Comparison of the biology of Myzus persicae Sulz. resistant and susceptible to dimethoate

Apterous Myzus persicae resistant to dimethoate reproduce for the same length of time as susceptible aphids, but the resistant ones reproduce significantly faster during the first 10 days of adult life (especially during the first 5 days). Thereafter, they reproduce more slowly, and eventually the susceptible aphids produce approximately the same number of larvae. Resistant aphids die significantly younger. Resistant aphids as larvae develop faster than susceptible ones and are significantly heavier when they first become adult. The resistant aphids do not excrete faster during the first few days but, as they produce more larvae during the first 10 days of adult life and have developed faster, they probably feed faster during development and early adult life or obtain more nutritious food. Resistant aphids were at least as effective as susceptible ones in transmitting sugar-beet mosaic and pea mosaic viruses, and plants showed symptoms sooner when resistant aphids were the vectors.     

怀头鲇早期发育阶段消化酶及碱性磷酸酶活性变化(英文)

采用动物性饵料和人工饲料培育1～10日龄怀头鲇(Silurus soldatovi)仔稚鱼,分析测定了全鱼酸性、碱性蛋白酶、淀粉酶、脂肪酶以及碱性磷酸酶的活性。结果表明:孵化后3天开口期仔鱼已具有较高的碱性蛋白酶活性,5日龄时碱性蛋白酶比活力达到较高值,8日龄时出现低值,总体变化呈波动上升趋势;酸性蛋白酶活性在1～8日龄处于较低水平,8日龄后开始迅速升高;淀粉酶活性在5日龄左右达到最高值,随后酶活性开始下降至较低水平;脂肪酶活性变化波动较大,表现为双峰型,两个峰值分别出现在3～4日龄和6～8日龄。摄食动物性饵料仔稚鱼消化酶活性和碱性磷酸酶活性均高于摄食人工饲料。在整个早期发育过程中,碱性蛋白酶比酸性蛋白酶活性高,碱性蛋白酶、淀粉酶比活力在约8日龄仔稚鱼转变期明显下降,而酸性蛋白酶活性开始迅速升高,这说明消化酶活性的变化与仔稚鱼发育过程中消化机能转换具有相关性。怀头鲇在10日龄内碱性磷酸酶活性呈上升趋势,表明怀头鲇胃肠道功能的逐步发育完善。     

Larval feeding behaviour affects the impact of staminate flower production on the suitability of balsam fir trees for spruce budworm

Laboratory rearing of spruce budworm, Choristoneura fumiferana, in conjunction with field rearing indicated that the feeding behaviour of the larvae, which is affected by the insect population density, significantly influenced the impact of balsam fir, Abies balsamea, staminate flowering on spruce budworm biology. At low budworm density, the production of pollen in the midcrown of host trees reduced the insect development time by 5 days without affecting pupal weight, fecundity and survival. However, at high budworm density, the small amount of current-year foliage produced by flowering branches forced old larvae (sixth instar) either to feed on 1-year-old foliage (backfeeding) or to move from the midcrown to the lower crown section where staminate flowers are absent and more current-year foliage is available. When old larvae fed on old foliage, they exhibited reduced pupal weight and fecundity without losing the advange in development time that they obtained from feeding on pollen during their early stages of development. On the other hand, when old larvae moved to the lower crown section, they avoided the negative effects of backfeeding but lost the advantage in development time that was gained from feeding on pollen. Results from this study indicated that the production of staminate flowers by balsam fir trees could have opposite effects on spruce budworm population dynamics depending upon the insect population density when flowering occurs.     

Larval development and post‐larval growth of Branchiomma bairdi (Annelida: Sabellidae) from a Mediterranean population

Branchiomma bairdi is a Caribbean fan worm introduced in several localities worldwide, including the Mediterranean Sea, where the species’ range has rapidly expanded. Reproduction in B. bairdi was previously investigated in both extra‐Mediterranean and Mediterranean areas, but no information is available on larval development and post‐larval growth. In the present article, we examined these features for a population from the Mar Grande of Taranto (Ionian Sea). The species is hermaphrodite, and fertilization occurs in situ. Mucus seems to play an important role in fertilization, and also in preserving eggs before fertilization. The trochophore stage develops within the mucus and after hatching, larvae swim for about 3 d before settlement. The trochophore showed a distinct prototroch and two red dorsolateral larval eyes. The pelagic stage takes only 96 h even though prototroch is maintained after settlement, disappearing at 5 d, when larvae showed three chaetigers and branchial crown consisted of four radioles. Some interesting observations concerning changes in the morphology of chaetae and in the number of uncini during growth are also reported, together with discussion of the development of stylodes, an important diagnostic feature in Branchiomma species identification.     

