Ancestral feeding and survival of offspring in European corn borer

Experiments were conducted to evaluate the influence of ancestral adult feeding by European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), on larval survival in the field and neonate movement behavior in laboratory. Larval survival was higher when either the grandparental or parental generation had fed, but the feeding sites of the surviving larvae were not affected by ancestral feeding condition. This is the first evidence that grandparental feeding could influence larval survival in the field. Larval movement was observed in the laboratory. Silking speed of neonates was faster when either grandparents or parents had fed, while walking speed was faster only when parents had fed. No broad-sense genetic correlation was found between silking speed and walking speed. Broad-sense heritability among feeding histories were not significant for silking speed, but was significantly greater than zero for walking speed when grandparents fed and parents did not. These intergenerational effects could induce complex population dynamics in this species.     

Factors influencing parasitism of Trichogramma dendrolimi on eggs of the Asian corn borer, Ostrinia furnacalis

Laboratory studies were made to determine the capacity of Trichogramma dendrolimi to parasitize eggs of Ostrinia furnacalis, as affected by the rearing host species, substrate of host eggs, host age, original locality of host populations, and cold storage of host eggs. Wasps reared from eggs of Antheraea pernyi showed parasitic capacity on eggs of O. furnacalis on average twice as high as that of the wasps reared from eggs of Corcyra cephalonica. When the age of O. furnacalis eggs at 26 °C increased from 0–6 h to 18–24 h, the proportion of wasps that successfully parasitized host eggs, the number of host eggs parasitized, and the rate of parasitization all decreased by >50%. The number of O. furnacalis eggs parasitized per female T. dendrolimi increased with the number of host eggs available, and reached 22.9 in a 24 h period. However, the parasitic capacity of female T. dendrolimi on eggs of O. furnacalis laid on plant leaves was similar to that of O. furnacalis eggs laid on wax paper. Levels of parasitism of O. furnacalis eggs from two widely separated localities, i.e. Changchun (43.50° N, 125.20° E) and Hangzhou (30.18° N, 120.07° E), were similar. Cold storage of O. furnacalis eggs at 4 °C for 5 days did not affect parasitization. Results obtained in this study indicate that although O. furnacalis is a less preferred and less suitable host than many other hosts, such as Dendrolimus punctatus, Actias selene ningpoane, Philosamia cynthia, A. pernyi, C. cephalonica, within the host-species range of T. dendrolimi, the parasitoid has the potential to achieve 50–60% or even higher rates of parasitization of O. furnacalis eggs in corn fields under suitable conditions, and could be used in the biological control of the pest.     

Cold storage of Trichogramma ostriniae reared on Sitotroga cerealella eggs

Efficient storage of the biological controlagent Trichogramma ostriniae couldimprove current parasitoid production methodsby making the system more flexible andefficient. Initial studies compared emergencerates of T. ostriniae reared onSitotroga cerealella eggs held at 6 °C, 9 °C, 12 °C,15 °C, and 24 °C for up to 8 weeks after parasitism.At 15 °C, emergence occurred in <2 weeks.Emeregence was >80% for parasitized eggsstored at 9 °C and 12 °C for 4 and 6 weeksrespectively. Storage at 6 °C caused asignificant decline in emergence after 2 weeks. Subsequent trials focused on fitness of storedT. ostriniae. Percentage of emergedfemales parasitizing eggs, female longevity,and fecundity were quantified after storage.The percentage of females successfullyparasitizing O. nubilalis eggs wasgreatest for the 9 °C four-week treatment(100%). Compared to 24 °C controls, storage at12 °C for 6 weeks or at 9 °C for 8 weeks reduced thepercentage of females parasitizing. Longevityof females held in cold storage was generallyless than that of controls. Rates of parasitismby stored Trichogramma was generallysimilar to controls after 2 to 4 weeks' storageat 9 °C and 12 °C but declined with storage longerthan 4 weeks. Emergence of progeny of cold-storedfemales was lower than controls for alltreatments. The percentage of female progenyfrom cold stored females was comparable tocontrols up to 4 weeks of storage.     

