Search

Ambient thermoperiod was found to play an important role in the larval growth and seasonal biology of the black cutworm, Agrotis ipsilon (Hufnagel). First and second instars were unable to survive prolonged exposure to very cool thermoperiods (e.g., 18C:6T (5°:12°), whereas third to sixth instars survived but grew very slowly under such conditions. Approximate simulation of autumnal thermoperiods in which temperatures started at 15C:9T (15°:25°) and declined over a period of about 42 d to stabilize at 18C:6T (5°: 12°) were used to estimate the cutworm's responses to seasonal temperatures. It was shown that such a regime resulted in mature, sixth-instar larvae that were unable to pupate until exposed to a more favorable temperature regime (about 20°C). If the simulated autumnal temperatures had not fallen below an approximate threshold of a daily average of about 8.5°C before the middle of the sixth stadium, the larvae would attain the pupal stage even in the presence of the otherwise prohibitively low thermoperiodic regime. The results of this study suggest that the black cutworm may survive many months of at least mildly cold conditions as larvae in a state of nondiapause dormancy.

L-Dopa inhibited survival, growth, pupation, and pupal weight of the black cutworm, Agrotis ipsilon (Hufnagel). It inhibited growth by reducing assimilation of food and by reducing the efficiency of conversion of assimilated food into insect tissue, but had no effect on amounts ingested. Catechol did not inhibit survival or ingestion, but inhibited growth and pupation. It inhibited growth by reducing the efficiency of conversion of assimilated food. Chlorogenic acid and dopamine had no apparent effect on survival, growth, pupation, or pupal weight.

Effects of temperature, photoperiod, and thermoperiod on growth of the black cutworm, Agrotis ipsilon (Hufnagel), were investigated. No evidence of a periodically regulated larval or pupal diapause was obtained. Using 12:12 (L:D) photoperiods at different constant temperatures, developmental threshold temperatures were estimated for each of the postembryonic developmental stages (first instar to adult). Thermoperiods were shown to stimulate larval growth (weight and head width). Thermoperiods also tended to result in lower developmental threshold temperatures and in shorter stadia than did comparable constant temperature photoperiods. However, the percentage of the total larval developmental period represented by each stadium was found to be independent of both photoperiod and thermoperiod. No evidence was obtained that suggested a differential response to temperatures among successive instars. Results are discussed regarding developmental and seasonal biology of the species.

A study was made of cold acclimation in the life stages of the black cutworm, Agrotis ipsilon (Hufnagel), and the role of acclimation and nondiapause dormancy in the overwintering strategy of the species. The cutworm was shown to be freeze-susceptible and capable of only very limited acclimation. Eggs and older larvae (fourth to sixth instars) could survive short periods of subfreezing temperatures, but young larvae, pupae, and adults showed no significant cold hardiness. Supercooling occurred to a minor degree but did not appear to play a role in survival under subfreezing temperatures. The possible roles of egg and larval cold hardiness and of the nondiapause dormancy of mature larvae in the overwintering capabilities of the black cutworm are discussed.

Larvae of the furniture carpet beetle, Anthrenus flavipes LeConte, possess a bundle of caudal spicisetae kept in constant vibration during locomotion. These setae originate from an elliptical cuticular plate situated at the upper middle portion of the last larval segment above the anus. This “supra-anal organ” occurs in all larval instars, and the number of associated spicisetae is specific for each instar. These vibrating caudal setae contribute to the overall defense of the larva against the attacks of both a pseudoscorpion predator, Chelifer sp., and a bethylid parasite, Laelius pedatus (Say).

Surface features of mouthparts of mature larvae of the black cutworm, Agrotis ipsilon (Hufnagel), were examined using the secondary emission mode of a scanning electron microscope. Particularly visible were 8 small sensilla basiconica at the distal extremity of the maxillary palp, 3 sensilla campaniformia on this palp and 2 sensilla styloconica on the galea. Additional features of the labrum, mandibles, hypopharynx and labial palps were displayed and discussed. A description is presented of coordinated mouth part function based on present structural findings and literature reports.

The black cutworm, Agrotis ipsilon (Hufnagel), is a highly polyphagous species; therefore, the larvae are subjected to a wide variety of allelochemics. We have tested the hypothesis that some allelochemics may exert chronic effects on rate of growth, ingestion of food, utilization of food, and pupation. Growth and pupation were inhibited by p-benzoquinone. It inhibited growth by reducing ingestion. The reduced form of p-benzoquinone, hydroquinone, was not biologically active in our experiments. Duroquinone, a synthetic, inhibited survival, growth, and pupation. It inhibited growth by reducing ingestion, the efficiency of conversion of assimilated food, and the overall efficiency of conversion of ingested food. The biologically active concentrations were well within the range at which many allelochemics occur in plants.