Feeding resumption, morphological changes and mortality during starvation in Japanese flounder larvae

Japanese flounder Paralichthys olivaceus larvae established first feeding 3 days after hatching (DAH) at c . 17° C. Non-fed fish reached irreversible starvation at age 5 DAH. Non-fed fish showed similar feeding rate and feeding intensity as the fed fish when they were provided with prey before 5 DAH, after which the starved larvae did not feed even when prey became available. None of the six morphological measurements examined (total length, body height, eye height, head height, gut height and myotome height) showed significant differences between the non-fed and fed larvae until 5 DAH. Normal development continued only in the fed group, and the non-fed larvae showed reverse growth or body collapse after 5 DAH. Owing to the shrinkage and collapse at the top of head due to starvation, head height could be a sensitive indicator of starvation in Japanese flounder larvae. In the fed treatments, high mortality occurred from first feeding (3 DAH) to irreversible starvation (5 DAH), accounting for about two-thirds to three-quarters of the overall mortality (46–52%) throughout the experiments. This mortality was not prey density or larval density dependent. Mortality during the same period in the non-fed larvae accounted for about a third of the overall mortality (100%).     

Brugia pahangi: infections and their effect on the lymphatic system of Mongolian jirds (Meriones unguiculatus)

Brugia pahangi has been found to be primarily a lymphatic-dwelling parasite in jirds when infections are induced by the subcutaneous injection of infective larvae or by allowing infected Aedes aegypti to feed.Migration to the regional lymphatics occurred as early as 1–4 days. Although some injected larvae remained in the skin for as long as 30 days and some became localized in the heart, lungs, pleural cavity, or peritoneal cavity, about three-fourths of the recovered filariae were found in the regional lymphatics. In contrast, when larvae were injected peritoneally they remained largely in the peritoneal cavity for at least 30 days.The relevant lymphatics and their drainage patterns in jirds have been described.The major pathological changes noted in jirds involved the regional lymphatic vessels and nodes, which were severely affected when they contained dead worms. Pulmonary granulomas due to dead microfilariae and occasionally to dead larvae or adult worms were noted.Observations are included on the susceptibility and course of B. pahangi infections in jirds.     

Complementary Behaviors of Maternal and Offspring <Emphasis Type="Italic">Spodoptera littoralis</Emphasis>: Oviposition Site Selection and Larval Movement Together Maximize Performance

The selection of oviposition and feeding sites within cotton plants by Spodoptera littoralis was investigated in the field in 2 years, 2007 and 2008. The female moths exhibited significant oviposition preference for young leaves (YL), particularly the 3rd and 4th leaves from top. The larvae originating from egg batches deposited on YL fed mostly in situ for about 5 days, after which they gradually moved their feeding site toward fully expanded or mature leaves on the same individual plant or on neighboring plants. Larvae hatching from batches deposited on fully expanded leaves (FE) fed in situ only for about 2 days, after which they moved toward younger leaves, where they fed for about 3 more days. After the fifth day, however, larvae of the two groups dispersed mainly downward and outward from their hatching site until the end of a 12-day observation. Larvae hatching from eggs deposited on mature or pre-senescent leaves (MP) moved mainly horizontally to other plants after a slight upward shift. The YL and FE larvae grew significantly faster than MP larvae, both in the field and in a laboratory experiment. In the laboratory experiment, the larval period was shorter and the pupal weight was higher when the animals were offered young leaves or young and fully expanded leaves, than when the animals were offered mature and pre-senescent leaves during the first 5 days after hatching. Possible causes and advantages of the exhibited oviposition preference, as well as the apparent ability of larvae to correct for small egg misplacements made by the females, are discussed.     