Free amino acids of the haemolymph of the southwestern corn borer and the European corn borer in relation to their diapause

The titres of free amino acids present in the haemolymph of diapausing larvae of the southwestern corn borer, Diatraea grandiosella and the European corn borer, Ostrinia nubilalis, were examined. High titres of serine were found in the haemolymph of both species. Serine may serve as a storage form of compounds that are required for the synthesis of uric acid and other purines. The high titres of proline found in the haemolymph of O. nubilalis during the fall and winter may contribute to the freezing tolerance of this species. Alanine accumulated in the haemolymph of both species during the winter.     

The effect of stem diameter on European corn borer behavior and survival: potential consequences for IRM in Bt-corn

The ability of non-crop plants to support complete development of insect pests is an important factor for determining the impact of those plants on resistance management programs for transgenic crops. We assessed the effect of one physical factor, plant stem diameter, on the ability of plants to support full development of the European corn borer (ECB), Ostrinia nubilalis Hübner (Lepidoptera: Crambidae), the target pest of transgenic Bt-corn. In the field, European corn borer larvae were significantly more likely to tunnel and survive in plants with larger stem diameters. Larvae were 40× more likely to survive on corn, the largest plant tested, compared to many of the smaller plants. In the laboratory, larvae were more likely to survive in and less likely to abandon the largest diet-filled artificial stems that varied only in stem diameter. In conditions simulating those that an ECB larvae would encounter upon abandoning a host, larvae survived up to three weeks and were able to locate corn as a new host with a significantly higher frequency than would be expected if they were foraging randomly. These results indicate that the probability of ECB larval survival to maturity on a plant other than corn is relatively low and thus these smaller stemmed non-corn plants may not make a substantial contribution to the pool of susceptible adults. Conversely, since more mature larvae are not as susceptible as neonates, any larvae that partially develop on non-corn plants and subsequently colonize Bt-corn may not be exposed to a lethal dose of the toxin. Since some proportion of the individuals that survive could be partially resistant heterozygotes the presence of non-corn host plants could facilitate the development of resistant ECB populations.     

Age-specific dose-mortality effects of Beauveria bassiana (Deuteromycotina: Hyphomycetes) on the European corn borer,Ostrinia nubilalis (Lepidoptera: Pyralidae)

Three isolates of Beauveria bassiana were evaluated under laboratory conditions for pathogenicity against the European corn borer, Ostrinia nubilalis. Dose-mortality regressions and nonparametric statistical analyses revealed significant differences in pathogenicity between isolates and across O. nubilalis instars. First instars were found to be the most susceptible of the five larval stages. Little difference was noted for instars 2, 3, and 5 within any of the three B. bassiana isolates. Fourth instar larvae were found to be the most tolerant in all cases.     

Behavioural study of plasticity in host preferences of Trichogramma maidis (Hym.: Trichogrammatidae)

Abstract. To test the relative importance of genetic and environmental factors in host preferences of Trichogramma maidis Pint. & Voeg., a polyphagous parasitoid, the oviposition behaviour was analysed on two host species: Anagasta kuehniella used for mass rearing) and Ostrinia nubilalis a target pest). Females were compared according to the species on which they had been reared, and to that on which they had an oviposition experience. To quantify an oviposition sequence, the most frequent behavioural succession was established for each experimental situation, individual sequences were then compared with this standard one to count the number of additional behaviours. An affinity coefficient positively related to host acceptance was then calculated from these additional behaviours. A preference for O.nubilalis versus A kuehniella appeared, but rearing on A. kuehniella enhanced the level of spontaneous affinity for this unnatural host. These initial preferences were modified by an oviposition experience: the affinity for a given host was higher after an oviposition on the same species, which suggests a female's ability to learn. This learning ability was higher on the non-preferred host, which led to an equivalent final parasitic performance on both hosts. Moreover, the learning ability was specific to a given host, since the oviposition on a given species did not provide any improvement in the level of affinity for the other species.     

