Larval development and post-settlement metamorphosis of the barnacle Balanus albicostatus Pilsbry and the serpulid polychaete Pomatoleios kraussii Baird: Impact of a commonly used antifouling biocide, Irgarol 1051

AbstractThe impact of a commonly-used antifouling algicide, Irgarol 1051, on the larval development and post-settlement metamorphosis of the barnacle, Balanus albicostatus Pilsbry (Crustacea: Cirripedia), and the larval metamorphosis of a serpulid polycheate, Pomatoleios kraussii Baird, was evaluated. In the case of B. albicostatus, larval mortality increased with an increase in the concentration of Irgarol 1051, and there was a shift in the larval stage targeted from advanced instars to early instars. Nauplii that survived to the cyprid instar stage when reared in the presence of Irgarol 1051 showed prolonged instar and total naupliar duration when compared to the controls. The post-settlement metamorphosis of cyprids significantly varied with Irgarol concentration and also with biofilm age. One and 2-d-old untreated biofilms showed higher metamorphosis when compared to 5-d-old biofilms. However, when the biofilms that promoted cyprid metamorphosis were treated with Irgarol 1051 at low concentrations, metamorphosis rates decreased. Cyprids were prevented from metamorphosing completely by biofilms treated at the highest concentration of Irgarol 1051. Inhibition of metamorphosis was also observed in the case of competent polychaete larvae when exposed to Irgarol 1051 compared to those exposed to metamorphosis inducers such as 3-iso-butyl-1-methylxanthine (IBMX) and natural biofilms. Identification of the pathway(s) that caused the promotory biofilms to become toxic when exposed to Irgarol 1051 is discussed.     

Impact of Irgarol 1051 on the larval development and metamorphosis of Balanus amphitrite Darwin,the diatom Amphora coffeaformis and natural biofilm

The effect of Irgarol 1051 on the biofilm-forming diatom, Amphora coffeaformis, and on natural biofilm (NBF) was assessed. A reduction in the number of A. coffeaformis cells within a biofilm was observed after treatment with Irgarol 1051, confirming its role as an inhibitor of photosynthetic activity. The impact of this compound on the development of nauplii of Balanus amphitrite was evaluated through its impact on Chaetoceros calcitrans, which was provided as food for the larvae. A reduction in the number of cells of C. calcitrans was observed when treated with Irgarol 1051. When larvae of B. amphitrite were reared using C. calcitrans in the presence of Irgarol 1051, their mortality increased with an increase in the concentration of Irgarol 1051 (13% at 1 µg l^?1 to 40% at 1000 µg l^?1) compared with the control (6%). Nauplii reared in the presence of Irgarol 1051 developed more slowly (6–7 days) compared with control larvae (4–5 days). Cyprid bioassay results indicated an increase in percentage metamorphosis (76%) when NBFs were treated with the highest concentration of Irgarol 1051, compared with untreated biofilm (28%). The enhanced rate of metamorphosis appeared to be related to an increase in bacterial numbers in the biofilm, which may have been due to lysis of diatoms caused by Irgarol 1051. A. coffeaformis biofilms grown in the presence of antibiotics showed a significant reduction in cell numbers, which on further treatment with Irgarol 1051 showed an increase in cell numbers. Thus, it can be hypothesised that A. coffeaformis cells that were subjected to stress twice may have expressed resistant genes. Furthermore, if plasmids are present in the biofilms, they may enhance transfer to the surviving cells making them more resistant to hostile conditions.     

Impact of Irgarol 1051 on the larval development and metamorphosis of Balanus amphitrite Darwin, the diatom Amphora coffeaformis and natural biofilm