Environmental induction of larval diapause and life-history consequences of post-diapause development in the Large Copper butterfly,Lycaena dispar (Lepidoptera: Lycaenidae)

Many insects in temperate zones withstand the adverse conditions of winter through entering diapause and the two most important environmental stimuli that induce diapause are photoperiod and ambient temperature. The Large Copper butterfly, Lycaena dispar Haworth (Lepidoptera: Lycaenidae), is a Palearctic butterfly that hibernates as larvae. Since this butterfly is a near threatened species in some regions, there has been a growing need for a standardized protocol for mass rearing of this butterfly based on the adequate knowledge of its ecology. In the present study, we first identified that L. dispar larvae were sensitive to the photoperiodic induction of diapause during their first larval instar. We then investigated to what extent the diapause-inducing effects of photoperiod could be modified by ambient temperatures in L. dispar larvae by exposing them to the range of day-lengths (L:D 14:10, 12:12, 10:14 and 8:16) at three different temperatures (15, 20 and 25 °C). All larvae were induced to enter diapause at low ambient temperature (15 °C) regardless of photoperiod, whereas most of them (86 %) exhibited direct development when temperature was high (25 °C). The photoperiodic induction of diapause was evident when day-length was shorter than 14 h at intermediate temperature (20 °C). Pre-diapause development was prolonged at low temperatures. Finally, we found that post-diapause development of L. dispar larvae was determined by both the chilling temperature experienced by diapausing larvae and the duration of larval diapause. Adult emergence was enhanced when larvae were chilled at 8 °C and when they had been under the state of diapause for 20 days before they were treated to terminate diapause.     

Influence of swim training on cardiac activity,tissue capillarization,and mitochondrial density in muscle tissue of zebrafish larvae

Larval zebrafish (Danio rerio) of two different age classes ("swim-up" larvae, 9 days old; "free-swimming" larvae, 21 days old) were exposed to either an endurance/continuous training or interval training. Control animals were kept in stagnant water. A comparison of cardiac activity of trained (either endurance or interval) and untrained animals at the end of the training regime revealed no differences in heart rate, end-diastolic and end-systolic ventricular volume, and cardiac output. Training also had no influence on the concentration of erythrocytes in the blood. Thus, at the level of total oxygen transport in the blood, training did not provoke any improvement during the first 32 days of development. Significant changes, however, were observed at the tissue level. In free-swimming larvae [i.e., between 21 and 32 days postfertilization (dpf)] endurance training increased the capillarization of both axial muscle caudal to the anus and the tail fin. In addition, mitochondrial density of red and intermediate muscle fibers increased significantly. In contrast to capillarization, even swim-up larvae, trained between 9 and 15 dpf, were affected. The observed increase in mitochondrial content indicates a high demand for oxygen and energy-rich metabolites for oxidative phosphorylation. In older larvae, this is met by the increase in capillarization that improves the blood supply and with it the required oxygen and metabolite supply of muscle tissue. Both of these adaptational changes result in a reduction of diffusion distances (between capillary and muscle fiber as well as mitochondria) and may contribute to a higher resistance toward oxygen deficiency. Furthermore, this study indicates that plasticity of muscle tissue is already established in early stages of development at both the tissue and cellular levels.     

Relationships between larval nutritional experience, larval growth rates, juvenile growth rates, and juvenile feeding rates in the prosobranch gastropod Crepidula fornicata