Electroantennogram response gradient on the antenna of the European corn borer, Ostrinia nubilalis

The electroantennogram (EAG) response of male moths of the European corn borer (Ostrinia nubilalis) to their two pheromone components, (Z)- and (E)-11-tetradecenyl acetates, were studied. The EAG amplitude of the fast initial phase was approximately proportional to the antennal length. Local EAG responses were obtained along the length of the antenna with multiple electrodes. Response-interaction studies indicated a unique spread of the EAG response in a proximal direction in the antenna. A possible mechanism of the EAG summation was considered. The EAG response characteristic was similar for both (Z)- and (E)-11-tetradecenyl acetate along the length of the antenna.     

In vivo temperature-dependent development of Beauveria bassiana (Deuteromycotina: Hyphomycetes) mycosis of the European corn borer,Ostrinia nubilalis (Lepidoptera: Pyralidae)

The in vivo incubation period of Beauveria bassiana mycosis of the European corn borer, Ostrinia nubilalis, was found to vary in response to temperature of incubation, level of initial exposure (dose), and the age of the host larvae. Incubation temperature was found to be the dominant factor affecting disease development within each of the host instars examined, while dose produced significant effects only in the early instars. A nonlinear regression model was used to construct three-dimensional stimulus-response surfaces for each host instar. This model has provided reasonable predictions of the disease incubation period when used within the temperature regimes found throughout New York State.     

Population consequences of diapause in a model system: the European corn borer

The diapause biology of the European corn borer (ECB), Ostrinia nubilalis (Hübn.), is described based on natural and controlled environment studies of feral and lab-reared ECB's in North Carolina (NC). The diapause response is described as a function of photophase (h of light/day) as well as a function of larval age (instar) at onset of diapause-inducing conditions. A critical photophase of 14.4 h and a critical mean larval instar of 3.3 is found in the lab studies and supported by three years of insectary studies. Seven years of black light trapping of ECB moths in Goldsboro, NC, revealed the likelihood of up to four moth flights/year.Information about the diapause biology of this insect is used to explain both the number of flights and the relative magnitude of the final moth flights. On average, the majority of ECB lineages pass through three generations/year with early maturing ECB's producing a significant and predictable fourth generation. The timing and magnitude of the fourth flight can be partly explained on the basis of the critical photophase and the timing and age structure of previous ECB generations. In most years, the fourth flight is smaller than the third due to the majority of the fourth generation's predisposition towards diapause. However, in at least one case (1977), the fourth flight was unusually large and could be predicted by slight temporal shifts in the previous three flights resulting in the majority of the fourth generation larvae averting diapause. The value of the ECB-diapause interaction as a model system for the explanation and prediction of dynamic phenological events is discussed.

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Résumé La diapause d'O. nubilalis Hubn. est décrite d'après des études en conditions naturelles et programmées de souches sauvages ou élevées au laboratoire en Caroline du Nord. La diapause est décrite comme une fonction de la photophase (heures de jour/24 heures) et du stade larvaire au début des conditions inductrices de la diapause. Une photophase critique de 14,4 h et un stade critique larvaire de 3,3 ont été établis au laboratoire après 3 ans d'études en insectarium. 7 ans de piégeage à la lumière noire à Goldsboro, ont montré la vraisemblance de l'existence de 4 vols par an. Les données sur la diapause de cet insecte sont utilisées pour expliquer tant le nombre de vols que l'importance relative des derniers vols. En moyenne, la majorité des lignées ont 3 générations par an, O. nubilalis précoces produisant une quatrième génération conséquente et prédictible. La data et l'importance du 4ème vol peuvent être partiellement expliquées d'après la photophase critique, et la data et la structure en âge des générations précédentes. La plupart des années, le 4ème vol est moins important que le 3ème par suite de la prédisposition à la diapause de la majorité de la 4ème génération. Cependant, dans un cas au moins, en 1977, le 4ème était anormalement important et pouvait être prédit par de faibles changements temporels dans les 3 précédents vols, détournant de la diapause la majorité des chenilles de 4ème génération. La discussion porte sur la valeur du modèle fourni par la diapause de O. nubilalis pour expliquer et prédire la dynamique des évéments phénologiques.

