Instar VII Research Articles

Life cycle and larval growth of Dynamis borassi (Coleoptera: Dryophthoridae), an emerging pest to the peach palm

Dynamis borassi Fabricius (Coleoptera: Dryophthoridae) is widely distributed in South America and is an economic pest in commercially important palms (Arecaceae). In Colombia, peach palm production is of socio-economic importance in the Pacific region but has decreased dramatically due to a weevil complex that attacks the top of the palm. Dynamis borassi is the principal cause of this damage. Despite its importance, the biology of this species is unknown. A rigorous study of life cycle duration, as well as each stage of development, is key to future ecological and behavioural studies and essential in the design of comprehensive pest management plans. We report details of the life history of this pest in a laboratory colony. Life cycle and the larval growth were studied under controlled laboratory conditions (27 ± 1 °C and 75 ± 5% RH) using two artificial diets: Diet 1 without peach palm inflorescences and Diet 2 with 100 g of inflorescences. The egg stage lasted 3.5 ± 0.1 days, the larval stage 165.5 ± 4.7 days for Diet 1 and 153.8 ± 3.9 days for Diet 2, and the pupal stage 37 ± 1.7 days for Diet 1 and 39.7 ± 1.2 days for Diet 2. Twelve instars were observed. The instar when pupation took place varied from instar VII to XII. The weight gain curve had four growth phases with both diets. Each diet produced a different life cycle duration and growth rate. No significant differences were found in the life cycle between the diets.

Effects of tributyltin at concentrations below ambient levels in seawater on Caprella danilevskii (Crustacea: Amphipoda: Caprellidae)

Hatched juveniles of Caprella danilevskii (Crustacea: Amphipoda) were exposed to one of two concentrations of tributyltin (TBT) (1.1 and 10.7 ng TBT L −1) for 49 d at 20 °C. These concentrations are near or below ambient levels in seawater. In both treatments and control, the survival rate was 100% at maturation, and >85% at the end of the experiments. Females reached maturation at 20 (median) to 21.5 d at instar VII, and repeated spawning 4–5 times during the experiment. The total number of juveniles per female decreased significantly from 39.5 in the control to 24.5 and 17.5 in 1.1 ng L −1 and 10.7 ng L −1 treatments, respectively. An earlier study reported that as the TBT concentration in seawater increased from a 0–10 ng L −1 regime to a 10–20 ng L −1 regime, the number of stations where Caprella spp. could be collected decreased along the coast of the Seto Inland Sea, of Japan. Thus, the present study indicates the possibility that the extremely low concentration of TBT measured in Japanese waters after 2000 lead to a reduction in reproductive success of Caprella spp.

Survivorship, growth and reproduction of the non-native Caprella mutica Schurin, 1935 (Crustacea: Amphipoda)

Caprella mutica Schurin is an epifaunal amphipod crustacean which originates in north-east Asia and has spread throughout the world, yet very little is known about fundamental aspects of this species biology. This paper examined the survivorship of C. mutica reared under laboratory conditions at 13–14 °C, 14 h light: 10 h dark photoperiod and fed commercial salmon feed, the diatom Cylindrotheca fusiformis Reumann and Lewin, the macroalgae, Fucus vesiculosus L. and given no additional feed. In addition, growth, maturation and reproduction of C. mutica fed C. fusiformis were assessed. No significant difference in survivorship of C. mutica was observed for the diet types over the experimental period. C. mutica was able to survive for upto 20 days without additional food. Average survival time of males and females fed the diatom, C. fusiformis was 68.8 d (range = 62–73 d) and 82.0 d (range = 76–92 d). Juvenile C. mutica emerged from the brood pouch at a body length of 1.33 mm and moulted at 5.0–11.0 day intervals. Males exhibited faster growth rates than females after Instar VII. Females produced their first brood at Instar VII, 24–26 days post-hatching and with an average body length of 8.5 mm. Each female had an average of two broods sequentially and these were released at 20.2 day intervals. Brood size for a single female increased from 11.3 (±9.9) hatchlings at Instar VII to 25.5 (±11.5) at Instar IX and the maximum number of hatchlings produced by a single female was 82. The results suggest that C. mutica exhibits a number of life-history traits that would potentially enable it to withstand global transportation and to rapidly become established in an introduced region, if environmental conditions are suitable.

