Sesamia Nonagrioides Research Articles

Molecular changes in the maize composite EPS12 during selection for resistance to pink stem borer

The pink stem borer (Sesamia nonagrioides Lefèvbre) is the most important pest of maize (Zea mays L.) throughout the Mediterranean area. The maize composite EPS12 has been chosen as the base population for a breeding program based on its resistance to pink stem borer, with the main selection criterion being resistance to stem tunneling. Yield was taken as a secondary selection criterion to avoid any unwanted negatively correlated response on this character. The aims of investigation were: (1) to monitor the effects of selection for resistance to pink stem borer on allele frequency at 70 simple sequence repeat (SSR) markers and their impact on the genetic structure of EPS12 and (2) to identify loci at which allelic frequencies changed significantly due to directional selection. Genetic diversity was reduced during the selection process (as expected since random genetic drift as well as selection could reduce genetic variability), but not significantly so. Although the loss of genetic variation was generally consistent with that expected in a model in which random genetic drift acts alone on neutral alleles, the changes observed in the frequency of five alleles were significantly greater than expected. Further, the linear trend of the departure from the random genetic drift model was significant for some allelic versions of two SSR markers, umc1329 and phi076; directional selection was therefore acting on these loci. The significant effect of directional selection on those markers suggests the presence of quantitative trait loci (QTLs) for tunnel length and/or for yield under artificial infestation with Sesamia nonagrioides on the long arm of chromosome 4.

Vegetative Phase Transition and Corn Borer Resistance of shrunken2 versus sugary1 Sweet Corn Near-isogenic Inbred Lines

The genes sugary1 (su1) and shrunken2 (sh2) are commonly used to produce sweet and super-sweet corn (Zea mays L.), respectively. In this work we compare corn borer [european corn borer (ECB) (Ostrinia nubilalis Hbn.) and pink stem borer (PSB) (Sesamia nonagrioides Lef.)] susceptibility in seven pairs of su1 and sh2 near-isogenic sweet corn inbreds (101t, C23, C40, C68, Ia453, Ia5125, and P39) and the relationship between corn borer resistance and vegetative phase transition. The seven pairs of near-isogenic inbreds were evaluated under corn borer infestation during 3 years in northwestern Spain. Differences among inbreds were significant for most of the traits, although resistance was partial. Ia5125su1 and C40su1 were the most resistant inbreds. Differences between a few pairs of near-isogenic su1 and sh2 strains were significant for some vegetative phase change and corn borer damage-related traits. Generally su1 strains flowered earlier, had a shorter juvenile phase, fewer PSB, and more ECB larvae than sh2 strains. However su1 and sh2 strains did not differ significantly for most traits related to phase transition and corn borer damage; notably ear damage was not significantly different between su1 and sh2 strains. These results suggest that theoretical and practical results of sweet corn (sugary1) breeding for corn borer resistance could be capitalized for super-sweet corn (shrunken2) breeding.

Dispersal capacity in the Mediterranean corn borer, Sesamia nonagrioides

AbstractCorn (Zea mays L.) borers are the primary target of Bacillus thuringiensis Berliner (Bt) transgenic maize. Management of corn borer resistance to Bt requires information on larval and adult dispersal capacities, a feature that is particularly unknown in Sesamia nonagrioides Lefèbvre (Lepidoptera: Noctuidae), the most damaging corn borer in Spain. Larval dispersal was studied over a 3 year period by infesting plants with egg masses and dissecting the neighbouring plants 7, 14, and 32 days later to measure larval dispersal at several ages. The number and age of larvae were recorded in the dissected plants. Only mature larvae dispersed in significant numbers; they moved at least to rows adjacent to those containing the infested plant, and down the row five plants. The percentage of larvae that dispersed from the infested plant was density‐dependent. Adult dispersal was studied with directional light and pheromone uni‐traps over 5 and 3 year periods, respectively. Directional light traps were placed in the margins between Bt and non‐Bt maize fields, half oriented towards each of the two kinds of maize field. Pheromone traps were placed in the Bt and non‐Bt fields at increasing distances (0–100 m) from the border. The numbers of males and females caught in directional light traps were not different in traps oriented towards Bt or non‐Bt fields, but the number of males caught in the third flight in Bt fields was lower than in non‐Bt fields. These results suggest that males from adjacent Bt and non‐Bt fields mate indiscriminately with females emerging in any of the two kinds of maize fields. However, male movement in the third flight may not be sufficient to randomly distribute males between the two fields.

