Survey of Natural Enemies of the Invasive Boxwood Moth Cydalima perspectalis in Southwestern Mediterranean Europe and Biocontrol Potential of a Native Beauveria bassiana (Bals.-Criv.) Vuill. Strain.

Cydalima perspectalis (Lepidoptera: Crambidae), a species native to East Asia, has been especially devastating in the Mediterranean region and Catalonia, northeast Spain, where Buxus sempervirens is an essential component of the natural forest. As an invasive species, the lack of biotic mortality factors in the arrival region has been one of the main factors allowing its expansion. Therefore, this study aimed to collect and identify possible indigenous natural enemies adapting to the new species in the boxwood of the southwest Mediterranean region. Later, the efficacy of some of the collected species for controlling C. perspectalis larvae was tested in laboratory conditions. The larval collection was carried out in successive years in the boxwood of the region. Several collected larvae were infected with an entomopathogen, Beauveria bassiana, or parasitized by Compsilura concinnata, both common in native Lepidoptera caterpillars. The B. bassiana strain was found to be highly virulent against the developed larvae of C. perspectalis, which suggests that B. bassiana may be an effective treatment in parks and gardens when the first overwintering larvae are detected. The biology of the parasitoid identified is not very well known in Europe, which suggests the necessity of studying its biology and alternative hosts in the region in order to improve its population.

Lymantria dispar (L.) (Lepidoptera: Erebidae): Current Status of Biology, Ecology, and Management in Europe with Notes from North America.

The European Spongy moth, Lymantria dispar (L.) (Lepidoptera: Erebidae), is an abundant species found in oak woods in Central and Southern Europe, the Near East, and North Africa and is an important economic pest. It is a voracious eater and can completely defoliate entire trees; repeated severe defoliation can add to other stresses, such as weather extremes or human activities. Lymantria dispar is most destructive in its larval stage (caterpillars), stripping away foliage from a broad variety of trees (>500 species). Caterpillar infestation is an underestimated problem; medical literature reports that established populations of caterpillars may cause health problems to people and animals. Inflammatory reactions may occur in most individuals after exposure to setae, independent of previous exposure. Currently, chemical and mechanical methods, natural predators, and silvicultural practices are included for the control of this species. Various insecticides have been used for its control, often through aerial sprayings, which negatively affect biodiversity, frequently fail, and are inappropriate for urban/recreational areas. However, bioinsecticides based on various microorganisms (e.g., entomopathogenic viruses, bacteria, and fungi) as well as technologies such as mating disruption using sex pheromone traps have replaced insecticides for the management of L. dispar.

Parental effects of Bt toxin and vitamin A on Helicoverpa armigera.

The increase in the area cultivated with vitamin-enriched transgenic crops producing Bt toxin raises the question of whether the addition of vitamins will in any way mitigates the effect of the toxin on the phytophagous insects that feed on those crops. On the other hand, the parental effect that feeding on these enriched transgenic crops may have on the offspring of the phytophagous that survive on them is not well known. In this work, the effect of vitamin A (ß-carotene) addition to diets with or without Bt toxin on Helicoverpa armigera larvae and their offspring was determined. The addition of vitamin A did not have any beneficial effect either for the larvae fed on enriched diets nor for their offspring. However, parental effects due to dietary feeding with the toxin were detected since adults from larvae fed on the Bt diet had higher mating success than those fed on the toxin-free diet, although there were no differences on the fertility of mated females regardless of whether their previous larvae fed on the Bt or non-Bt diet. A certain adaptive effect to the toxin was also noted since the mortality of larvae whose previous generation fed on diet with Bt was lower than that of the larvae that came from larvae fed on a non-Bt diet. It would be interesting to determine if H. armigera adults prefer to mate and lay eggs in the same type of crops in which they have developed or if feeding on different crops, such as corn or alfalfa, causes different paternal effects on the offspring. These aspects can be of great importance in the development of resistance of this species to the Bt toxin.

Fitness Costs of Two Maize Lepidopteran Pests Fed on Bacillus thuringiensis (Bt) Diets Enriched with Vitamins A and C.

