The response of Gregarina niphandrodes (Apicomplexa: Eugregarinida: Septatina) to host starvation in Tenebrio molitor (Coleoptera: Tenebrionidae) adults.

Numerous studies of host starvation have emphasized pathological effects of parasites on their insect host, but little attention has been focused on the effects of host starvation on the parasites. This study addressed the possibility that parasite life-cycle events could be manipulated by withholding food from the host. The system used was Gregarina niphandrodes (Apicomplexa: Eugregarinida) in Tenebrio molitor (Coleoptera: Tenebrionidae) adults. Gregarine gametocyst formation and shedding ceased after 1 day in starved beetles but continued in fed controls. There were no statistically significant differences between total lengths of associated (3 of 5 trials) or unassociated (5 of 5 trials) gregarines found between experimental and control groups, but average numbers of the 2 life cycle events were generally higher in fed hosts than in starved ones. If infected, fed control beetles continued to form gametocysts throughout the 7-day trial periods, and gametocysts could be observed in the gut. Starved experimental beetles had no gametocysts in their guts. Refeeding of starved beetles after 4 days resulted in resumption of gametocyst formation and shedding. The studies demonstrated that the gregarine life cycle could be stopped and then started at the gametocyst formation stage like an off/on switch, simply by withholding food from, then refeeding, the host.     

Individual and population effects of eugregarine, Gregarina niphandrodes (Eugregarinida: Gregarinidae), on Tenebrio molitor (Coleoptera: Tenebrionidae)

Gregarines are single-celled parasites in the phylum Apicomplexa that infect invertebrates. They are highly abundant on three levels: among a large diversity of invertebrates, in the proportion of population of organisms they infect, and within individually infected organisms. Because of their remarkable prevalence, we hypothesize that they play an important role in support of their hosts. However, studies done to date on the impact of gregarines on their host are conflicting. Therefore, we studied the impact of gregarines on their host using a model Gregarina niphandrodes infection in Tenebrio molitor. The impact of infection was measured by comparing beetles with no or low infection to those with artificially induced high infection. The numbers of individuals in each of the three easily visible developmental stages of the T. molitor (larva, pupa, and adult) were censused weekly. From these observations, fertilities and probabilities of survival with transition between stages were estimated. These estimated vital rates were used to construct a stage-classified projection matrix model. We also measured the longevity of individual beetles with low and high infection that were grown in isolation. The results indicate that there is no significant difference in the population dynamics of beetles with low and high infection. However, the longevity was significantly different between beetles with low infection than the deliberately highly infected group.     

Pheromone production by male Tribolium castaneum (Coleoptera: Tenebrionidae) is influenced by diet quality

Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), the red flour beetle, is a common cosmopolitan pest exploiting a variety of stored products. We experimentally manipulated diet nutritional quality by using non-nutritive filler to examine how this influenced pheromone production and olfactory attractiveness of T. castaneum adult males. Volatiles released by individual males reared on high versus low nutrition diets were collected using solid phase microextraction, and gas chromatography coupled to mass spectrometry was used to identify and quantify the Tribolium aggregation pheromone 4, 8-dimethyldecanal (DMD). Males kept on high nutrition diet showed a three-fold increase in daily DMD production, which suggests the possibility that this pheromone could act as a condition-dependent mating signal. In pitfall trap assays, there was no significant difference in the mean response of virgin females to discs kept with low versus high nutrition males, although discs carrying male cues were significantly more attractive than blank discs. These results suggest that DMD production rates by T. castaneum males will depend on the nutritional quality of various stored products, but such differences may not alter males' ability to attract females.     