Cell Differentiation Is a Primary Growth Process in Developing Limbs of Artemia

The limb of the brine shrimp Artemia develops over a four-instar period when the protopod, endite, exopod, endopod, and epipod are defined and cell differentiation (change in cell shape) occurs. To understand the importance of cell differentiation in limb growth, development of the epidermis was studied in the first thoracopod of instar V-VIII larvae. Each region was established by instar V, and the larval epidermal cells developed into general epidermal (GEC), tendinal, setal, or transport cells by instar VI. Basal extensions of the GECs formed pillar structures. The epidermal cells decreased in height from 10 to 4 microm by instar VI. Increase in length and width resulted from both cell replication and expansion of the apical cell surface in differentiating cells. Growth occurred mainly by cell replication in instar V, whereas expansion of the cell surface in GEC and setae was the major growth process in instar VII. Increase in apical cell surface area occurred primarily by change in cell shape from columnar to squamous during instar V and by increase in total cell surface in subsequent instars. The results demonstrated that cell differentiation is a significant component of growth during limb development.

Effects of photoperiod on survival, feeding and development of larvae of the red frog crab, Ranina ranina

Ranina ranina zoea was reared from hatching to megalopa under five photoperiods, from 0-h to 24-h light phase per day (0–24 L) with 6-h intervals, to test their effects on the survival rate, intermolt period, growth, external morphology, food consumption and cannibalism. Continuous light had a negative effect on the larvae; however, continuous darkness was advantageous, except during the final instar and metamorphosis. The survival rate to the megalopa stage was significantly lower under 0 and 24 L conditions than under 12 L conditions, but the rate to the final instar under 0 L conditions was similar to that under 6–18 L conditions. The frequency of normal metamorphosis tended to be low under 0 L conditions. The intermolt period was similar in each group, but accumulated zoeal duration was significantly longer under 24 L conditions than in the other groups, at instars VI and VII. The carapace length was smaller with increasing photoperiod at instars III, V and VII. The number of setae on several appendages was similar in each group, but morphogenesis was retarded on the segmentation of several appendages under 24 L conditions, at instar VII. The amount of food consumed daily was significantly lower under 0 L conditions than under 18 and 24 L conditions at instars I, III and VII. Under 0 L condtions little cannibalism occurred, in contrast with those reared under 6–24 L conditions. A light-dark regime is recommended for the rearing of the larvae.

Developmental changes in body weight and elemental composition of laboratory-reared larvae of the red frog crab, Ranina ranina (Decapoda: Brachyura)

Ranina ranina larvae were reared at 29°C from hatching to the megalopa stage to measure daily changes in body weight, water content and elemental composition. Energy, estimated from carbon content, was also examined. The water content was 85 to 92% of body weight immediately after ecdysis but decreased with days after ecdysis. Gains in body weight, carbon, nitrogen, hydrogen and energy during each instar ranged from 52 to 245% and increased with instar after instar II (body weight and carbon), instar III (hydrogen and energy), and instar IV (nitrogen). Cumulative gains of these elements from hatching to 2 d before metamorphosis into megalopa ranged from 11 567% (carbon) to 12 209% (energy). Most cumulative gains (57 to 59%) in elemental composition were contributed by instar VII. Carbon, nitrogen and hydrogen content in body weight decreased to a minimum on the day of ecdysis and increased on the subsequent days. C:N ratios after instar IV were lowest on the day after ecdysis and reached a plateau by the second day. Energy, estimated as J mg-1 dry weight (DW), decreased with instar and within a molt cycle, and was at a minimum on the day after ecdysis. Gains in elemental composition could be described by an exponential function of days after hatching and by a quadratic function in each instar.