Planktonic larvae experiencing short periods of starvation or reduced food supply often grow and develop more slowly, have poor survival, fail to metamorphose, metamorphose at smaller sizes, or grow slowly as juveniles. In this study, we examined the impact of short periods of food limitation at various stages of larval development on larval and juvenile growth in Crepidula fornicata. In addition, we considered whether juveniles that were stressed as larvae grew poorly because of reduced rates of food collection due to impaired gill function. For 5 experiments, larvae were either starved for several days beginning within 12 h of hatching or were starved for the same number of days following 1 or more days of feeding at full ration (cells of the naked flagellate Isochrysis galbana, clone T-ISO, at 18×10⁴ cells ml⁻¹). In one experiment, larvae were transferred for 2 or 4 days to seawater with extremely low phytoplankton concentration (1×10⁴ cells ml⁻¹). In all experiments, larvae were returned to full ration following treatment. Control larvae were fed full ration from hatching to metamorphosis. When larvae reached shell lengths of about 900 μm they were induced to metamorphose and then reared individually at full ration in glass bowls, with phytoplankton suspension replenished daily. Larval and juvenile growth rates were determined by measuring changes in shell length (longest dimension) over time. Juvenile feeding rates were determined by monitoring changes in phytoplankton concentration over 2–3 h at the end of the growth rate determinations. In general, larval growth rates for the first 2 days after the resumption of feeding were inversely proportional to the length of time that larvae were starved. However, larval growth rates ultimately recovered to control levels in most treatments. Starving the larvae caused a significant reduction in initial juvenile growth rates (first 3–4 days post-metamorphosis) in most experiments even when larval growth rates had recovered to control levels prior to metamorphosis. Juvenile growth rates were not significantly reduced when larvae were subjected to reduced food availability (1×10⁴ cells ml⁻¹), even for treatments in which larval growth rates were compromised. Mean weight-specific filtration rates for juveniles were significantly reduced (p<0.05) following larval feeding experience in only one or possibly 2 of the 4 experiments conducted. Our data suggest that although larvae of C. fornicata may fully recover from early nutritional stress, the resulting juveniles may exhibit poor initial growth due to impaired gill function, reduced digestive capability, or reduced assimilation efficiency.     

Feeding behaviour of Japanese flounder larvae under laboratory conditions

Tank–reared Japanese flounder larvae, Paralichthys olivaceus , had a major feeding peak in the morning and a secondary peak in the afternoon throughout the larval development, with light being the primary factor regulating their feeding activity. The larvae consumed rotifers in preference to Artemia for up to 10 days, after which the food preference shifted to Artemia . Feeding rates of the larvae prior to 10 days post–hatch depended on prey density, but in the old larvae, feeding rates were independent of prey density. Maximum feeding rate occurred at 19° C. The occurrence of the attack posture, after its onset at first feeding (2 days post–hatch), increased up to 25 days, began to decrease when the larvae prepared to settle down, then disappeared after settlement. The occurrence frequency of the attack posture was positively related to fish density, but inversely related to starvation duration, and occurred most frequently at 19° C. This posture depended on prey density in larvae prior to 10 days post–hatch, but became independent of prey density as the larvae developed. It was obvious that, for flounder larvae, attack posture was a behavioural character closely related to feeding and subject to larval development and environmental factors.     

Timing of the water-to-land transition and metamorphosis in the land hermit crab Coenobita compressus H. Milne Edwards: evidence that settlement and metamorphosis are de-coupled

After metamorphosing from the last larval stage to the transitional megalopal stage in the marine plankton, the hermit crab Coenobita compressus moves ashore where it undergoes a second metamorphosis to the first juvenile instar on land. In two experiments using laboratory-reared crabs, I moved megalopae from water to land after different amounts of time at this stage and investigated the impact of this manipulation on the timing of and survival through the second metamorphosis. In the Involuntary Settlement experiment, megalopae were moved to land when they were 3, 6, 9, 12, or 15 days old. None of those moved between the ages of 3 and 6 days survived through metamorphosis, but the majority of 9-day-old megalopae survived, as did most 12- and 15-day-old megalopae. This suggests that developmental changes early in the megalopal stage prepare C. compressus for terrestrial life. Once on land, megalopae that had been moved to land at 9 days spent about nine additional days there before metamorphosing, while 12- and 15-day-old megalopae metamorphosed after spending about 5 and 4 days, respectively, on land. In the Voluntary Settlement experiment, megalopae were given access to land when they were 1, 5, 10, or 15 days old, but were not forced to make the transition. Those given access to land after 1 day voluntarily left their dishes for the first time after an average of 7 days in water. Those given access when they were 5 days old remained in water about 4 days longer, while those given access when they were 10 and 15 days old left after less than a day. In both experiments, the timing of metamorphosis relative to settlement (i.e., transition to land) showed that these events are dissociated to a degree and revealed the presence of a metamorphic clock. I discuss why the dissociation of settlement and metamorphosis may have been favored in the land hermit crab and in another anomuran crab.     