     

Sex pheromone blend discrimination in two races and hybrids of the European corn borer moth, Ostrinia nubilalis

Abstract. The response specificity of males of two races, and hybrids, of the European corn borer moth, to a large series of doses/ratios of E- and Z11-14:OAc, was determined in a sustained-flight tunnel. For both races an area of peak response was determined, which included the natural ratio eliciting peak levels of source contact, and other treatments eliciting response profiles over the behavioural sequence not significantly different from the peak. Consistent with studies on other moth species response specificity was controlled by two threshold effects, one affecting locking-on to odour plumes of lower doses and off-ratios containing lower proportions of the E or Z isomer than the natural blend, and the other resulting in arrestment of upwind flight to higher doses and off-ratios containing higher proportions of the E or Z isomer man the natural blend. A comparison of the size of the areas of peak response showed that males of the univoltine Z race (UZ) using a 3:97 E:Z mix displayed greater specificity and sensitivity than did males of the bivoltine E race (BE) responding to a 99:1 E:Z pheromone mix. At doses higher than those eliciting peak response (<100 μg) response specificity was lower for both races, but especially for the BE race, with increased levels of upwind flight and source contact occurring to off-ratios. Finally, consistent with a previous behaviour/genetic study on this species, F₁ hybrid males displayed peak levels of source contact not only to their natural isomer ratio (65:35 E:Z), but also to an expanded range of doses of ratios ranging from 2% to 98% E.     

Immunofluorescent localization of a substance immunologically related to insulin in the protocerebral neurosecretory cells of the European corn borer

Summary A substance immunologically related to mammalian insulin was demonstrated by immunofluorescence in one of five types of neurosecretory cells in the protocerebrum of the European corn borer, Ostrinia nubilalis. This A₂ cell type contains a secretory material stainable with paraldehyde fuchsin.E.R.A. CNRS n° 850     

Simulation models for European corn borer postdiapause morphogenesis and early infestation of maize in Missouri, USA

 The European corn borer is one of the most damaging insect pests to maize in the United States. Different methods exist for the estimation of time of damage to corn by first generation European corn borer. The most commonly used method is the linear thermal constant concept of phenology which by convention calculates cumulative thermal units from January 1 or another arbitrary date. Linear and nonlinear models based on the thermal units concept developed were to predict and simulate postdiapause development of the European corn borer and subsequent infestation of the maize crop using early spring temperatures (May 1–15) in central Missouri. The developmental rates of European corn borer were obtained from growth chamber investigations that simulated those temperatures, the operational temperatures being selected from a compilation of archival meteorological data from 1948 to 1989. The linear and polynomial regression models were developed to predict phenological stages of the European corn borer using thermal units as developmental rates. The models were compared against each other to determine the better predictor of estimation values: each explained 94 and 98% of the variation in developmental stages, respectively. In addition, the models were tested against independent field data and both models gave good predictions of developmental stages, indicating that either model would be a good predictor. Received: 9 September 1994 / Revised: 28 December 1995 / Accepted: 8 August 1996     

Variation in flight response of the specialist parasitoidMacrocentrus grandii goidanich to odours from food plants of its European corn borer host

The specialist parasitoidMacrocentrus grandii Goidanich (Hymenoptera: Braconidae) appears to parasitize its polyphagous host, European corn borer (Ostrinia nubilalis (Hübner)) (Lepidoptera: Pyralidae), in only certain habitats. To determine whether it differed in its olfactory response to host-habitat odours, volatiles from four plants were isolated using Tenax. Wind tunnel bioassays of the extracts revealed that, besides corn which was tested in an earlier study, olfactory stimuli for attraction ofM. grandii females were present in potato and snap bean but not in pepper or soybean. To further characterize the response to pepper and soybean, these extracts were bioassayed in combination with an attractive extract. The results indicated that pepper volatiles evoked a neutral response inM. grandii while response to soybean volatiles appeared to be neutral or slightly negative. The innate response to soybean volatiles was altered to one of attraction after oviposition experience on soybean. Seven days after oviposition, experienced females continued to respond positively to soybean volatiles. Components of soybean volatiles responsible for the change in flight behaviour resulting from oviposition experience were eluted by nonpolar and slightly polar solvents. These results support the idea that plant odour may be a factor determining the range of plants on whichM. grandii parasitizes its host. The study indicates the occurrence of associative learning of plant-related volatiles during oviposition inM. grandii, and suggests the involvement of diverse plant compounds in the learning process.     