Resistance of early maturing sweet corn varieties to damage caused by Sesamia nonagrioides (Lepidoptera: Noctuidae).

In Mediterranean countries, the principal pest of maize, Zea mays L., is Sesamia nonagrioides Lefebvre. The objective of this work was to study the resistance of the four early maturing varieties of sweet corn, Baby Orchard, Orchard Baby, Dorinny Sweet, and Golden Early Market, and to check the relationship among resistance to S. nonagrioides and infestation dates. In a previous study, these varieties had showed a confusing behavior, being the most resistant varieties to S. nonagrioides attack in some environments and the most susceptible in others. These varieties were again evaluated along with three medium maturing varieties, used as testers because they were more stable in both environments, by using two infestation dates. Plants were more damaged in the late infestation, but the effect of the infestation depends on the variety studied. Orchard Baby and Baby Orchard were the most resistant varieties under two infestation dates. These two varieties are closely related. Therefore, we can use either one as a source of precocity and resistance for modern sweet corn. Although many studies showed that early maturing inbreds had greater damage caused by S. nonagrioides and European corn borer than late maturing inbreds and hybrids, our results showed that the earliest maturing varieties were the most resistant.

Reproductive responses to photoperiod and temperature by diapausing and nondiapausing populations of Sesamia nonagrioides Lef. (Lepidoptera − Noctuidae)

Abstract. The influence of long‐ and short‐day cycles on ovipostion and egg hatch of the corn stalk borer, Sesamia nonagrioides were investigated at a range of temperatures. Oviposition was suppressed when insects are exposed to long days through their immature stages and then transferred to short days after mating. Moreover, mean oviposition and egg hatch increased from 15 to 27.5 °C, whereas oviposition declined significantly at 30 °C at both photoperiodic regimes. Females derived from a diapausing population exposed to long days after mating showed a significantly higher egg production compared to females derived from a nondiapausing population. However, when females from a diapausing population were left to oviposit under short days, fewer eggs were produced compared to those exposed to long days after mating. Thus, photoperiod appears to affect reproductive traits of this species in a quantitative manner. Larval diapause duration is positively correlated with fecundity of the adults. There is also a positive correlation between pupal weight of individuals derived from a diapausing population and the postdiapause fecundity of adults.

Yield Evaluation of Maize Cultivars across Environments with Different Levels of Pink Stem Borer Infestation

Yield under infestation by the pink stem borer [Sesamia nonagrioides (Lefebvre)] has been proposed as the best estimator of maize (Zea mays L.) performance under pink stem borer attack. Yield is a complex trait that greatly interacts with the environment. Several methods could be used to study the genotype × environment (GE) interaction. The objective of this work was to study the GE interaction for yield of 49 maize hybrids in five different environments by the Site Regression (SREG) and factorial regression methods. Locations presented different levels of natural infestation by the pink stem borer. The biplot obtained by applying the SREG method allowed visual cultivar evaluation. The factorial regression method incorporated genotypic and environmental covariates that enhanced biological interpretation of GE interaction. Hybrid A637 × EP42 would be recommended in northwestern Spain under medium and high natural infestation by the pink stem borer because it showed high and stable yielding ability. Genotypic and environmental covariates explained approximately 75% of the GE interaction variation, but other genotypic covariates could be introduced in the model to reduce GE residual variation to a nonsignificant level. In general, GE effects for grain yield were mainly due to earliness, vigor effects, and environmental yield limiting factors such as the mean of minimum temperature and percentage of air humidity.

