Showing papers on "Larva published in 1987"

Adult recruitment in chorus frogs: effects of size and date at metamorphosis'

Abstract: A cohort of tadpoles of the chorus frog, Pseudacris triseriata, on Isle Royale, Michigan, was marked to determine the effect of body size and date at metamorphosis on survivorship to maturity. The cohort was classified at metamorphosis into four categories based on size and date of metamorphosis: large-early, small-early, large-late, and small- late. The number of frogs in each category that returned to breed on the study area was monitored for the following 2 yr. Long larval period and small body size at metamorphosis influenced recruitment to the breeding population by delaying maturity. Frogs that meta- morphosed at large size maintained their size advantage at maturity. Large body size and early date at metamorphosis increased survivorship to maturity by enhancing the chance that reproductive size was attained within 1 yr of metamorphosis. Frogs that were recap- tured in the 2nd yr after metamorphosis, when all frogs had attained mature size, were from all four categories in the same proportions marked at metamorphosis, indicating that unless breeding during the Ist yr led to higher mortality of large individuals, survival rate after metamorphosis was not related to size or date at metamorphosis.

Paederus, Sensu Lato (Coleoptera: Staphylinidae): Natural History and Medical Importance

Abstract: Staphylinids (Coleoptera) are known as predators of Diptera and other arthropods of medical and veterinary importance, but the genus Paederus has achieved greater notoriety. Paederus includes over 600 described species distributed in all temperate and tropical continents. Many species exist in moist habitats, and some have their life cycles attuned to seasonal fluctuations in water level. Temperate-zone species may have a single annual breeding season in the warmer months, but in tropical species timing of the breeding season appears to depend upon rainfall seasonality. Widely distributed species with a broad latitudinal range seem to be multivoltine, with more generations at lower latitudes. Adults of some species are capable of running on water, navigating in response to light. Unlike most staphylinid adults, which avoid daylight, Paederus adults are active in the open in daylight. However, flight seems largely restricted to nights of high temperature. Adults of some species are wingless, and in other species adults show individual variation in wing length. Adults of at least some species are attracted at night to incandescent and fluorescent lights. Eggs are laid singly on a moist substrate and are susceptible to desiccation. There are 2 larval instars. Larvae remain in concealed, moist habitats and are largely predatory. Pupation occurs in earthen cells. Adults, too, are largely predatory but will feed on certain plant materials. Enormous populations of adults have been recorded in some agricultural habitats; in these cases the beetles are beneficial to agriculture owing to their predation on insect pests. However, they are highly susceptible to insecticides. Adults inadvertently come into contact with humans, especially in the tropics and by attraction to light at night. Hemolymph is released when the insects are crushed on human skin (deliberately or by accident) and can be introduced into the eyes. This hemolymph contains a potent contact toxin that causes dermatitis linearis and conjunctivitis in humans. Epidemics of dermatitis linearis are recorded for many tropical and some temperate countries. The epidemics can be mitigated by simple precautions. The dermatitis can be severe, painful, and unsightly, with erythema persisting for months. Conjunctivitis can result in temporary blindness. The toxic effects of Paederus were unknown to Western medicine until this century, but they were known to Chinese medicine 1,200 years earlier. The principal toxin is pederin, the most complex nonproteinaceous insect secretion known. Pederin occurs in all developmental stages of Paederus fuscipes , the Old World species on which most research has been performed. It has been synthesized and, in pure form, is a crystalline amide soluble in alcohol and water. It is a DNA inhibitor and acts at the cellular level by blocking mitosis. Experimentally, it has suppressed cancerous tumors in mice, rats, and plants, has stimulated regeneration of damaged tissues, has healed chronic, necrotic lesions in geriatric patients, and has induced cell fusion in human skin fibroblasts. It is more toxic externally and internally to rabbits, rats, mice, and guinea pigs than to hedgehogs, chickens, frogs, and toads. It is not known to be toxic to insects, is not attractive to insects, and has little effect against bacteria. Its function as a defensive secretion has not been demonstrated.