The effect of Irgarol 1051 on the biofilm-forming diatom, Amphora coffeaformis, and on natural biofilm (NBF) was assessed. A reduction in the number of A. coffeaformis cells within a biofilm was observed after treatment with Irgarol 1051, confirming its role as an inhibitor of photosynthetic activity. The impact of this compound on the development of nauplii of Balanus amphitrite was evaluated through its impact on Chaetoceros calcitrans, which was provided as food for the larvae. A reduction in the number of cells of C. calcitrans was observed when treated with Irgarol 1051. When larvae of B. amphitrite were reared using C. calcitrans in the presence of Irgarol 1051, their mortality increased with an increase in the concentration of Irgarol 1051 (13% at 1 microg l(-1) to 40% at 1000 microg l(-1)) compared with the control (6%). Nauplii reared in the presence of Irgarol 1051 developed more slowly (6-7 days) compared with control larvae (4-5 days). Cyprid bioassay results indicated an increase in percentage metamorphosis (76%) when NBFs were treated with the highest concentration of Irgarol 1051, compared with untreated biofilm (28%). The enhanced rate of metamorphosis appeared to be related to an increase in bacterial numbers in the biofilm, which may have been due to lysis of diatoms caused by Irgarol 1051. A. coffeaformis biofilms grown in the presence of antibiotics showed a significant reduction in cell numbers, which on further treatment with Irgarol 1051 showed an increase in cell numbers. Thus, it can be hypothesised that A. coffeaformis cells that were subjected to stress twice may have expressed resistant genes. Furthermore, if plasmids are present in the biofilms, they may enhance transfer to the surviving cells making them more resistant to hostile conditions.     

Preferential attachment of barnacle larvae to natural multi-species biofilms: Does surface wettability matter?

We tested the hypothesis that surface wettability does not alter the positive effect of natural biofilms on larval attachment in the barnacle Balanus amphitrite. We also answered the question: Does substratum-biofilm interaction affect the larval choice in barnacle? We developed natural multi-species biofilms of different ages on both high (glass) and low (polystyrene) wettability surfaces at mid-intertidal height (native habitat of B. amphitrite). Attachment choice of both young (0-d-old) and old (6-d-old) larvae to biofilms was determined using still water choice bioassay. Irrespective of larval age, cyprid preferred to attach to un-filmed glass than to un-filmed polystyrene. In contrast to aged larvae, young larvae preferred old (6-d-old) biofilms on polystyrene to young (3-d-old) biofilms on glass. In this study, we were also able to examine the interaction between surface wettability, biofilms and larval attachment, by characterizing bacterial community composition in biofilms. Bacterial community composition showed significant differences between biofilms of different ages. Old biofilms positively influenced larval attachment, irrespective of the type of substrata, thereby supporting the hypothesis that surface wettability does not alter the positive effect of natural biofilms on larval attachment.     

Influence of thyroid hormones on neuronal death and differentiation in larval Rana pipiens.

The sphingid moth, Manduca sexta, typically passes through five larval instars, a pupal, and an adult stage. The larval labial glands secrete silk in the first instar and a viscous lubricant in the fifth. During metamorphosis the glands develop into salivary organs which produce an invertase-rich secretion. In normal development, the uniform population of cells in the duct of the larval gland transforms into the four sequentially arranged regions of secretory and conductive cells of the adult gland. In order to determine when competence to form the adult gland is established, fragments of labial gland ducts from first through fifth instar larvae were implanted into pupae. These gland fragments underwent metamorphosis with their hosts, passing through the same developmental phases. Glands from as early as the first instar were competent to form histologically and functionally normal adult regions. In later instars, transplants of measured fragments demonstrated that larval cells were programmed in situ to develop into the four adult cell types.     

Combined effect of cyprid age and lipid content on larval attachment and metamorphosis of Balanus amphitrite darwin

Various algal diets of different lipid content and composition were used to rear batches of naupliar larvae of Balanus amphitrite. The cyprids in these larval batches differed in lipid content and were used to investigate the combined effect of cyprid lipid content and cyprid age on attachment and metamorphosis. For this purpose, cyprids were aged for 0,3 and 6 d at 8°C prior to utilization in laboratory attachment assays. The percentage attachment of cyprids with similar lipid content differed significantly among the three age categories. A strong and a weak positive relationship between cyprid lipid content and attachment were monitored in young and old cyprids, respectively. A significant interaction (two‐way ANOVA) between cyprid age and lipid content was observed, indicating that these factors jointly affect larval attachment and metamorphosis in B. amphitrite from the beginning of the cyprid stage.     