PTERYLOGRAPHY, PLUMAGE DEVELOPMENT AND MOULT OF JAPANESE QUAIL COTURNIX C. JAPONICA IN CAPTIVITY

Japanese Quail were kept in small cages under controlled conditions of temperature and light, and their pterylography and moult are described. There are 10 primaries, 14 secondaries and corresponding numbers of greater upper and lower wing coverts. The alula has four feathers and the tail from five to six pairs of feathers. There is an apterium in the dorso-pelvic tract similar to that in other quail genera. The arrangement of feathers in the ventral and cervical tracts appears to differ from that described for some North American quail.
The chicks hatch with a covering of natal down. Pre-juvenile moult can be seen when the chicks are three days old. Juvenile body plumage is complete in about 30 days; the sides of the face, around the eyes, are the last places to acquire feathers. The tenth and last juvenile primary to grow is mature when the chicks are 41 days old.
The moult in which the juvenile plumage is replaced overlaps the post-natal moult and in part of the ventral tract natal down is replaced by the first adult feathers. This makes it possible to sex the quail at 14 days old. The first adult moult is complete, in the body tracts, by the time the birds are five to six weeks old. The dropping of juvenile primaries commences at about three weeks old and ceases when about eight weeks old. Only from three to six primaries are replaced; most birds studied replaced five. The significance of this difference from other Galliformes is discussed; it is thought to be associated with the species' migratory behaviour. Quail which remained in the controlled laboratory environment did not undergo any further moult. All birds moulted when both temperature and light period were reduced and most birds moulted when the light period alone was reduced. Adult birds housed in small cages in an unheated, unlit shed underwent a complete moult between August and December in which all primaries were replaced. This moult took 8–14 weeks to complete.     

Dispersal and spatial distribution of western corn rootworm larvae in relation to root phenology

• 1 Despite the increasing economic importance of root feeding pests such as the western corn rootworm (WCR) Diabrotica virgifera virgifera, basic parameters about their below ground biology are only partly understood. The present study investigated the dispersal and distribution of WCR larvae in the maize root system during their development at two growth stages of maize (BBCH 13–14 and BBCH 17–18).
• 2 Dispersal of the WCR larvae increased as they developed; the larvae moved off their original place of emergence and into deeper soil layers. Overall, changes in the horizontal distribution of the larvae were more extensive than changes in the vertical distribution.
• 3 The spatial analysis of distance indices revealed that the larvae had an aggregative distribution throughout their development. The feeding site of larvae in the root system was determined by the stage of larval development. Initially, WCR larvae started feeding in close proximity to their emergence location and moved to more developed root tissue towards the end of their development.
• 4 Differences in root phenology mainly influenced the distribution of the larvae at the end of their development, when larvae exhibited increased vertical movement at a later growth stage of maize.
• 5 The mechanisms of these distributional changes and the implications for the management of WCR larvae are discussed, especially with regard to chemical control, because fewer larvae are expected to be targeted at a later growth stage of maize.

     

Larval development of two parasitic flies (Conopidae) in the common host Bombus pascuorum

Abstract.

• 1 Whenever parasitism by more than one female occurs, larvae of parasitoids not only have to resist host defence but also face competition with other (unrelated) larvae. Competition is particularly important in solitary parasitoids where only one larva is able to complete its development. Such a situation is found in Conopidae (Diptera) parasitizing adult bumble bees where larvae of two species of conopid flies, Sicus ferrugineus L. and Physocephala rufipes F. often compete within the common host Bombus pascuorum Scopoli. This study analysed the larval development of the two species and asks how competition among larvae may be regulated.
• 2 Parasitized workers of B.pascuorum were caught in the field and kept according to different experimental schedules in the laboratory. This provided stage-structured data for the temporal course of development of the parasitic larvae. For the analysis, a simulation model was constructed that estimated the duration of all parasitic stages (Manly, 1990, first method). In both species the egg stage was found to be approximately 2 days, first instar 3 days, second instar 4 days, and third instar 3 days. The total development time is an estimated 10.8 days from oviposition in S.ferrugineus and 11.4 days in P.rufipes. S.ferrugineus develops faster in the beginning, probably because of its larger egg size, whereas P.rufipes pupates at larger size. First-instar larvae of both species possess strong, pointed mandibles.
• 3 The success of conopid larvae seems only marginally affected by host defence, for a single larva per host almost always completes development. Under competition, however, mortality rate increases substantially, and most larvae die in their first instar. Moreover, they show signs of melanization. The estimates for developmental times and the patterns found in this study suggest that conopid larvae seem capable of physical attacks, particularly during the first instar, when elimination of competitors is most common, and that S.ferrugineus has a time advantage because of its faster early development. Because most studies have previously been carried out with hymenopteran parasitoids, this study provides new information about the other large group of parasitoid insects, the Diptera, and demonstrates convergent patterns.