Further evidence is presented in support of the hypothesis that allelochemics may exert chronic effects on rates of larval growth, ingestion, and utilization of food. Resorcinol inhibited ingestion and growth, but did not inhibit pupation or pupal weight of the black cutworm, Agrotis ipsilon (Hufnagel). Phloroglucinol inhibited survival, growth, and pupation. It inhibited growth by reducng the efficiency of conversion of assimilated food and the efficiency of conversion of ingested food. Gallic acid inhibited growth, survival, pupation, and assimilation of food.

Scanning electron micrographs and serial longitudinal and cross sections of the western corn rootworm, Diabrotica virgifera LeConte , antennae revealed that the antennal structure of males and females was similar. However, the longer ♂ antennae have more sensilla and possess 6 types of sensilla on the terminal antennal segment not found on the terminal segment of ♀ antennae; the ultimate antennal segment of the female possesses 4 sensillar types not found on the comparable antennal segment of the male.

A meridic diet, developed for Trogoderma glabrum (Herbst), contains lactalbumin, glucose, fructose, cholesterol, the McCollum-Davis no. 185 salt mixture, linoleic and linolenic methyl esters, and 11 vitamins. Criteria used to determine optimal source and concentration of each nutrient were the weight of larvae and pupae and the incidence of pupation. Characteristics of growth on meridic and oligidic media were compared for other Trogoderma (5 species), Anthrenus, Attagenus (2 species), Dermestes, and Thylodrias. For most species tested, growth was improved on the newly developed diet. Contrary to previous reports, adults of Trogoderma were observed to feed.

Hemocytes were isolated from Periplaneta americana (L.) adults and prepared by the critical-point method for examination with a scanning electron microscope (SEM). Micrographs obtained from intensity, and Y-modulation of the SEM beam revealed mainly spherical or broadly ellipsoidal hemocytes, 6-8 μ. diam, with irregular surfaces composed of small evaginations and indentions. Hemocytes which began to migrate exhibited slender processes which projected radially from a well-defined cell margin. In an advanced state of presumed motility, the pseudopodlike extensions had coalesced into a reticulated, stellate-tipped, membranous veil. The externally noted similarity of all examined hemocytes supports the concept of very few or 1 basic cell type with a capacity for several functional states.

It has long been recognized that the successful rearing of an organism may depend on factors contributing to the acceptability of the diet as well as those responsible for adequate nutrition. The importance of influences on feeding behavior is apparently very great in the case of most plantfeeding insects, as the host plant must serve not only as food, but also as the principal environment of the insect.

Feeding behavior of fifth-instar nymphs was studied utilizing a photographic technique with exposures on color film made, usually, at 60-second intervals. On the natural diet of milkweed seed, feeding occurred in cycles averaging about 22 hours, separated by inactive intervals of 2 to 6 hours. Feeding activities occupied about 75% of each major feeding cycle. No feeding was done during the 48 hours preceding the imaginal (final) ecdysis. Intensity of feeding and characteristics of feeding behavior were markedly influenced by the presence or absence of the milkweed seed coat. The seed coat factors important to normal feeding have not been identified, but are presumed to be chemotactic in nature. The apparent deficiencies of a purified diet developed in earlier work were shown not to be nutritional; instead, they were related to a failure of this diet to meet the feeding requirements of the bug.

The neuroendocrine complex in the head of the European corn horer Ostrinia nubilalis (Hubner), is composed of 40 neurosecretory cells in the brain and 14 in the 2 fused corpora allata-cardiaca. The 20 cells in each hemisphere of the brain are in 3 groups; medial, lateral, and posterior. The neurosecretory cells of the brain, stained with paraldehyde fuchsin, showed no differences between mature diapause and nondiapause types. No size or staining reaction differences associated with a photoperiodic stimulus were detected. Borers collected from the field showed a decreased amount of paraldehyde fuchsin-positive material with increased time in the cold.

That plant tissues may contain substances which are toxic to insects is well known. The insecticidal effectiveness of plant-derived materials such as rotenone, pyrethrums, nicotine, and many others, testifies to both the existence and the potency of such biological compounds. The role that toxic plant products might play in the resistance of a given plant toward infestation by insects has not been investigated to any great extent. In a few instances, however, some degree of correlation has been shown between host plant resistance and the presence of deleterious substances in the plant tissues (reviewed by Painter (1951) Kuhn and Low (1955)).

