A possible therapy by juvenile hormone I to Spodoptera littoralis (Boisd.) larvae previously treated by precocene II

An effective constant dose (55 μg) of precocene II (PII) was topically tested against the last three instars of Spodoptera littoralis (Boisd.) larvae. Application of PII induced morphogenetic abnormalities typical of juvenile hormone (JH) excess. The resultant imperfect insects included larval‐pupal mosaic and partial or severe cases of untanned pupae. The sixth‐instar larvae were more sensitive to PII administration than the two preceding instars. However, sensitivity of the last larval instar to PII varied with the timing of dose application relative to the developmental status of the larvae. Whereas the newly ecdysed (0‐day old) larvae were more sensitive, the older larvae of the same sixth‐instar showed sharp decrease in their sensitivity to PII with a concomitant increase of their age. Application of a single dose (5 μg) of JH I to PII pre‐treated larvae significantly (P < 0.001) reduced the production of imperfect insects where many PH‐treated larvae developed successfully to apparent normal pupae. Although a single dose of PII was more effective on S. littoralis larvae than repeated daily doses, the effectiveness of JHI‐therapy to PH pre‐treated larvae by repeated doses was less effective in producing perfect insects than JH‐therapy to PII pre‐treated larvae by single doses. The reversal of any of these by applied JHI is quite interesting but the mechanisms remain to be unraveled.     

The setae of parasitic Liphyra brassolis butterfly larvae form a flexible armour for resisting attack by their ant hosts (Lycaenidae: Lepidoptera)

Caterpillars of the lycaenid butterfly, Liphyra brassolis, live inside the nests of arboreal weaver ants, Oecophylla smaragdina, and eat their brood. Observations of mature larvae suggest that they are impervious to relentless ant molestation, yet they lack sclerotized cuticular plates. We document a novel form of integumental defence that imparts protection from ant attack whilst maintaining the flexibility necessary to walk with a hydraulic skeleton. Analysis of the trunk integument and cuticular structures of early and late instars of L. brassolis using light microscopy, scanning electron microscopy, and histology revealed three new setae types (disc, clavate, and lanceolate), as well as three new cuticular structures (pored sockets, cuticular pores, and cuticular domes). The unique cuticle is covered with lanceolate setae, which act as endocuticular struts, and overlapping scale‐like sockets, which form a hard, flexible integument. The imperfect armour of the early‐instar larvae suggests that abundant, putatively secretory pores are likely to be homologous to pore cupola organs (PCOs) found in other lycaenid larvae and thus may exude semiochemicals to allay ant aggression. The importance of these pores presumably wanes as structural (setal) cuticular defenses are reinforced in later instars, when adult ants have been observed attacking caterpillars to no avail. The caterpillar's antennae are unusual and seem to be involved in manipulating ant larvae into the caterpillar's mouth. Behavioural observations indicate that the dexterity of these structures is associated with eating ants (myrmecophagy).     

Cornicle secretions of Uroleucon nigrotuberculatum (Homoptera: Aphididae) as the last bullet against lady beetle larvae

Aphids have evolved various defense strategies against natural enemies, including secretions from their cornicles. We assessed the defensive function of cornicle secretions by the goldenrod aphid, Uroleucon nigrotuberculatum (Olive), against larvae of the lady beetles Coccinella septempunctata bruckii Mulsant and Propylea japonica (Thunberg) (Coleoptera: Coccinellidae). The aphid secreted red droplets from its cornicles when attacked by the larvae. Two‐thirds of the C. septempunctata bruckii larvae and 46.7% of the P. japonica larvae that preyed on the aphids died before reaching the pre‐pupal stage. The secretions caused molting failure when smeared on the larvae's heads or glued to the larvae's mouthparts, killing 56.7% of C. septempunctata bruckii larvae and 36.7% of P. japonica larvae. Second instar larvae were affected most. About 40% of third and fourth instar larvae of C. septempunctata bruckii vomited soon after ingesting the aphids. In the field, up to 40% of first and second instar larvae were smeared with red secretions. Our results show that these cornicle secretions are an effective and active defense against earlier instars of coccinellid larvae.     