Stylocephalus occidentalis n. sp. (Apicomplexa: Eugregarinida: Stylocephalidae) from Trimytis pruinosa (Coleoptera: Tenebrionidae) in the Nebraska Sandhills

Stylocephalus occidentalis n. sp. (Apicomplexa: Eugregarinida) is described from Trimytis pruinosa (Coleoptera: Tenebrionidae) collected from Keith County in the Sandhills of western Nebraska. Measurements are means in micrometers. Developing trophozoites solitary; epimerite a complex of terminal epimerite and intercalating diamerite; epimerite shallowly ovoid to transversely elliptoid, with transverse basal constriction at junction with diamerite, length 0.5-1 times width, approximately 3-4 times that of diamerite; width approximately equal to that of diamerite; diamerite roughly cylindrical to spindle-shaped, without significant anterior taper, little or no evidence of longitudinal folds, length approximately twice width. Association late, frontal, isogamontic. Gamont protomerite depressed ovoid to very broadly ovoid, length 27.3, width 35.1, anterior distance to widest point 15.4. Protomerite-deutomerite septum clearly marked and constricted, width 34.6. Deutomerite often with distinct marginal crenulation, narrowly obovoid to very narrowly obovoid, length 356.5, maximum width 57.6, anterior distance to widest point 26.3, equatorial width 35.1, +/-12.5, 29. Total length 381.5. Nucleus ellipsoid, length 32.5, width 18.8; with 0 or 2 polysomal endosomes. Gametocysts roughly spherical; diameter 205.0; wall desiccating to become paper-like, slightly papillated, dehiscing by simple rupture, releasing oocysts in coiled chains, epispore packet absent, gametocyst residuum present. Oocysts dark brown to black, axially asymmetric, broadly deltoid, gibbous in lateral aspect, slightly keeled in dorsal aspect; length 9.8, height 7.9; with slight terminal protuberances and 2 central, spherical residua.     

Effects of temperature on the development of Gregarina cubensis (Apicomplexa: Eugregarinida) parasitizing Blaberus discoidalis (Blattaria: Blaberidae)

Gregarina cubensis is an apicomplexan parasite that infects the intestinal lumen of the death's head cockroach (Blaberus discoidalis). This study evaluated the effects of 3 temperatures on the development and viability of G. cubensis. Three groups of B. discoidalis were inoculated with G. cubensis oocysts and maintained at 15, 27, and 40 C. The alimentary canal was removed from 3 cockroaches in each group every 24 hr until mature gametocysts were found in the rectum or feces, and prepared for histological examination. Gregarina cubensis establishment and development were more rapid at 15 C than at 27 C. Development of G. cubensis at 40 C did not progress beyond the intracellular stage.     

Gregarina coronata N. Sp. (Apicomplexa: Eugregarinida) Described from Adults of the Southern Corn Rootworm, Diabrotica undecimpunctata howardi (Coleoptera: Chrysomelidae)

ABSTRACT. Gregarina coronata n. sp. (Apicomplexa: Eugregarinida) is described from the adults of the Southern Corn Root Worm, Diabrotica undecimpunctata howardi (Coleoptera: Chrysomelidae). Measurements given are means, in micrometers, taken from mature gamonts in association. Primite: protomerite hemi-ellipsoidal with basal tumidus, length 47.6, width 44.0, with cytoplasmic granule, apical crown apparent; deutomerite elongate ellipsoidal, length 227.9, width 81.3; epimerite absorbed into anterior in gamont, globular in trophozoite. Satellite: protomerite hemi-ellipsoidal, truncated at association interface to appear trapezoidal, length 39.2, width 49.6, with cytoplasmic granule; deutomerite elongate ellipsoidal, length 240.6, width 80.2; epimerite absorbed into anterior in gamont. Association caudofrontal and often precocious, occurring during growth of trophozoites. Gametocysts spherical, 115.3 in diameter, 132.9 with hyaline coat; producing multiple oocyst chains under moist storage in 24–36 h. Oocysts very uniform in shape and size, dorsad: doliform, length 6.4, equatorial width 3.4, polar width 2.9; pleuron: dorso-ventrally flattened, corpus concave with bicondylic termina; corpus height 0.98, width 4.44; terminus height 1.96, width 0.98.     