Serious malnutrition problems occur in developing countries where people's diets are mainly based on staple crops. To alleviate this, high-production crops are being developed that are better adapted to climate change, enriched in micronutrients and vitamins, or resistant to pests. In some cases, new varieties have been developed with several of the characteristics mentioned above, such as biofortified and pest-resistant crops. The development of biofortified Bacillus thuringiensis (Bt) crops raises the question of whether vitamin enrichment of Bt crops can in any way favor those pests that are not very susceptible to the Bt toxin that feed on these crops, such as Helicoverpa armigera (Hübner) or Mythimna unipuncta (Haworth) (Lepidoptera: Noctuidae). In this study, the response to a Bt diet enriched with vitamins A (ß-carotene) and C (ascorbic acid) was somewhat different between the two species. M. unipuncta was less sensitive to the toxin than H. armigera, although the ingestion of the Bt diet resulted in oxidative stress (longer larval development and lower pupal weight) which was not mitigated by the vitamins. However, the two vitamins reduced the mortality of H. armigera larvae fed on a Bt-enriched diet; in addition, ß-carotene reduced the activity of the antioxidant glutathione S-transferase (GST) of both species, suggesting it has an antioxidant role. The results obtained here indicate that biofortified Bt crops will not favor the development of H. armigera very much and will not affect M. unipuncta's development at all, although the effect of the increase in vitamins may be very variable and should be studied for each specific phytophagous.

ß-carotene and Bacillus thuringiensis insecticidal protein differentially modulate feeding behaviour, mortality and physiology of European corn borer (Ostrinia nubilalis).

Maize with enhanced ß-carotene production was engineered to counteract pervasive vitamin A deficiency in developing countries. Second-generation biofortified crops are being developed with additional traits that confer pest resistance. These include crops that can produce Bacillus thuringiensis Berliner (Bt) insecticidal proteins. Currently, it is unknown whether ß-carotene can confer fitness benefits through to insect pests, specifically through altering Ostrinia nubilalis foraging behaviour or development in the presence of Bt insecticidal toxin. Therefore the effects of dietary ß-carotene plus Bt insecticidal protein on feeding behaviour, mortality, and physiology in early and late instars of O. nubilalis larvae were investigated. The results of two-choice experiments showed that irrespective of ß-carotene presence, at day five 68%-90% of neonates and 69%-77% of fifth-instar larvae avoided diets with Cry1A protein. Over 65% of neonate larvae preferred to feed on diets with ß-carotene alone compared to 39% of fifth-instar larvae. Higher mortality (65%-97%) in neonates fed diets supplemented with ß-carotene alone and in combination with Bt protein was found, whereas <36% mortality was observed when fed diets without supplemented ß-carotene or Bt protein. Diets with both ß-carotene and Bt protein extended 25 days the larval developmental duration from neonate to fifth instar (compared to Bt diets) but did not impair larval or pupal weight. Juvenile hormone and 20-hydroxyecdysone regulate insect development and their levels were at least 3-fold higher in larvae fed diets with ß-carotene for 3 days. Overall, these results suggest that the effects of ß-carotene and Bt protein on O. nubilalis is dependent on larval developmental stage. This study is one of the first that provides insight on how the interaction of novel traits may modulate crop susceptibility to insect pests. This understanding will in turn inform the development of crop protection strategies with greater efficacy.

Carotenoids moderate the effectiveness of a Bt gene against the European corn borer, Ostrinia nubilalis.

