2nd Larval Instars Research Articles

Insect lipophorin and vertebrate lipoproteins support larval development of the endoparasitoid Venturia canescens (Hymenoptera: Ichneumonidae) as dietary lipid sources.

We previously reported that lipophorin, an insect lipoprotein, is essential for in vitro development of the larval endoparasitoid Venturia canescens from the 1st larval instar to the 2nd instar. In this study, we compared the effect of various lipoproteins from insects and vertebrates to clarify whether the growth promotion effect of lipophorin is caused by its lipid moiety. As well as the permissive host (the greater wax moth) lipophorin, lipoproteins from a nonpermissive host (the silkworm) and vertebrates (chicken and human) also promoted V. canescens development to the 2nd larval instar, suggesting that essential factors for the first larval ecdysis are ubiquitous in a wide range of animals. When total lipids from the permissive host were emulsified in a lipoprotein-free medium with multilaminar vesicles of phosphatidylcholine (liposome), V. canescens larvae underwent ecdysis in the medium. In contrast, lipophorin lipid-depleted by lipase treatment promoted larval growth less than intact lipophorin. These results indicated that the growth-promotion effect of lipophorin is mainly due to the lipid moiety of lipophorin.

Characterization of an SRY-like gene, DSox14, from Drosophila

We have characterized the DSox14 gene, a new member of the family of transcription factors related to the mammalian sex determining factor, SRY. It contains two exons and the intron is large for Drosophila at 2.8 kb. The encoded protein consists of 691 amino acids (72 kDa) and includes an HMG box domain, which is closely related to the mouse Sox4 DNA binding domain. Expression of the DSox14 HMG box domain in vitro shows that it binds the sequence AACAAT with a Kd of 190 nM, generating a bend angle of 48.6°. At higher protein concentrations, a second HMG box binds at the recognition sequence, increasing the bend angle by 5°. DSox14 is variably expressed throughout development as three alternative transcripts but not at all during the 1st and 2nd larval instars. The several mRNA transcripts are produced primarily from different transcriptional start sites. Analysis of the expression of DSox14 mRNAs during early development shows that they are maternally contributed at a low level and ubiquitously expressed during embryogenesis. The widespread pattern of expression suggests that DSox14 affects a large number of target genes.

Induction and development of winter larval diapause in a drosophilid fly, Chymomyza costata

Photoperiodic response during induction of larval hibernal diapause of Chymomyza costata was characterized and the course of diapause development was analyzed in the laboratory. C. costata becomes sensitive to photoperiodic stimuli during an unspecified stage of its early development (embryo, 1st larval instar); the sensitivity gradually increases during the 2nd and early 3rd larval instars and reaches its maximum just before the moment when it abruptly ceases at the age of 15–19 days after oviposition. Diapause intensifies during a period of 2–3 weeks after induction and, later, is maintained without apparent development until death (between 150 and 250 days) under 18°C and a short-day photoperiod (L10:D14, SD). Diapause may be terminated in a horotelic process by exposure to a low temperature (2°C) during which larvae subsequently (1) synchronize their post-diapause development (requires up to 14 days of chilling), (2) lose photoperiodic sensitivity (2 months), and finally (3) terminate diapause (5 months). Alternatively, diapause may be terminated in a tachytelic process by exposure to a high temperature (18°C) and long-day photoperiod (L16:D8, LD) during which no synchronization occurs and pupariation takes place after a mean of 25.2 days (with a broad range from 8 to more than 50 days). Larvae that are transferred from LD to SD during their sensitive period switch their developmental programming from pupariation to diapause. Proliferation of adult primordial structures (imaginal discs, neuroblasts) slows down within 1 day after transfer. In contrast, whole body growth continues for at least 3 days before its rate slows down and matches the rate characteristic for SD conditions.

Titres of juvenile hormone I, II and III in Spodoptera littoralis (Noctuidae) from the egg to the pupal moult and their modification by the egg–larval parasitoid Chelonus inanitus (Braconidae)

Physico-chemical analysis of juvenile hormones (JHs) of Spodoptera littoralis revealed highest quantities in the second half of embryonic development and in newly hatched 1st instar larvae. At these stages, mostly JH II, JH I and little JH III were found, while in later stages only JH II and JH III were found. Titres fluctuated in a similar manner in all larval instars, being lowest during the moults. In last (=6th) instar larvae, JHs disappeared in the late feeding–digging stage and again increased in the early prepupal stage. Parasitisation with Chelonus inanitus, a solitary egg–larval parasitoid which induces in its host the precocious onset of metamorphosis in the 5th instar, did not alter JH homologue composition but led to a disappearance of JHs in the 5th instar. Implantation of a parasitoid larva into early 5th instar larvae containing polydnavirus/venom caused a drop in the JH titre which indicates that the parasitoid larva plays an important role in the manipulation of the host's JH titre. In the parasitoid larva, only JH III was found; titres were highest in the 2nd larval instar, a stage when the host is in the 5th instar and contains almost no JHs. Thus, JHs of the parasitoid and the host fluctuate in an independent manner.