Consequences of the last glacial maximum on Nyctelia confusa (Coleoptera: Tenebrionidae) in Patagonia

The Last Glacial Maximum (LGM) has affected the population size and spatial distribution of a number of organisms in southern Patagonia. It has been hypothesized that species were able to persist in isolated refuges, which has generated processes of population expansion and genetic structure of populations after the LGM. In the present study, we evaluate these hypotheses and their association with local morphotypes in the endemic species Nyctelia confusa, a coleopteran that has low vagility and restricted distribution in the region. Accordingly, sixty‐nine specimens were sequenced for the gene for mitochondrial cytochrome c oxidase I. Effective population size was estimated through time, along with population structure and the phylogenetic signal of the morphs. The results suggest the existence of recent population expansion (10 Kyr BP), although there was no evidence of population structure or the phylogenetic signal for the described morphs. We propose that, during the LGM, N. confusa survived in multiple refuges, probably in the oriental slopes of the Andes range. The surviving populations would have expanded once the steppe was re‐established after the glaciers receded. This may have produced various secondary contact zones, homogenizing the genetic diversity, which would explain the observed pattern of panmixia. The morphological differentiation reported previously may be a result of local ecological adaptation not associated with the historical events of the LGM.     

Identification, cloning, and expression of a GHF9 cellulase from Tribolium castaneum (Coleoptera: Tenebrionidae)

The availability of sequenced insect genomes has allowed for discovery and functional characterization of novel genes and proteins. We report use of the Tribolium castaneum (Herbst) (red flour beetle) genome to identify, clone, express, and characterize a novel endo-β-1,4-glucanase we named TcEG1 (T. castaneum endoglucanase 1). Sequence analysis of a full-length TcEG1 cDNA clone (1356 bp) revealed sequence homology to enzymes in glycosyl hydrolase family 9 (GHF9), and verified presence of a change (Gly for Ser) in the conserved catalytic domain for GHF9 cellulases. This TcEG1 cDNA clone was predicted to encode a 49.5 kDa protein with a calculated pI of 5.39. Heterologous expression of TcEG1 in Drosophila S2 cell cultures resulted in secretion of a 51-kDa protein, as determined by Western blotting. The expressed protein was used to characterize TcEG1 enzymatic activity against two cellulose substrates to determine its specificity and stability. Our data support that TcEG1 as a novel endo-β-1,4-glucanase, the first functional characterization of a cellulase enzyme derived from an insect genome with potential applications in the biofuel industry due to its high relative activity at alkaline pH.     

Self-selection of two diet components by Tenebrio molitor (Coleoptera: Tenebrionidae) larvae and its impact on fitness

We studied the ability of Tenebrio molitor L. (Coleoptera: Tenebrionidae) to self-select optimal ratios of two dietary components to approach nutritional balance and maximum fitness. Relative consumption of wheat bran and dry potato flakes was determined among larvae feeding on four different ratios of these components (10, 20, 30, and 40% potato). Groups of early instars were provided with a measured amount of food and the consumption of each diet component was measured at the end of 4 wk and again 3 wk later. Consumption of diet components by T. molitor larvae deviated significantly from expected ratios indicating nonrandom self-selection. Mean percentages of dry potato consumed were 11.98, 19.16, 19.02, and 19.27% and 11.89, 20.48, 24.67, and 25.97% during the first and second experimental periods for diets with 10, 20, 30, and 40% potato, respectively. Life table analysis was used to determine the fitness of T. molitor developing in the four diet mixtures in a no-choice experiment. The diets were compared among each other and a control diet of wheat bran only. Doubling time was significantly shorter in groups consuming 10 and 20% potato than the control and longer in groups feeding on 30 and 40% potato. The self-selected ratios of the two diet components approached 20% potato, which was the best ratio for development and second best for population growth. Our findings show dietary self-selection behavior in T. molitor larvae, and these findings may lead to new methods for optimizing dietary supplements for T. molitor.     

Directional and correlated effects of selection on amylase activity,weight and developmental time in Tribolium confusum (Coleoptera,Tenebrionidae)

The interrelationships of amylase activity, weight and developmental time in a strain of Tribolium confusum were studied by selecting, in turn, for one of these traits and monitoring other, non-target characters, in all lines.Experimental lines were selected for high and low amylase activity (AH, AL), for heavy and light adult weight (WH, WL) and for fast and slow development (DF, DS). The variables monitored every generation in all lines were mean amylase activity (measured colorimetrically), mean individual adult weight, median egg-to-pupa developmental time, mean productivity (offspring per fertile pair) and % sterile pairs.The six lines may be grouped by their response to selection in a meaningful way. AH, WH, and DS all had higher amylase activity, heavier adult weight, slower development and lower fitness (lower productivity, higher percent sterility) than the corresponding AL, WL, and DF, although a different variable was under selection in each pair of lines. These results demonstrate that amylase activity, developmental time and individual weight are intercorrelated.     