Intraspecific Competition in the Tephritid Fruit Fly Rhagoletis Pomonella

Abstract: At densities found in nature, competition among larvae of the frugivorous fruit fly Rhagoletis pomonella (Diptera: Tephritidae) was pronounced. In fruits of Crataegus mollis, a small native host of the fly, survivorship dropped sharply when > 1 larva developed per fruit. Multiple infestation also caused decreased size of pupae, which resulted in pro- longed maturation of females and lower daily fecundity. Our findings suggest that inter- ference competition occurs among rival R. pomonella larvae within the same fruit and that older larvae may be competitively dominant. In most instances, when 2 d separated the introduction of two larvae into unpicked fruits of Crataegus oxyacantha, a very small ornamental hawthorn, the first larva pupated while the subsequent larva failed to complete development. Rhagoletis pomonella marks its oviposition site with a contact pheromone. The amount of pheromone deposited following a single egg-laying in C. mollis fruit was sufficient to deter most females from laying more eggs. By avoiding marked fruits in which a larva is already developing, a female may conserve eggs and add measurably to her fitness. Because most C. mollis fruits can support more larvae to puparium formation than they actually do, it appears that the strategy of host marking by females and monopolization of fruit by larvae may leave some fruit resources unexploited.

Experimental studies of exploitative competition in a grazing stream insect

Abstract: Field and laboratory experiments were conducted to determine whether intraspecific competition for food occurs during the larval stage of the periphyton-grazing caddisfly Glossosoma nigrior (Trichoptera: Glossosomatidae). Larvae were placed in field enclosures at densities less than, equal to, or greater than their natural densities. Most of these individuals began to pupate after ∼3 weeks, whereupon the mass of each individual was determined. Final mass declined significantly as larval densities increased, whereas neither developmental rate nor mortality/emigration rate was significantly affected by density manipulations. a supplemental experiment comparing the final mass of individuals grown at reduced densities in a laboratory stream with individuals from a natural stream bottom confirmed the results of the more extensive field experiment: reductions in density resulted in significant increases in final mass. Periphyton availability in field enclosures declined according to a negative exponential function as larval densities increased. Over the ∼25-fold range of larval densities used in these experiments, the final mass of individuals increased linearly with periphyton standing crops. This result suggests that Glossosoma larvae may compete for food even at densities below those employed in this study. Path analysis was used to explore the importance of indirect (i.e., exploitative) and direct (i.e, interference) mechanisms for the observed competitive effects. The analysis indicates that a model based solely on exploitation explains nearly as much of the variance in mass as a model incorporating both interference and exploitation.

Postembryonic neurogenesis in the CNS of the tobacco hornworm, Manduca sexta. II. Hormonal control of imaginal nest cell degeneration and differentiation during metamorphosis.

Abstract: The nervous system of an adult moth is comprised of retained larval neurons that are remodeled during metamorphosis and a set of new adult specific neurons. The new neurons arise from a stereotyped array of stem cells (neuroblasts) that divide during larval life to generate nests of up to 100 arrested postmitotic immature neurons, the imaginal nest (IN) cells. At the onset of metamorphosis, some of the IN cells die while the remainder differentiate into mature functional neurons. Metamorphosis in insects is regulated by 2 classes of hormones, the ecdysteroids and the juvenile hormones. The transition from larva to pupa requires the disappearance of juvenile hormones followed by 2 releases of ecdysteroids: a small "commitment peak" and a larger "prepupal peak." Through a series of endocrine manipulations, we demonstrate that the death and differentiation observed among the abdominal IN cells at metamorphosis are both influenced by these hormonal cues. If the abdomen was isolated from the hormonal sources in the anterior half of the larva before the onset of metamorphosis, death and differentiation of the IN cells were prevented. Infusion of ecdysteroids into such abdomens, to mimic the prepupal peak, resulted in the IN cells showing the same fate as seen in control animals during the early phases of metamorphosis. The response of the IN cells to the small commitment peak of ecdysteroids was heterogeneous. Exposure to this small peak of steroids caused some cells to become committed to resume their development, making them resistant to juvenile hormone application.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of pool size on recruitment of predatory insects and on mortality in a larval anuran

Abstract: Artificial pools of three sizes were established in natural surroundings to determine whether colonization by predatory insects and tadpole survival were affected by pool size. After the passage of several weeks to allow such colonization, the pools were stocked with 1-wk-old larvae of Hyla cinerea. Subsequently, disappearance of the larvae and densities of predatory insects were monitored, but larval disappearance was attributed to predation only when it exceeded loss from predator-free pools. Most larval mortality occurred within 1 wk after introduction. Pools of the smallest size had significantly lower densities of predatory insects and significantly lower disap- pearance of larvae than larger pools. These results suggest that reduction of predation on larvae has been a major advantage of evolutionary shifts of anuran oviposition sites to small quantities of water.

