Comparative toxicity of some synthetic insecticides,and a growth inhibitor,in the migratory locust,Locusta migratoria

1. The comparative toxicity of four synthetic insecticides (Dieldrin, Methomyl, Fenitrothion and Permethrin) in the different developmental stages of the migratory locust shows that resistance tends to increase with the developmental larval stages except in the adults which show lower resistance than the fifth larval stage.2. The resistance to a growth inhibitor, Teflubenzuron in the different developmental stages shows the reverse phenomenon—the younger larvae were more resistant than the fourth and fifth larval stages while the adults were almost not affected by this product.3. A comparison of the toxicity of the synthetic insecticides in the two forms of the insect, the solitarious and the gregarious, shows that the solitary insects were more resistant than the gregarious ones.     

Effects of gamma-radiation on the organisation of polytene chromosomes ofGlyptotendipes salinus Michailova (Chironomidae,Diptera)

A series of laboratory experiments onGlyptotendipes salinus were carried out in order to assess cytogenetic effects of different doses of gamma-radiation on polytene chromosomes, isolated from salivary glands. Chrinonomid larvae (III–IV larval stage) were irradiated with doses varying from 0.05 to 1.00 Gy (5–100 rad) and were bred under laboratory conditions until the fourth larval stage. Cytogenetic slides were analyzed for an estimation of occurrence of changes in the organization of the polytene chromosomes caused by gamma-radiation. A specific heterochromatin effect was found in certain chromosomes of the investigated species after 1.00 Gy irradiation. Decondensation of the centromeric heterochromatin and increased functional activity of Balbiany ring 2 were observed in the fourth (G) chromosome. Regression of the nucleolus of the first (AB) chromosome was detected.     

Sublethal effects of Bacillus thuringiensis on the spruce budworm, Choristoneura fumiferana

Exposing larvae of the spruce budworm, Choristoneura fumiferana (Clemens), to sublethal ( 50% lethal dose) levels of Bacillus thuringiensis subsp. kurstaki at various stages of their development significantly increased development time to the pupal stage and reduced pupal size and number of eggs laid per female, but did not affect the proportion of embryonated eggs. The changes in larval development time, pupal weight and fecundity depended on the larval stage that was treated. Exposure of fourth instars delayed larval development and reduced only male pupal weights with no effects on fecundity. Exposure of sixth instars delayed larval development to a lesser extent than exposure of fourth instars but had a pronounced effect on weight of both male and female pupae. The effect on pupal weight was sex dependent, as males tended to be more affected than females. The reduction in male pupal weight did not appear to influence fecundity, because the effect of exposure was explained by the change in female pupal weight. Effects on larval growth and pupal weight were proportional to the dose that was ingested during exposure, and were observed at doses as low as one-tenth of the LD₅₀. Ingestion of an LD₅₀ caused a 29 or 45% delay in development of, respectively, female or male larvae when exposed as fourth instars and a 30% reduction in female pupal weight when larvae were exposed as sixth instars.     

Effects of RH-5992 on ecdysteroidogenesis of the prothoracic glands during the fourth larval instar of the silkworm, Bombyx mori

Stage-dependent effects of RH-5992 on ecdysteroidogenesis of the prothoracic glands during the fourth larval instar of the silkworm, Bombyx mori, were studied in the present report. When larvae were treated with RH-5992 during the early stages of the fourth larval instar (between day 0 and day 1), initially ecdysteroid levels in the hemolymph were inhibited. However, 24 h after RH-5992 application, ecdysteroid levels were greatly increased as compared with those treated with acetone. The examination of the in vitro prothoracic gland activity upon RH-5992 application during the early stages of the fourth larval instar confirmed a short-term inhibitory effect. When RH-5992 was applied to the later stages of the fourth larval instar, no effects on both hemolymph ecdysteroid levels and prothoracic gland activity were observed. Addition of RH-5992 to incubation medium strongly inhibited ecdysteroid secretion by the prothoracic glands from the early fourth instar, indicating direct action of RH-5992 on ecdysteroidogenesis by prothoracic glands. Four hours after application with RH-5992 on day 1.5, prothoracic glands still showed an activated response to PTTH in both PTTH-cAMP signaling and the extracellular signal-regulated kinase (ERK) signaling. Moreover, addition of RH-5992 to incubation medium did not interfere with the stimulatory effect of the glands to PTTH in ecdysteroidogenesis. These results indicated that both PTTH-cAMP signaling and PTTH-ERK signaling may not be involved in short-term inhibitory regulation by RH-5992.     

A comparison of superoxide dismutase (SOD, EC:1.15.1.1) distribution in gastro-intestinal nematodes.