When confronted with a choice of two or more purified diets or plant tissues, larvae of the European corn borer tend to feed selectively on the diet or tissue containing the highest concentration of sugars (Beck 195(5 a, b). This behavior characteristic has been named saccharotrophism (Beck 1950 b). A detailed investigation of the saccharotrophic response of the borer disclosed that the sugar content (glucose, fructose, or sucrose) of the dietary substrate influenced the maintenance of larval feeding; the length of time a larva remained at a given feeding site was in direct proportionality to the sugar concentration of the site (Beck 1956 c). Saccharotrophism, operating in conjunction with thigmotaxis and negative phototaxis, was found to be an important factor in the orientation of borer larvae on the corn plant (Beck 1956 b).

The European corn borer is a non-host-specific insect, and has been reported feeding on over 200 different plant species (Caffrey and Worthley 1927, Hodgson 1928, and others). The borer's native Eurasian host was probably wild hop or one of the larger grasses, such as millet (Caffrey and Worthley 1927). Corn, being of American origin, could not have been the native host, but has proved to be the preferred host wherever the geographical distributions of the plant and insect coincide. The broad range of possible host plants is of considerable significance to the study of the relationships between the borer and the corn plant. It indicates that the plant characteristics required for successful borer establishment and growth are present in a large number of plant species and are not peculiar to corn alone.

Some developmental characteristics of Trogoderma glabrum (Herbst) are considered in relation to the biological adaptations of the species. Larvae in five different physiological states—normal, Dauer, retrogressed, regrown, and Dauer-regrown—were compared with respect to environmental stimuli controlling the induction of pupation. The responses of the larvae showed that retrogression led to a requirement not only for food but also for long-day photoperiods and the presence of males as stimuli inducing pupation of female larvae. The Dauer condition did not in itself influence competence to pupate. Retrogressive ecdyses were found to exact only very small expenditure of the larval reserves of energy and material. The function of retrogressive ecdyses is postulated to be the adjustment of body size to maintain a constant physiological state, density, and water content. Retrogression and the Dauer larval condition were compared with the diapause state as currently defined and were postulated to be unrelated to diapause or any form of dormancy.

Neural and hormonal regulation of development from the last larval ecdysis to pupation was studied in the greater wax moth, Galleria mellonella (L.). An obligatory prepupation feeding period of about 24 hr followed the larval ecdysis. Endocrine competence of the brain fell to a low level at this time, and its subsequent increase depended on the functioning of the suboesophageal ganglion during the 2 or 3 days immediately following ecdysis. The maintenance of brain endocrine activity–presumably prothoracotropic hormone (PTH) production–was required during most of the stadium. During this period, the endocrine activity of the brain could be suppressed by: (1) brief exposure of the larvae to low temperatures; (2) severance of the ventral nerve cord in the 1st abdominal segment; (3) extirpation of the terminal terminal ventral ganglion; and (4) ligation of the abdomen at segment 6. Using H. Piepho's system of developmental staging based on degree of eye pigment retraction, it was found that dependency on terminal ganglion function ended early in eye pigment stage 3 (31); proctodone dependency ended late in that stage (32); dependence on PTH ceased at a point intermediate between stages 3 and 4; and dependency on ecdysone continued until early in stage 4. Pupation could also be inhibited by enforced distortion of body form, up to eye pigment stage 4. Distortion inhibited pupation by the suppression of ecdysone production; the administration of crystalline ecdysone promoted continued development among distorted larvae.

Under standard culturing conditions (basal rearing medium, 30°C, 65–70% RH) Trogoderma glabrum (Herbst) larvae displayed either 5 (males) or 6 (females) larvae stadia. No sex difference was detected in head-capsule widths of the successive instars, but the additional female stadium resulted in a pronounced sex difference in the size and weight of the prepupal instar. The larval growth period was from 26 to 30 days among the males, and from 32 to 36 days among the females; only a very small proportion of female larvae underwent a supernumerary 7th larval stadium and a delay of pupation. When isolated without nutrient medium, 6th-instar females failed to pupate and entered a period of retrogressive larval development. They molted periodically to progressively smaller larval dimensions (here termed “retromolts”). During 1 year of complete deprivation, the larvae retromolted from 5 to 8 times. Retromolts did not represent a simple reversal of larval development, in respect to weight and head-width; the weight and dimensional changes associated with a retromolt were much slighter than those accompanying normal larval growth, even though opposite in sign. Although all isolated larvae underwent the 1st retromolt within 2 weeks after isolation, subsequent retromolts occurred irregularly, and no temporal pattern could be discerned. The rate of weight loss tended to be highest among larvae that retromolted the most frequently, but retromolt frequency was not determined by the rate of weight loss. Headwidth following the retromolt was closely correlated with larval weight rather than with retromolt number. These characteristics were interpreted as suggesting that the physiological mechanisms controlling the molting cycle were relatively independent of those controlling metabolism and weight loss. The rate of oxygen uptake declined rapidly following larval isolation and stabilized at a level representing about 5% that of 6th-stage larvae on medium. During retrogressive development the larvae maintained a normal balance of body water, compensating for ecdysial water loss by absorption of atmospheric moisture. The adaptive significance of retrogressive development, in comparison with diapause, is discussed.

