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The southwestern corn borer, Diatraea grandiosella , enters diapause as an immaculate mature larva which is a polymorphic variant of the spotted non-diapause larva. Because dormant immaculate larvae could be obtained by treating last stage non-diapause larvae with a juvenile hormone mimic (JHM), experiments were conducted to determine whether these hormonally induced immaculate larvae (HIL) were physiologically comparable to the normal environmentally induced immaculate diapause larvae (EIL). Comparative data obtained about pupation rates, response to JHM, metabolic reserves, oxygen consumption, and the state of spermatogenesis of HIL and EIL led to the conclusion that the HIL were physiologically similar to the EIL. The results demonstrate that the developmental programme of non-diapause larvae could be switched and ‘diapause’ induced solely by the topical application of JHM. We believe that the data further support our hypothesis that the larval diapause of D. grandiosella is initiated and maintained by the juvenile hormone.

The influence of low temperature on the survival and geographical distribution of Diatraea grandiosella was examined. Data from both climatological and laboratory observations indicated that low-temperature mortality of diapause larvae is the principal reason that the species has not colonized northern corn-growing states within the U.S.A. Results showed that diapause larvae are susceptible to freezing and cannot successfully overwinter in field conditions where the 10-year-mean January temperature falls below −7°C. This finding correlated with information obtained about the species' coldhardiness. Diapause larvae were found to freeze at ca. −2°C and to supercool to only ca. −8.5°C. Severe mortality occurred when larvae were exposed to −4°C for 2 or 4 weeks. These results provide a basis for predicting the eventual distribution of the species within the United States.

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.

The hormonal mechanism which controls the larval diapause of the southwestern corn borer was examined. The onset of this facultative mature larval diapause is marked by a transition from a spotted to an immaculate larval form, and during diapause individuals may undergo one or more stationary larval ecdyses. Experiments were designed to uncover the nature of the humoral mechanism regulating this diapause state. The finding that injecting diapause larvae with 20-hydroxyecdysone only brought about a stationary larval ecdysis suggests that diapause was not maintained by the lack of ecdysone. Neck ligations performed on larvae which had just entered diapause resulted in a premature termination of diapause, and larval-pupal ecdysis occurred in the thoraco-abdominal section, suggesting that a cephalic factor was necessary for the maintenance of diapause. This finding was further supported by the discovery that injecting 20-hydroxyecdysone into the thoraco-abdominal section of previously ligated diapause larvae also resulted in a premature termination of diapause and larval-pupal ecdysis, indicating that ecdysone only initiated the pupal moulting cycle when the cephalic factor was absent. Further experiments led to the conclusion that the juvenile hormone is the cephalic factor. Topical treatment with a juvenile hormone mimic caused non-diapause mature larvae to become immaculate and enter diapause. Periodical topical application of this mimic to diapause larvae prolonged diapause and increased the number of stationary larval ecdyses. These findings suggest that the initiation and maintenance of diapause are regulated by juvenile hormone titre. Results indicate that larvae retain a high titre of juvenile hormone until the last stages of diapause. Injection of 20-hydroxyecdysone into early or middiapause larvae only caused stationary larval ecdyses, while the same injection into larvae in the late stages of diapause caused some of them to pupate. Histological studies of the neurosecretory cells, corpus cardiacum-allatum complex, and prothoracic glands showed that the endocrine system was not inactive during diapause. A new hypothesis is therefore proposed which recognizes the existence of hormonal activity during larval diapause and emphasizes the principal regulatory role of juvenile hormone.