Ecological Segregation of Two Species of Hydropsyche (Trichoptera: Hydropsychidae) in a European Second-Order Stream (Essonne, France)

ABSTRACT Life-history patterns and food habits are described for two sympatric species of Hydropsyche (H. pellucidula and H. contubernalis) sampled for 15 months in a second-order stream, the Essonne (France). Both species showed univoltine life-cycles with remarkable differences in winter. H. contubernalis overwintered mainly in the 4th or 5th larval instar; whereas, the more abundant H. pellucidula overwintered in the 2nd or 3rd larval instar. The main larval growth periods of the two species were also different, and this could be due to ecological segregation, which allows both species to share a similar ecological niche. The two species shared the same food habits throughout all larval instars; however, they both changed their food habits as they passed from one instar to another, and earlier instars were more predatory than the older ones.

Host‐age discrimination during host location by Cotesia glomerata, a larval parasitoid of Pieris brassicae

AbstractSome 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 parasitoid Cotesia 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 that C. glomerata can discriminate between young and old larval instars of P. 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.

The effect of host age ofLymantria dispar larvae [Lep.: Lymantriidae] on the development ofGlyptapanteles liparidis [Hym.: Braconidae

The endoparasitic development ofG. liparidis was examined in 3 different host stages of gypsy moth larvae. Hatching ofG. liparidis-larvae occurred 3 to 5 days after oviposition in hosts parasitized during their premoulting period, and after 5 to 7 days in those parasitized in the 3rd midinstar state. The parasites generally moulted to the 2nd larval instar between the 11th and 13th day in the first group, and between the 13th and 15th day in the latter, when they had reached a volume of 0.04–0.05 mm3. The positive correlation between host ecdysis and the ecdysis of 1st stadium larvae to L2 suggested that host moulting influenced the development of the parasitoid larvae. Emergence from the host larvae occurred at 20°C after 27 days on average, and coincided with the parasites moulting to the 3rd instar. Five to 7 days after spinning their cocoons near the developmentally arrested host larva, the male, and 1 to 2 days later the female wasps eclosed. Due to the variation in the number of parasites per host, no difference was observed between the hosts parasitized at various stages; however, a tendency for later parasitized hosts to contain more parasite larvae was evident. The nutritional conditions of the moth parental generation influenced both host and parasite development. On the other hand no influence of host age was observed on emergence dates of larvae and wasps.

Toxicity of four common pollutants to the freshwater macroinvertebratesChironomus riparius Meigen (Insecta:Diptera) andGammarus pulex (L.) (Crustacea:Amphipoda)

The lethal toxicities of the four pollutants 3,4-dichloroaniline (DCA), atrazine, copper, and lindane were determined for the 2nd larval instar of the insect Chironomus riparius Meigen and the juvenile stage (2nd or 3rd moult) of the crustacean Gammarus pulex (L.). Median lethal concentrations (LC50s) were determined over a 240 h test period. The order of toxicity of the test chemicals is different for each species. For C. riparius, lindane was the most toxic, followed by copper, DCA, and atrazine. During the first 96 h of exposure, the order for G. pulex was copper, lindane, then DCA and atrazine with similar LC50 values. However, at 240 h lindane replaced copper as the most toxic chemical to G. pulex. The relative sensitivity of the two species was dependent on both the toxicant and the exposure period. The lethal concentrations determined for the four chemicals are compared to the results of other toxicity studies and discussed with respect to current standard test methods.

Physiological aspects of nm-g mutant: An ecdysteroid-deficient mutant of the silkworm, Bombyx mori

We examined physiological and endocrinological properties of the nm-g mutant of the silkworm, whose development was arrested at 1st or 2nd larval instar. The larva of the nm-g homozygote continued to feed and grow past the stage when a normal larva moulted to the next instar. The nm-g larva attained more than twice the body weight of a normal moulting larva, but remained in the same instar with no sign of the moulting until it finally died. The ecdysteroid concentration in the haemolymph of the nm-g larva was reduced and an increase in the titre, which occurred before moulting in the normal larva, was not observed. Injection of 20-hydroxyecdysone induced the nm-g larva to moult and ecdyse to the next larval instar. From these results, we conclude that nm-g is an ecdysteroid-deficient mutant.