Sympatric host races of the European corn borer: adaptation to host plants and hybrid performance

The European corn borer (ECB), Ostrinia nubilalis, is a major pest of maize crops. In Europe, two sympatric host races are found: one feeds on maize (Zea mays) and the other mainly on mugwort (Artemisia vulgaris). The two host races are genetically differentiated, seldom crossing in the laboratory or in the field, and females preferentially lay eggs on their native host species. We conducted two independent experiments, in field and greenhouse conditions, to determine whether the two host races are locally adapted to their host species. The effect of larval density and the performance of hybrids were also investigated. Despite some differences in overall larval feeding performance, both experiments revealed consistent patterns of local adaptation for survival and for larval weight in males. In females the same trend was observed but with weaker statistical support. F1 hybrids did not seem to be disadvantaged compared with the two parental races. Overall, our results showed that both host races are physiologically adapted to their native host. The fitness trade-off between the two host plants provides a potential driving force for ecological speciation in this species.     

Changes in calling behaviour and mating success in the European corn borer (Ostrinia nubilalis), caused by relative humidity

We examined the calling behaviour of O. nubilalis virgin females, held at three different constant conditions of relative humidity from the time of emergence through their sixth night of calling, as well as the incidence of mating over time at low or high relative humidity conditions. The mean age at which females initiated calling in their life was independent of relative humidity conditions, although more variable at low humidity. On successive nights of calling, fewer virgin European corn borer females called under low compared with high humidity conditions, and those that did began later in scotophase, had fewer calling bouts, and spent less time calling. These changes in the female prereproductive behaviour were reflected on the incidence of mating which, in the first two days following emergence, was significantly less at low than at high humidity conditions. The ecological significance of these results is discussed in relation with the susceptibility of O. nubilalis to desiccation.

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Résumé Nous avons étudié le comportement d'appel des femelles vierges d'Ostrinia nubilalis maintenues sous trois conditions constantes d'humidité relative, depuis l'émergence jusqu'à la sixième nuit d'appel, ainsi que l'incidence d'accouplement d'individus placés en milieu sec ou humide pour diverses périodes de temps. Les conditions d'humidité n'ont pas significativement affecté l'âge moyen auquel les femelles ont commencé à appeler au cours de leur vie, bien qu'il ait été plus variable à 53% h.r. Les nuits subséquentes, le comportement d'appel des femelles maintenues à basse humidité a débuté plus tard dans la nuit, s'est exprimé pour une période de temps plus courte avec moins de séquences d'appel que celui de leurs congénères placés en milieu humide, et la proportion de femelles en appel a toujours été plus faible à 53% h.r. Ces changements du comportement préreproducteur des femelles se sont répercutés sur l'incidence d'accouplement qui, les deux premiers jours suivant lémergence, a été significativement plus faible à basse humidité qu'elle ne l'a été en milieu humide. Ces résultats seront discutés en relation avec l'écologie de O. nubilalis et associés à sa susceptibilité à la dessication.

     

Two multiplex sets of eight and five microsatellite markers for the European corn borer,Ostrinia nubilalis Hübner (Lepidoptera: Crambidae)

Primer sequence and polymorphism data are presented for 13 microsatellite loci isolated from the European corn borer moth, Ostrinia nubilalis, as part of a project to construct a linkage map for the two pheromone strains. Experimental conditions are described for polymerase chain reaction (PCR) multiplexing, which allows genotyping in two electrophoresis runs of eight and five markers each. In a sample of 27 individuals coming from one European locality, the number of alleles per locus ranged from one to 12, and gene diversity from 0 to 0.859. Seven loci showed a deficit of heterozygotes. Eleven loci cross‐amplify in the related Ostrinia furnacalis.     