Seasonal phenology and stage-specific parasitism of the apple ermine moth, Yponomeuta malinellus Zeller, in Korea

The apple ermine moth, Yponomeuta malinellus Zeller (Lepidoptera: Yponomeutidae), is a tent caterpillar that feeds on Malus spp. in Korea. Populations of the moth in native areas appeared to be regulated by the assemblage of parasitoids. Phenological associations between host stages and parasitoids, susceptible stage(s) of the host for each parasitoid, and stage‐specific parasitism were studied. The egg larval parasitoid Ageniaspis fuscicollis (Dalman) had highest parasitism of first instar larvae (24%), with 14% parasitism of other larval stages. Dolichogenidea delecta (Haliday) was recovered from all larval instars with the highest parasitism rate of second instar larvae (20.1%), followed by 19.9% parasitism of mid‐larval hosts. Herpestomus brunicornis Gravenhorst was reared from second instar larvae through to pupal collection, and had the highest parasitism rate (29.9%) at the pupal stage. The larval pupal parasitoid Zenillia dolosa (Meigen) was recovered from mid‐larval to pupal stages with the highest parasitism rate (5.5%) occurring in third to fourth instar larvae. The host stages for developing A. fuscicollis completely overlap with those of D. delecta, and with those of H. brunicornis to some degree. A statistically significant negative correlation exists between A. fuscicollis and these dominant parasitoids, indicating competitive interaction within the host.     

Reduction of Delia radicum attack in field brassicas using a vertical barrier

According to life‐history theory, longer development time may result in bigger adults. However, reaction norms describing age and size at maturity often follow an L‐shaped form. This relationship is attributable to the simple notion that slowly growing individuals may not lengthen their development excessively after the maturation decision has been made, for example, when development is time limited in seasonal environments. In arthropods, growth occurs within instars, and thus the optimal growth strategy might be mediated by the phenotypic adjustment of instar numbers. We studied the relationship between age and size at maturity of a lichen‐feeding moth, Eilema depressum (Esper) (Lepidoptera: Arctiidae: Lithosiinae), and the variability of instar numbers in relation to achieved adult body mass and time used for maturation. A positive relationship between age and size at maturity was found across developmental pathways and a negative one within the developmental pathways. Directly developing larvae had higher growth rates, attained smaller pupal mass, and passed fewer instars than larvae maturing after overwintering. Host quality did not affect whether larvae matured during the remaining or the next season. High variation in the number of instars together with variable growth rates indicates high plasticity in adaptation to varying environmental conditions. Our results also confirm previous results that instar number variability may be a key characteristic mediating age and size at maturity in insects.     

Dimorphic growth patterns and sex‐specific reaction norms in the butterfly Lycaena hippothoe sumadiensis

Directly developing larvae of the butterfly Lycaena hippothoe sumadiensis exhibited two growth strategies with one cohort passing four larval instars at high growth rates, and the other five instars at lower growth rates. The 4‐instar‐cohort displayed decreased development times, in combination with slightly reduced pupal and adult weights. In addition to adjustment of growth rate, omitting a larval instar may comprise a further mechanism to decrease development time when needed. Using the 4‐instar‐cohort, sex‐related differences in reaction norms were investigated over a temperature gradient. At high temperatures, protandrous males showed early emergence at a reduced size, whereas weight of females remained similar throughout. These differences suggest that large size is more important for female than for male fitness. The pattern is similar to that previously reported for alpine L. tityrus, indicating that sex‐specific reaction norms might be widespread in species living under severe time constraints.     

Pine processionary moth (Thaumetopoea pityocampa,Lepidoptera: Thaumetopoeidae) larvae are highly susceptible to the entomopathogenic fungi Metarhizium brunneum and Beauveria bassiana

The larvae of the pine processionary moth (PPM), Thaumetopoea pityocampa, feed on the needles of pine and cedar. The urticating hairs of older instars pose a threat to human and animal health. Strains of the entomopathogenic fungi, Metarhizium brunneum (V275, ARSEF 4556) and Beauveria bassiana (KTU-24), were assayed against first to fourth instar T. pityocampa using doses ranging from 1?×?10⁵ to 1?×?10⁸ conidia mL^?1. The three strains differed slightly in their virulence but caused 100% mortality of all instars at the highest dose. The newly emerged or first instar larvae were extremely susceptible with 100% mortality being achieved 2–4 days post inoculation with V275 at all but the lowest dose. The fourth instar larvae appeared to be less susceptible than earlier instars. There was good horizontal transmission of conidia from treated to un-inoculated larvae. However, mortality was higher in third and fourth instars and where the ratio of inoculated versus untreated larvae was high. This we presume is due to spores being more readily trapped by the urticating hairs found on third and older instar larvae. Injection of the nests offers a simple and environmentally friendly way of controlling the pest with reduced risk to operators.     