A sterile holidic diet was formulated that has sustained 18 generations of the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), an aphid generally restricted to legumes. Although apparently satisfactory for continuous propagation, the diet did not promote optimum growth and reproduction. Pea aphids reared on the diet showed a mean adult weight of 1.6 mg, 68% of that of plant-reared aphids. The mean number of progeny per diet-reared aphid per day was 0.54, compared to a mean of 6 per day among plantreared aphids. The mean generation period was 13.1 days for the first 10 generations on the holidic diet. A feeding apparatus was developed that allowed the aphids to feed undisturbed for a week, yet permitted the diet to be changed more frequently. The feeding apparatus consisted of a refillable diet chamber with a Parafilm® membrane above an aphid chamber. The aphids were placed directly on the membrane of the diet chamber when they were transferred from one feeding apparatus to another, eliminating the need for them to climb up to the membrane. As many as 200 adults were reared in a single cage, and adult populations of 600–1000 were maintained.

The problem of identifying the factors underlying the host plant relationships of phytophagous insects is made up of many interrelated facets. Although there is a voluminous body of literature on the subject of insect-host plant relationships, there is a paucity of precise information. This situation has been caused by the various contributing aspects not having been adequately isolated for experimental analysis. Insect-plant adaptations are of sufficient biological and practical importance to merit more study than has been devoted to them in the past.

Pupation of female Trogoderma glabrum (Herbst) is inhibited by small rearing containers and stimulated by relatively high population density. In the absence of a granular substrate and males of the species, mature females fail to pupate, and they undergo additional larval molts. Pupation is weakly stimulated by long-day photo-periods. Female larvae that have undergone several retromolts regain weight and maturity rapidly when incubated in nutrient medium. Regrown larvae fail to pupate at optimal rate unless exposed to both long-day photoperiods and males of the species.

A bioassay was developed to investigate the feeding behavior of Scolytus multistriatus (Marsham) on extracts of elm bark. An apparatus was designed to give test beetles a choice between an extract or control station. Aqueous and benzene extracts of elm bark stopped the locomotory activity of randomly wandering beetles on contact, and by this criterion of behavior were defined as arrestants. Because they also stimulated beetles to feed they were called feeding stimulants. The highest response usually occurred in the first hour of exposure to the bark extracts. Subsequent exposure evoked decreasing responses. These two behavior patterns were explained in terms of a concept of falling and rising thresholds of response to chemical stimuli from the active extracts. Leaf extracts were biologically inert, as were those from current growth collected early in the growing season. The most active extracts were derived from the bark of second- to fourth-year growth. Most of the feeding in the field occurs on twigs within this range of growth. Beetles responded to feeding stations containing as little as 0.1 mg. extract in 99.9 mg. starch but no correlation between concentration and intensity of response was demonstrated. Moisture played an important role in the insects' response. In the absence of chemical stimuli from active extracts, beetles with a low water threshold responded to moisture. Responses to inert materials such as powdered cellulose, cellucotton, and leaf residues were attributable to moisture. Some of the chemical fractions from elm bark evoked intense positive responses; others produced negative effects.