In vivo effect of mixtures of allelochemicals on the life cycle of the European corn borer, Ostrinia nubilalis

The phenylpropanoid, dillapiol, a compound capable of inhibiting the activity of cytochrome P-450 epoxidase in microsomal preparations of midguts of the European corn borer (ECB), Ostrinia nubilalis Hubner (Lepidoptera), did not enhance the toxicity of two insecticidal allelochemicals from the Asteraceae: the sesquiterpene lactone, tenulin or the phenylacetylene, phenylheptatriyne, when ingested simultaneously. Dillapiol alone was toxic to ECB larvae, and inhibited their growth. Possible reasons for the lack of synergism or potentiation by dillapiol of the insecticidal activity of the other allelochemicals are considered.

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Résumé Le dillapiole, un phénylpropanoide monomère d'un lignan et contenant un groupement méthylènedioxyhphényl (MDP), a la capacité d'inhiber in vitro les enzymes d'oxydations multiples à cytochrome P-450 (PSMO) utilisées par la pyrale du maïs (ECB), Ostrinia nubilalis, pour detoxifier les substances allélochimiques. Les composés contenant un groupe MDP comptent parmi les plus nombreux et puissants synergistes d'insecticides. Cependant, aucun synergisme n'est observé lorsque le dillapiole est ingéré par la pyrale en association avec l'une ou l'autre ou les deux substances secondaires insecticides des Astéraceae, la lactone sesquiterpène ténuline ou/et le polyacétylène phénylheptatriyne (PHT). Plutôt, le dillapiole est une toxine qui diminue la prise de poids des larves et retarde leur développement. Les effets toxiques sont plus importants avec le dillapiole seul que lorsque celui-ci est associé à la ténuline ou/et au PHT. Les expications possibles de ces résultats sont discutées.

     

Characterization of six antibacterial response genes from the European corn borer (Ostrinia nubilalis) larval gut and their expression in response to bacterial challenge

Six cDNAs encoding putative antibacterial response proteins were identified and characterized from the larval gut of the European corn borer (Ostrinia nubilalis). These antibacterial response proteins include four peptidoglycan recognition proteins (PGRPs), one β-1,3-glucanase-1 (βglu-1), and one lysozyme. Tissue-specific expression analysis showed that these genes were highly expressed in the midgut, except for lysozyme. Analysis of expression of these genes in different developmental stage showed that they were expressed in larval stages, but little or no detectable expression was found in egg, pupa and adult. When larvae were challenged with Gram-negative bacteria (Enterobacter aerogenes), the expression of all six genes was up-regulated in the fatbodies. However, when larvae were challenged with Gram-positive bacteria (Micrococcus luteus), only PGRP-C and lysozyme genes were up-regulated. This study provides additional insights into the expression of antibacterial response genes in O. nubilalis larvae and helps us better understand the immune defense response in O. nubilalis.     

Effect of host availability on reproduction and survival of the parasitoid wasp Trichogramma minutum

Abstract.

• 1 We tested the hypothesis that females of the egg parasitoid, Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae), could adjust their fecundity schedule according to host availability and that there was a negative correlation between reproduction and survival in these wasps.
• 2 Newly-emerged females were provided with an unlimited or limited number of hosts in the first trial and with either unlimited, limited or zero hosts in the second trial.
• 3 When hosts were unlimited, wasps had the highest rate of reproduction in the first day, which decreased dramatically thereafter. When hosts were limited, wasps from the two trials differed in their response. In Trial I, females with limited hosts had lower first-day fecundity than, and the same subsequent-day fecundity as, those with unlimited hosts. However, in Trial II, females with limited host had a lower first-day but a higher subsequent-day fecundity than those with unlimited hosts. This indicates variation in Trichogramma's ability to shift its fecundity schedule in response to host availability.
• 4 There was a positive (rather than a negative) correlation between reproduction and survival. Wasps that oviposited (in host-unlimited treatment) had greater longevity than those that could not (in host-unavailable treatment).
• 5 The sex ratio of the progeny produced by wasps in both host-unlimited and limited treatments shifted gradually from a female to a male bias as the wasps aged.
• 6 We consider the ability of parasitoids to adjust their fecundity schedule as an adaptation to changing host resources and discuss our findings with regard to theories of life history evolution.