Morphological and molecular characterizations of the Gregarina sp. (Apicomplexa: Protozoa) parasitizing on Phaedon brassicae (Coleoptera: Chrysomelidae)

A gregarine parasite (Eugregarinida: Gregarinidae) was observed in the population of daikon leaf beetle, Phaedon brassicae Baly, (Coleoptera: Chrysomelidae) in Korea. Gregarines are well known species-specific parasites of various Arthropoda. This Gregarina sp. also confirmed a species-specific parasite in P. brassicae. Based on 1.727 kb of 18S rDNA sequence (FJ481523), this gregarine species was grouped in eugregarine and a 5.258 kb of full length rDNA replicon was cloned (JF412715). We also observed interaction of trophozoite or gamonto of gregarine and epithelium of a host midgut using a light microscope and a scanning electron microscope. Although the developmental period of the infected host is delayed half a day in every larval stage, there was no significant difference in the developmental period of P. brassicae whether Gregarina sp. was infected or not. Gregarina sp. was a kind of facultative parasite from P. brassicae. This is the first report of a gregarine parasite in P. brassicae.     

Revision of the genus Xiphocephalus and description of Xiphocephalus ellisi n. sp. (Apicomplexa: Eugregarinida: Stylocephalidae) from Eleodes opacus (Coleoptera: Tenebrionidae) in the western Nebraska Sandhills

Xiphocephalus is revised, clarifying diagnosis of the epimerite complex, gametocyst, and oocyst. Xiphocephalus ellisi n. sp. (Apicomplexa: Eugregarinida) is described from Eleodes opacus (Coleoptera: Tenebrionidae) collected from Keith County in the Sandhills of western Nebraska. Measurements are means in micrometers. Developing trophozoites solitary; epimerite a complex of terminal epimerite and intercalating diamerite: epimerite elongate, ensiform, with transverse basal tumidus, length 2-3 times width of basal tumidus; width approximately half that of basal tumidus; tumidus toroidal, concavoconcave in anterioposterior axis: diamerite roughly cylindrical, no longitudinal fold apparent, length approximately twice width. Association late, frontal, isogamontic. Protomerite depressed ovoid, length 84.1, width 114.9, anterior distance to widest point 50.8. Protomerite-deutomerite septum clearly marked and constricted, width 99.3. Deutomerite narrowly obovoid, length 1,094.0, maximum width 197.0, anterior distance to widest point 137.8, equatorial width 163.3. Total length 1,204.4. Nucleus ellipsoid, length 64.9, width 42.2; typically with 2-3 polysomal endosomes. Gametocysts roughly spherical, length 376.1, width 348.2, wall paperlike, papillated, dehiscing by simple rupture, releasing oocysts in coiled chains, epispore packet absent, gametocyst residuum present. Oocysts brown to black, broadly deltoid, gibbous in lateral aspect, slightly keeled in dorsal aspect, length 9.7, height 8.5; with terminal protuberances and a single, central, spherical residuum.     

Influence of environmental and physical factors on capture of Tribolium castaneum (Coleoptera: Tenebrionidae) in a flour mill

Variation in environmental and physical factors within food processing facilities can influence both the distribution of stored-product pests and trapping efficiency. Data from a long-term Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) monitoring program was used to evaluate spatial variation in captures among trap locations and to determine relationships with environmental and physical variables. From the complete monitoring data set, different subsets were created for the cool and warm seasons, and period of time when environmental and physical factors were measured (2009-2010), with all data sets showing significant differences among trap locations in terms of beetle captures and proportion of time that traps exceeded 2.5 beetles per trap per monitoring period. There was also considerable temporal variation in distribution among the different levels of the mill. Among the environmental and physical variables measured, mean temperature and flour dust accumulation showed the most significant positive relationships with variation of beetle captures at trap locations. More beetles were captured in traps located in close proximity to milling equipment. Presence of equipment near traps was also associated with an increase in flour dust accumulation and temperature. Overall the environmental and physical factors seemed to have a limited influence on variation in captures among trap locations, with temporal variation in distribution perhaps overwhelming potential influences of local trap conditions.     

