Seasonal adaptations of populations of the southwestern corn borer, Diatraea grandiosella, from tropical and temperate regions

Seasonal adaptations of populations of the southwestern corn borer, Diatraea grandiosella, obtained from south-central Mexico (19°N latitude) and southeast Missouri (37°N latitude) were compared. Day length and temperature were found to serve as environmental cues to programme the larval diapause of both populations, but different critical values were observed. The critical day length for diapause induction was about 13 hr light/day for Mexican larvae and about 15 hr light/day for Missouri larvae, and was relatively stable at 20 to 30°C. Mexican larvae displayed a less-intense diapause than did Missouri larvae. Some diapausing Mexican larvae maintained at 25 or 30°C pupated in about 15 days, regardless of the day length to which they were exposed. The rate of diapause development of Mexican larvae was high at day lengths between 14 hr and 16 hr, whereas that of Missouri larvae was accelerated at day lengths of 16 hr at 25 and 30°C. Diapause development of Mexican larvae was virtually unaffected by chilling at 10°C, whereas that of Missouri larvae continued at a low rate at 10°C. Selection of Mexican larvae for diapause showed that only four generations were needed to significantly increase the incidence of diapause.     

Protein release from the larval fat body of the southwestern corn borer, Diatraea grandiosella: An in vitro study

The release of protein from the perivisceral fat body of non-diapausing, pre-diapausing and diapausing larvae of the southwestern corn borer, Diatraea grandiosella, was examined in vitro. Time course studies showed a selective release of proteins into macromolecule-free Grace's medium. The rate of release of individual proteins differed. The release of some proteins was partially inhibited by the incorporation of potassium cyanide (10^?2 M) and ouabain (5 × 10^?3 M) into the medium. During a 5 min incubation a single major high molecular weight protein fraction was released at a high rate from the fat body of both non-diapausing and diapausing larvae. A low molecular weight protein (the diapause-associated protein) was also released readily from the fat body of diapausing larvae. Although most proteins released from the fat body in vitro appeared to be present in the haemolymph in vivo, one notable exception was the absence of the diapause-associated protein from the haemolymph. The method holds promise for facilitating further studies of protein release from insect fat body.     

Brain neurosecretory cell and ecdysiotropin activity of the non-diapausing,pre-diapausing and diapausing southwestern corn borer, Diatraea grandiosella Dyar

The location and number of brain neurosecretory cells were studied in the larval southwestern corn borer. One posterior, two median and two lateral groups of paraldehyde-fuchsin positive cells were found in each cerebral hemisphere.Implantation of brain parts containing different groups of neurosecretory cells revealed that the median neurosecretory cells contained higher ecdysiotropic activity than the other cell groups. In vitro culture of ecdysial gland with brain or brain-parts extract showed also that the median neurosecretory cells contained much higher ecdysiotropic activity than other neurosecretory cells. To estimate the ecdysiotropic activity of pre-diapausing 6th instar larvae, their brain or brain extract was incubated in culture medium containing an ecdysial gland from a day-4 last-instar non-diapausing larva. Data showed that the ecdysiotropic activity in the pre-diapausing larvae was far lower than in non-diapausing and diapausing larvae.     

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.     

Haemolymph ecdysteroid titres in diapause and nondiapause larvae of the European corn borer, Ostrinia nubilalis

The ecdysteroid titres of last-instar prediapausing, diapausing and nondiapausing larvae of Ostrinia nubilalis were determined by radioimmunoassay. In the nondiapause larvae a major peak of ecdysteroid activity preceded pupation by 24 h and continued through the pupal ecdysis. This peak was correlated with head and thorax critical periods as well as with changes in behaviour and physiology marking the transition from feeding larva to prepupa. Nondiapause larvae also displayed a rise in ecdysteroid titre during the feeding phase of development. This rise was approx one tenth that of the major peak and lasted 32 h. It was not correlated with any overt changes in larval physiology or behaviour. The diapause ecdysteroid profile was distinctive in that the levels measured were all lower than the lowest of the nondiapause curve. No peaks were observed in the diapause titres. Prepupal changes such as spinning and the cessation of feeding were not correlated with any increase in ecdysteroid levels. During diapause termination, under a long-day photoperiod, no increases in ecdysteroid titre were observed for the first 10 days. After 12 days individuals began to show ecdysteroids above the diapause levels. Pupation started after 16 long days.     

