Environmental and genetic control of the larval diapause of the Southwestern corn borer, Diatraea grandiosella

ABSTRACT. The interaction of photoperiod and temperature in the regulation of the induction and termination of the larval diapause of the Southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera), was examined. A population originating from south-eastern Missouri had critical daylengths for diapause induction of about 15h 5min (ecological threshold) and llh (physiological threshold). The ecological threshold was more stable than was the physiological threshold at temperatures lower than 25°C. Above 25°C the diapause response was suppressed. The insect appears to measure photoperiods in a stationary manner since a stepwise increase or decrease in photoperiod did not affect the incidence of diapause. In the critical region of the photoperiodic response curve, a higher incidence of diapause was found among females than among males. Females entered diapause later than did males, but resumed active development earlier than males. The rate of diapause development was more temperature dependent than was the rate of diapause induction, yet it was also clearly under photoperiodic control. The temperature coefficient (Q₁₀) for this process was about 4. Several other factors including sex-linkage, age, and geographic adaptations are involved in controlling the rate of diapause development, even more so than they are in controlling diapause induction. In the laboratory, the intensity of diapause declined gradually without larvae being exposed to non-diapause inducing conditions. Incubation of field-collected larvae revealed that their sensitivity to diapause maintaining photoperiods had ended by January. Three generations of selection of a Mississippi population of D. grandiosella at 30°C and LD 12:12 led to the production of an essentially diapause-free strain and a diapause strain.     

Temperature and photoperiodic regulation of diapause of the southwestern corn borer,Diatraea grandiosella

The effect of temperature and photoperiod on the onset and termination of the mature larval diapause of the southwestern corn borer, Diatraea grandiosella, was examined. The results showed that diapause induction was an extremely temperature-dependent process. Larvae reared at 23°C under short days all entered diapause whereas 90 per cent of those reared at 27°C developed continuously. A photoperiodic response was only demonstrable at 25°C, when diapause was instituted following larval exposure to daily photophases ranging from 8 to 14 hr. An examination of the sensitivity of immature larvae to low temperatures revealed that all instars showed some susceptibility to low temperature induction of diapause. No intermediate instar was found in which the developmental programme could be switched entirely from a diapause to a non-diapause one, or vice versa.Diapause development was also found to be primarily temperature regulated. The rate of termination of diapause at 30°C was significantly higher than that at 25 or 23°C. Continuous exposure to light rather than a daily photoperiod produced the highest rate of diapause development. It was also shown that a period of chilling (5°C) did not accelerate diapause development. The significance of the results in relation to the evolution and geographical distribution of the species is discussed.     

Juvenile hormone titer determinations in the southwestern corn borer, Diatraea grandiosella, by electron capture-gas chromatography.

A procedure is described for analysis of the three known juvenile hormones (JHs) at physiological levels in 5–10 gram samples of insect hemolymph or whole bodies. The method employs conversion of the oxirane ring of the JHs to their respective 11-methoxy-10-pentafluorophenoxyacetate esters, allowing use of gas-liquid chromatography/electron capture detection for qualitative and quantitative analysis at picogram levels. The method is used to determine the JH titers of the southwestern corn borer, $\text{Diatraea}$$\text{grandiosella}$, as a function of developmental stage. The results show that diapausing larvae contain significant titers of all three known juvenile hormones, thereby supporting the theory that larval diapause in this species is under the control of the corpus allatum.     

Photoperiodic and thermoperiodic interactions in the regulation of the larval diapause of Diatraea grandiosella

The effect of various combinations of photoperiod and temperature on the induction and termination of the mature larval diapause of a Missouri strain of the southwestern corn borer. Diatraea grandiosella, was examined. Larval exposure to regimes in which the low phase of a 30°:23°C thermoperiod coincided with a scotophase of 10 to 14 hr duration led to high incidence of diapause. Larval exposure to 30°:24°C, 33°:21°C, and 36°:18°C thermoperiods with half cycles of 12 hr in continuous darkness yielded a diapause incidence of 16%, 22%, and 59%, respectively, whereas exposure to a 30°:24°C thermoperiod in continuous illumination yielded a completely nondiapause generation. Larval exposure to one of a series of 36°:18°C thermoperiods in which the duration of the high phase was increased in 2 hr increments from 0 to 24 hr in continuous darkness showed that “short-day” thermoperiods yielded a high incidence of diapause. However, no clearly defined critical thermoperiod was observed. An examination of photoperiodic and thermoperiodic effects on diapause development showed that, in general, those combinations of temperature and light cycles which were diapause inductive also retarded diapause development. The relationship between seasonal photoperiods and thermoperiods in southeastern Missouri was examined.     