Impairment of reproduction in the red flour beetle, Tribolium castaneum (Herbst) (Col., Tenebrionidae) due to larval feeding on triflumuron-treated diet

The larvae of Tribolium castaneum (Herbst) of different ages were exposed to various concentrations viz., 0.0001, 0.001 and 0.01 ppm of triflumuron up to pupation. The adults were allowed to feed on untreated diet. The preoviposition period, fecundity, egg viability and incubation period of the eggs laid were studied. Triflumuron significantly lengthened the preoviposition and incubation periods (P < 0.001). Fecundity and egg viability were also reduced (P < 0.001) due to the treatment. Both the strains were affected by the treatment.     

Toxic effects of some insecticides,herbicides, and plant essential oils against Tribolium confusum Jacquelin du val (Insecta: Coleoptera: Tenebrionidae)

Cereals are staple food for many countries and are grown on millions of hectares of land, but much of the harvest is wasted due to losses by pests. To minimize these losses, many pesticides are used which are damaging to the environment and human health. There are debates to get rid of these chemicals but they are still in use at large scale. An alternative control strategy for insect pests in storage houses is the use of botanicals. In this study, four plant essential oils, two plant extracts, two herbicides, and two insecticides were used against Tribolium confusum and the comparison of toxicity was made by calculating LC₅₀ and LT₅₀ values. LC₅₀ values were higher for abamectin (2.09–10.23 mg/L) and cypermethrin (3.41–11.78 mg/L) insecticides followed by neem essential oil (7.39–19.24 mg/L) and citrus extract (10.14–24.50 mg/L). However, LC₅₀ values were maximum in case of jaman plant extract (22.38–176.42 mg/L) followed by two herbicides, Logran (19.66–39.72 mg/L) and Topik (29.09–47.67 mg/L) However, LC₅₀ values were higher for topic herbicide (24.098 ppm) and jaman essential oil (16.383 ppm) after four days of treatment. Abamectin and cypermethrin insecticides, neem essential oil and citrus plant extract also killed adults of T. confusum quicker as compared other essential oils, extracts and herbicides. Results revealed that botanical formulations being environmentally safe could be used instead of highly hazardous pesticides for stored products’ pests. This study also elaborates the non-host toxicity of herbicides commonly applied in our agroecosystem.     

Influence of processing and substrate variety on survival and development of Tribolium confusum (Coleoptera: Tenebrionidae)

Tribolium confusum is a major pest of grains and grain products. Some legumes hitherto not used as major food are gaining interest due to increase in human population and the need of food and feeds. Susceptibility of fresh and processed Glycine max and Cajanus cajan flours, and white wheat flour (control) to T. confusum was studied towards effective storage techniques and cheap insect diet. Ten copulating pairs of the beetle were introduced into twenty grams of each flour. Number of eggs laid, emerged larvae, pupae, eclosed adults, and duration of development of each stage was used as indices of survival of T. confusum. Proximate composition, saponin; and α-amylase and protease inhibitors determined suitability of flours as insect diet. This work discusses the significance of proximate composition and anti-nutrient properties in fresh and roasted processed flours on the development and survival of T. confusum.     

Plant essential oils: a substitute for conventional insecticides against Tribolium species (Coleoptera: Tenebrionidae)-achievements and challenges

Abstract

The literature on efficacy of plant essential oils and their constituents for the management of Tribolium spp. (T. castaneum and T. confusum), instigating infestation of a variety of stored grains and their products is reviewed here. Both species caused significant losses in the diverse food grains and their products through infestation. Essential oils of higher plants showed potential activity in the management of these infestation driven losses. Researchers have found that essential oils and their chemical constituents have significant toxicity against both the species of Tribolium via different modes of action like repellent, insecticidal, ovicidal, larvicidal, pupicidal, ovipositional and feeding deterrent actions. Concerning repellency and in vivo bioassays, few studies have been done with the essential oils against T. confusum, thus, more investigations are required to find the repellent agents against this insect. There are some essential oil-based botanical insecticides which have been proved effective for the protection of food grains from both beetles during storage. These botanical insecticides also exhibited behaviour altering properties against both beetles, thus, reducing the problem of pest resistance which is a problem with conventional insecticides. Therefore, essential oils-based botanical insecticides may be preferred option than conventional insecticides for protecting stored grains and their products against Tribolium infestation.     