Cocoon Mimicry and Predation by Myrmecophilous Diptera (Diptera: Syrphidae)

Three species of myrmecophilous Microdon (Diptera: Syrphidae) M. albicomatus Novak, M. cothurnatus Bigot, and M. Piperi Knab, exhibit aggressive mimicry as immatures. In nests of their host ants (species of Camponotus and Formica), the 1st and 2nd larval instars resemble the ant cocoons upon which they prey and are transported with the cocoons by workers. Immatures are not attacked by their host ants and appear to possess chemical as well as physical attributes providing integration with their host.

Field Evaluation of Doryphorophaga doryphorae (Diptera: Tachinidae), a Parasite, and its Host the Colorado Potato Beetle (Coleoptera: Chrysomelidae)

The maximum parasitism rate by Doryphorophaga doryphorae (Riley) of the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), approached 75%. However, this occurred in late August and September, when the CPB larvae had already damaged the crop. The effectiveness of the parasite was limited by its low abundance during the first generation of the CPB. Although 9, 30, and 61% of the 2nd, 3rd, and 4th larval instars of CPB, respectively, were parasitized, parasitic maggots did not develop until the fourth-stage CPB larva entered the soil to pupate. Thus, there was a delay of about 7 days in fly emergence from hosts that had been parasitized as 2nd-instar rather than 4th-instar CPB larvae. We estimated that as much as 39% of the emerging fly were delayed over a 7-day period

An investigation of the sensitive periods for hydroxyproline-induced morphological and biochemical abnormalities in Drosophila

Abstract The sensitive period(s) for hydroxyproline (OHP)-induced morphological abnormalities was compared to the timing and extent of OHP-induced changes in free amino acids in Drosophila . While OHP was shown to reduce the proportion of free proline during both 2nd and 3rd larval instars only feeding in the latter part of the 3rd instar resulted in morphological alterations. The evidence suggests that sufficiently low proline levels at the time of pupation may result in developmental abnormalities.

Morphology and biometry of larval instars of Pimpla instigator (F.) (Hymen-optera: Ichneumonidae)

AbstractLarvae of Pimpla instigator (F.) were found to pass through five larval instars during development. Initial studies of external morphology identified only three morphological groups: the primary larva (L1) the intermediate larvae (L2−4) and the final instar larvae (L5). Biometrical study of the maximum head width, width of buccal mask, inter-metatentorial distance and diameter of spiracles permitted morphological separation of all five larval instars. Under a 16 h photophase (at 25±1°C; 70±10% r.h.) and an 8 h scotophase (at 15±l°C; 80±10% r.h.) the 2nd, 3rd and 4th larval instars were found to last about 24 h each, and the 5th instar 9±1 days. Progressive development of the genital buds during the 5th instar and prepupal stages facilitated sexing of the larvae.

Culturing of Chrysopa rufilabris (Neuroptera: Chrysopidae)

A method was developed for mass production of Chrysopa rufilabris Burmeister. The 1st larval instars of C. rufilabris were fed cabbage looper eggs; 2nd and 3rd larval instars were fed cabbage looper 4th larval instars. Plastic grill panels (14.5 x 14.5 cm) of 100 individual cells served as larval rearing units. Brown paper bags (45 x 20 x 14 cm) housed the adults and served as oviposition substrates. This rearing procedure is adequate for large scale rearing of C. rufilabris.

THE UNDESCRIBED MALE AND IMMATURE STAGES OF CULICOIDES INTERROGATUS LEE AND REYE

ABSTRACTThe species Culicoides interrogatus Lee and Reye was previously known from 6 females collected in New South Wales. This paper describes the breeding site, the unknown male and immature stages (pupa, 2nd, 3rd and 4th larval instars) based on material collected at Granite Creek, Queensland.

Mosquito control agents derived from petroleum hydrocarbons. 3. The effect of FLIT MLO on first and second larval instars.

The petroleum hydrocarbon, FLIT MLO, markedly retarded the development of the 1st and 2nd larval instars of the southern house mosquito, Culex pipiens quinquefasciatus Say (=C. fatigans Wiedmann) , and the yellow-fever mosquito, Aedes aegypti (L.), when applied to the water surface in 11¾, × 7-inch enameled pans at dosage rates of 0.5, 1, 2, and 4 gal per acre. Maximum delay in development and maximum mortality were obtained at the rate of 2 gal per acre, which delayed the onset of pupation as much as 9 days and prolonged larval development for as long as 42 days. Gross and microscopic observations of “stunted” specimens revealed abnormalities in the tracheal system, alimentation, pigmentation and response to external stimuli.