Studies on the biology of Chaoborus flavicans (Meigen) (Diptera: Chaoboridae) in a fish-free eutrophic pond,Japan

Population dynamics of Chaoborus flavicans larvae of various instars was studied from November 1986 to December 1987 in a eutrophic, fish-free pond, Japan. First and 2nd instar larvae were observed from late April to late October, indicating a reproductive period of about half a year. C. flavicans overwintered in the 4th instar larvae. In water column samples, total density of all instars was 680–23680 m^-2, and pupal density 0–2600 m^-2; larvae of the 1st, 2nd, and 3rd instars showed 5–6 density peaks in 1987, suggesting that 5–6 generations occur during a year (peaks of the 4th instar larvae were not clear, probably due to their longer development than those of younger instars). In sediment samples, no 1st and 2nd instar larvae were found, 3rd instar larvae were found occasionally but density of the 4th instar larvae was 280–18600 m^-2, and pupal density varied between 0–502 m^-2. Fouth instar larvae accumulated in sediment in the cold season and in the water column in the warm season; high temperature and low oxygen concentration were the most important factors limiting the distribution of larvae in the sediment in summer in the NIES pond. The dry weight of total C. flavicans larvae was 0.08–4.2 g m^-2 in sediment samples and 24–599 μg l^-1 (0.10–2.40 g m^-2) in water column samples. Comparisons of maximum densities in the NIES pond in different years and in waters of different trophic status show that density is generally higher in eutrophic than in oligotrophic habitats. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ontogenetic shifts in the functional response and interference interactions of Rhyacophila dorsalis larvae (Trichoptera)

1. Ontogenetic shifts in predator behaviour can affect the assessment of food‐web structure and the development of predator–prey models. Therefore, it is important to establish if the functional response and interference interactions differ between life‐stages. These hypotheses were tested by (i) comparing the functional response of second, third, fourth and fifth larval instars of Rhyacophila dorsalis, using three stream tanks with one Rhyacophila larva per tank and one of 10 prey densities between 20 and 200 larvae of Chironomus sp.; (ii) using other experiments to assess interference within instars (two to five larvae of the same instar per tank), and between pairs of different instars (one, two or three larvae per instar; total predator densities of two, four or six larvae per tank). 2. The first hypothesis was supported. The number of prey eaten by each instar increased with prey density, the relationship being described by a type II model. The curvilinear response was stronger for fourth and fifth instars than for second and third instars. Mean handling time did not change significantly with prey density, and increased with decreasing instar number from 169 s for fifth instars to 200 s for second instars. Attack rate decreased progressively with decreasing instar number. Handling time varied considerably for each predator–prey encounter, but was normally distributed for each predator instar. Variations in attack rate and handling time were related to differences in activity between instars, fourth and fifth instars being more active and aggressive than second and third instars, and having a higher food intake. 3. The second hypothesis was partially supported. In the interference experiments between larvae of the same instar or different instars, mean handling time did not change significantly with increasing predator density, and attack rate did not change for second and third instars but decreased curvilinearly for fourth and fifth instars. Interference between some instars could not be studied because insufficient second instars were available at the same time as fourth and fifth instars, and most third instars were eaten by fourth and fifth instars in the experiments. Prey capture always decreased with decreasing attack rate. Therefore, interference reduced prey consumption in fourth and fifth instars, but not in second and third instars. The varying feeding responses of different instars should be taken into account when assessing their role in predator–prey relationships in the field.     

Untersuchungen zur Veränderung der Unkrautflora bei mehrmaligem Getreidenachbau auf einer Tonschwarzerde des Thüringer Beckens

The latent effects of precocenes I and II (PI and PH) and juvenile hormone I (JHI) when topically applied to the last three instars of Spodoptera littoralis (Boisd.) larvae have been studied. Application of both PI or PII resulted in morphogenetic abnormalities resemble some effects induced by administration of JHI, e.g., larval‐pupal intermediate, partial or severe cases of untanned pupae and imperfect moths. In PII‐treatments, the effect was instar‐dose‐dependent. The intermediate dose (55 μg) was more effective on S. littoralis larvae than other doses. The effectiveness of both doses of 40 or 70 μg in production of deformed larvae and pupae decreased when applied as repeated doses instead of single ones. In Pi‐treatments, the lower dose (25 μg) was more harmful to Spodoptera larvae than the higher dose (70 μg). Repeated application by either lower or higher doses did not enhance the production of imperfect insects. Application of JHI induced symptoms ranging from supernumerary instars, larval‐pupal intermediate, untanned pupae and deformed adults. The effect was dose‐dependent. In all tested compounds, there apparently was a latent or delayed effects. Although the insects were treated while they were larvae the complete effects were not apparent until after the insect had become a pupa or an adult. More efforts will be needed to understand how does precocene interferes with the process of tanning or sclerotization?     