Sex allocation in Telenomus busseolae, a solitary parasitoid of concealed eggs: the influence of host patch size

Abstract Telenomus busseolae Gahan (Hymenoptera: Scelionidae) is an important egg parasitoid of noctuid stem borers of gramineous crops, attacking egg masses of Sesamia spp. Under natural conditions, and whatever the host species attacked, these egg masses are generally concealed under the leaf sheaths or other narrow spaces, and vary greatly in size. In the work presented here, the influence of host patch size (4, 8, 16, 32, 64, or 128 eggs per mass) on the sex ratio and sex sequence pattern of ovipositing T. busseolae was investigated in the laboratory using Sesamia nonagrioides (Lefebvre) (Lepidoptera: Noctuidae) as host. The results are similar to those described for other parasitoids of aggregated hosts, and are in accordance with the Local Mate Competition model. With increasing egg mass size, the overall sex ratio (proportion of males) decreased, although additional males were laid at the end of the sequence in the larger masses (64 and 128 eggs). Sex sequence pattern always followed a males‐first strategy, i.e., with a higher proportion of males at the beginning, but the whole sex ratio sequence was influenced by the size of the egg mass. Such results in a parasitoid of concealed eggs are compared to those observed in parasitoids of exposed eggs and discussed in terms of parasitoid reproductive strategies and evolutionary adaptations.

Evaluation of the European Union Maize Landrace Core Collection for resistance to Sesamia nonagrioides (Lepidoptera: Noctuidae) and Ostrinia nubilalis (Lepidoptera: Crambidae).

Two corn borer species are the principal maize insect pests in Europe, the European corn borer, Ostrinia nubilalis (Hübner), and the pink stem borer, Sesamia nonagrioides (Lefebvre). Hence, it would be advisable to evaluate the European maize germplasm for corn borer resistance to generate European varieties resistant to corn borer attack. The creation of the European Union Maize Landrace Core Collection (EUMLCC) allowed the screening of most of the variability for European corn borer resistance present among European maize local populations from France, Germany, Greece, Italy, Portugal, and Spain, testing a representative sample. The objective of this study was the evaluation of stem and ear resistance of the EUMLCC to European corn borer and pink stem borer attack. Trials were made at two Spanish locations that represent two very different maize-growing areas. Populations that performed relatively well under corn borer infestation for stem and ear damage were 'PRT0010008' and'GRC0010085', among very early landraces; 'PRT00100120' and 'PRT00100186', among early landraces; 'GRC0010174', among midseason landraces; and 'ESP0070441', among late landraces. Either the selection that could have happen under high insect pressure or the singular origin of determined maize populations would be possible explanations for the higher corn borer resistance of some landraces. Landraces 'PRT0010008', 'FRA0410090', 'PRT00100186', and 'ESP0090214' would be selected to constitute a composite population resistant to corn borers and adapted to short season, whereas populations 'ESP0090033', 'PRT00100530', 'GRC0010174', and 'ITA0370005' would be used to make a resistant composite adapted to longer season.

Responses of the olfactory receptor neurons of the corn stalk borer Sesamia nonagrioides to components of the pheromone blend and their inhibition by a trifluoromethyl ketone analogue of the main component.

Two types of olfactory hairs and three types of olfactory receptor neurons (ORN) have been characterized on the antennae of male Sesamia nonagrioides Lef for the first time. Type A sensilla housed a cell which fired large spikes in response to (Z)-11-hexadecenyl acetate (Z11-16:Ac), the major component of the sex pheromone, and a second cell firing smaller spikes in response to (Z)-11-hexadecenal (Z11-16:Ald), a minor component of the pheromone blend. Type B sensilla housed one cell firing large spikes to Z11-16:Ac and a cell firing smaller spikes to another minor component of the pheromone blend, (Z)-11-hexadecenyl alcohol (Z11-16:OH). No cell responding to dodecyl acetate, another minor component of the natural extract, was found. Fluorinated ketones were tested as inhibitors of the cell responses to pheromone compounds. The fluorinated derivatives tested, (Z)-11-hexadecenyl trifluoromethyl ketone (Z11-16:TFMK), n-hexadecyl trifluoromethyl ketone (16:TFMK), (Z,E)-9,11-tetradecadienyl trifluoromethyl ketone (Z9,E11-14:TFMK), 3-octylthio-1,1,1-trifluoropropan-2-one (OTFP), (Z)-11-tetradecenyl trifluoromethyl ketone (Z11-11:TFMK) and 1,1-difluoro-(Z)-11-hexadecenyl methyl ketone (Z11-16:DFMK), had no or only weak excitatory effects. However, the neuron responses to the pheromone compounds were significantly decreased in the presence of a constant stimulation with Z11-16:TFMK and the effect was reversible. The latencies of the responses to the acetate and aldehyde cells were significantly increased. The effects were not specific, since Z11-16:TFMK also inhibited the responses of the ORNs of Spodoptera littoralis Boisd. Correspondingly, Z9,E11-14:TFMK, an analogue of the main component of the pheromone of this latter insect, inhibited responses of S nonagrioides ORNs. Implications of these results on the utilization of Z11-16:TFMK as a communication disruptant are discussed.