     

The role of exogenous JH I,JH III and Anti-JH (precocene II) on queen induction of 4.5-day-old worker honey bee larvae

Worker larvae at an age of 4½ days were fed one of several mixtures of reconstituted royal jelly adjusted to a refractive index of 1.3825 and supplemented with JH I, JH III or Anti-JH (precocene II). In addition, juvenile hormone was topically applied to larvae of the same age. It was readily apparent that caste induction is concentration-dependent and that 4?-day-old worker larvae can still develop into queens under laboratory conditions, providing that they have not stopped feeding or can be induced to commence feeding again. These findings are contrary to the general belief that queen induction is not possible after a socalled sensitive period of 3–3½ days. Queens resulted only from honey bee larvae exposed to royal jelly containing 1 μg of JH I. In addition, oral application at this concentration resulted in the only case in which the normal mean weights of worker honey bees were exceeded. All other concentrations of juvenile hormone were not sufficient to initiate queen induction, although its lower concentration may have influenced the production of intercastes.Precocene II did not play a role in queen induction and it also did not interfere with the growth of developing larvae or adults. In addition, the lack of malformations in honey bees treated with precocene II indicates that the use of such a compound as a control agent in insect populations will probably not be detrimental to honey bee larvae that are at least 4½ days old. However, large doses of precocene will quickly kill most 3½-day-old honey bee larvae.The evidence presented here clearly indicates that caste determination is regulated by the endocrine system in honey bee larvae. Food intake in honey bee larvae may well be regulated by the endocrine system. Thus, an apparently inhibited corpus allatum (C.A.) could be reactivated by food intake coupled with juvenile hormone. The food intake restriction that worker larvae normally encounter in the hive probably results in a cessation of C.A. activity. The increase in food intake by queen larvae, on the other hand, carries an increase in growth and accompanying morphological changes necessary for queen development. This concept may also explain the development of intercastes encountered in in vitro studies. Only those larvae that follow a normal food intake sequence, i.e. moderate during the first 3–4 days or so, will develop into queens. Conversely, those larvae that take in too much food during the early portion of development may achieve incomplete development of the neurosecretory system and, thus, develop into intercastes.     

School Formation and Concurrent Developmental Changes in Carangid Fish with Reference to Dietary Conditions

The ontogeny of schooling behaviour was studied in comparison to the development of sensory and swimming organs and taxis in carangid fish. Striped jack, Pseudocaranx dentex, larvae showed strong phototaxis at 3 days after hatching (3.5 mm in TL) when they developed pigmentation in the retina. Rheotaxis and optokinetic responses were apparent at 4.0-6.0 mm TL as larvae completed development of the basic structure of their eyes. A major inflection of allometric growth occurred at 9 mm, and fin ray formation was completed at these stages. Schooling behaviour, represented by one TL of inter-individual distance and parallel orientation, only appeared at 16 mm TL, and just prior to this behaviour, fish showed mutual attraction through vision at 12 mm TL. Canalization of buccal lateral lines was complete at 18 mm TL, whereas that of trunk lateral lines started at 23 mm TL and was complete at 30 mm TL. With these results, we assumed that critical factors of the ontogeny of schooling behaviour in carangid fish include not only the development of sensory or swimming organs, but also other factors such as development of the central nervous system. To show this, we reared another carangid species, the yellowtail Seriola quinqueradiata, with dietary depletion of DHA (docosahexaenoic acid), which is indispensable for the development of the central nervous system. Although DHA-free fish showed optokinetic response, they did not show schooling behaviour when they attained their schooling size. Tracer experiments using radioisotope labelled DHA showed that DHA is incorporated into the brain, spinal cord, and retina of juvenile fish. Under natural conditions, carangid fish larvae should intake enough DHA through diet to develop schooling behaviour, the fluctuation of dietary quality in zooplankton might therefore influence the development of indispensable antipredatory behaviour. Morphological changes of striped jack occurred in two steps; first at 9-12 mm (fin formation and inflection of allometric growth) and then second at 20-30 mm (scale and lateral line formation), and these changes corresponded with the development of schooling and recruitment to coastal waters, respectively. Since the onset of schooling is the first step of active antipredatory behaviour, we considered that 12 mm TL is the size at which they attain the juvenile period.     