Cold hardiness of larvae of the southwestern corn borer, Diatraea grandiosella

The cold-hardening capacity of field-collected larvae from southeast Missouri and laboratory-reared larvae of the southwestern corn borer, Diatraea grandiosella Dyar, was examined. Supercooling points of non-diapause and diapause larvae collected from maize plants grown in Missouri (36°30 N lat.) were ca.-7.0°C. The hemolymph melting points of diapause field larvae (-0.8°C) were significantly lower than those of non-diapause larvae collected in July (-0.5°C). The supercooling points of hemolymph from non-diapause and diapause field larvae ranged randomly from-10° to-18°C. Supercooling points of non-diapause laboratory larvae increased from-13° to-10°C prior to pupation, whereas those of diapause larvae increased similarly before the onset of diapause, but then decreased during diapause to ca.-17°C. No change in supercooling points or capacity to survive in the presence of ice was observed in diapause laboratory larvae acclimated at 4°C for 63 days. Laboratory and field larvae began to freeze at ca.-1.5°C in the presence of ice, but survived to several degrees below their melting points. The high supercooling points of field larvae appeared to be due to the presence of an environmental ice-nucleator. Although data for laboratory larvae indicate sufficiently low supercooling points to permit winter survival in southeastern Missouri, considerable larval mortality occurs in the field due to inoculative freezing and the presence of an ice-nucleator.     

Observations on the nutritional requirements of the southwestern corn borer, Diatraea grandiosella

The southwestern corn borer was reared on a meridic diet containing wheat germ and wheat germ oil as its only plant adjuvants. The insect's requirements for protein, a mineral mixture, and L-ascorbic acid were studied using a bioassay based on larval growth rate and adult wing condition. The principal results showed that dietary supplements of casein (5.0%), a mineral mixture with nine components (0.9%), and L-ascorbic acid (0.5%) were essential for optimum growth and development of the insect.

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Résumé Diatraea grandiosella ou Southwestern Corn Borer, a été élevé sur un aliment de type méridique et on a déterminé ses besoins quantitatifs en protéïne, en sels minéraux et en acide ascorbique. Un test biologique a été conçu, basé sur le pourcentage de chrysalides obtenues et sur les conditions de développement des ailes, cela dans chaque test et dans le groupe témoin. Un supplément alimentaire de 5% de vitamine sans caséine, a permis une croissance et un développement optima.Une modification de la teneur en caséine de 2% a un effet défavorable sur la vitesse de la croissance larvaire. L'insecte exige un mélange de sels minéraux; une concentration de 0,9% de ce mélange est optima. En l'absence de ce supplément, la croissance larvaire est significativement ralentie. L'acide L. ascorbique a aussi été reconnu indispensable, sa présence, au taux de 0,5%, donne les meileurs résultats. La plupart des larves élevées sur milieux manquants d'acide L. ascorbique meurent au cours de la mue, entre le 4ème et le 5ème stade. La comparaison entre les présents résultats et deux d'autres chercheurs sont discutés.

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Contribution from the Missouri Agricultural Experiment Station, Columbia, as journal series no. 7116.     

Juvenile hormone and diapause in the Mediterranean corn borer,Sesamia nonagrioides

Juvenile hormone content of Sesamia nonagrioides larvae reared under different environmental conditions that induce diapause was studied using a bioassay on newly-emerged Tribolium confusum pupae. Two analytical methods were also used to measure JHIII content. Extracts from larvae that developed under different conditions of photoperiod and temperature caused different effects in T. confusum pupae. This can be related to different diapause intensities. Extracts from diapausing larvae produced a higher juvenilizing effect than the expected, considering their JHIII titer calculated by the chromatographic analysis. This indicates that hormones other than JHIII must be present in extracts of diapausing larvae of S. nonagrioides. The analytical procedures confirm that diapausing larvae have a higher JHIII titer in the haemolymph than non-diapausing larvae. This shows that JH is involved in the maintenance of diapause in this species.     

Influence of fertilizer on southwestern corn borer, Diatraea grandiosella, infestation and damage to field corn

Nitrogen (N) and phosphorus (P) fertilizers have differing effects on southwestern corn borer (SWCB). Diatraea grandiosella Dyar, densities and damage to field corn, Zea mays L. Nitrogen fertilization of corn is associated with an increase in number of stalks infested and girdled by corn borers, while addition of P has the opposite effect. When combinations of N and P were applied, there were no significant differences in SWCB infestation or damage from plots receiving no fertilizer. The effect of combinations of N and P on SWCB were intermediate to either element alone.