Mean generation analysis of the damage caused by Sesamia nonagrioides (Lepidoptera: Noctuidae) and Ostrinia nubilalis (Lepidoptera: Crambidae) in sweet corn ears.

Sesamia nonagrioides (Lefebvre) and Ostrinia nubilalis (Hübner) are the main maize (Zea mays L.) pests in Mediterranean countries. To develop insect-resistant cultivars, it is helpful to know the genetic control of the resistance. Our objective was to determine the genetic control of the resistance to both borers. For each of two crosses (EP59 x P51 and 15125 x EP61), six generations were evaluated (P1, P2, F1, F2, BC1, and BC2). Genetic effects x environment interactions were not significant. For the O. nubilalis resistance traits; both crosses fitted an additive-dominance model. EP59 x P51 had important dominance and additive effects, whereas for 15125 x EP61 we did not detect significant genetic effects, but significant year effects were detected. For S. nonagrioides infestation, both crosses fitted to an additive-dominance model. There were additive effects for most traits in EP59 x P51. The cross I5125 x EP61 showed significant dominance effects for several traits. Resistance to both corn borers fit an additive-dominance model, but genetic effects depend on the cross evaluated. In the resistance to S. nonagrioides, additive effects were important for shank resistance, which is a useful trait for avoiding S. nonagrioides damage on the ear. Early sowings are recommended to make good use of the resistance to both corn borers. In the late sowings, damage is so high that resistant plants are not able to control the pest.

Resistance monitoring of field populations of the corn borers Sesamia nonagrioides and Ostrinia nubilalis after 5 years of Bt maize cultivation in Spain

AbstractApproximately 22 000 hectares (5% of the total maize growing area) of transgenic maize expressing the Cry1Ab toxin from Bacillus thuringiensis (Bt maize) have been planted annually in Spain since 1998. Changes in the susceptibility to Cry1Ab of Spanish populations of the Mediterranean corn borer (MCB), Sesamia nonagrioides (Lefebvre) (Lepidoptera: Noctuidae), and the European corn borer (ECB), Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), were assessed by annual monitoring on Bt maize fields. No increase in resistance was detected in the MCB populations from Ebro, Albacete, and Badajoz, nor in the ECB populations from Ebro and Badajoz during the period 1999–2002. The susceptibility of the MCB population from Madrid fluctuated from year to year, but a gradual trend towards higher levels of tolerance was not observed. Laboratory selection assays for eight generations yielded selected strains of MCB and ECB that were 21‐ and 10‐fold significantly more tolerant to Cry1Ab than the corresponding unselected strains, respectively. Nevertheless, none of the field‐collected or laboratory‐selected larvae were able to survive on Bt maize. Considering these data, no consistent shifts in susceptibility were found for Spanish populations of MCB nor ECB after 5 years of Bt maize cultivation, but systematic field monitoring needs to be continued.

Development of Immature Stages of <I>Sesamia nonagrioides</I> (Lepidoptera : Noctuidae) Under Alternating and Constant Temperatures

Laboratory studies on the temperature-dependent development of Sesamia nonagrioides (Lefebvre) were performed under five constant temperatures ranging from 20 to 30°C as well as under the corresponding alternating temperatures of 25:10, 27.5:12.5, 30:15, 32.5:17.5, and 35:20°C, at a photoperiod of 16:8 (L:D) h. Both linear and nonlinear (Lactin formula) models provided a reliable fit of developmental rates versus temperature for all immature stages either at constant or alternating temperatures. Developmental thresholds that were estimated by a linear model for eggs, larvae, or pupae were approximately the same and estimated to be 10.57, 8.89, and 10.75°C, respectively, at constant temperatures. Lower values were estimated when immature stages were exposed to the corresponding alternating temperatures (7.23, 6.20, and 6.50°C for eggs, larvae, and pupae). Therefore, the evaluation of the development of immature stages under constant temperatures resulted in an overestimation of the lower thresholds. The Lactin-2 model also was applied, and larval and egg developmental thresholds did not differ from those that were estimated by the linear model. Differences, however, occurred at the pupal stage. Nevertheless, the differences in the estimated values of the lower developmental thresholds of the immature stages under constant or alternating temperatures indicate that a model predicting phenology in the field should be based on fluctuating temperature.