Development of the jamming avoidance response and its morphological correlates in the gymnotiform electric fish, Eigenmannia.

The electric fish, Eigenmannia, will smoothly shift the frequency of its electric organ discharge away from an interfering electric signal. This shift in frequency is called the jamming avoidance response (JAR). In this article, we analyze the behavioral development of the JAR and the anatomical development of structures critical for the performance of the JAR. The JAR first appears when juvenile Eigenmannia are approximately 1 month old, at a total length of 13-18 mm. We have found that the establishment of much of the sensory periphery and of central connections precedes the onset of the JAR. We describe three aspects of the behavioral development of the JAR: (a) the onset and development of the behavior is closely correlated with size, not age; (b) the magnitude (in Hz) of the JAR increases with size until the juveniles display values within the adult range (10-20 Hz) at a total length of 25-30 mm; and (3) the JAR does not require prior experience or exposure to electrical signals. Raised in total electrical isolation from the egg stage, animals tested at a total length of 25 mm performed a correct JAR when first exposed to the stimulus. We examine the development of anatomical areas important for the performance of the JAR: the peripheral electrosensory system (mechano- and electroreceptors and peripheral nerves); and central electrosensory pathways and nuclei [the electrosensory lateral line lobe (ELL), the lateral lemniscus, the torus semicircularis, and the pace-maker nucleus]. The first recognizable structures in the developing electrosensory system are the peripheral neurites of the anterior lateral line nerve. The afferent nerves are established by day 2, which is prior to the formation of receptors in the epidermis. Thus, the neurites wait for their targets. This sequence of events suggests that receptor formation may be induced by innervation of primordial cells within the epidermis. Mechanoreceptors are first formed between day 3 and 4, while electroreceptors are first formed on day 7. Electroreceptor multiplication is observed for the first time at an age of 25 days and correlates with the onset of the JAR. The somata of the anterior lateral line nerve ganglion project afferents out to peripheral electroreceptors and also send axons centrally into the ELL. The first electroreceptive axons invade the ELL by day 6, and presumably a rough somatotopic organization and segmentation within the ELL may arise as early as day 7. Axonal projections from the ELL to the torus develop after day 18.(ABSTRACT TRUNCATED AT 400 WORDS)     

Depth regulatory behavior of the first stage zoea larvae of the sand crab Emerita analoga Stimpson (Decapoda: Hippidae)

Laboratory studies of the behavior of first stage zoea larvae of the sand crab Emerita analoga Stimpson have shown that while newly-hatched larvae are strongly photopositive, this response lasts only about four hours, as the larvae rapidly become photonegative. After becoming photonegative, a large proportion of the larvae remain so throughout the first four days of life if they are fed Artemia nauplii; if starved, the larvae become significantly more photopositive than when fed. Both the photopositive response of newly-hatched larvae and the reversal to photopositive behavior in response to starvation are only apparent under horizontal test conditions. Increases in hydrostatic pressure stimulate swimming activity among the larvae; responsiveness to pressure being greatest at hatching and decreasing thereafter. The pressure response is strongly oriented to light; pressure-stimulated larvae will swim towards a light source regardless of whether this involves upward, downward, or horizontal motion. Experiments suggest that the pressure response provides the primary mechanism for depth regulation among young larvae; gravity and light may augment the pressure ‘sense’ by serving as primary orientational cues. The nutritional status of an individual larva may alter its depth-regulatory capabilities, but this effect is not yet clear.