The effect of water on diapause and the resumption of morphogenesis of the southwestern corn borer was examined. Diapause larvae were held under dry conditions or with access to water in various environmental regimes known to permit different rates of diapause development. Results showed that diapause development occurred at a higher rate in larvae held dry than in those continuously supplied with contact water. Larvae did not, therefore, require an exogenous water source to complete diapause development. Although the availability of water promoted the post-diapause pupal moulting cycle of larvae which had completed diapause development, those which maintained a tissue water content > ca. 55% did not require contact water to complete this cycle. The loss of water in diapause larvae held under dry conditions or with access to water along with the quantity imbibed following various periods of dehydration was estimated. The physiological significance of the results in relation to other similar data is discussed. Zusammenfassung DIE BEDEUTUNG DES WASSERS FUR DIE DIAPAUSE UND FUR DIE WIEDERAUFNAHME DER MORPHOGENESIS BEIM SUDWESTLICHEN MAISBOHRER, DIATRAEA GRANDIOSELLA Es wurde der Einfluss von Wasser auf Diapause und Wiederaufnahme der Morphogenesis bei Diatraea grandiosella untersucht. Reife Diapauselarven wurden aus Laborzuchten erhalten oder im Freiland in Sudost-Missouri gesammelt. Sie wurden trocken gehalten oder hatten Zugang zu Wasser und zwar in verschiedenen Umgebungsbedingungen, bei denen bekannter-massen die Diapauseentwicklung mit verschiedener Geschwindigkeit erfolgt. Die Ergebnisse zeigten, dass die Diapauseentwicklung rascher ablief bei Larven, die trocken gehalten wurden als bei solchen mit dauerndem Kontaktwasser. Die Larven brauchen demnach keine exogene Wasserquelle zur vollstandigen Diapauseentwicklung. Zwar begunstigt die Verfugbarkeit von Wasser nach der Diapause das Einsetzen der Verpuppungsphase; dennoch brauchten diejenigen Larven, deren Gewebswassergehalt bei uber ca. 55% lag, uberhaupt kein Kontaktwasser, um diese Phase, d.h. die Verpuppung, abzuschliessen. Der Wasserverlust von Diapauselarven bei trockenen und nassen Bedingungen wurde bestimmt und ebenso die aufgenommene Wassermenge nach Trockenperioden. Die physiologische Bedeutung der Ergebnisse in Beziehung zu anderen, ahnlichen Daten wird diskutiert.

The effect of dietary carbohydrates on feeding behaviour, food consumption, and survival of adult rice weevils, Sitophilus oryzae , was investigated. Weevils survived well on diets containing 72 per cent (w/w) cereal starches, dextrins, amylopectin, and glycogen but died prematurely on diets containing amylose, cellulose, inulin, mono-, and disaccharides. It was shown that dietary polysaccharides which permitted good survival were feeding stimulants while those which caused early mortality were either feeding deterrents or did not provide suitable physical feeding substrates. Starvation rather than digestive enzymatic lesions was therefore the principal cause of early adult mortality on the test diets. It was concluded that the branched-chain amylopectin portion of the cereal starches in the weevil's natural diet serves as both a feeding stimulant and an essential nutrient.

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.

Larvae of Diatraea grandiosella Dyar (Lepidoptera: Crambidae) reared under 2 photoperiods were found to have a higher growth rate than those reared in continuous darkness. At 30°C, the highest rate of growth occurred in larvae that were between 8 and 14 days old. During this period their mean weight increased from 23 to 139 milligrams per larva. Three nutritional indices were measured for 13- to 15-day-old larvae. On average, the insect retained 44% of the meridic diet, of this 22% went for tissue synthesis. Larvae had either 5 or 6 instars, depending largely on their sex. We found that 90% of the males had only 5 instars while 68% of the females underwent an additional larval ecdysis.

The metabolic reserves of Magicicada cassini , a periodical cicada with a 17 year life cycle, were examined. Analysis of males and females which were collected shortly after emergence and just before death provided information about the nature and fate of the reserves which had been accumulated during the attenuated larval period. Results showed that young females had a mean weight of 565 mg compared with only 351 mg for equivalent males. Lipids and soluble proteins were the principal reserve materials. Glycogen was a relatively minor reserve of both sexes. While young females contained about twice as much soluble protein (110 mg) as the males (51 mg), they contained three times as much total lipid material (58–19 mg). Lipids were fractionated into neutral and phospholipids and the absolute amounts of each class were determined; triglycerides were the main component. Further analyses of old females provided information about the utilization of reserves for oogenesis. The data showed that even though the adults feed, lipids and soluble proteins stored during the larval stages are essential for egg maturation. The results are discussed in relation to the special requirements of an insect which has a protracted immature stage, yet a fleeting adult existence.

Immaculate larvae which lack cuticular pigmentation are the typical diapause larvae of Diatraea grandiosella Dyar. Results snowed that mature spotted larvae reared under diapause-inducing conditions underwent a stationary ecdysis to become immaculate larvae. This stationary ecdysis occurred earlier when mature larvae were held at 30°C than at 23°C. Mature spotted larvae had a high weight loss until the immaculate ecdysis, after which their weight decreased slowly. During this period mature larvae became partially dehydrated and 10 days after the immaculate ecdysis had a mean water content of only 65%. A comparison of laboratory-reared and field-collected spotted and immaculate larvae revealed no physiological differences. However, field larvae were heavier and contained a significantly higher concentration of hemolymph pigments than the laboratory ones. These pigments were found to be carotenoids which were absorbed from ingested host plant tissues. The possible nature of hormonal mechanisms regulating diapause induction and development are discussed.