We assessed the effectiveness of a biofortified maize line (4BtxHC) which accumulates high levels of antioxidant carotenoids that also expressed the insecticidal Cry1Ac Bacillus thuringiensis (Bt) gene against the European corn borer Ostrinia nubilalis. This line had been previously engineered to accumulate carotenoids specifically in the seed endosperm, whereas the Bt gene was expressed constitutively. The concentrations of Bt toxin (Cry 1Ac) in the leaves of the 4Bt and 4BtxHC lines were not significantly different at 47±6 µg/g of fresh weight (FW); neither were they in the kernels of both lines (35±3 µg/g FW). The kernels and leaves were toxic to the larvae of O. nubilalis. However, the insecticidal activity was substantially lower (ca. 20%) than that of lines that expressed only Bt in spite that the two lines showed a quantity of toxin not significantly different in kernels or in leaves. Although the reduced effectiveness of Cry1Ac in kernels may not be entirely surprising, the observation of the same phenomenon in vegetative tissues was unexpected. When semi-artificial diets containing kernels from 4Bt supplemented with different levels of ß-carotene were used in insect bioassays, the ß-carotene moderated the effectiveness of the Bt similarly to the plant material with carotenoid enrichment. To elucidate the biochemical basis of the reduced effectiveness of Bt toxin in the carotenoid-enriched plants, we measured the activity of three enzymes known to be implicated in the detoxification defence, namely, catalase, superoxide dismutase and glutathione S-transferase. Whereas Cry1Ac expression significantly increased SOD and CAT enzymatic activity in the absence of carotenoids, carotenoids, either in 4BtxHC or in artificial diets enriched with ß-carotene, significantly lowered CAT activity. Carotenoids can therefore moderate the susceptibility of the maize borer O. nubilalis to Cry1Ac, and we hypothesize that their role as antioxidants could explain this phenomenon via their scavenging of reactive oxygen species produced during Cry1Ac detoxification in the larvae. The involvement of this mechanism in the decreased mortality caused by Cry1Ac when carotenoids are present in the diet is discussed.

Do Sesamia nonagrioides (Lepidoptera; Noctuidae) gravid females discriminate between Bt or multivitamin corn varieties? Role of olfactory and visual cues.

The Mediterranean corn borer, Sesamia nonagrioides Lefèbvre, is a key pest of corn and a main target of Bacillus thuringiensis (Bt) corn in Northeast Spain. Trends for future biotechnology crops indicate that Bt, non-Bt, and stacked corn varieties with metabolic pathways for vitamin-increased traits could coexist in same region. Knowledge of the oviposition response of gravid females of S. nonagrioides to these different varieties could be extremely important for managing strategies aimed for delaying resistance development. In dual-choice assays, we examined the host preference of gravid females of S. nonagrioides for four corn varieties: a new transgenic corn with increased vitamin levels, its near isogenic counterpart (M37W), a Bt corn plant, and its near isogenic counterpart. Olfactory cues were the predominant ones when gravid females looked for a suitable host to lay eggs, and no synergistic effects were observed when both visual and olfactory cues were present. When the plant was visible, the females preferred the odors emitted by the nontransgenic to its multivitamin transgenic counterpart and when they only could detect the volatiles they also preferred the nontransgenic M37W variety to the Bt corn variety. If gravid females are less attracted to corn with an increased level of vitamins, this could impact insect resistance management and the value of refuge plants, if such traits are stacked with an insect resistance trait.

Response of last instar Helicoverpa armígera larvae to Bt toxin ingestion: changes in the development and in the CYP6AE14, CYP6B2 and CYP9A12 gene expression.

Bt crops are able to produce Cry proteins, which were originally present in Bacillus thuringiensis bacteria. Although Bt maize is very efficient against corn borers, Spanish crops are also attacked by the earworm H. armigera, which is less susceptible to Bt maize. Many mechanisms could be involved in this low susceptibility to the toxin, including the insect's metabolic resistance to toxins due to cytochrome P450 monooxygenases. This paper examines the response of last instar H. armigera larvae to feeding on a diet with Bt and non-Bt maize leaves in larval development and in the gene expression of three P450 cytochromes: CYP6AE14, CYP6B2 and CYP9A12. Larvae fed on sublethal amounts of the Bt toxin showed reduced food ingestion and reduced growth and weight, preventing most of them from achieving the critical weight and pupating; additionally, after feeding for one day on the Bt diet the larvae showed a slight increase in juvenile hormone II in the hemolymp. Larvae fed on the non-Bt diet showed the highest CYP6AE14, CYP6B2 and CYP9A12 expression one day after feeding on the non-Bt diet, and just two days later the expression decreased abruptly, a finding probably related to the developmental programme of the last instar. Moreover, although the response of P450 genes to plant allelochemicals and xenobiotics has been related in general to overexpression in the resistant insect, or induction of the genes when feeding takes place, the expression of the three genes studied was suppressed in the larvae feeding on the Bt toxin. The unexpected inhibitory effect of the Cry1Ab toxin in the P450 genes of H. armigera larvae should be thoroughly studied to determine whether this response is somehow related to the low susceptibility of the species to the Bt toxin.