Geographic variation in acid tolerance of Connecticut wood frogs

Abstract: Acid waters are often toxic to amphibians, but the ability of these animals to survive in acidic conditions varies considerably within and among species. We examined geographic variation in the acid tolerance of wood frog (Rana sylvatica) embryos and larvae from eight ponds in Connecticut, which differed in their levels of acidity. Embryos produced by adult frogs from the different ponds varied significantly in the ability to hatch in acidic solutions. Hatching success of the embryos was not correlated with the acid levels in the ponds. Tadpole survival in low pH solutions also differed among the ponds, and acid tolerance of tadpoles was correlated with pond pH (tadpoles produced by adults from acidic ponds tended to be more acid tolerant). Results of genetic crosses among frogs from different ponds suggested that the geograhic differences in acid tolerances of embryos are not genetically determined, but population differences in the tolerance of tadpoles to acidity appear to have some genetic basis.

Habitat duration, length of larval period, and the evolution of a complex life cycle of a salamander, ambystoma texanum.

Abstract: In many organisms, genotypic selection may be a less effective means of adapting to unpredictable environments than is selection for phenotypic plasticity. To determine whether genotypic selection is important in the evolution of complex life cycles of amphibians that breed in seasonally ephemeral habitats, we examined whether mortality risk from habitat drying in natural populations of small-mouthed salamanders (Ambystoma texanum) corresponded to length of larval period when larvae from the same populations were grown in a common laboratory environment. Comparisons were made at two levels of organization within the species: 1) among geographic races that are under strongly divergent selection regimes associated with the use of pond and stream habitats and 2) among populations within races that use the same types of breeding habitats. Morphological evidence indicates that stream-breeding A. texanum evolved from pond-breeding populations that recently colonized streams. Larvae in streams incur heavy mortality from stream drying, so the upper bound on length of larval period is currently set by the seasonal duration of breeding sites. We hypothesized that selection would reduce length of larval period of pond-breeders that colonize streams if their larval periods are inherently longer than those of stream-breeders. The results of laboratory experiments support this hypothesis. When grown individually in a common environment, larvae from stream populations had significantly shorter larval periods than larvae from pond populations. Within races, however, length of larval period did not correlate significantly with seasonal duration of breeding sites. When males of both races were crossed to a single pond female, offspring of stream males had significantly shorter larval periods than offspring of pond males. Collectively, these data suggest that differences in complex life cycles among pond and stream-breeders are due to genotypic selection related to mortality from habitat drying. Stream larvae in the common-environment experiment were significantly smaller at metamorphosis than pond larvae. Yet, the evolution of metamorphic size cannot be explained readily by direct selection: there are no intuitively obvious advantages of being relatively small at metamorphosis in streams. A positive phenotypic correlation was observed between size at metamorphosis and length of larval period in most laboratory populations. A positive additive genetic correlation between these traits was demonstrated recently in another amphibian. Thus, we suspect that metamorphic size of stream-breeders evolved indirectly as a consequence of selection to shorten length of larval period.

An experimental study of population regulation in the salamander, Notophthalmus viridescens dorsalis (Urodela: Salamandridae).

Abstract: The roles of density-dependent larval survival and cannibalism of larvae as potential mechanisms of population regulation in the newt (Notophthalmus viridescens dorsalis) were evaluated in laboratory and field experiments. In laboratory containers, adults cannibalized larvae and large larvae cannibalized smaller larvae. In artificial ponds, larval survival did not depend on initial larval density. No cannibalism could be demonstrated in the complex environment, although the experiment was powerful enough to detect an ecologically relevant difference in survival. Adult growth was negatively correlated with the final biomass of larval newts, suggesting that the two life stages competed for resources. Larval growth rates were negatively correlated with final larval density, suggesting that larvae competed with each other. The proportion of larvae that became sexually mature at age 7 months (paedomorphs and adults that skipped the eft stage) varied inversely with larval density. Therefore, the potential regulatory mechanisms identified in this study are competition within and between life stages.

Production of fertile salamanders by transfer of germ cell nuclei into eggs

Abstract: In amphibians, the ability of somatic cell nuclei to give rise to embryos in nuclear transplantation experiments has been thoroughly investigated and shown to be limited, except in Xenopus laevis . Similar experiments have been performed with primordial germ cells from genital ridges and spermatogonia. In the present paper, we have studied the capacity of germ cell nuclei to promote development of complete and fertile adults in the urodele amphibian Pleurodeles waltl . Germ cell nuclei were taken from larvae at progressive stages of larval development up to metamorphosis and transplanted into enucleated eggs. Two nonlethal chromosomal mutations were used as nuclear markers in two control series. Nuclei from all developmental stages tested were able to initiate larval development. Furthermore, nine individuals underwent metamorphosis (representing 3% of normal blastulae) and six of these animals are now adults. When two of these six animals, a male and a female, were mated to each other, the offspring were normal. These results show conclusively, for the first time in amphibians, that germ cell nuclei remain totipotent at least during the larval period.