Biology of Microplitis kewleyi (Hymenoptera: Braconidae): A parasite of Agrotis ipsilon (Lepidoptera: Noctuidae) larvae

Microplitis kewleyi Muesebeck is a gregarious internal parasite of larvae of the black cutworm Agrotis ipsilon (Hufnagel). Studies of the biology of the parasite revealed that there was an inverse relationship between host instar and parasite preference. Duration of development from egg to pupa ranged from 18 days at 27°C to 68.7 days at 16°C. Development from egg to pupa took 13.5–21.6 days when fourth and first instar host larvae, respectively, were parasitized. A larger number of parasites emerged from hosts parasitized in the fourth instar (22.4) than the first instar (11.5). Parasite pupation occurred when the host was in the fifth/sixth instar, depending on the instar parasitized. Thirty‐nine per cent of host larvae exposed as first instars to parasites died before parasite emergence. This decreased to 0% for host larvae exposed as fourth instars. The sex ratio was 1:1.2 (M:F). Thirty‐seven per cent of hosts exposed diurnally were stung, compared to 24% exposed nocturnally. Mean daily progeny was highest (12) on the first day, decreasing to zero after 20 days. Percent host parasitism was also highest on the first day (35%) decreasing to nearly 0% after 18 days. There appear to be three parasite larval instars. Host larvae often remained alive after parasite emergence.     

Metamorphosis in the Cirripedia Rhizocephala and the homology of the kentrogon and trichogon

The Rhizocephala are considered to be monophyletic due to several synapomorphies in the ontogeny of the cndoparasitic phase. The various types of metamorphosis described in the Rhizocephala are discussed and compared to metamorphosis in the Cirripedia Thoracica and Acrothoracica. In males and females of the suborder Kentrogonida. the cyprid settles and metamorphoses into a new instar, in males the trichogen and in females the infective kentrogon. The kentrogon goes through yet another. incomplete moult associated with the development of the stylet. Within the three kentrogonidan families. the Iernaeodiscid-peltogastrid type of kentrogon differs from the sacculinid type in the mode of attachment to the host. in the complexity of internal anatomy. in the position and penetration of the stylet, and in whether or not the cyprid carapace must be shed prior to penetration of the stylet. In the Akentrogonida metamorphosis never results in a new instar. Where observed (Clistosaccidae and Thompsoniidae). both male and female cyprids settle and penetrate into their substrate (female parasite or new host) with one of the antennules. Using the antennule as a syringe. male cyprids inject spermatogonia while female cyprids injects embryonic cells developing into an endoparasite. By comparison with metamorphosis in the Cirripedia Thoracica and Acrothoracica it is concluded that the presence of a metamorphic moult leading to a post-cyprid instar is plesiomorphic and that the trichogon and kentrogon are homologous with the first metamorphosed juvenile in these outgroups. The abbreviated ontogeny in the Akentrogonida without metamorphic moult and post-cyprid larval instars is considered apomorphic. This contradicts the long-held supposition that the Akentrogonida are the most‘primitive’Rhizocephala and dovetails with new information that this suborder contains many advanced traits. Within the Kentrogonida. the lernacodiseid-peltogastrid type of kentrogon is considered more plesiomorphic than the sacculinid type, which resembles the clistosaccidthompsoniid type in having the antennules involved in the penetration process. The homologization of the kentrogon with a juvenile barnacle indicates that presence of a kentrogon is plesiomorphic within the Rhizocephala and that the Kentrogonida is paraphyletic.     

How whale and dolphin barnacles attach to their hosts and the paradox of remarkably versatile attachment structures in cypris larvae