Antennal Drumming,Trophallaxis, and Colony Development in the Social Wasp Polistes fuscatus (Hymenoptera: Vespidae)

Parental care is an important component of social behavior in both vertebrates and invertebrates. Social wasps are a useful system for investigating the interplay between behaviors associated with the feeding of larvae by adults and their role in the evolution and maintenance of sociality. Females of the primitively eusocial wasp genus Polistes perform conspicuous vibratory behaviors closely associated with adult–larva feeding interactions. Prior research strongly indicates that these signals are directed toward the larvae, but their function(s) remain unclear. Existing hypotheses on the function(s) have posited releaser effects on larvae, either stimulating or inhibiting release of larval saliva, a nutrient‐rich glandular secretion attractive to adults. Polistes fuscatus queens perform antennal drumming (AD), a behavior in which they rapidly beat their antennae synchronously on the rims of the nest cells during the feeding of larvae. We used radiolabeled prey to show that adults extract juice from the prey, which they subsequently regurgitate to larvae immediately following each AD burst. We also show that no saliva is imbibed by the queen during the contact. These results are consistent with the inhibition hypothesis on the function of AD, but not the stimulation hypothesis. We further demonstrate that AD is first performed on nests when the oldest larvae reach the third instar, and that the third instar is the first to produce measurable volumes of larval saliva. Removal of third‐, fourth‐, and/or fifth‐instar larvae from single‐foundress, pre‐pupal‐stage colonies did not cause a reduction in the queen’s AD rates compared with controls, suggesting that later‐stage larvae do not maintain AD behavior via an immediate releaser effect. We propose instead that third‐instar larvae, possibly via chemical components of the salivary secretion itself, modulate the physiology of queens so as to indirectly cause the onset and maintenance of AD behavior.     

Contrasting diel activity and feeding patterns of four instars of Rhyacophila dorsalis (Trichoptera)

1. Ontogenetic shifts in prey choice and predator behaviour can affect food‐web structure. Therefore, it is important to establish if the diet and feeding activity differ between life‐stages of the same species. This hypothesis was tested for second, third, fourth and fifth larval instars of Rhyacophila dorsalis by comparing their diel activity and feeding patterns. Second to fifth instars collected from two streams were used either for gut analyses or for observations of their activity and feeding patterns in three stream tanks. Food was provided in excess; being organisms living in bryophytes on top of a large stone in each tank, augmented by different‐sized larvae of Ephemeroptera, Simuliidae and Chironomidae. As few first instars for gut analyses were found in the field, the diet of first instars reared in the laboratory was also studied. 2. Larvae for gut analyses were taken 1 h before dusk or dawn (n = 50 larvae per instar for each day or night sample). First and second instars fed on the smaller food items with no significant day‐night differences in diet. Gut contents indicated a progressive trend from feeding chiefly at night in third instars to almost exclusively at night in fifth instars. Fourth and fifth instars fed on the larger food items, whilst the diet of the third instar larvae overlapped with that of both the earlier and later instars. 3. Diel activity patterns of single larvae differed between instars but not within each instar (n = 20 larvae per instar). Second instars were active throughout the 24 h, with peaks at dusk, around midnight, dawn and around midday. A similar pattern was shown by third instars but the peak of activity at midday was less than the other three peaks. Prey were captured only during these peaks for both instars. Fourth and fifth instars were most active, and fed only, at night. They used an ambush strategy to capture more active prey at dusk and dawn (e.g. Baetis, Gammarus), and a searching strategy to capture more sedentary prey during the night (e.g. chironomids, simuliids). These experiments provided support for the hypothesis under test. If competition and/or interference occur between instars, then it could be reduced between earlier and later instars because of differences in their diet and diel pattern of feeding activity.     

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.     