Feeding behaviour of newly hatched larvae of the Angoumois grain moth was investigated. A bioassay was developed based on larval response to various test materials which were added to corn starch and glycerol pellets placed in a circular arena. The distribution of larvae between two test and two control pellets in each arena was usually determined after 4 hr incubation to determine what factors influenced the initial phase of the insect's feeding behaviour. When components of a refined diet (casein, yeast, wheat germ, bran, and cholesterol) were assayed for their effect on feeding behaviour only wheat germ was found to evoke a strongly positive response. Further study revealed that the lipid portion of wheat germ contained potent arrestants and probably also contained biting incitants and feeding stimulants. An investigation into the nature of some of the active components in this lipid fraction revealed that triglycerides and, to a lesser extent, fatty acids served as arrestants. The classification of the measured behavioural response is discussed.

Larvae of the Angoumois grain moth readily established in refined diets moulded into pellets. A bioassay based on larval establishment, weight, and numbers of adults was used to determine the insect's major nutritional requirements. The results showed that test diets containing corn starch (49–64%), glycerol (15–19%), casein (9%), yeast (7·5%), and wheat germ (2·6%) permitted good establishment and normal development. No further improvements were obtained when diets were supplemented with a mineral or vitamin mixture, cholesterol, or ascorbic acid. It was concluded that yeast and wheat germ supplied the insect with adequate amounts of lipids, vitamins, and minerals. However, even the best diets lacked some undetermined growth promoting factor because larvae grew better in a natural product control diet.

Spermatogenesis rate was compared during the larval stages of Diatraea grandiosella Dyar programmed for a mature larval diapause or continuous development. Larval exposure to a 23°C 12L:12D regime induced diapause, while exposure to a 30°C 12L:12D regime permitted continuous development. The rate of spermatogenesis was evaluated from measurements of testicular volumes and histological examination of germ cells taken from prediapause and nondiapause larvae. Results showed that the testicular volume of mature diapause larvae was about 10 times smaller than that of equivalent nondiapause larvae. Histological data revealed that spermatogenesis progressed at a low rate in testes of prediapause larvae. In the 3rd instar spermatogonia were the principal germ cells, while primary and then secondary spermatocytes were detected in testes of the 4th and 5th instars. At the beginning of diapause in the 6th instar the secondary spermatocytes began to degenerate. In contrast, testes of 4th-stage nondiapause larvae contained secondary spermatocytes which then further differentiated into spermatids and sperm bundles in the 5th and 6th instars.

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. A study of the species fatty acid requirements revealed that dietary supplements of methyl linoleate or linolenate, but not methyl oleate or stearic acid, permitted normal wing development. The dosage required was low and as little as 0·03% methyl linoleate resulted in a high incidence of normal wing development. Dietary fatty acids, however, only marginally improved the larval growth rate. A study of sterol requirements revealed that (1) a dietary sterol was essential for larval growth, (2) β-sitosterol (0·18%) permitted a significantly higher larval growth rate than either cholesterol, 7-dehydrocholesterol, or stigmasterol. A dietary supplement of ergosterol did not support larval growth. The present results are discussed in relation to known lipid requirements and metabolism in other plant-feeding insects.

A simple method for rearing the Angoumois grain moth, Sitotroga cerealella , in an artificial diet is described. Although the larvae normally feed within grain kernels, they readily became established in pellets containing a mixture of five natural products. An evaluation of the growth rate in this medium revealed a marked sex difference. The males attained a maximum mean larval weight of 7·2 mg at 22 days compared with 12·3 mg for mature females at 24 days. Both sexes were found to pass through four larval instars. A study of the pupation rate showed that males reached 50 per cent pupation a full 5 days before females. While both sexes spent about 6·7 days in the pupal-pharate adult stage, the mean weight of newly-ecdysed female adults was 77 per cent greater than that of the males.

Nutritional and behavioral assays were designed to study the effect of dietary carbohydrates on the Angoumois grain moth, Sitotroga cerealella (Oliv.). Nutritional results showed that larvae grew better in artificial pellets containing cornstarch (60%, w/w) than rice or potato starch. Dietary amylo- pectin and glycogen supported development while larvae did not grow in diets containing amylose, cellulose, or inulin as the sole test carbohydrate. Whole or partial replacement of dietary cornstarch with mono- and disaccharides resulted in poor growth because of the inferior physical consistency of the test pellets. Behavioral results showed that the growth suppression caused by dietary amylose could be attributed to an inability to digest amylose rather than to any feeding deterrency. It was concluded that the insect has a specific dietary requirement for a branched-chain polymer of glucose with a (1 â€"» 4) and a (1 â€"» 6) linkages. The nature of insect digestive amylases is briefly discussed. J. Nutr. 102: 187-194, 1972.