Observations on the rate of growth and disruption of moulting in the larvae and pupae of Tribolium castaneum (Herbst) (Coleoptera, Tenebrionidae) at sub-threshold temperatures

When Tribolium castaneum is grown at 20° and 70% R.H., most individuals attain the adult form but are unable to free themselves from the pupal skins. Pupae bred at 30° will become normal adults at 20° but they do not emerge as adults at 17.5° unless they spend 2 days or more at 30°. Exposure for more than 3 weeks to 15° is fatal, usually because of failure in the sloughing of the pupal cuticle. Young larvae moved from 30 or 25° to 15° die if they are close to moulting and prepupae yield distorted adults because of moulting failures. Freshly hatched larvae are killed by 56 days at 17.5° and by 14 days at 15°, but many half grown larvae survive 84 and 28 days respectively at these temperatures. Exposure of prepupae to 17.5° for 28 days, to 15° for 21 days, to 10° or 5° for 7 days inhibits the pupal moult of some individuals although development to adult proceeds inside the larval skin. Normal growth and development of larvae proceeds for 42 days at 17.5° and of pupae for 21 days at 15° C. Development of pupae at 15° continues for at least 36 days but the adults formed are distorted by entanglement with the partially sloughed pupal exuviae. Compared with 30°, the rates of pupal growth are reduced 18 times at 15°, 5 times at 17.5° and 3 1/2 times at 20°, and those of larval growth by 12 times at 17.5° and by 4, 6 and 10 times over successive 28 day periods at 20°. Larval growth persists only a few days at 15°.

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Zusammenfassung Kleine Gruppen isolierter Individuen von Tribolium castaneum wurden mit entsprechendem Futter in verschiedenem Alter, von frisch geschlüpften Larven bis zu mittleren Puppenstadien, für bestimmte Zeitintervalle Temperaturen von 20, 17,5, 15, 10 und 5° C ausgesetzt. Die Insekten wurden bei 30° und 70% rel. Luftfeuchtigkeit gezüchtet und nach dem Versuch gewöhnlich wieder in diese Umgebung zurückgebracht. Die schärfsten Versuchsbedingungen töteten alle Versuchstiere, die mildesten keine. Mittlere Bedingungen töteten nur junge, häutungsreife Larven oder verursachten bei Präpuppen und Puppen eine Reihe von Häutungsstörungen, die gewöhnlich tödlich waren. Einige Larven verpuppten sich, ohne zum Abstreifen der Larvenhaut befähigt zu sein, und die Imagines hatten in verschiedenem Umfange Schwierigkeiten beim Abwerfen der Puppenhaut. Die meisten dieser Erwachsenen waren zu verstrickt, um lange leben zu können. Die schwächsten, behindernden Mißbildungen bestanden in gedehnten Hinterflügeln und aufgeblähten Elytren. T. castaneum kann sich bei konstant 20° und 70% rel. Luftfeuchtigkeit verpuppen, aber —wenn überhaupt — vermögen sich bei dieser Temperatur nur wenige zu lebensfähigen Erwachsenen zu entwickeln, es sei denn, sie werden nach 30° überführt. Bei 30° gebildete Puppen können bei 20° als Erwachsene schlüpfen, aber bei 17,5° mißlingt den meisten normaler Schlupf, außer die Puppen waren bereits 3 Tage alt. Eben gebildete Puppen werden durch 15 Tage bei 15° nicht geschädigt, aber nach 21–30 Tagen schlüpfen die meisten Erwachsenen mit gedehnten Hinterflügeln. Längere Einwirkung, bis zu 42 Tagen, verursachte heftigere Verzerrungen und 56 Tage waren tödlich. Bei 15° tritt nur eine sehr langsame Puppenentwicklung ein.Wenn Larven aus 30° in einem Alter von 7 oder weniger Tagen konstant 20° ausgesetzt werden, entwickeln sich keine normalen Imagines, bei 8–12 Tage alten bilden sich normale Erwachsene, während 13 Tage alte Larven wieder mißgebildete Erwachsene ergeben. Werden Larven verschiedenen Alters 15° ausgesetzt, so ist die Sterblichkeit bei frühen Larvenstadien, die kurz vor der Häutung stehen, groß. Ebenso führt die Einwirkung auf Präpuppen zur Störung der Imaginalhäutung.Frisch geschlüpfte Larven entwickeln sich nach 42 Tagen bei 17,5° normal, jedoch sind 56 Tage für fast alle verhängnisvoll. Die Entwicklungsperioden der Larven lassen vermuten, daß bei dieser Temperatur etwa 42 Tage lang ein gewisses Wachstum erfolgt. Etwa 14 Tage bei 15° und 7 Tage bei 5° tötet alle frisch geschlüpften Larven. Halbwüchsige Larven werden durch 21 Tage bei 15° getötet, jedoch starb keine bei der Einwirkung von 17,5° für weniger als 84 Tage.Werden große Larven für nur 21 Tage 15° oder für 7 Tage 10 oder 15° ausgesetzt, so verpuppen sich einige oder alle anormal ohne Abstoßung der Larvenhaut. Einige der nach 28tägiger Behandlung mit 17,5° gebildeten Puppen ergaben gestörte Erwachsene und die 56 Tage ausgesetzten blieben bei der Imaginalreife innerhalb der Puppenhaut in der Verpuppungslage stecken, während die meisten der nach Einwirkung von 15 und 10° gebildeten Puppen normale Imagines ergaben.