Relationship between maize stem structural characteristics and resistance to pink stem borer (Lepidoptera: Noctuidae) attack.

The pink stem borer, Sesamia nonagrioides (Lefebvre), is one of the most important insect pests of maize (Zea mays L.) in northwestern Spain. The objectives of this work were to evaluate, at different times during the growth of maize, structural traits related to the entry point and tissues on which larvae feed and to determine the relationship between these structural traits and the stem borer resistance. Six inbred lines with different levels of stem resistance to S. nonagrioides were evaluated in several trials. Potential structural resistance factors included rind and pith puncture resistance (RPR and PPR), rind thickness, length of the meristematic area (LMA), and pith parenchyma interlumen thickness (PPIT). Surprisingly, the inbred lines that showed the strongest stalks, EP42 and EP47, were not stem resistant to pink stem borer attack, while the stem resistant inbreds A509, CM151, and PB130 were among the least resistant to rind puncture. There were no significant differences among resistant and susceptible inbreds for the rind thickness. However, the susceptible inbred EP42 had the softest internode pith, and the resistant inbred PB130 showed the hardest, as was expected. Susceptible inbred lines in general showed higher values for the LMA, while the PPIT was important for individual inbreds. The results suggest that the usefulness of these characters as estimators of pink stem borer resistance is limited to some genotypes. Besides, even among those genotypes, other mechanisms of resistance that do not involve stalk strength could be present. Among the traits considered, the LMA was the most promising as an indicator of resistance to pink stem borer, although further experimentation is necessary.

Relationship Between Maize Stem Structural Characteristics and Resistance to Pink Stem Borer (Lepidoptera: Noctuidae) Attack

The pink stem borer, Sesamia nonagrioides (Lefebvre), is one of the most important insect pests of maize (Zea mays L.) in northwestern Spain. The objectives of this work were to evaluate, at different times during the growth of maize, structural traits related to the entry point and tissues on which larvae feed and to determine the relationship between these structural traits and the stem borer resistance. Six inbred lines with different levels of stem resistance to S. nonagrioides were evaluated in several trials. Potential structural resistance factors included rind and pith puncture resistance (RPR and PPR), rind thickness, length of the meristematic area (LMA), and pith parenchyma interlumen thickness (PPIT). Surprisingly, the inbred lines that showed the strongest stalks, EP42 and EP47, were not stem resistant to pink stem borer attack, while the stem resistant inbreds A509, CM151, and PB130 were among the least resistant to rind puncture. There were no significant differences among resistant and susceptible inbreds for the rind thickness. However, the susceptible inbred EP42 had the softest internode pith, and the resistant inbred PB130 showed the hardest, as was expected. Susceptible inbred lines in general showed higher values for the LMA, while the PPIT was important for individual inbreds. The results suggest that the usefulness of these characters as estimators of pink stem borer resistance is limited to some genotypes. Besides, even among those genotypes, other mechanisms of resistance that do not involve stalk strength could be present. Among the traits considered, the LMA was the most promising as an indicator of resistance to pink stem borer, although further experimentation is necessary.

Photoperiodic and temperature effects on the intensity of larval diapause in Sesamia nonagrioides