How larvae of whale and dolphin epibionts settle on their fast-swimming and migrating hosts is a puzzling question in zoology. We successfully reared the larvae of the whale and dolphin barnacle Xenobalanus globicipitis to the cyprid stage. We studied the larval developmental ecology and antennular morphology in an attempt to assess whether an epibiotic lifestyle on this extreme substratum entails any unique larval specializations. Morphological parameters were compared with five other barnacle species that also inhabit extreme substrata. We found no larval specializations to a lifestyle associated with marine mammals. The external morphology of the antennules in Xenobalanus cyprids is morphologically similar to species from strikingly different substrata. We found variation only in the structures that are in physical contact with the substratum, i.e., the third segments carrying the villi-covered attachment disc. The third segments of the Xenobalanus cyprid antennules are not spear-shaped as in the stony coral barnacles, which are here used to penetrate the live tissue of their hosts. The presence of a cyprid cement gland implies that Xenobalanus uses cement protein when attaching to its cetacean host. Naupliar instars developed outside of the mantle cavity, indicating dispersal is planktonic. Our results militate against the idea that the cyprids settle during ocean migrations of their hosts. We suggest cyprids settle during coastal aggregations of the cetacean hosts. We conclude that the ecological success of barnacles has ultimately depended on a larva that with little structural alteration possesses the ability to settle on an amazingly wide array of substrata, including cetaceans.

     

Variation in growth and instar number in field and laboratory Manduca sexta

The tobacco hornworm Manduca sexta has been an important model system for understanding physiological control of growth, development and metamorphosis of insects for more than half a century. Like all Manduca, M. sexta typically has five larval instars, with developmental commitment to metamorphosis occurring early in the 5th (final) instar. Here we show that M. sexta from a field population in North Carolina (USA) shows substantial intraspecific variation in the number of larval instars when feeding on a modified artificial diet. Individuals with six instars consistently exhibited slower growth rates during early larval development than individuals with five instars. The frequency of individuals with six instars decreased with increased rearing temperature. In contrast, M. sexta from a laboratory colony consistently had five instars, and had more rapid larval growth rates than M. sexta from the field. We identify a threshold body size at the start of the 5th instar that predicts whether an individual will have five (greater than 600mg) or six instars (less than 600mg). Variation in field populations in Manduca provides an important resource for understanding physiological control, developmental plasticity and evolution of growth rate, body size and instar number.     

Growth and development of Cardiochiles nigriceps viereck (hymenoptera,braconidae) larvae and their synchronization with some changes of the hemolymph composition of their host,Heliothis virescens (F.) (Lepidoptera,Noctuidae)

Larval development of the parasitoid Cardiochiles nigriceps Viereck occurs in the last instar larva of its host, Heliothis virescens (F.). This allows the parasitoid to exploit the nutritional increase in the biosynthetic activity occurring in the host in preparation for metamorphosis. To understand the biochemical basis of this host parasitoid developmental synchrony, we undertook host ligation studies and analyzed host hemolymph for proteins and glycerol esters. Parasitization affected the biochemical profile of the host. The hemolymph protein concentration of parasitized last instar H. virescens larvae increased through time, whereas unparasitized (control) larvae were characterized by a decrease in the protein titer when they reached the prepupal stage. The effect of parasitism on glyceride titers of host hemolymph was not as pronounced as the effect on proteins. Ligation conducted on 5th instar hosts, which were parasitized as 4th instars, affected parasitoid development in a time-dependent way. The percentage of successfully developing C. nigriceps larvae increased with the increase of the time interval between parasitization and ligation. Ligation performed before day 2 of the 5th larval instar of H. virescens completely inhibited parasitoid development. Ligations that disrupted parasitoid developmentwere associated with a low host hernolymph protein concentration. Parasitoid development was successful when hernolymph protein titer was high, as occurred when ligations were performed after day 3 of the 5th host instar in both control and parasitized larvae. Ligations in both situations resulted in a slight increase in glyceride titers. The results suggest that host proteins and/or some factor(s) associated with them may play a role in parasitoid growth and development. © 1993 Wiley-Liss, Inc.     