Effects of artificially altered foliar nitrogen levels on development and survival of young instars of western spruce budworm, Choristoneura occidentalis Freeman

Abstract: The influence of foliar nitrogen levels in Douglas-fir Pseudotsuga menziesii (Mirb.) on various biological characteristics of the young instars of the western spruce budworm, Choristoneura occidentalis Freeman, was studied. Seedlings were grown under greenhouse conditions and provided with nutrient solutions to maintain 9 foliar nitrogen levels ranging from 0.74–5.02%. Third instar larvae confined to treated seedlings were monitored through the next generation. Larval mortality was highest and adult emergence lowest, at both the upper and lower extremes of foliar nitrogen. Maximum survival occurred in larvae confined to seedlings containing 2.51% foliar nitrogen. Total development time and mean pupal weight varied significantly across nitrogen levels. Total number of eggs and total mass of eggs produced per female were lowest at the high and low extremes of foliar nitrogen levels and highest from treatments with foliar nitrogen of 2.51% nitrogen. Zusammenfassung Auswirkung von kunstlich verandertem Stickstoffgehalt der Nadeln auf die Entwicklung und Uberlebensrate von Junglarven des Wicklers Choristoneura occidentalis Freeman Ziel dieser Untersuchung war es, den Einflus des Stickstoffgehaltes der Nadeln der Douglasie, Pseudotsuga menziesii (Mirb.) auf Choristoneura occidentalis-Junglarven zu untersuchen. Im Gewachshaus wurden Samlinge gezogen und so mit Nahrlosungen behandelt, das schlieslich 9 verschiedene Stickstoffgehalte der Nadeln erzielt wurden (0,74-5,02 % N). Larven des dritten Stadiums wurden auf die gedungten Samlinge angesetzt und bis zur nachsten Generation durchgezuchtet. Bei den niedrigsten und hochsten N-Gehalten war die Larvenmortalitat am hochsten und die Schlupfrate der Falter am niedrigsten. Die hochste Uberlebensrate der Larven wurde bei 2,51 % N-Gehalt der Nadeln beobachtet. Die Gesamtentwicklungszeit und das mittlere Puppengewicht unterschieden sich signifikant in Abhangigkeit vom N-Gehalt. Die Zahl der insgesamt abgelegten Eier und die Gesamteizahl/Weibchen war beim niedrigsten und hochsten N-Gehalt am niedrigsten und bei einem N-Gehalt von 2,51% am hochsten.

Mites of the family Macrochelidae as predators of two species of dung-breeding pest flies

Abstract: Nine species of macrochelid mites [Macrocheles “glaber” (Muller),M. aestivus Halliday,M. mammifer Berlese,M. peniculatus Berlese,M. robustulus (Berlese),M. merdarius (Berlese),M. peregrinus Krantz,M. eurygaster Krantz,Glyptholaspis confusa (Foa) were tested in the laboratory as predators of 2 species of dung-breeding pest flies (Musca vetustissima Walker,Haematobia irritans exigua de Meijere). The mites varied in their ability to attack the 2 fly species at both egg and larval stages. larger mites were generally more effective predators than the smaller species. The level of predation imposed byM. “glaber” onMusca vetustissima also varied with the developmental stage of both predator and prey.

Effects of infection with a granulosis virus on larval growth, development and ecdysteroid production in the cabbage looper, Trichoplusia ni

Abstract: . Granulosis virus-infected Trichoplusia ni (Hubner) larvae exhibited an increased larval life span with no supernumerary moult and no pupation. Weight gain was not affected. Insects infected shortly after hatching were slower in reaching the fourth and fifth stadia than were control insects. Haemolymph ecdysteroid titres were lower in virus-infected insects than control insects, but these differences were only significant (P<0.05) in the fifth stadium. Electron microscopic examination of the pro thoracic glands revealed extensive granulosis virus infection, and glands from virus-infected insects produced no RIA-detectable ecdysteroids in vitro. Injection of 20-OII-ecdysone into virus-infected larvae at various concentrations and times did not induce pupation.