Comparative analysis of hemolymph proteome maps in diapausing and non-diapausing larvae of Sesamia nonagrioides.

BACKGROUND: Sesamia nonagrioides is a noctuid that feeds on maize, sugar cane and sorghum in North Africa and Southern Europe. Larvae reared under long day conditions pupate after 5 or 6 larval instars, whereas larvae reared under short day conditions enter diapause and undergo up to 12 molts before dying or pupating. To better understand the mechanism of larval development and diapause, we identified proteins with different expressions in the sixth instar of diapausing and non-diapausing larvae. RESULTS: A total of 52 differentially regulated proteins were detected in the hemolymph of the diapausing or non-diapausing larvae at the beginning or end of the sixth instar. From these proteins, 11 were identified by mass spectrometry (MALDI-TOF MS or MALDI-TOF/TOF MS/MS): 5 were upregulated in the hemolymph of non-diapausing larvae and 6 in the hemolymph of the diapausing larvae. Interestingly, some proteins were expressed only in non-diapausing larvae but none was expressed only in the hemolymph of diapausing larvae. The possible functions of some of these proteins related to diapause maintenance or to larval-pupal metamorphosis are discussed. CONCLUSIONS: The 2-DE proteomic map of S. nonagrioides hemolymph shows differential protein expression in diapausing and non-diapausing larvae. Some proteins that showed higher expression in the diapausing larvae at the end of the sixth instar could be involved in JH level maintenance thus in the diapause status maintenance. On the contrary, other proteins that showed the highest expression or that were expressed only in the non-diapausing larvae could be involved in larval-pupal metamorphosis.

UHPLC-MS analysis of juvenile hormone II in Mediterranean corn borer (Sesamia nonagrioides) hemolymph using various ionization techniques.

The juvenile hormones (JHs) have been considered the most versatile hormones in the animal kingdom. JH-II is the most abundant JH in Sesamia nonagrioides, important maize pests in the Mediterranean basin. This study compared the sensitivities and matrix effects of four ionization modes on analyzing JH-II in S. nonagrioides hemolymph using ultrahigh-performance liquid chromatography-mass spectrometry (UHPLC-MS) in single ion monitoring (SIM) mode. The ionization techniques tested were electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI), and APPI with the lamp turned off, which corresponds to atmospheric pressure thermospray ionization (APTSI). ESI was discarded because of the high matrix effect. APPI was discarded because the correlation responses between solvent and matrix on the instrumental quality parameters were worse than those for APTSI and APCI. In our analytical conditions, APCI has shown the best validation parameter values. APCI ionization is widely available in instrumental laboratories.

Modification of hormonal balance in larvae of the corn borer Sesamia nonagrioides (Lepidoptera: Noctuidae) due to sublethal Bacillus thuringiensis protein ingestion.

Bacillus thuringiensis (Bt) corn, Zea mays L., is highly efficient against the corn borer Sesamia nonagrioides (Lefèbvre) (Lepidoptera: Noctuidae) when the larvae feed only on the transgenic plants. However, when they feed on Bt leaves during only part of their development, thus ingesting sublethal amounts of Bt toxins, some larvae survive. A previous study reported a prolonged development and precocious diapause induction in larvae fed on a diet with sublethal amounts of Cry1Ab protein. To determine whether these effects were accompanied by a modification of the hormonal balance, S. nonagrioides larvae were fed on sublethal amounts of Bt protein provided in Bt leaves or in the diet. The larvae that survived had higher levels of juvenile hormone (JH), whereas their level of ecdysteroids did not increase sufficiently to allow pupation, leading to a longer larval development and more larval molts. This response may be considered a defense mechanism that allows some larvae to survive toxin ingestion; it is similar the response to insecticidal toxins or viruses observed in other larvae. Changes in the hormone levels in diapausing larvae were undetectable, probably because these changes were masked by the higher level of JH in the hemolymph of diapausing larvae and because of lack of ecdysteroid titer increase, a phenomenon that is usually observed a few days before pupation in nondiapausing larvae. These results should be taken into account in the establishment of non-Bt refuges to prevent development of Bt-resistance in S. non-agrioides populations.