Host-age discrimination during host location byCotesia glomerata, a larval parasitoid ofPieris brassicae

Some parasitoids are restricted with respect to the host stage that they attack and even to a certain age within a stage. In this paper we investigate whether the parasitoidCotesia glomerata can discriminate between old and young caterpillar instars of its host,Pieris brassicae, before contacting these hosts, since contacts with older instars are very risky with a chance of being killed, due to the aggressive defensive behaviour of the caterpillars. Flight chamber dual choice tests showed that volatile chemicals emitted by Brussels sprouts plants (Brassica oleracea var. gemmifera) after feeding damage by 1st and 5th larval instars are equally attractive to the wasps. Simulated herbivore damage by 2nd and 5th larval instars, obtained by treating mechanically damaged leaves with carterpillar regurgitant, was also equally attractive, even when the wasps were exposed to repeated experience on different larval instars to increase their discriminatory ability. In contrast, single choice contact bioassays showed that the time spent searching on a leaf with feeding damage of 1st instar larvae was significantly longer than the time spent on 5th instar feeding damage or on mechanically damaged leaves. Both flight and contact bioassays did not show any effect of egg-related infochemicals. The results demonstrate thatC. glomerata can discriminate between young and old larval instars ofP. brassicae, without contacting the caterpillars. This is not done through volatile herbivore-induced synomones but through cues that are contacted after arrival at a caterpillar-infested leaf.     

Physiological and biochemical changes during the larval development of a brachyuran crab reared under constant conditions in the laboratory

Larvae of the spider crabHyas araneus were reared in the laboratory at constant conditions (12°C; 32‰S), and their feeding rate (F), oxygen consumption (R), nitrogen excretion (U), and growth were measured in regular intervals of time during development from hatching to metamorphosis. Growth was measured as dry weight (W), carbon (C), nitrogen (N), hydrogen (H) protein, and lipid. All these physiological and biochemical traits revealed significant changes both from instar to instar and during individual larval moult cycles. AverageF was low in the zoea I, reached a maximum in the zoea II, and decreased again in the megalopa. In the zoeal instars, it showed a bell-shaped pattern, with a maximum in the middle (zoea I) or during the first half of the moult cycle (zoea II). MaximumF in the megalopa was observed still earlier, during postmoult. Respiration (R) increased in the zoeal instars as a linear function of time, whereas it showed a sinusoidal pattern in the megalopa. These findings on variation inF andR during larval development confirm results obtained in previous studies onH. araneus and other decapod species. Excretion (U) was measured for the first time with a high temporal resolution in crab larvae. It showed in all three larval instars a bell-shaped variation pattern, with a maximum near the middle of the moult cycle, and significantly increasing average values from instar to instar. The atomicO/N ratio followed an inverse pattern, suggesting a maximum utilization of protein as a metabolic substrate during intermoult. Growth data from the present study and from a number of previous studies were compiled, showing consistency of growth patterns, but a considerable degree of variability between larvae from different hatches reared under identical conditions. The data show the following consistent tendencies: during the first part of each larval moult cycle (in postmoult, partly in intermoult), lipids are accumulated at a higher rate than protein, whereas an inverse growth patterns is typical of the later (premoult) stages. These two different growth phases are interpreted as periods dominated by reserve accumulation in the hepatopancreas, and epidermal growth and reconstruction (morphogenesis), respectively. Differences between individual larval instars in average biochemical composition and growth patterns may be related to different strategies: the zoeal instars and the early megalopa are pelagic feeding stages, accumulating energy reserves (principally lipids) necessary for the completion of larval development, whereas the later (premoult) megalopa is a semibenthic settling stage that converts a significant part of this energy to epidermal protein. The megalopa shifts in behaviour and energy partitioning from intense feeding activity and body growth to habitat selection and morphogenesis, preparing itself for metamorphosis, i.e. it shows an increasing degree of lecithotrophy. Data from numerous parallel elemental and biochemical analyses are compiled to show quantitative relationships betweenW, C, N, H, lipid, and protein. These regressions may be used as empirical conversion equations for estimates of single chemical components in larvalHyas araneus, and, possibly, other decapods.     

Larval settlement and metamorphosis of the mussel Mytilus coruscus in response to natural biofilms

Settlement and metamorphosis of pediveliger larvae of Mytilus coruscus in response to natural biofilms was investigated in the laboratory. Pediveliger larvae settled and metamorphosed in response to biofilms and post-larval settlement and metamorphosis increased with biofilm age. The activity of the biofilm was positively correlated with biofilm age, dry weight, bacterial density and diatom density, but had no apparent relationship with chlorophyll a concentration. The change in bacterial community composition corresponding to biofilm age may explain differences in the age-dependent inducing activities of biofilms, which in turn may play an important role in larval settlement in this species.     