Diapause of the southwestern corn borer, Diatraea grandiosella: Further evidence showing juvenile hormone to be the regulator

Further evidence is presented to demonstrate the involvement of juvenile hormone (JH) in regulating diapause in the final larval stage of the southwestern corn borer. Diatraea grandiosella. JH titres in the haemolymph were measured throughout the entire diapause period. Additional results showed that actively secreting corpora allata are necessary to maintain diapause because allatectomized larvae terminated diapause prematurely. A topical application of JH mimic 2 days after the allatectomy prevented this premature termination of diapause. Intact nervous connections between the brain and the corpora allata were necessary for the maintenance of JH secretion. Other surgical work showed that the brains of nondiapausing larvae exhibited a higher ecdysiotropic activity than those of pre-, early-or mid-diapausing larvae.A single application of a JH mimic was more effective in maintaining a diapause-like state in nondiapausing larvae than were repeated topical applications of C₁₈-JH or an implantation of active corpora allata, suggesting that JH was more rapidly metabolized than was the JH mimic. The oxygen consumption of diapausing larvae which had received repeated topical applications of JH mimic was not significantly elevated over that of the controls indicating that treated larvae maintained a low metabolic rate even though they reverted to the spotted morph. A single application of 0.03 μg JH mimic/larva was sufficient to prolong diapause, thereby confirming that JH is necessary for diapause maintenance.     

Genetic control of geographic variation for cannibalism in the southwestern corn borer,Diatraea grandiosella

The southwestern corn borer,Diatraea grandiosella Dyar, is a subtropical insect whose range has expanded northward within this century. Geographic variation exists between populations at the extremes of the range for a suite of morphological and behavioral characters, including cannibalism. Laboratory colonies established from a Missouri population (37°N lat.) with a high cannibalism rate and a Mexican population (19° N lat.) with a low cannibalism rate were used to examine the genetic basis of cannibalism by means of a controlled breeding design. When larvae were held in pairs on artificial diet in 30 ml plastic cups at 30° C 16L:8D, the highest incidence of cannibalism in both Missouri and Mexican populations was found in larvae 15 to 18 days-of-age (5th and 6th instars). Under these conditions, cannibalism was expressed in 33% of the pairs formed from Missouri larvae and 11% of the pairs formed from Mexican larvae. First and second generation crosses between Missouri and Mexican populations showed an intermediate level of cannibalism, whereas backcrosses to the parental generations showed a regression to the parental phenotypes. These results indicate that cannibalism is under additive genetic control. Larvae from the Missouri parental population were more likely to consume their victim (i.e., cannibalize) once intraspecific killing had occurred than were larvae from the Mexican parental population or from any of the crosses, and female larvae were cannibals more often than were males. Under the conditions employed, no advantage was detected for cannibalism over instraspecific killing for larval weight gain or growth rate.     

Polyunsaturated fatty acid and sterol requirements of the southwestern corn borer, Diatraea grandiosella

The southwestern corn borer, Diatraea grandiosella, was reared on a meridic diet and its lipid requirements were determined. A dietary supplement of wheat germ oil was found to contain factors which were essential for larval growth and normal wing development. An investigation into the nature of these factors showed that linoleate or linolenate promoted normal wing development whereas β-sitosterol enhanced the larval growth rate.     