Control of larval-pupal-adult molt in the moth Sesamia nonagrioides by juvenile hormone and ecdysteroids.

Sesamia nonagrioides (Lepidoptera: Noctuidae) larvae reared under long day (LD; 16L:8D) conditions pupate after 5 or 6 larval instars, whereas under short day (SD; 12L:12D) conditions they undergo up to 12 additional molts before pupating. This extended period of repeated molting is maintained by high levels of juvenile hormone (JH). Previous work demonstrated that both LD and SD larvae decapitated in the 6th instar pupate but further development is halted. By contrast, about one-third of SD larvae from which only the brain has been removed, undergo first a larval molt, then pupate and subsequently developed to the adult stage. Debrained LD larvae molt to larvae exceptionally but regularly pupate and produce adults. Implanted brains may induce several larval molts in debrained recipient larvae irrespectively of the photoperiodic conditions. The results of present work demonstrate that the prothoracic glands (PGs) and the corpora allata (CA) of debrained larvae continue to produce ecdysteroids and JHs, respectively. PGs are active also in the decapitated larvae that lack JH, consistent with the paradigm that CA, which are absent in the decapitated larvae, are the only source of this hormone. Completion of the pupal-adult transformation in both LD and SD debrained insects demonstrates that brain is not crucial for the development of S. nonagrioides but is required for diapause maintenance. Application of JH to headless pupae induces molting, presumably by activating their PGs. It is likely that JH plays this role also in the induction of pupal-adult transformation in debrained insects. Application of the ecdysteroid agonist RH 2485 (methoxyfenozide) to headless pupae also elicits molting: newly secreted cuticle is in some cases thin and indifferent, in other cases it bears distinct pupal or adult features.

Gene encoding the prothoracicotropic hormone of a moth is expressed in the brain and gut.

The molts of lepidopteran insects are typically controlled by the brain-derived prothoracicotropic hormone (PTTH) that stimulates ecdysteroidogenesis in the prothoracic glands (PGs). We report here that the larvae and pupae of the moth Sesamia nonagrioides can molt without brain (PGs must be present), suggesting that there might be a secondary source of PTTH. We addressed this issue by characterizing spatial and temporal expression patterns of the PTTH gene. To this end we identified a major part of the corresponding cDNA. Protein deduced from this cDNA fragment consisted of 128 amino acids and showed 48-85% homology with the matching regions of PTTHs known from other Lepidoptera. Quantification of PTTH expression in major body organs of the last instar larvae revealed high expression in the brain (fading in post-feeding larvae) and considerable expression in the gut (with a maximum in post-feeding larvae). The content of PTTH message in the gut was enhanced after decapitation. It is concluded that the molts of S. nonagrioides larvae are driven by PTTH gene expression in the gut.

Brain-independent development in the moth Sesamia nonagrioides.

The caterpillars of Sesamia nonagrioides developing under long-day (LD) photoperiod pupate in the 5th or 6th instar whereas under short day (SD) conditions they enter diapause and undergo several extra larval molts. The diapause is terminated within 1-3 instars upon transfer of SD larvae to the LD conditions. Brain removal from the 6th instar larvae promotes pupation followed by imaginal development; however, one third of the SD larvae and 12% of the LD larvae debrained at the start of the instar first undergo 1-2 larval molts. The incidence of larval molts is enhanced by the brain implants. Exclusively pupal molts occur in the LD larvae debrained late in the 6th instar. Decapitation elicits pupation in both LD and SD larvae, except for some of the 4th and 5th and rarely 6th instar that are induced to a fast larval molt. The pupation of decapitated larvae is reverted to a larval molt by application of a juvenile hormone (JH) agonist. No molts occur in abdomens isolated from the head and thorax prior to the wandering stage. Abdomens isolated later undergo a larval (SD insects) or a pupal (LD insects) molt. Taken together the data reveal that in S. nonagrioides (1) several larval molts followed by a pupal and imaginal molt can occur without brain; (2) an unknown head factor outside the brain is needed for the pupal-adult molt; (3) brain exerts both stimulatory and inhibitory effect on the corpora allata (CA); (4) larval molts induced in CA absence suggest considerable JH persistence.