Effects of prey density on survival, feeding rate and development of zoeas of the red frog crab Ranina ranina (Crustacea, Decapoda, Raninidae)

The effects of prey density on growth and survival of larval Ranina ranina were examined. Five levels of prey density (0.05−5 Artemia nauplii ml −1) were tested for their effects on survival, intermolt period and growth at all the zoeal instars. Six or seven levels of prey densities (1−10 ml −1) were examined for feeding rate at instars I, III, V and VII. Survival decreased with decreasing prey density. Survival rate dropped to around 50% in 0.05 ml −1 to instar I, 0.1 ml −1 to instar II, 0.5 ml −1 at instar V, and 1 ml −1 after instar VI. Metamorphosis rate increased with increasing prey density, from 0% at 0.1 ml −1 to 100% at 5 ml −1. Intermolt period and duration of the zoeal stages were longer at 0.05 and 0.1 ml −1 compared to 0.5−5 ml −1. Growth of several body parts was lower at 0.05 and 0.1 ml −1 than at higher prey densities for instars III, V and VII. The external morphology of several appendages was less affected than was growth. A regression equation, F= M (1 − e − kp ) ( F=feeding rate, k=constant, M=calculated maximum feeding rate, p=prey density), was derived for the relationship between observed prey density and feeding rate. The optimal prey density necessary to ensure highest survival and the shortest intermolt period calculated using this regression equation was similar to results measured from the experiment in terms of survival, intermolt period and growth: it was 0.5 ml −1 at instar I, 0.6 ml −1 at instar III, 1.8 ml −1 at instar V, and 2.3 ml −1 at instar VII.

Larval feeding rhythms and food consumption by the red frog crab Ranina ranina (Decapoda, Raninidae) under laboratory conditions

Newly hatched R. ranina zoeas were held individually and fed a fixed number of Artemia nauplii at 25 and 29°C, to examine feeding rhythms and the quantities consumed. During the daytime zoeas ate on average 2.6 times more at 25°C and 2.8 times more at 29°C than at night, through all zoeal instars. Feeding activity during an instar was described by parabola-shaped quadratic or polynomial functions of days after ecdysis in later instars, although large individual variation was observed at both temperatures. Total quantities of prey consumed during each instar were expressed as exponential functions of an instar. Zoeas at 29°C ate 1.05–1.45 times as much prey during each instar and 1.47–1.90 times as much daily compared with those at 25°C. The total quantities of prey consumed during a day and during an instar were extremely high compared with other decapod species. Instar VII zoeas consumed 55% of the total prey intake during the zoeal period at 25°C and 51% at 29°C.

Growth and reproduction of the epifaunal amphipod Caprella okadai Arimoto (Crustacea: Amphipoda: caprellidea)

Growth, maturation and reproduction of Caprella okadai Arimoto, an amphipod crustacean endemic to the Japanese coast, were studied under laboratory conditions at 20°C, and 14 h light: 10 h dark photoperiod. The diatom Cylindrotheca closterium (Ehrenberg), and the red alga Gelidium amansii (Lamouroux) were provided for food and clinging substratum. Juveniles newly emerged from the brood pouch molted at 2.9–6.8-day intervals. Body lebgth increased per instar of both males and females represented a sigmoid curve. On average, females reached sexual maturity at instar VII at 20.1 days of age, produced their first brood at 20.6 days, and had 3.8 successive cutches at 5.0–6.0-day intervals. The number of embryos per brood increased from 10.8 at instar IX. A female produced an average of 36.1 offspring throughout her life span. The similarity of life history patterns of C. okadai and C. Danilevskii Czerniavski indicates that habitat segregation of these two species results from morphologicaal adaptations of caprellids to their respective localities.

Studies on rearing larvae of the red frog crab, Ranina ranina-V. Effects of Salinity on Survival, Feeding, and Development of Larvae of the Red Frog Crab Ranina ranina.