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Résumé Nous avons étudié les corrélations entre l'utilisation d'engrais azotés et phosphatés d'une part, l'infestation et l'alimentation de D. grandiosella sur maïs en champs d'autre part. Les formules d'engrais comparées étaient: pas d'engrais, 90 et 179 kg N/ha sans P, 45 et 90 kg P/ha sans N, et les combinaisons de ces deux teneurs en N et P.La contamination était plus élevée dans les lots ayant reçu de l'azote que dans ceux traités sans N, mais la présence d'azote n'a pas réduit le décapage des tiges et la verse dus à l'alimentatin larvaire. A l'inverse, les lots n'ayant reçu que du phosphore avaient des pourcentages plus faibles de tiges contaminées par D. grandiosella et ainsi décapées et versées, que ceux qui n'avaient pas reçu P. Il n'a pas eu de différences significatives dans les contaminations ou les dégats entre les lots ayant reçu différentes combinaisons de N et P, et les effets de ces combinaisons sur l'insecte étaient intermédiaires à ceux de N et P seuls.

     

Phenological adaptations of a colonizing insect: The southwestern corn borer,Diatraea grandiosella

Summary The developmental rate, critical photoperiod, and diapause intensity were determined for three populations of the southwestern corn borer, Diatraea grandiosella, from Missouri, Mississippi and Kansas. Mississippi larvae grew at the highest rate and Missouri larvae grew at the lowest rate. The zero developmental temperatures (°C) for the Missouri population were estimated from regression lines as follows: 10.5° (eggs), 10.8° (diapausing larvae), 13.3° (non-diapausing larvae) and 11.4° (pupae). The required heat units were: 85° (eggs), 588° (diapausing larvae), 333° (non-diapausing larvae) and 149° days (pupae). However, the observed low temperature limit for larval growth under constant temperature regimes was approximately 17°C.The critical day lengths for diapause induction observed at 25°C were: 15 h 11 min (Missouri); 15 h 20 min (Mississippi); and 15 h 22 min (Kansas). The photoperiodic response of the Mississippi larvae was more or less retained at 30°C, whereas the response of the Missouri larvae was completely suppressed at this temperature. Diapause was most easily terminated in the Kansas larvae. The most intense diapause was observed in the Mississippi larvae.Model seasonal life cycles of the three geographic populations were constructed using photothermograms. Although the models showed good agreement with the field situation for the Missouri and the Kansas populations, some unknown factor(s) remains to account for an extremely long critical photoperiod in the Mississippi population.Contribution from the Missouri Agricultural Experiment Station, as journal series no. 9001     

Regulation of larval diapause by juvenile hormone in the European corn borer,Ostrinia nubilalis

The effects of juvenile hormone (JH) on the larval diapause of the European corn borer, Ostrinia nubilalis, were investigated. The larval period was prolonged and the development of gonads was retarded if non-diapause larvae were treated with JH. Pupation of diapausing larvae was accelerated by allatectomy. It was concluded that the diapause of this borer is largely regulated by JH.     

Assembly and secretion of lipophorin by the larval fat body of the southwestern corn borer,Diatraea grandiosella: An in vitro study

The synthesis, processing, and secretion of lipophorin by the larval fat body of the southwestern corn borer, Diatraea grandiosella, was examined using in vitro techniques. Pulse-labeling of lipophorin with [³⁵S]methionine showed that apolipophorin-I and -II were each synthesized and secreted from the fat body into Grace's medium with an intracellular transit time of about 45 min. Secretion of the apolipoproteins from the fat body became insensitive to the presence of monensin, which disrupts protein processing in the Golgi complex, at 30 min, indicating that most of the pulse-labeled apolipoprotein has transited the Golgi complex by this time. Three inhibitors of protein processing, carbonylcyanide m-chlorophenyl hydrazone, monensin, and brefeldin A, inhibited secretion of lipophorin into medium. Puromycin treatment did not appear to result in the secretion into the medium of lipophorin particles containing incomplete translation products of apolipophorin-I or -II. Incubation of fat bodies with [³H]oleate resulted in the secretion of lipophorin containing [³H]glycerides, a process that was inhibited by cycloheximide, puromycin, and monensin, indicating that apolipoprotein synthesis is required for secretion of [³H]glyceride on nascent lipophorin particles. In contrast, suramin, which has been shown to block the binding of lipophorin to plasma membrane receptors, inhibited the synthesis and secretion of lipophorin, but it did not appear to inhibit the transfer of [³H]lipid from the fat body to lipophorin. Inhibitors of protein synthesis and processing, therefore, can be used to distinguish between secretion of lipophorin-associated lipids and secretion of lipids mediated by the lipid-transfer particle outside the plasma membrane of the fat body.     