     

Effects of variations in casein and dextrin content of a synthetic diet on larvae of Ctenicera aeripennis destructor (Brown) (Coleoptera: Elateridae)

Larvae reared aseptically on pellets of synthetic diet in which the ratio of casein to dextrin was varied over the full range, gained most weight in a two-month period when the ratio was either 20:80 or 70:30. When the ratio was varied by smaller amounts in the region of these concentrations, the larvae gained most weight in a narrow range of 21 to 23 parts casein and also in a broad range of 65 to 71 parts casein. This bimodal response may occur because deleterious effects of large quantities of casein or dextrin in the diet are counteracted by small quantities of the corresponding component.

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Sommaire Des larves du taupin des graminées, Ctenicera aeripennis destructor (Brown), ont été élevées individuellement et aseptiquement sur des régimes synthétiques dans des éprouvettes pourvues de coton humide. D'une part, les régimes variaient de l'un à l'autre par une augmentation de 10 parties de caséine depuis 0 jusqu'à 100, pendant que la dextrine diminuait également par 10 parties depuis 100 jusqu'à 0. D'autre part, elles augmentaient de deux parties de caséine, à partir de 15 jusqu'à 25 parties et de 65 jusqu'à 75, pendant que la concentration de dextrine diminuait également de 85 jusqu'à 75 parties et de 35 jusqu'à 25 parties. Ces régimes étaient donnés sous forme de boulette sur le coton.Les larves étaient pesées à 0.1 mg près au commencement des essais et la différence entre les poids initial et final de chacune était exprimée en quantités de milligrammes par milligramme de poids initial.Les larves ont également bien survécu avec tous les régimes. La meilleure augmentation pondérale était obtenue avec un régime contenant 21, 23, ou 67 parties de caséine. Ce dernier résultat n'était pas du tout surprenant. Il est probable que ni un manque complet ni une surabondance de protéine ou d'hydrates de carbone ne profite aux taupins. Si les petites quantités peuvent favoriser l'accroissment des larves, il est fortement probable que 20 parties de caséine soient suffisantes pour détruire n'importe quel effet défavorable d'un surcroît de dextrine (80 parties). De même, une teneur de 30 parties de dextrine pourrait donner assez de vigeur aux larves pour surmonter l'effet d'un niveau alimentaire de 70 parties de caséine. Aux autres concentrations, l'action de l'un est antagoniste de l'autre et probablement leurs effets réciproques s'annulent.

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Contribution No. 94, Canada Department of Agriculture Research Station, Saskatoon, Sask.