Response of Mythimna unipuncta males to components of the Sesamia nonagrioides pheromone.

Several sympatric lepidopteran species feed on maize plants, and the different components of their species-specific female sex pheromones may play a role in attracting conspecifics and/or deter heterospecific males. In this study, we analyzed the content of Mythimna unipuncta pheromone glands and tested the response of males to components of their own pheromone blend and that of Sesamia nonagrioides in the wind tunnel. Whole pheromone glands, and lures where (Z)-9-hexadecenyl acetate, Z)-11-hexadecen-1-ol or (Z)-9-hexadecenyl acetate + (Z)-11-hexadecen-1-ol were added to the major component, (Z)-11-hexadecenyl acetate, elicited significantly higher responses by M. unipuncta males than lures with main component alone, although the levels varied with concentration. In the field a rather different outcome was observed, as the addition of other compounds found in the female pheromone gland did not improve trap catch over lures with only (Z)-11-hexadecenyl acetate. The addition of (Z)-11-hexadecenal, a compound of the S. nonagrioides pheromone, to (Z)-11-hexadecenyl acetate significantly reduced attraction of M. unipuncta males both in the wind tunnel and in the field, as well as the number of sympatric clover cutworm, Discestra trifolii, under field conditions. The addition of (Z)-9-hexadecenyl acetate, a minor component of the M. unipuncta pheromone blend, reduced the number of S. nonagrioides captured in field traps that were baited with the S. nonagrioides lure. The significance of such inhibition in the reproductive isolation of sympatric species that attack maize is discussed.

Juvenile hormone esterase activity in the pupating and diapausing larvae of Sesamia nonagrioides.

The development of the Mediterranean corn borer, Sesamia nonagrioides, under long-day (LD) photoperiod is associated with juvenile hormone (JH) decline and pupation in the 5th or 6th larval instar. The larvae grown under short-day (SD) conditions maintain a moderate JH titer and enter diapause during which they undergo several extra larval molts. Both types of larvae exhibit similar levels of juvenile hormone esterase (JHE) activity that increases in each instar during the period of low ecdysteroid titer and drops when the titer rises to a molt-inducing peak. A suppression of JHE activity within 24h after application of an ecdysteroid agonist suggests that the drop of activity is a rapid and possibly direct response to ecdysteroids or their agonist. Esterase inhibitor 3-octylthio-1,1,1-trifluoro-2-propanone (OTFP) suppressed more than 98% of the JHE activity without affecting pupation timing and adult development. The data indicate that JHE is not crucial for the switch between larval development, diapause, and metamorphosis in S. nonagrioides.

Factors affecting the natural duration of diapause and post-diapause development in the Mediterranean corn borer Sesamia nonagrioides (Lepidoptera: Noctuidae).

Sesamia nonagrioides responds to photoperiod for diapause termination at high temperature with a Type II response curve, and only photoperiods longer than 12:12 terminate diapause. However, these photoperiods never occur in the field when diapausing larvae are competent to terminate diapause. Under a temperature similar to the natural field temperatures diapause terminates spontaneously in approximately 4 months, which ensures that the larvae reach the middle of winter without pupation. S. nonagrioides larvae pupate after going through a specific number of light-dark cycles or days: the required day number (RDN) for diapause completion. This RDN could be modulated by temperature but more research is necessary to clarify this point. In post-diapause development, when a suitable temperature threshold is considered, the absolute accumulation of heat is more important than whether the temperature received is fluctuating or constant. The temperature threshold for diapause and post-diapause development was lower than the temperature threshold of larvae in continuous development. This is important for adjusting phenological models in S. nonagrioides and in other species, and may explain why in many cases adults appear in the field when the supposed temperature threshold for development has not been attained.

Effects of ecdysteroid agonist RH-2485 reveal interactions between ecdysteroids and juvenile hormones in the development of Sesamia nonagrioides.