The number of larval stadia occuring in the life cycle of Trogoderma glabrum (Herbst) is an indeterminate characteristic. Under optimal, uninterrupted rearing conditions, there may be as few as 5 (males) or 6 (females) larval stadia, but there is no apparent species-typical maximum number of ecdyses possible. Under retrogressive conditions, ecdyses continue to occur and are accompanied by a reduction in larval size and weight. Under conditions that permit growth but prohibit pupation, a stable maximum larval size is attained (Dauer-larvae), and ecdyses continue to occur, but without significant changes in larval weight or dimensions. Different but relatively constant frequencies of ecdyses were observed under each of the 3 culturing conditions tested (progressive growth, retrogressive growth, and Dauer-larval conditions). The rates of occurrence of the molting cycle appeared to be determined by the general metabolic rates of the larvae, rather than by nutritional state or by increment of weight change (either positive or negative). Determination of post-ecdysial form is controlled, at least in part, by the titer of juvenile hormone (JH). JH at a concentration of 70 ppm in the dietary medium effectively inhibited pupation of regrown, previously retrogressed, larvae under conditions otherwise known to stimulate pupation. Exogenous JH also stimulated larval growth. Wing anlagen and other imaginal discs could not be demonstrated in larvae prior to their having been committed to pupation, supporting the interpretation that the duration of larval life is indeterminate and that an indefinite series of larval ecdyses is not complicated or limited by a concurrent differentiation of adult structures.

Methods employed in the study of host plant resistance to the European corn borer are described and analyzed. Procedures for plant sampling, chemical fractionation, and bioassay are discussed. Laboratory rearing of the corn borer on purified dietary media is described in detail. Application of the experimental methods to investigations of plant resistance problems involving other insect and plant species is discussed.

The feeding behavior of Oncopeltus fasciatus (Dallas) was studied from the standpoint of its being divisible into four behavioral components: (1) Orientation to the dietary substrate was found to be an antennal function, but could occur from only very short distances. Attractants in the milkweed seed coat elicited an orientation response. (2) Initiation of feeding involved contact of the labium with the diet. Labial contact was followed by stylet penetration and release of salivary secretions. Contact chemoreceptors on the labium were stimulated by unidentified chemical factors occurring in the milkweed seed coat. (3) Maintenance of feeding was found to be primarily dependent on sensory input from chemoreceptors situated internal to the stylets. Sugars and amino acids, as well as unidentified stimulants in the seed coat, played a role in determining the duration of feeding. (4) Cessation of feeding occurred as the result of sensory adaptation to the feeding stimulants and, probably, depletion of the insect's supply of salivary secretion. The feeding behavior pattern was followed by a water drinking behavior, mediated by hygroreceptors of the antennae and possibly unidentified internal receptors. After sensory disadaptation and renewal of salivary secretions, the bug was again ready to go into the feeding behavior pattern.

Female larvae of Trogoderma glabrum (Herbst) were subjected to repeated retrogressions of either 20 or 36 weeks' duration. Rates of survival, regrowth, pupation, and reproduction were lowered by repeated retrogression. Both the rate of weight loss and frequency of retromolts tended to increase with successive retrogressions. The biological significance of these effects is discussed.

Host-plant resistance to the European corn borer is manifested as increased larval mortality, inhibition of larval growth, and reduction in larval feeding. Leaf lesions caused by larval feeding are smaller and fewer per infesting borer on resistant lines than on susceptible lines of corn. Resistance factor A (6-methoxybenzoxazolinone) exerted a deleterious effect on feeding of firstinstar larvae, acting as a feeding deterrent and not as a simple repellent. Reducation in duration of larval feeding was proportional to RFA concentration, but inhibition of larval growth by RFA could not be accounted for on this basis. No significant correlation between feeding suppression and growth inhibition was found in experiments using a series of 15 benzoxazolinone and benzothiazole analogs. Lowering of RFA inhibitory action by high concentration of dietary sugar was not caused by a masking of RFA effects on feeding behavior. The available evidence indicates that RFA inhibited larval growth by metabolic action, not via behavioral effects. Under field conditions, larval mortality on borer-resistant plants was higher than that observed in the laboratory among larvae on purified diets containing comparable concentrations of RFA. The reduced feeding and inhbiited growth induced by RFA probably tends to increase larval mortality through prolonging the exposure of the weakened larvae to adverse environmental conditions.

A meridic dietary medium containing no foliage, wheat germ, or other crude plant fractions has been developed. This medium appears to be completely satisfactory for continuous culturing of laboratory populations of Ostrinia nubilalis (Hubner). Omission of plant materials from the rearing medium was made possible by the development of a simplified, balanced mineral salt mixture. Because of inorganic contaminants contained in other organic constituents of the medium, the insect's requirement for individual inorganic elements could not be determined with acceptable accuracy.

Under conditions favoring development without arrest, spermatogenesis begins in the fourth larval instar and spermatozoa are found in the prepupa. Under conditions inducing diapause, spermatogenesis is retarded, and after the onset of diapause, spermatocytes that have matured beyond the pachytene stage undergo degeneration.