Salinity effects on the survival, intermolt period, growth, and morphogenesis of Ranina ranina larvae were examined under 11 levels ranging from 17 to 51‰ S. Zoeas metamorphosed into megalopas at 24 to 37‰ S. The optimum range of salinity for survival became narrower in later instars. Intermolt periods were prolonged at lower and higher salinities. The metamorphosis rate increased with increasing salinities. Morphogenesis proceeded without change in all salinity levels until instar V but was delayed at 20, 24, and 41‰ S from instar VII. Larval food consumption was examined under 5 salinity levels from 20 to 48‰ S with zoeas at instars I, III, V, and VII. It was the highest at 34‰ S and decreased at the other salinities. The retarded growth was correlated with decreased food consumption at lower and higher salinities in instars III, V, and VII. The optimum range of salinity for rearing larvae of this species was 27-34‰ S. Food energy seemed to be utilized for survival first, molting second, morphogenesis and growth last

Growth and reproduction ofCaprella danilevskii (Crustacea: Amphipoda) reared in the laboratory

Caprella danilevskii Czerniavski, an epifaunal amphipod crustacean, was successfully reared for two generations under laboratory conditions. Amphipods were maintained in pairs or fours in a Petri dish. Temperature and photoperiod were maintained at 20°C, and 14 h light: 10 h dark, respectively. Colonies of the diatomCylindrotheca closterium (Ehrenberg) Reumann and Lewin were provided as food source. The red algaGelidium amansii (Lamouroux) Lamouroux was used to provide an attachment substrate for the caprellids. Juveniles that emerged from the brood pouch were described as instar I. Subsequent instars were identified by molts. Juveniles molted successively at 2.5 to 6.5 d intervals. The body length of males at each instar increased exponentially, while that of females followed a sigmoid curve. A different pattern of flagellar segment addition in the antenna I of males and females was revealed. At the age of 20.8 d, females reached instar VII, and produced their first embryos. After 5.1 d, juveniles emerged from the brood pouch. On average, females produced 5.4 clutches successively at 5.0 d intervals. The number of offspring per spawning increased from 6.3 at instar VII to 22.0 at instar XII. The total number of offspring was 69.0 for a female throughout her life span.

Colonization of Perspex Strips by Larvae of Austrosimulium-Bancrofti (Taylor) Near Willawarin, Nsw

A total of 14 113 larvae of the taxon Austrosimulium bancrofti (Taylor) was collected from perspex strips placed in the MacLeay River. The method of multiple mixture modelling separated larvae into seven instars. Highest numbers of instar III and fewest of instar VII were collected. Significant effects influencing colonisation of the perspex strips were incorporated into a statistical model. This permitted generation of fitted estimates of the number of larvae colonising strips under defined conditions. Fitted captures indicated that higher numbers of larvae colonised strips with increasing water depths (7 less-than-or-equal-to X less-than-or-equal-to 46 cm) and when there was no vegetation beneath the strips. Strip texture, quadratic terms for distance from one river bank and their interaction significantly influenced numbers collected. Fitted estimates demonstrated fewest larvae colonised strips in midstream but this decline was most distinct for the smooth strips. Quadratic terms for water velocity and their interaction with strip thickness also influenced larval colonisation. Fitted estimates were highest when water velocity was in the range 1.05-1.25 m s-1 for each strip thickness.

A laboratory study on the life cycle of Sericostoma personatum (Kirby & Spence), and light dark-dependent food consumption

The life cycle of Sericostoma personatum (Spence) was studied at 6 °C, 10 °C and 14 °C and at each temperature at 8 and 14 hrs daylength. Embryogenesis was not temperature dependent in the 12°–18°C range. Only 7 of 38 (app. 18%) had a direct development, the rest remained in diapause with partly developed larvae. Hatching success of single egg masses was over 95%. At 6 °C at both LDs, about 452 days are required for larval development. At 10 °C 370 days (LD 8/16), or 320 days (LD 14/10) and at 14° C 319 days (LD 8/16) and 295 days (LD 14/10) were required. Duration of instars III and IV was longer at 6 °C (both LDs), compared with all other groups. Vth instar larvae of the 14 °C (LD 14/10) group grew fastest. Instar VI larvae of the 10 °C short day group developed faster than all others. Instar VII larvae of both 14 °C groups and of the 10 °C long day group develop faster than the rest. Duration of pupal instar is only temperature dependent, regardless of light regime. The field life cycle of S. personatum may require 2–5 years. Larvae are night active. They feed on Coarse Particular Organic Material (CPOM) on the sediment surface at night. They release faeces (Fine Particular Organic Material, FPOM) into the sediment where they rest by day at a few cm depth. Their burrowing behavior thus contributes to the retention of FPOM in the stream channel. Daily food consumption at constant 10 °C is significantly dependent on night length (r 2 = 0.979, p < 0.05). Two factors thus may limit food consumption: in winter, low temperatures, and in summer short nights. The species thus avoids competition by day-active shredders and predation by day-active predators.