Abstract. The intensity of larval diapause in Sesamia nonagrioides Lef (Lepidoptera: Noctuidae) was investigated under laboratory conditions. Newly hatched larvae were exposed to different stationary photoperiods (from LD 7 : 17 h to LD 14 : 10 h), at a constant temperature of 25 °C. Diapause incidence was higher when larvae were exposed to daylengths shorter than the critical value (LD 12 : 12 h), whereas the within‐treatment variation in the larval period appeared to be significantly correlated with the photoperiod applied. The incidences of diapause and the duration of larval development were also measured after exposing larvae to short photoperiods (LD 8 : 16 h, LD 10 : 14 h or LD 12 : 12 h) in combination with various temperatures (20, 22.5 or 25 °C). Although an increase in the incidence of diapause appeared with the lowering of the temperature, no statistical differences were observed in the time needed for pupation within the photoperiodic treatments at the temperatures of 20 and 22.5 °C. Furthermore, when diapausing larvae were transferred to the long photoperiod of LD 16 : 8 h, they immediately proceeded to pupation, regardless of the photoperiod or the temperature to which they had been previously exposed, indicating that there were no differences in the intensity of diapause. Photoperiodic changes from LD 10 : 14 h to LD 12 : 12 h or to LD 14 : 10 h at different larval ages reduced the intensity of diapause with (a) early age of transfer and (b) increase of daylength. By contrast, when larvae were transferred from the long photoperiod of LD 14 : 10 h to shorter, such as LD 10 : 14 h or LD 12 : 12 h, a small increase in the intensity of diapause with the shortening of the daylength was apparent. These results support the hypothesis that insects may compare the duration of the photoperiod and could classify them as either longer or shorter in relation to the critical value.

SURVEY OF THE INSECT POPULATION ON A PROTEA PLANTATION IN THE SOUTHWEST OF PORTUGAL

During June and July of 1999, a Protea plantation was established in Zambujeira do Mar, in the Southwest of Portugal. The plantation comprised a diversity of species and varieties of Protea, Leucadendron and Leucospermum along with species from different families in the Fynbos. Since then, work has been done in order to define the insect populations affecting the Proteaceae. It is our goal to know the main pests causing damage to the crop and to identify the beneficials present in order to establish an IPM program for the crop in the region. The plantation was established late in the season in 1999, but in the first year we immediately identified two key pests, Helicoverpa armigera and Sesamia nonagrioides, and could observe the importance of the beneficial insect population. In the spring of 2000, pheromone traps for the two Lepidoptera species were installed and a weekly survey in the fields was started, The survey was repeated in 2001. From these preliminary surveys, we compiled information on the insect population and dynamics in the fields. The H. armigera and S. nonagrioides populations in 2000 reached levels that required six to eight insecticide treatments. In 2001, these pests were replaced in importance by a secondary pest of 2000, the Torticidae Cacoecimorpha pronubana. Its attacks again justified insecticide interventions. Other pests identified were mainly scale insects, mealybugs, stink bugs, weevils and leafhoppers. Among the beneficial insects, we identified several species of Coccinelidae, Cantharidae, Anthocoridae, Chrysopidae, Ichneumonidae and Braconidae.

Thermoperiodic effects on diapause of Sesamia nonagrioides (Lepidoptera: Noctuidae)

The role of the thermophotoperiod on larval diapause induction and development of Sesamia nonagrioides was investigated under laboratory conditions. The incidences of diapause by TC 12 : 12 thermoperiods under DD, in which the thermophase was 30°C and cryophases varied from 10 to 25°C, were compared to the effects of thermophotoperiods with the same configuration. Higher incidences of diapause were recorded when larvae were exposed to thermophotoperiods with cryophases of 15-25°C, than under thermoperiods under constant darkness. In addition, larvae exhibited significantly lower percentages of diapause when exposed to cryophases < 15°C under either thermo- or thermophotoperiodic condition. Diapausing larvae when exposed to photoperiods 16L : 8D h and different temperatures of 25-30°C proceeded to development in 14-16 days. Moreover time needed for the pupation of diapausing larvae after their transfer to 12L : 12D h, was reduced from approximately 49 to 12 days depending on temperatures of exposures (25-30°C). Diapause termination was also compared under 12L : 12D h and constant temperature of 25°C or a thermoperiod of TC 12:12 (30°: 20°). Days needed for pupation at constant temperature or under the mentioned thermoperiodic regime, were approximately the same when the high temperature of the thermoperiod coincided with the scotophase, while with the co-occurrence of the high temperature of the thermoperiod and the photophase significantly additional time was needed for diapause development. Significantly shorter time was also needed for diapause development after exposure of diapausing larvae to continuous light, than to continuous darkness under 25°C. Thermoperiods of different amplitudes with the same mean temperatures proved that the higher temperature of scotophase led to higher rate of diapause development in spite of the relatively low temperature of the photophase tested. It is suggested that thermoperiod could hasten the time needed for diapause development, but it is not the crucial factor for the termination of diapause.

