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1. Action of fenoxycarb on metamorphosis and cocoon spinning in Chrysoperla carnea (Neuroptera: Chrysopidae): identification of the JHA-sensitive period

Creator:
Bortolotti, Laura, Micciarelli Sbrenna, Anna, and Sbrenna, Giovanni
Type:
article, model:article, and TEXT
Subject:
Chrysoperla carnea, juvenoids, fenoxycarb, development, metamorphosis, and JH sensitive period
Language:
English
Description:
Fenoxycarb is an insecticide with a juvenile hormone mimicking effect, which disturbs metamorphosis in several insect species, including the neuropteran Chrysoperla carnea. Administration of different doses of fenoxycarb to third instar larvae causes a dose dependent inhibition of metamorphosis and cocoon spinning. When treated within 48 h of the last larval ecdysis, this insect shows a temporary inhibition of metamorphosis and cocoon spinning, which leads to a prolongation of the third larval instar. When treated after 60 h into the last instar, most of larvae were unable to metamorphose and spin a cocoon. Thus, C. carnea is most sensitive to this juvenoid in the period after 60 h into the last larval instar.
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public

2. Characters of larvae - what are they?

Creator:
Urho, Lauri
Type:
article and TEXT
Subject:
early ontogeny, development, ecology, metamorphosis, juvenile, and habitat changes
Language:
English
Description:
The larval period in fishes has several definitions, each one deviating slightly from the other. Small discrepancies in the definitions, especially concerning the end of the larval period, can create misunderstandings when applied in practice. I examine the different definitions of a larva, the larval period, including metamorphosis, and the juvenile period. Various criteria used to identify the transition from the larval to juvenile periods are contradictory and refer mostly to the length of the larval period. Ignorance of definitions used to identify the juvenile period has caused many larvae to be regarded as juveniles. I discuss the feasibility of various definitions and the nomenclature on the basis of character evaluation. The occurrence of larval morphological characters, i.e. larval fin fold, differentiation of fins, temporary organs, absence of scale cover, non-adult like body proportions and pigmentation, is examined and some features are compared in eleven species. Irrespective of the different definitions of a larva, there are considerable differences in the schedule and duration of development in certain characters between species and, in terms of duration, also within species owing to environmental conditions. Ontogenetic processes seem to be sufficiently flexible to allow larvae to adapt to their environment, which on the other hand may also shape the phenotype. Determination of the environment in which a larva develops depends not only on the location of the spawning grounds but also on the dispersion of larvae. Dispersal strategies are examined in light of larval morphology and behaviour. After fin differentiation, the transition from larva to juvenile would seem to be best described by the dominant morphological changes in body proportions and coloration, combined with behavioural aspects and habitat changes. I suggest the differences and functional aspects of larvae be examined. The main character of larvae is that they are adapted to make use of resources not normally used by adults.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/

3. Correlation between metabolic depression and ecdysteroid peak during embryogenesis of the desert locust, Schistocerca gregaria (Orthoptera: Acrididae)

Creator:
Sláma, Karel
Type:
article, model:article, and TEXT
Subject:
Acrididae, Schistocerca gregaria, ecdysteroids, oxygen consumption, morphogenesis, metamorphosis, embryogenesis, respiratory metabolism, and pharate stages
Language:
English
Description:
Respiratory metabolism of developing eggs of Schistocerca gregaria has been individually monitored by means of scanning microrespirography. The freshly oviposited eggs consumed 7 nl of O2 /min./egg (50 µl O2/g/h) while the pharate 1st instar larvae shortly before hatching consumed 141 nl of O2/min./egg (550 µl O2/g/h), which shows 20-fold metabolic increase during the egg stage. The output of CO2 was also regular, without discontinuous bursts throughout the whole embryonic development. The amounts of CO2 produced were constantly close to R.Q. ratio of 0.7, suggesting that lipid was the main energetic source. The vermiform, pharate 1st instar larvae emerging from the eggs exhibited very high respiratory rates (up to 3,000 µl O2/g/h). During initial phases of the egg stage, O2 consumption steadily increased until day 6, which was associated with katatrepsis or blastokinesis stage of the embryo (61 nl of O2/egg/min. = 240 µl O2/g/h). Since blastokinesis, respiratory metabolism of the egg remained constant or decreased steadily until day 10, when it rose sharply again towards hatching. The temporary metabolic depression was closely correlated with endogenous peak in ecdysteroid concentration within the embryo. These results corroborate validity of the reciprocal, high ecdysteroid - low metabolism rule previously known from insect metamorphosis. They extend its application into the period of embryogenesis. Practical implications of certain physiological, morphological and evolutionary consequences of these findings are discussed with special emphasis on the connecting links between embryogenesis and metamorphosis.
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public