Diapause of the southwestern corn borer, Diatraea grandiosella: Utilization of fat body and haemolymph reserves

The utilization of metabolic reserves of mature southwestern corn borers held in two regimes (23° 12L:12D and 30° 24L:0D) which permitted different rates of diapause development was studied. Diapause larvae which had been reared on a meridic diet or host-plant tissue were compared. Data were obtained on the fate of lipid, glycogen, protein and amino acid reserves of the fat body and haemolymph during diapause. The major results showed that lipids comprised ca. 80% of the fat body dry weight and formed the principal reserve of diapause larvae. Thin layer chromatographic analyses showed that triglycerides made up >90% of the fat body lipids. Protein, amino acids and glycogen were found to be of secondary importance during diapause since they made up <15% of the fat body dry weight. In contrast, the haemolymph had a high protein and low amino acid, lipid, and glycogen content. Haemolymph proteins supplemented the fat body lipid reserves and were drawn upon during the later stages of diapause.

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Zusammenfassung Die Art und das Schicksal der Stoffwechselreserven des Fettkörpers und der Haemolymphe diapausierender Südwest-Maiszünsler, Diatraea grandiosella, wurden untersucht. Im Labor herangezogene und im Freien gesammelte junge Diapause-Raupen wurden zwei verschiedenen Regimen unterworfen, welche signifikant verschiedene Diapause-Entwicklungsraten gewährleisteten: 23° 12L:12D und 30° 24L:0D. Als Daten wurden festgestellt: Verpuppungsraten, Gesamtkörpergewicht und der Verbrauch der Fett-, Glykogen-, Protein- und Aminosäure-Reserven des Fettkörpers und der Haemolymphe während der Diapause unter beiden Bedingungen. Obwohl die Freilandraupen im allgemeinen größer als die Labortiere waren, wurden doch wenig qualitative Unterschiede zwischen beiden Gruppen gefunden. Als Hauptergebnis zeigte sich, daß die Fette, die 80% des Fettkörper-Trockengewichts ausmachen, die hauptsächliche Stoffwechsel-Reserve darstellen. Sie bestehen überwiegend (>90%) aus Triglyceriden und wurden während der Diapause allmählich verbraucht. Eiweiß, Aminosäuren und Glykogen machen nur weniger als 15% des Fettkörper-Trockengewichts aus. Im Gegensatz dazu wies die Haemolymphe der diapausierenden Raupen einen relativ hohen Eiweiß- und geringen Aminosäure-, Fett- und Glykogen-Gehalt auf. Haemolymphe-Proteine ergänzten die Fettreserven des Fettkörpers und wurden während der späteren Stadien der Diapause abgebaut.

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Contribution from the Missouri Agricultural Experiment Station, Columbia, as journal series no. 6546.     

Dietary carbohydrates: role in feeding behavior and growth of the southwestern corn borer, Diatraea grandiosella

The effect of carbohydrates on feeding behaviour and growth and development of the southwestern corn borer, Diatraea grandiosella, was examined. A feeding behavioural biossay based on establishment of first stage larvae on test or control stations within 24 hr was employed. A nutritional bioassay evaluated larval growth rates and metamorphic success of larvae reared on test or control diets. The principal results showed that glucose, fructose, sucrose, and dextrins were feeding stimulants and permitted optimum growth and development. A dietary supplement of amylopectin allowed reasonably good growth while amylose was not a utilizable carbohydrate. The pentoses, arabinose, ribose, and xylose, as well as galactose, mannose, and sorbose, were found to inhibit larval growth. Since of all these sugars only xylose acted as a feeding deterrent it was proposed that at high concentrations they or metabolic derivatives were toxic. The results are discussed in relation to those obtained with several other insect species.     

Factors controlling the distribution of a subtropical corn borer,Diatraea grandiosella (Lepidoptera: Pyralidae)

During this century the southwestern corn borer, Diatraea grandiosella (Lepidoptera: Pyralidae), has extended its range from subtropical Mexico into the United States, below 38° N latitude. This maize‐feeding insect is now found from Arizona east to Alabama and north to Kansas, Missouri, and Tennessee. The species has adapted to the shorter growing seasons, longer summer daylengths, and lower winter temperatures present in the southern US than are present in Mexico. Life history, morphological, and behavioral traits were compared for populations of D. grandiosella from southeastern Missouri and southcentral Mexico and revealed differentiation in a suite of characters, some of which show clear adaptation to a northern climate while others are obviously less adaptive. An electrophoretic comparison of enzymes from D. grandiosella from the central portion of its range in the US and from a population from southcentral Mexico indicated that considerable genetic differentiation has occurred. Quantitative genetic studies should be undertaken on the original and dispersed populations to differentiate between those characters that have been directly responsible for the adaptation of this insect to northern maize‐growing regions and those that have changed merely due to genetic correlations with characters undergoing selection. Data from such studies, together with available information about the dispersal of this insect, should provide insight into factors regulating the movement of tropical insects into temperate regions.     