Chemical stimuli from corn plants affect host selection and oviposition behavior of Sesamia nonagrioides (Lepidoptera: Noctuidae).

The role of chemical stimuli in host selection and oviposition of Sesamia nonagrioides (Lef) was studied in the laboratory using eight corn hybrids. Female oviposition preference was evaluated on plants of the eight hybrids, their extracts in pentane and methanol, and volatiles collected by steam distillation in ether. Results from two-choice bioassays indicate various degrees of female preference to the hybrids. Four hybrids received more eggs than control plants, whereas the remainder received fewer eggs. Relatively similar results were obtained when filter paper sticks baited with pentane and steam distillation extracts were evaluated. Methanol extracts from all eight hybrids received fewer eggs than the methanol controls. Results showed that pentane and steam distillation extracts contain chemicals that elicit female oviposition response, while methanol extracts may contain chemicals that deter or repel females to oviposition.

New fluorinated derivatives as esterase inhibitors. Synthesis, hydration and crossed specificity studies

A variety of new fluorinated chemicals have been prepared for the first time and tested as inhibitors of esterases, one of the main enzymes involved in pheromone catabolism, in two economically important pests, the Egyptian armyworm Spodoptera littoralis ( SL) and the Mediterranean corn borer Sesamia nonagrioides ( SN). Using the respective major component of the pheromone as substrate, the K m and V max of the antennal esterase of both insects resulted to be 5.66×10 −4 M and 8.47×10 −6 Mmin −1 for SL and 1.61×10 −7 M and 1.25×10 −7 Mmin −1 for SN, pointing out that SN esterase has a higher affinity for its corresponding substrate than SL. In general, the trifluoromethyl ketones (TFMKs) exhibited higher inhibitory potency than the corresponding difluoromethyl ketones (DFMKs) or difluoroaldehydes (DFAs). The compounds appeared to hydrate differently in aqueous solution, the extent of hydration following the order: α,α-DFMKs<α,α-difluoro-β-thioalkylmethyl ketones<TFMKs<β-thiotrifluoromethyl ketones<α,α-DFAs. No clear correlation has been found between the K hyd and the inhibitory potency and no specificity has been found when the chemicals were assayed on extracts of both insects.

Activity of octylthiotrifluoropropan-2-one, a potent esterase inhibitor, on growth, development, and intraspecific communication in Spodoptera littoralis and Sesamia nonagrioides.

A series of experiments were conducted to examine the effect of 3-octylthio-1,1,1-trifluoro-2-propanone (OTFP) on growth, development, and behavior of the cotton leafworm, Spodoptera littoralis (Lepidoptera: Noctuidae), and the corn stalk borer, Sesamia nonagrioides (Lepidoptera: Noctuidae). The chemical behaved as an oviposition deterrent and, when added to the diet of the second-instar larvae of both insects, reduced diet consumption and growth, pupation, and adult emergence. Treatment of 100-5000 ng of the compound on fourth-instar larvae for 3-24 h, however, did not produce significant differences in the amount of diet ingested. Our results suggest that the effect of OTFP is long-lasting and that the inhibitor is not fully detoxified by the detoxification enzymes of the digestive tract of the insects. In behavioral assays, adult males which had been treated with the chemical at the larval stage were less attracted to the pheromone source than regular untreated males. When Sp. littoralis untreated females were used as the attractant source, treated males also displayed significantly fewer contacts with the cage-containing females than untreated or solvent-treated males. In the presence of treated females, only 27% of treated males successfully completed the flight in comparison to animals responding to solvent-treated females (54.5%). By contrast, when Se. nonagrioides females, whether they had been subjected or not to the treatment, were used as the attractant source, males were similarly attracted to them regardless of whether they had been treated or not at the larval stage. Analyses of gland extracts of Sp. littoralis treated females showed no difference from control insects in the qualitative or quantitative composition of the pheromone blend. The results obtained, in combination with other results previously reported by us (Riba, M.; Sans, A.; Bau, P.; Grolleau, G.; Renou, M.; Guerrero, A. J. Chem. Ecol. 2001, 27, 1879-1897), provide new and relevant information about the possible utility of these chemicals in future studies directed to the development of new approaches for pest control.