Endocrine interactions controlling the larval diapause of the southwestern corn borer, Diatraea grandiosella

The effect of hormone treatments on larvae of the southwestern corn borer, Diatraea grandiosella, was examined to explore endocrine interactions which regulate its mature larval diapause. This species is especially suitable for investigating the endocrine control of larval diapause because it ecdyses from a spotted to an immaculate morph at the onset of diapause, and the immaculate morph may undergo up to three stationary ecdyses during diapause. The response of prediapause larvae to a β-ecdysone injection showed that the larvae have the potential to transform into the immaculate morph early in the final larval instar, but under normal conditions this ecdysis occurs after larvae reach maturity. Since a high rate of pupation occurred among early diapause larvae which received a head ligature, followed 17 days later by a β-ecdysone injection, diapause larvae retain active corpora allata. Since a head ligature prevented diapause larvae from responding to repeated topical applications of a juvenile hormone (JH) mimic or JH 1, the intermediate titer of JH associated with larval diapause may inhibit the synthesis or transport of ecdysiotropin, or its release from the corpora cardiaca. Current results suggest, therefore, that an interaction between the cerebral neurosecretory system and the corpora allata regulates the initiation, maintenance, and termination of this larval diapause.     

Larval esterases of the southwestern corn borer, Diatraea grandiosella: Temporal changes and specificity

Disc electrophoresis was used to examine and characterize the esterases present in the fat body, haemolymph, and midgut of last stage larvae of the southwestern corn borer, Diatraea grandiosella. Significant temporal changes were observed in the pattern of the 4 major esterases of the fat body and 3 major esterases of the haemolymph. These changing profiles presumably relate, in part, to a requirement for the degradation of juvenile hormone (JH) in preparation for metamorphosis.The binding capacity of esterases present in the larval midgut towards JH I and three JH mimics (alkyl-3,7,11-trimethyl-2,4-dodecadienoates) was also examined. The midgut of last stage nondiapausing larvae was shown to contain a carboxylesterase which bound all three JH mimics. Another esterase which bound JH I, but not the mimics, was also present. An esterase with a similar electrophoretic mobility was detected in the haemolymph and integument. Since the JH I binding esterase did not bind the JH mimics, the mimics do not appear to synergize JH by inhibiting its ester hydrolysis.     

Haemolymph protein reserves of diapausing and nondiapausing codling moth larvae, Cydia pomonella (L) (Lepidoptera: Tortricidae)

Haemolymph from diapausing codling moth larvae contain a dominant soluble protein, which is of minor significance in the haemolymph of nondiapausing larvae. This haemolymph protein is accumulated during the ultimate larval instar and its concentration is maintained throughout diapause development. Larvae induced into a diapause-like condition following topical treatment with a juvenile hormone mimie stored the haemolymph protein.     

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.     

Proteins of the fat body of non-diapausing and diapausing larvae of the southwestern corn borer, Diatraea grandiosella: Effect of juvenile hormone

The proteins of the fat body of non-diapausing, pre-diapausing, and newly-diapaused larvae of the southwestern corn borer, Diatraea grandiosella, were examined. Since a low titre of juvenile hormone (JH) is present in the haemolymph throughout the final instar of non-diapausing larvae, the hormone does not appear to stimulate the pre-metamorphic synthesis of proteins. In contrast, the high titre of JH in the haemolymph during the final instar of pre-diapausing larvae appears to stimulate the synthesis of selected proteins. For example, pre-diapausing larvae store in their fat body a low molecular weight protein which has been named the ‘diapause-associated protein’. When non-diapausing larvae were treated topically with C₁₇-JH or a JH mimic, from 50 to 70% entered a diapause-like state as fully grown larvae. These hormone-treated larvae accumulated the diapause-associated protein and a high molecular weight protein in their fat bodies. Both of these proteins were shown to be released from the fat body of newly-diapaused larvae in vitro, and may function in the haemolymph during diapause. The high molecular weight protein, isolated from the haemolymph, was shown to contain neutral and polar lipids, including biochromes. Its storage in the fat body and release into the haemolymph may be essential for the transport of lipids during diapause. The fat body proteins of newly-diapaused larvae of the southern cornstalk borer, Diatraea crambidiodes, were also examined electrophoretically. They were found to contain a similar protein pattern to that of D. grandiosella, including the presence of a diapause-associated protein.     

