests effectively.

Abundance of a Native MothHomoeosoma electellum(Lepidoptera: Pyralidae) and Activity of Indigenous Parasitoids in Native and Agricultural Sunflower Habitats

Insect herbivores have been assumed to be more abundant in agricultural habitats than in native habitats; however, this hypothesis is rarely tested explicitly by comparing field populations of domesticated plants and their wild ancestors. This study examined the abundance of the sunflower moth, Homoeosoma electellum (Hulst), and its parasitism by natural enemies in agricultural and native sunflower habitats. Nutrient levels and plant population factors in the two habitat types were measured to identify factors associated with the patterns of herbivory and parasitism. Adult male and larval H. electellum were consistently more abundant in agricultural habitats. In contrast, parasitism of H. electellum was 6–10 times higher in native sunflower habitats than in agricultural habitats. Also, fewer parasitoid species were found in agricultural habitats, and parasitism by individual parasitoid species was reduced by 90%. Larval densities per flower head were higher on agricultural plants, but parasitoids failed to respond to the higher densities. The relationship between flower age and larval infestation differed between agricultural and wild flowers; larval age tracked agricultural flower age, but on wild flowers, larvae moved from older to younger flowers. Among the three nutrients sampled, only nitrogen was positively correlated with habitat differences. These results indicate that patterns of trophic interactions varied by habitat type and were related to plant phenotypic changes and environmental habitat factors such as crop domestication, nitrogen fertilization, and plant phenology.

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.

Very Long-Chain Methyl-Branched Alcohols and Their Acetate Esters in the Internal Lipids of Lepidopteran Pupae: Cochylis hospes, Diatraea grandiosella, Homoeosoma electellum, Heliothis virescens and Helicoverpa zea

Very long-chain methyl-branched alcohols (VLMA; C35 > C46) and their acetate esters were characterized in the internal lipids of developing mid-stage pupae of the banded sunflower moth Cochylis hospes, the southwestern corn borer Diatraea grandiosella, the sunflower moth Homoeosoma electellum, the tobacco budworm Heliothis virescens and the corn earworm Helicoverpa zea. Minor amounts of long-chain methyl-branched alcohols (LMA; C25–C34) were also found largely in H. virescens and H. zea. Five homologous series of primary alcohols were identified in all species: n-alcohols, internally branched monomethyl alcohols, 2 series of dimethyl branched alcohols, and a series of trimethyl branched alcohols. The 4 methyl-branched series were characterized, e.g., by one of their major components: 24-methyltetracontanol, 24,28-dimethyltetracontanol, 24,36-dimethyltetracontanol, and 24,28,36-trimethyltetracontanol. A fifth methyl-branched series was identified only in H. electellum, the internally branched trimethyl alcohols characterized by 22,26,30-trimethyltetracontanol. The incorporation of [3H]acetate and [1-14C]propionate into the internal lipids of mid-stage pupae (developing pharate adults) of H. electellum and H. virescens, showed that polar lipids, and VLMA and their acetate esters, were the major lipid classes synthesized from acetate. The major lipid classes synthesized from propionate, the precursor of the methyl branches, were the methyl-branched lipids, e.g., VLMA and their acetate esters and hydrocarbons. Aldehydes also were a component in H. virescens but did not incorporate radioactivity. The wax ester fraction of H. virescens incorporated radioactivity which was limited to the fatty acid moieties.

Effect of Thermoperiod and Photoperiod on the Eclosion Rhythm of the Sunflower Moth (Lepidoptera: Pyralidae)

The sunflower moth, Homoeosoma electellum (Hulst), has a distinct eclosion rhythm in either a light–dark constant temperature photoperiod, or in constant darkness, or in constant light with alternating temperatures. Eclosionis arrhythmic in either constant light or constant darkness with constant temperatures. With a 12:12 light–dark, constant-temperature regimen, there is a broad eclosion peak occurring over ≍6 h before lights turn off as well as over the first part of the dark phase. Some individuals eclose during all hours of the day regardless of the regimen. With a regimen of 12 h each at 26° and 17°C. (both in constant light or darkness or light–dark with the low temperature during the dark), a bimodal periodicity of eclosion is initiated with a high peak immediately preceding the temperature drop and a low peak shortly after the temperature rise. The rhythm damps out rather quickly in constant darkness at constant temperatures.