Effect of weak electromagnetic radiation on larva development and metamorphosis of grain beetle Tenebrio molitor

The effect of weak electromagnetic radiation (36 GHz, 100 mu W/cm2) on the development of the grain beetle Tenebrio molitor was studied. Insects were irradiated in different larval instars and at the pupal stage. It was found that weak electromagnetic radiation stimulated the molting and pupation of larvae and the metamorphosis of pupae. The stimulating effect of radiation was weak when animals were exposed in the initial period of the instar and the pupal stage and was more pronounced if the irradiation was carried out in the second half of the current instar and the pupil stage. The effect of weak electromagnetic radiation on the development of beetle can be related to the function of the hormones of metamorphosis.     

Short-term and latent post-settlement effects associated with elevated temperature and oxidative stress on larvae from the coral Porites astreoides

Coral reefs across the Caribbean are undergoing unprecedented rates of decline in coral cover during the last three decades, and coral recruitment is one potential process that could aid the recovery of coral populations. To better understand the effects of climate change on coral larval ecology, the larvae of Porites astreoides were studied to determine the immediate and post-settlement effects of elevated temperature and associated oxidative stress. Larvae of Porites astreoides were exposed to 27 °C (ambient) and +3.0 °C (elevated temperature) seawater for a short duration of 24 h; then, a suite of physiological parameters were measured to determine the extent of sublethal stress. Following the +3.0 °C treatment, larvae did not show a significant difference in maximum quantum yield of PSII (F _v/F _m) or respiratory demand when compared to controls maintained at 27 °C. The addition of micromolar concentrations of hydrogen peroxide did not impact respiration or photochemical efficiency. Catalase activity in the larvae increased (>60 %) following exposure to elevated temperature when compared to the controls. Short-term larval survival and settlement and metamorphosis were not affected by increased temperature or the H₂O₂ treatment. However, the settled spat that were exposed to elevated temperature underwent a 99 % reduction in survival compared to 90 % reduction for the control spat when examined 24 days following the deployment of 4-day-old settled spat on settlement tiles in the field. These results show that short-term exposure to some stressors might have small impacts on coral physiology, and no effects on larval survival, settlement and metamorphosis. However, due to post-settlement mortality, these stressors can cause a significant reduction in coral recruitment.     

Developmental variation in the forest tent caterpillar: life history consequences of a threshold size for pupation

In insects, size and age at adult emergence depend on larval growth that occurs in discrete steps or instars. Understanding the mechanisms controlling stepwise larval growth and the onset of metamorphosis is essential to the study of insect life history. We examined the patterns of growth of forest tent caterpillars Malacosoma disstria to quantify variation in the number of instars that larvae undergo before pupation, to identify the mechanisms underlying variation in larval development, and to evaluate the life history consequences of this variation. All caterpillars were reared under the same conditions; at each molt, the date, the head capsule width and the mass of the freshly molted insect were recorded. Logistic regression analysis showed that a threshold size (measured either as mass or head capsule width) must be reached at the beginning of a stadium for pupation to occur at the next molt. This threshold size was higher for females than for males, and as a result, females attained a higher pupal mass than males. To achieve this larger size, females often required more instars than males, despite a higher growth ratio (size increase within an instar). Within each sex, slow growing individuals exhibited more larval instars and longer larval development time, but attained the same pupal mass as faster growing individuals. The combination of a threshold size for pupation, discrete growth steps and variation in the number of these steps can thus complicate relationships between growth rate, pupal mass and larval development time. In our study, growth ratio and number of instars were correlated with development time but not with pupal mass, and no relationship was observed between development time and pupal mass. These findings imply that, in species with variable instar number, one cannot extrapolate overall larval growth from growth during a single instar. Given the constraints of discrete larval growth, variation in instar number provides greater flexibility for insects to compensate for poor growing conditions. In this case, inferior larval growth conditions don't necessarily lead to smaller adult size.     