Some aspects of activity regulation of Galleria mellonella PTTH cells

Using the Galleria prothoracicotropic bioassay, five small neurosecretory cells occurring in each dorsolateral part of protocerebrum of Galleria mellonella brain were identified as prothoracicotropic hormone (PTTH) cells. It was found that the critical period for the release of PTTH from a brain implanted in neck-ligated larva lasts up to the third day after implantation. The content of paraldehyde-fuchsin positive neurosecretory material (NSM) in PTTH cells was determined during the penultimate and last larval instar, during pupal instar, and in starved or poststarvation fed or space-deprived last instar larvae. Two peaks of NSM in PTTH cells were found in the penultimate instar (in freshly molted, and 76-h-old larvae), four peaks in the last instar larvae (in freshly molted, and in 67-, 132-, and 174-h-old larvae), and one peak in the pupal instar (in 56-76-h-old pupae). It was also observed that upon starvation NSM accumulated in PTTH cells, while after 3 h of poststarvation feeding it was released. In permanent space-deprived last instar larvae no NSM occurred in PTTH cells. In all investigated larval instars a rapid release of NSM from PTTH cells was found a few hours after molt associated with the beginning of the feeding period. The significance of the NSM content in PTTH cells is discussed in relation to ecdysteroid titer.     

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.     

Effect of dietary selenium supplementation on resistance to baculovirus infection

We have examined the effects of dietary selenium (Se) supplementation on larval growth and immunocompetence of the lepidopteran pest, the cabbage looper, Trichoplusia ni. Supplementation of the diet of T. ni larvae with 10–20 ppm Se resulted in a 1 day delay in pupation. The effects of the addition and/or removal of dietary Se on total Se bioaccumulation and sequestration were determined by neutron activation analysis of pupae. Early penultimate instar larvae moved from selenium containing diet to basal diet lost total pupal Se content down to the level of those fed basal diet. Conversely, larvae moved from basal diet to diet containing additional Se rapidly attained pupal Se levels comparable to larvae fed Se throughout larval development. Therefore, dietary Se is rapidly accumulated or lost during larval development, but significant amounts are sequestered from diet into pupae. Larvae were reared on diet supplemented with 5 or 10 ppm Se until the onset of the penultimate instar then infected per os with increasing concentrations of the fatal baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV). Larvae fed Se in the penultimate and ultimate instars were more resistant to viral infection than larvae not fed Se in the final instars. This study indicates that dietary Se levels rapidly impact Se assimilation and sequestration and that tissue Se levels are an important factor in resistance to AcMNPV infection in larval T. ni.     

In vitro bioassay for the effect of Ajuga reptans phytoecdysteroids on Trialeurodes vaporariorum larval development

A rapid and reliable in vitro bioassay method to test the effects of synthetic and natural compounds on the development of greenhouse whitefly Trialeurodes vaporariorum Westwood (Homoptera Aleyrodidae) is described.Leaf fragments of Nicotiana glauca Graham infested with eggs of whitefly were cultured under aseptic conditions on half-strength Murashige-Skoog medium. The development of the insect in vitro and in vivo were comparable except for a higher mortality rate in the first larval instar.Ecdysteroids from Ajuga reptans L. were applied to leaf fragments by immersion in aqueous solution of the compounds or by addition to the culture medium. A high mortality rate of first larval instars was detected with 29-norsengosterone and ajugalactone treatments. This effect was specially pronounced when the products were incorporated in the medium. A significant increase in mortality was also recorded in the pupal state with a 20-hydroxyecdysone treatment. This effect was never observed before, because all whitefly larvae on A. reptans leaves die in the first larval instar.     

Age‐dependent changes in tolerance to cold and accumulation of cryoprotectants in overwintering and non‐overwintering larvae of European corn borer Ostrinia nubilalis

Abstract The age‐dependent cold hardiness profile of Ostrinia nubilalis is compared between nondiapausing and diapausing larvae, as well as with field‐collected larvae. The results suggest that both cold tolerance and accumulation of cryoprotectants depends upon the age of O. nubilalis larva. Late fifth‐instar nondiapausing larvae are more cold tolerant than younger fifth‐instars because they show enhanced ability to withstand sub‐zero temperatures. No appreciable difference is observed between the experimental groups of diapausing larvae as far as their supercooling ability and tolerance at sub‐zero temperatures above the supercooling point. In general, both field‐collected and diapausing larvae are more cold tolerant than nondiapausing larvae, indicating a direct link between diapause and cold hardiness. The age of diapausing larvae affects the ability to accumulate glycerol. Glycerol levels of 45‐day‐old diapausing larvae are significantly higher (2.7‐fold) compared with 90‐day‐old diapausing larvae. Moreover, diapausing larvae display a five‐ to 13‐fold higher glycerol content compared with nondiapausing larvae. There is a trend for an age‐dependent cold hardiness profile in O. nubilalis and further tests that could demonstrate a causal relationship between age and cold tolerance are needed.