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.

     

Hydrolysis of juvenile hormone in diapausing and non-diapausing larvae of the southwestern corn borer,Diatraea grandiosella

Summary The role of juvenile hormone (JH) esterases in relation to the diapause state of the southwestern corn borer,Diatraea grandiosella, was examined. The facultative larval diapause of this insect is dependent upon the presence of JH. Plasma, fat body, midgut, and body wall extracts metabolized [³H]JH I and [³H]JH III to JH-acid in vitro. JH-diol, JH-acid-diol, or conjugated polar metabolites were not detected. A longer half life of [³H]JH I was found in vitro in the plasma of diapausing larvae than in that of non-diapausing larvae. Although JH hydrolytic activity was relatively low in the plasma of pre-diapausing and diapausing larvae, systematic changes were observed suggesting that JH esterases may be involved in regulating the JH titer during this period. The JH hydrolytic activity found in the plasma of diapausing larvae was 3 to 5 times lower than that found in the plasma of mid-last instar non-diapausing larvae. Gel filtration profiles obtained from the plasma of diapausing and non-diapausing larvae suggested that JH esterases and -naphthyl-acetate esterases are different enzymes. Multiple overlapping peaks of JH hydrolytic activity with an apparent molecular weight range of 43,000 to 75,000 were detected, whereas 2 separate peaks of -naphthyl-acetate hydrolytic activity (apparent mol. wt. ca. 54,000, and 120,000) were detected. Gel filtration of supernatants of fat body indicated that JH was hydrolyzed at a lower rate by the fat body of pre-diapausing larvae than by that of non-diapausing larvae.     

Relationship between the fatty acids of fat body triacylglycerol and lipophorin diacylglycerol of non-diapause and diapause larvae of the southwestern corn borer,Diatraea grandiosella

The fatty acids of the triacylglycerol reserves in the fat body and of the diacylglycerol of lipophorin in the hemolymph of non-diapause and diapause larvae of D. grandiosella were compared. For both non-diapause and diapause larvae palmitate, palmitoleate, oleate, and linoleate were the predominant fatty acids present in fatty body triacylglycerol, and palmitate, oleate, and linoleate were the predominant fatty acids present in lipophorin diacylglycerol. However, differences were detected in the relative amounts of oleate and linoleate present in lipophorin diacylglycerol of non-diapause and diapause larvae. The relative amount of linoleate in lipophorin diacylglycerol declined during diapause, whereas that of oleate remained relatively high during diapause. The fatty acid profile of lipophorin diacylglycerol from non-diapause larvae treated with a juvenile hormone analog to induce a diapause-like state more closely matched that of diapause larvae than that of non-diapause larvae. The differences detected in the fatty acid composition of lipophorin diacylglycerol in non-diapause and diapause larvae appear to be due mainly to the different physiological states rather than to the different rearing temperatures employed. The results are discussed in relation to the essential role fatty acids, especially oleate, play in the survival of diapause larvae.     

Juvenile hormone esterases in diapause and nondiapause larvae of the European corn borer, Ostrinia nubilalis

Haemolymph levels of juvenile hormone esterase, 1-naphthyl acetate esterase, and juvenile hormone were measured in synchronously staged diapause and nondiapause larvae of the European corn borer, Ostrinia nubilalis. Juvenile hormone esterase levels were monitored using juvenile hormone I as a substrate while juvenile hormone titres were measured with the Galleria bioassay. Haemolymph of nondiapause larvae showed two peaks of juvenile hormone hydrolytic activity: one near the end of the feeding phase and a smaller one just prior to pupal ecdysis. These peaks of enzyme activity correlated well with the low levels of haemolymph juvenile hormone. Juvenile hormone titres were high early in the stadium then showed a second peak during the prepupal stage coinciding with low esterase activity. Diapause haemolymph had peak juvenile hormone esterase activity nearly 4 times the nondiapause level, reaching a peak near the end of the feeding phase. Diapause-destined larvae retained high juvenile hormone titres even during the rise of the high esterase levels. 1-naphthyl acetate esterase levels did not correlate with the juvenile hormone esterase levels in either the diapause or nondiapause haemolymph. High levels of 1-naphthyl acetate esterase activity were associated with moulting periods.     