The ontogeny of multiple hemoglobins in Chironomus thummi (Diptera): The effects of a compound with juvenile hormone activity

The multiple hemoglobins (Hbs) of Chironomus thummi show distinct and significant ontogenetic changes during development from the third instar through the fourth instar and metamorphosis into the pupa. A total of nine Hbs are resolved by 12.7% acrylamide gel electrophoresis (pH 8.65). Hbs 2 and 3, which are stage specific for the fourth instar, are first detected on the fourth day of this stage by electrophoresis and immunoprecipitation. Hb 4 is the predominant Hb species in the early and middle fourth instar, but during the late fourth instar and prepupa, Hb 1 predominates. The concentrations of Hbs 5–9 remain relatively constant in middle instars and decrease during later development. The Hb content of larval hemolymph exhibits changes that coincide with developmental stages; molting is characterized by low Hb content, whereas, the hemolymph of intermolt animals contains relatively high levels of Hbs. Treatment of fourth instars with a juvenile hormone analog, Altosid, prolongs this stage and inhibits the progress of normal development resulting in the formation of larval-pupal intermediates. Altosid also appears specifically to inhibit the accumulation of soluble hemolymph proteins related to pupation and metamorphosis, without affecting the concentration of Hb. Most significantly, it induces the precocious appearance of Hbs 2 and 3, which remain elevated above control levels in the late larval and prepupal stages. The present results strongly suggest that Altosid stimulates the appearance and accumulation of larval-specific proteins in vivo, while it inhibits the appearance of pupation-related proteins.     

Morphogenetic and physiological effects of a juvenile hormone analogue on the light brown apple moth,Epiphyas postvittana (Lepidoptera: Tortricidae)

Abstract

The juvenile hormone analogue ZR-619—ethyl 11-methoxy-3,7,11-trimethyl-(2E,4E-dodecadienethiolate) —produced morphological and physiological effects when fed via artificial diet to larvae of Epiphyas postvittana (Walker). Morphological effects included changes in larval head and antennal structures after instar V (supernumerary instars); deformation of pupal and adult structures, particularly in genitalia and wings; and development of individuals with varying mixtures of larval and pupal structures. Physiological effects included prolongation of larval life, increase in larval weight, increase in larval instars, and decrease in fecundity. Effects were directly related to dosage concentrations.     

Inter- and intra-specific differences in the number of larval instars in British populations of 24 species of stoneflies (Plecoptera)

1. Ontogenetic changes during the life cycle of aquatic insects are important not only in life‐history studies but also in evaluating food‐web structure. They require information on the growth and number of larval instars but such information is lacking for many species, including Plecoptera. Therefore, the chief objectives of the present study were to determine inter‐ and intra‐specific differences in the number of larval instars in British populations of 24 species of stoneflies, to test Dyar’s hypothesis that growth followed a geometric progression, and to synthesise this information with previously published values for four British species. 2. Larvae were reared at constant temperatures in the laboratory from eggs from 63 populations (one to six populations per species). First instars from each population were divided into three batches and each batch was reared at one of three constant temperatures. For each species, the rearing temperature and source population had no significant effect on the mean size of each larval instar. 3. The relationship between the geometric mean length of each instar and instar number was well described by an exponential equation (P < 0.001, r² > 0.9 for all species), thus supporting Dyar’s hypothesis. Only one species, Brachyptera risi, had the same number of instars for males and females (12–13). For the other 15 herbivorous species and the four smaller carnivorous ones, the number of instars was higher for females than males (range 11–16 for males, 12–17 for females). The larger size of the females was due to their additional instars, not a sex difference in growth rates. In contrast, there was a clear growth separation of the sexes after the 9th or 10th instar for the four largest carnivores. The number of larval instars was highest for these four species (range 16–19 for males, 18–23 for females), and females were much larger than males. 4. A multiple regression equation with data from the present and previous studies (n = 27) showed that variability in the mean length of the first instar and the maximum number of larval instars for each species accounted for 88% and 91% of the variability in the mean length of the final instar for males and females, respectively. 5. Values for Plecoptera in other countries were in general agreement with those in the present study, especially in the same families. Two old, but widely quoted, high values are doubtful. The present study and four previous ones provide a sound basis for ontogenetic studies on 28 species of Plecoptera and their role in aquatic ecosystems.