The Symbiosis of Acarid Mites, Genus Ctenocolletacarus (Acarina, Acariformes), and Stenotritid Bees, Genus Ctenocolletes (Insecta, Hymenoptera)

Abstract: Details of the life history of acarid mites of the genus Ctenocolletacarus have emerged from studies of nests of their hosts, Ctenocolletes albomarginatus and Ce. nicholsoni, and from rearing mites in the laboratory. The mites are closely associated with their hosts at all stages and their complete breeding cycle occurs in the hosts' sealed brood cells. Only the phoretic deutonymph leaves the cells. The mites, like their hosts, are univoltine. One to a few hypopi dismount from nesting females into each new brood cell and rapidly transform through non-mobile tritonymphs to adults of both sexes. Female mites oviposit on the ceiling of the cell during the host larva's early instars, giving rise to hundreds of larvae and then protonymphs by the time the host larva has completed feeding. Protonymphs metamorphose to hypopi once the host larva has defaecated and entered the prepupal phase. Hypopi remain with the dormant prepupa until the following season when they secrete themselves beneath the terga of the newly emerged adult bee. Circumstantial evidence, suggesting that hypopi are transmitted venereally between adult bees, is discussed. Adult, larval and protonymphal mites ingest pollen and the late protonymphal stage invades the faeces of the larval host. Sanitary control is a possible pay-off for the hosts.

Threshold Temperature and Degree-day Estimates for Development of Immature Southern Pine Coneworms (Lepidoptera: Pyralidae) at Constant and Fluctuating Temperatures

Abstract: First- and fourth-instar Dioryctria amatella (Hulst) were reared on an artificial diet at six constant temperatures in the laboratory and outdoors. Threshold temperature for larval development was 13°C, and development from newly hatched larva to pupa and larva to adult required 303 and 493 degree-days (DD), respectively. Mean DD for development of immatures in a shaded area outdoors during spring and early summer of 1984 varied only 8 DD from estimates derived from constant-temperature data. Threshold temperature did not vary with larval age.

Biotic interactions in relation to prey-predator relationship with special reference to some thrips species (Thysanoptera: Insecta)

Abstract: Comparative predatory efficiency, feeding behavior, fecundity and life cycle of three species of polyphagous predatory thrips, Erythrothrips asiaticus, Franklinothrips megalops and Androthrips flavipes were studied under field conditions. Adults of both F. megalops and E. asiaticus fed only on eggs of the prey thrips, whereas their larvae fed both on the larvae and adults of prey thrips. Significant variation in prey consumption was shown by each developmental stage of E. asiaticus . The II instar larva was more efficient in prey consumption than the first instar larva. The adult prey was least preferred and the first instar larva of the prey was highly preferred. Females fed on more eggs than the males.

The callajoppine parasitoids of sphingids in Central America (Hymenoptera: Ichneumonidae)

Abstract: An illustrated key is presented to the three genera of the ichneumonine subtribe Callajoppina that are known to occur in Central America A new species, Tricyphus respinozai, is described from north-western Costa Rica and brief notes are given about its biology as a larval/pupal parasitoid of Manduca dilucida Hiibner (Lepidoptera: Sphingidae) The cephalic capsules of the final instar larva and a preultimate instar larva of Trespinozai are described

Hydroscapha granulum (Motschulsky, 1855) description of the larva and ecological notes

Abstract: The most northern Eurasian occurrence of Hydroscapha granulum in the Lower Ardeche River (France) is discussed. After a systematical, biogeographical and ecological review, the larva is described and compared to the only previously known larva of//, natans which was found in North America. H. granulum is a rheophilic species, which lives in sandy and cobble substrate and is sensitive to organic pollution.

Thermal Ecology of the Screwworm Larva, Cochliomyia hominivorax (Coquerel) (Diptera: Calliphoridae)

Abstract: The thermal environment of the screwworm larva was studied under natural and mass-rearing developmental conditions. A}rtificially infested ovine and bovine experimental hosts were used to monitor larval (myiasis wound) and rectal temperatures over the course of parasite development. Temperatures in infestations in ovine wounds increased from mean initial values of 37 to near 41°C after 2 d, then decreased slowly for 3 d to 40°C as larvae matured. Wound temperature was positively related to larval density in the wound, but larval development rates were negatively related to density. Ovine hosts, but not bovine, became febrile in response to infestation, effectively increasing mean wound temperatures approximately 1°C in large infestations. In bovines, temperatures throughout the developmental period followed patterns similar to those in ovines, but were approximately 2°C lower. Temperatures in mass-rearing conditions, with minimal exogenous temperature control, showed that larvae can maintain temperatures above ambient and within a narrow range. Under such conditions they simulate the natural host's thermal environment during all but the final 36–48 h of development, when temperatures descend rapidly to as low as 32°C. Periodic feedings at late stages may abruptly alter temperatures for short periods. Implications of the role of temperature in the evolution of the screwworm from a carrion-feeding ancestor, and as a stress factor in mass rearing, in terms of present mass-rearing techniques, are discussed.