Studies on rearing larvae of the red frog crab Ranina ranina-IV. Influence of temperature on survival, feeding and development of larvae of the red frog crab, Ranina ranina (Crustacea, Decapoda, Raninidae).

In order to examine temperature effects on several larval characters, zoeas of Ranina ranina were reared under 5 temperature levels ranging 17 to 33°C. Survival decreased at lower temperatures and optimum range for the survival seemed to become narrower in later instars. The molting depended significantly on the temperature, and molting intervals increased exponential-ly at lower temperatures. The optimum temperature was 25 to 29°C for growth and morphogenesis during all zoeal instars. The growth decreased and morphogenesis delayed at lower and higher temperatures out of optimum range. Food intake tended to increase at higher tem-perature at instars I to V but was the maximum at 25°C at instar VII. At higher temperature, reduction of growth and delay of morphogenesis were observed, in spite of a large amount of food intake in early instars. Unusual high temperature, which is not observed in nature, might affect the physiological condition of the larvae.

A preliminary report on the life-history of &lt;I&gt;Caprella danilevskii&lt;/I&gt; Czerniavski (Crustacea, Amphipoda) reared in the laboratory

TAKEUCHI, Ichiro and Reijiro HIRANO (Department of Fisheries, Faculty of Agriculture, University of Tokyo). 1988. A preliminary report on the life-history of Caprella danilevskii Czerniavski (Crustacea, Amphipoda) reared in the laboratory Benthos Research (Bull. Jap. Assoc. Benthology), 32 : 37-41.Caprella danilevskii Czerniavski was successfully reared two generations under laboratory conditions. This report presents an outline of the life cycle. Animals were maintained in pairs or four individuals in petri dishes (5.7 cm in diameter and 5.6 cm in depth) containing filtered seawater at 20°C. Colony of Cylindrotheca closterium (Ehrenberg) Reimann et Lewin was supplied as a source of food, and the red alga Gelidium amansii (Lamouroux) Lamouroux was given as a site of attachment for caprellids.Juveniles, 1.5 mm in body length, released from brood pouch were prescribed as the instar I. Following instars were decided by affirmation of molts. They molted successively at 2.5-6.5 days intervals. Body length of males increased exponentially, and that of female represented a sigmoid curve. Body length of instar VII was 6.5 mm in male and 5.5 mm in female, and that of X was 10.9 mm in male and 7.0 mm in female. Average life span was 46.5 days in male (n=15) and 46.0 days in female (n=8). At the age of 20.8 days, females reached instar VII and produced first eggs, and juveniles were released 5.1 days later. Females reproduced eggs 5.4 times successively at about 5 days intervals, and the total number of offspring was 69.4 individuals per female.

Juvenilizing effect of cooling on Galleria mellonella

Cooling of larvae of G. mellonella in the final instar results in a serious disturbance in their later development. Such disturbance concerns the transition to additional larval stages, loss of the ability to spin cocoons, and the formation of individuals incapable of continuing normal development. The kind of disturbances and their degree depends on the age of cooled larvae and the cooling time applied. Cooling of 1- and 2-day-old larvae results in their transition to additional larval stages, while cooling larvae aged from 3 to 7 days of the duration of instar VII causes the formation of a large number of individuals incapable of further development. The loss of the capacity to spin cocoons depends solely on the cooling time applied.