The role of juvenile hormone in the larval diapause of the European corn borer,Ostrinia nubilalis

The possible role of juvenile hormone (JH) in the induction and termination of larval diapause in the European corn borer, Ostrinia nubilalis, was investigated using topical applications of both JH I and a JH mimic as well as by monitoring JH titers with the Galleria bioassay. Neither JH nor the JH mimic ZR515 was capable of influencing diapause termination when administered topically. The Galleria bioassay revealed little or no JH in the hemolymph of mid diapause (>30 days) insects, indicating no demonstrable role for JH in diapause maintenance. When ZR515 was administered to nondiapause, newly ecdysed fifth instar larvae the pupal molting cycle was delayed. By use of photoperiodic regimes we were able to show that the molting delay was not equivalent to diapause induction. The Galleria bioassay showed differences in JH titer profiles between diapause and nondiapause animals during the final larval stadium. The nondiapause insects showed titers that decline rapidly to trace amounts following the molt to fifth instar then rose prior to pupation. The diapause insects had generally higher titers and exhibited a more gradual decline after the molt. No evidence was obtained to support the hypothesis that JH plays a key role in the induction, maintenance, or termination of larval diapause.     

Ultrastructure and respiration of the fat body of diapausing and non-diapausing larvae of the corn borer,Diatraea grandiosella

A comparative study of the fat body of diapausing and non-diapausing larvae of the corn borer, Diatraea grandiosella, was undertaken using the electron microscope and the oxygen electrode. The electron microscopic results showed a shift from a synthetic to a storage function taking place in a 1 to 2 day period during the final instar of non-diapausing larvae, and in a 4 to 8 day period in that of pre-diapausing larvae. This transition was characterized by a decrease in the number of mitochondria and amount of rough endoplasmic reticulum, and by an increase in the number of proteinaceous granules and lysosomes. In vitro measurements using the oxygen electrode showed that the fat body is a normal aerobic respiratory tissue. The tissue reacted in a predictable manner to inhibitors of oxidative metabolism, including malonate, rotenone, oligomycin, and antimycin, and to the uncoupler, dinitrophenol. During the last instar the observed decrease in the respiratory rate of the fat body coincided with the observed ultrastructural changes in its cells. The fat body of 75 day old environmentally induced and juvenile hormone induced diapausing larvae consumed 90% and 78% less oxygen, respectively than that of 14 day old non-diapausing larvae.     

Synthesis and release of lipophorin in larvae of the southwestern corn borer,Diatraea grandiosella: An in vitro study

The source of the lipophorin present in the larval haemolymph of the southwestern corn borer, Diatraea grandiosella, was examined in vitro. Although lipophorin was shown to be one of several proteins released from cultured fat body and midgut, only fat body was shown to synthesize lipophorin. Fat body, incubated in a medium containing [³H]leucine, was shown to release radiolabelled lipophorin using immunoprecipitation. Similar studies using midguts incubated in a medium containing [³H]leucine did not reveal any synthesis of lipophorin. Lipophorin was isolated by density-gradient ultracentrifugation from media in which the fat bodies of about 600 diapausing larvae had been incubated for 4 hr. The isolated lipophorin had a peak density of 1.11 g/ml, and contained various lipids including diacylglycerol, triacylglycerol, sterol, hydrocarbon, free fatty acid, phosphatidyl choline, phosphatidyl ethanolamine and sphingomyelin.     

Juvenile hormone and regulation of dichotomous spermatogenesis during the larval diapause of the codling moth

Spermatogenesis ceases during diapause and resumes after diapause. A possible causal relationship between the regulation of these phenomena and the fluctuations of the juvenile hormone titre connected with the diapause was examined in the codling moth. Spermatocyte lysis and spermatogenesis arrest are directly and reversibly related to these fluctuations. They are induced in the last-larval instar by sole application of the juvenoid Altosid to the penultimate-instar larvae predetermined not to enter diapause. Conversely, allatectomy of early last-instar larvae predetermined to diapause induces renewal of spermatogenesis and disruption of diapause. However, the continuation of the arrest of the spermatogenesis during diapause is not directly related to the presence of a high titre of juvenile hormone. The arrest extends throughout diapause which may continue for months, although no juvenile hormone could be detected in the species after 35 days of larval diapause.