Seasonal adaptations of different geographical populations of the sunflower moth, Homoeosoma electellum

A photothermogram constructed for a central Missouri population (ca. 39°N latitude) of the sunflower moth, Homoeosoma electellum (Hulst) predicted that this population has a seasonal life cycle of 2 complete and a partial third generation per year, and that daylengths of less than 13 h 30 min light/day and mean temperatures of less than 20°C induce the mature larval diapause. A test of the predicted life cycle revealed that larvae entered diapause when they were exposed from their first instar onwards to natural conditions in central Missouri beginning September 15, 1982. Sunflower moths obtained from northwest Texas (ca. 35°N latitude) and northeast South Dakota (ca. 45°N latitude) displayed shorter critical photoperiods for diapause induction at 20°C (12 h 30 min light/day and 12 h 15 min light/day, respectively) than did those from Missouri. The population of the sunflower moth obtained from South Dakota does not, therefore, appear to be adapted to local conditions, and moths might disperse from lower latitudes to establish transiet populations each year.     

Thermal and thermoperiodic effects on larval development and diapause in the European corn borer, Ostrinia nubilalis

Effects of temperature and thermoperiod on larval development and the induction of diapause were investigated in the European corn borer, Ostrinia nubilalis. Developmental threshold temperatures characteristic of the first four larval instars were estimated under both thermoperiods and constant temperatures. Threshold values were similar under the two conditions, but the 4th-larval instar was shown to display a significantly lower developmental threshold temperature than was characteristic of the earlier instars. Although developmental times (days per instar) were not greatly affected by fluctuating temperature regimes, the quantity of growth (weight, head width) during the 4th and 5th (last) stadia was found to be much greater under thermoperiodic regimes than under comparable constant temperature conditions. By means of thermoperiodic regimes having identical mean temperatures but different cryophase durations, it was demonstrated that the induction of diapause is dependent on the duration of the cryophase rather than on the mean temperature of the thermoperiod. To be effective, the cryophase must be colder than the insect's thermoperiodic response threshold. It was also demonstrated that thermoperiodic responses that are readily produced under continuously dark rearing conditions are not manifested under continuous light.     

Oviposition deterrents from the egg masses of the adzuki bean borer, Ostrinia scapulalis and Asian corn borer, O. furnacalis

Bioassays using gravid females of the adzuki bean borer, Ostrinia scapulalis (Walker), and the Asian corn borer, O. furnacalis (Guenée) (Lepidoptera: Crambidae), showed that the presence of an egg mass of a conspecific deters oviposition. Volatile chemicals emanating from the egg mass were responsible for the deterrence, and these deterrents could be extracted from the egg mass with hexane. When fractionated using a Sep‐Pak® Plus NH₂ cartridge, the deterrents were eluted with a 98 : 2 mixture of diethyl ether and acetic acid (polar lipid fraction). The polar lipid fraction contained free fatty acids with 14–20 carbons, and palmitic acid, palmitoleic acid, and oleic acid were predominant. A blend of all identified fatty acids, a blend of six major fatty acids (palmitic, palmitoleic, stearic, oleic, linoleic, and linolenic acids), a blend of the two Z‐9‐alkenoic acids (palmitoleic and oleic acids), palmitoleic acid alone, and oleic acid alone showed deterrence against O. scapulalis which was comparable to that provoked by the full egg extract. The dose‐dependency of the deterrent effects of palmitoleic acid and oleic acid was verified in O. scapulalis. The binary blend of palmitoleic acid and oleic acid was also confirmed to deter oviposition in O. furnacalis.