The total lipid content of the fat-body reached a maximum of about 4.5 mg. per insect in mature larvae and only changed slightly through the pharate pupal stage. The lipid content of the haemolymph (about 0.5 mg. per insect) also remained fairly constant at the onset of metamorphosis. During this period triglycerides formed about 90 per cent of the neutral fatbody lipids with 1,2-diglycerides and sterols comprising the other 10 per cent. In contrast, 1,2-diglycerides and sterols made up about 65 per cent of the haemolymph neutral lipids. Triglycerides, free fatty acids, sterol esters, and hydrocarbons were only minor components. The significance of these analytical results and the function of some of the lipid components are discussed.

The midgut lipids of the southwestern corn borer, Diatraea grandiosella Dyar, were examined during its metamorphosis from larva to pupa. Results showed that the highest midgut lipid content (approximately 0.38 mg. per insect) was found in actively feeding, 14-day larvae. Following pupation the midgut lipid content dropped to only 0.04 mg. per insect. Thin-layer chromatography revealed that five neutral lipid classes could generally be detected in midgut extracts. For example, 14-day larval midguts contained the highest concentration of neutral lipids in the following proportions: triglycerides, 42 per cent; sterol esters, 29 per cent; sterols, 16 per cent; 1,2-diglycerides, 6 per cent; and traces of fatty acids and hydrocarbons. The titres of triglycerides, diglycerides, and sterol esters varied more than those of the other constituents at different nutritional and developmental stages. These lipid classes, along with free sterols, are apparently involved in neutral lipid storage or transport in midgut cells. Results obtained from midguts of insects which had been starved or fed lipid-free diets supported this interpretation. Possible mechanisms for lipid absorption, storage, and transport were evaluated.

Until recently the characteristics of image converters have confined their use almost entirely to the conversion of infra-red to visible radiation. The idea of using such a tube as an optical shutter is not new, but the application has awaited the development of a suitable tube.The paper compares the performance of various types of image converters and discusses in detail the characteristics of a new type of tube with special emphasis on its use for high-speed photography.

The present exploratory investigation examined the physical and chemical feeding requirements of Sitotroga cerealella (Olivier). Larvae which normally feed within kernels accepted nutritionally adequate test diets compacted into gelatine capsules. A nutritional bioassay was developed based on larval growth and adult emergence. Various combinations of natural products were tested as dietary media. Of those tested, a modified Haydak medium in which corn meal, whole wheat flour, yeast, hone), and glycerol were the essential components, was found to be best. Further experiments designed to formulate more refined diets proved reasonably successful, and the most satisfactory relined diet contained corn starch, casein, glycerol, and yeast as its major components. Although the insect developed on this medium, the overall results were not comparable to those obtained with the best diets of natural products. The future of mass-rearing this species on artificial diets and its nutritional chemistry are discussed.

The cabbage looper, Trichoplusia ni (Hubner), was reared on a meridic diet containing wheat germ (oil and solids) as the only plant adjuvant. Some attempts were made to determine the specific nutrients contained in wheat germ which are essential for Trichoplusia. Wheat-germ residue after chloroform: methanol extraction contained a factor required for normal larval growth, and the lipid fraction contained a factor required both for larval growth and normal wing development. Lack of the wing development factor resulted in various gradations of wing deformity or in failure of the moths to emerge from the pupal case. The factor was contained in the saponifiable portion of wheatgerm oil. A dietary supplement of methyl linoleate promoted larval growth and normal pupation, but did not produce normal wings. Ascorbic acid was also demonstrated to be an essential dietary requirement for Trichoplusia. Deficiency of ascorbic acid resulted in complete larval mortality at an immature stage.

The endocrine glands and related nerves of diapause and nondiapause larvae of Diatraea grandiosella Dyar were examined. The form and anatomical relationships of the brain, corpus cardiacum-allatum complex (CC-CA), prothoracic glands, and associated nerves were determined. While no anatomical differences were detected between diapause and nondiapause larvae, morphometric data revealed that diapause larvae had significantly larger CC-CA complexes than nondiapause larvae.