Larvae of Sesamia nonagrioides developing under long day (LD) conditions pupate in the 5th or 6th instar, whereas under the short day (SD) conditions, they undergo several supernumerary larval molts and are regarded as diapausing. The development in early larval instars occurs in the LD larvae at a moderate and in the SD larvae at a high juvenile hormone (JH) titer; ecdysteroid titer cycles similarly under both conditions. The transformation to pupa is initiated by a burst of ecdysteroids at undetectable JH levels, whereas extra larval molts in the diapausing larvae are associated with moderate JH titer and irregular rises of ecdysteroids. Application of 0.2 ppm RH-2485 to the diet of the 6th instar larvae promotes hormonal changes supporting metamorphosis in the LD larvae and slightly accelerates larval molts in the diapausing SD larvae. The 0.5- and 1-ppm doses revert these patterns of endocrine regulations to a mode typical for early larval instars. Particularly dramatic is a JH titer increase provoked within 24 h in the LD larvae. After the treatment, both the LD and SD larvae undergo a series of larval molts, suggesting that hormonal programming of the larval development has been stabilized. A few insects receiving 1 ppm RH-2485, and a high proportion of those fed with 5 ppm RH-2485, deposit two cuticles within a single apolysis and die.

Inhibition of pheromone response in Sesamia nonagrioides by the pheromone of the sympatric corn borer, Ostrinia nubilalis.

Sesamia nonagrioides Lef. and Ostrinia nubilalis (Hübn.) are two corn borers present in the Mediterranean area that share a similar feeding habitat. The female sex pheromones of the two species consist of (Z)-11-hexadecenyl acetate, (Z)-11-hexadecen-1-ol, (Z)-11-hexadecenal and dodecyl acetate (77:8:10:5 w/w) and (Z)-11-tetradecenyl acetate and (E)-11-tetradecenyl acetate (97:3 w/w) respectively. Although the pheromones share no common components, previous work had shown the inhibition of the response by O. nubilalis males to their own pheromone owing to the presence of S. nonagrioides pheromone. In this study, the pheromone of O. nubilalis and its two components separately were shown to inhibit the attraction of S. nonagrioides males to the synthetic female pheromone in both laboratory wind-tunnel bioassay and field trapping studies. In the wind tunnel, the number of contacts of S. nonagrioides males with the source were significantly (P < 0.05) reduced by the single pheromone components of O. nubilalis. In the field, the addition of 1% of O. nubilalis pheromone significantly (P < 0.05) reduced the catches of S. nonagrioides males. The components of both pheromones also elicited electroantennographic responses from antennae of male S. nonagrioides moths. The ecological consequences and the possibilities of applying this cross-inhibition for mating disruption techniques are discussed.

Pheromone antagonism in the European corn borer moth Ostrinia nubilalis.

Mixing the sex pheromones of the Mediterranean corn borer, Sesamia nonagrioides, and the European corn borer, Ostrinia nubilalis, results in significantly lower captures of O. nubilalis when compared to traps loaded with its pheromone alone. Rubber septa loaded with a constant concentration of the pheromone of O. nubilalis and different percentages of the S. nonagrioides pheromone (from 1 to 100%) causes dose-dependent antagonism in the field. Electroantennograms of O. nubilalis males showed high antennal responses to its own pheromone components, followed by smaller responses to the major, [(Z)-11-hexadecenyl acetate (Z11-16:Ac)], and two minor components [dodecyl acetate (12:Ac) and (Z)-11-hexadecenal (Z11-16:Ald)] of the S. nonagrioides pheromone. There was almost no response to the S. nonagrioides minor component (Z)-11-hexadecenol (Z11-16:OH). Field tests that used traps baited with the O. nubilalis pheromone plus individual components of S. nonagrioides showed that Z11-16:Ald causes the antagonism. Adding 1% Z11-16:Ald to the pheromone of O. nubilalis reduced oriented flight and pheromone source contact in the wind tunnel by 26% and 83%, respectively, and trap captures in the field by 90%. The other three pheromone components of S. nonagrioides inhibited pheromone source contact but not oriented flight of O. nubilalis males and did not inhibit capture in the field. Cross-adaptation electroantennogram suggests that Z11-16:Ald stimulates a different odor receptor neuron than the pheromone components of O. nubilalis. We conclude that Z11-16:Ald is a potent antagonist of the behavioral response of O. nubilalis.