An examination of the distribution of superoxide dismutase (SOD) activities in whole worm homogenates from six gastro-intestinal nematodes, at different life-cycle stages, demonstrated that the third larval stages of each species contained notably more activity than the corresponding adults. Significant SOD activities were detected in culture fluids following in vitro maintenance of third and fourth larval stage and adult Trichostrongylus vitrinus and Teladorsagia circumcincta (formerly Ostertagia circumcincta). Marked interspecies variation was observed when SOD isoenzyme profiles of adult and third larval stage Nippostrongylus brasiliensis, Trichostrongylus vitrinus, Teladorsagia circumcincta and Haemonchus contortus were compared. In addition, SOD activity and isoenzyme polymorphism were greater in Nippostrongylus brasiliensis harvested from primed rats compared to parasites recovered from naive rats.     

Laboratory evaluation of Alsystin, a chitin synthesis inhibitor, against Culex pipiens pipiens L. (Dip., Culicidae): effects on development and cuticle secretion

Alsystin, a benzoylphenylurea derivative, was evaluated on Culex pipiens pipiens L. Treatment was made on newly third- and fourth-instar larvae for 24 h. Mortality occurred at various developmental stages following treatment. However, death as larvae was relatively important compared with the mortality recorded for the other later developmental stages. Treatment resulted in a dose-dependent reduction in adult emergence. Moreover, treatment caused morphological aberrations depending upon the importance of larval–adult transformation and significantly increased the duration of both third and fourth larval instars. A histological study conducted on fourth instar larval integument, revealed that Alsystin delayed the ecdysis and significantly reduced the thickness of both larval and pupal cuticles secreted compared with controls. Moreover, the apolysis that occurred at day 4 in controls was not affected by treatment.     

Functional response of larval and adult stages of Hippodamia variegata (Coleoptera: Coccinellidae) to different densities of Aphis fabae (Hemiptera: Aphididae)

We compare the efficiencies of different stages of Hippodamia variegata (Coleoptera: Coccinellidae) preying on Aphis fabae (Scolpoli) (Hemiptera: Aphididae) by estimating the functional responses of all stages. The experiments were carried out on leaf disks in petri dishes with 15-20 replicates. Our results revealed that all larval instars and adult males and females of H. variegata exhibited type II functional responses on different densities of prey. The rate of searching efficiency and handling time were estimated as 0.063 h(-1) and 6.933 h for first instar, 0.059 h(-1) and 3.343 h for second instar, 0.103 h(-1) and 1.909 h for third instar, 0.114 h(-1) and 0.455 h for fourth instar, 0.159 h(-1) and 1.194 h for male, 0.093 h(-1) and 0.409 h for female, respectively. Thus, handing time decreased from first instar to female. Handling times of males were significantly greater than those of females. The most effective stages of H. variegata were females, fourth instars, and males. The efficiency of females was nearly three times greater than that of males. The voracity of larval stages and male and female adults of H. variegata were estimated as 2.93, 5.85, 12.13, 45.13, 18.33, and 44.60 (aphids/d), respectively.     

Influence of larval stage and virus inoculum on virus yield in insect host Neodiprion abietis (Hymenoptera: Diprionidae)

Virus yield produced by dead larvae of balsam fir sawfly, Neodiprion abietis (Harris) (Hymenoptera: Diprionidae), that had been infected at four different larval stages (second, third, fourth, or fifth instar) with two virus concentrations (10(5) polyhedral inclusion bodies (PIB) /ml or 10(7) PIB/ml), were analyzed and compared to determine the effects of instar and amount of virus inoculum on virus production. The results indicate that both larval stage and inoculation dosage significantly affect virus yield. On average, each dead larva produced 1.36-12.21 x 10(7) PIB, depending upon larval age and virus concentration of inoculation. Although each dead larva produced more PIB when it was inoculated in the fourth or fifth stage, inoculation of these larvae did not result in the highest virus yield because of low larval mortality. In terms of net virus return, third instars would maximize virus yield when they are inoculated with a virus concentration that can cause 95-100% larval mortality.     

FUCTIONAL RESPONSE AND PLANT PREFERENCE OF NEPHASPIS OCULATUS (COLEOPTERA: COCCINELLIDAE), PREYING ON BEMISIA ARGENTIFOLII (HOMOPTERA: ALEYRODIDM) IN THE LABORATORY

Abstract The predatory behavior and functional response of all larval stages and adults of Nephpis oculatus (Blatchley), a predacious coccinellid, on various egg densities of Bemisia argentgolii Bellows & Pemng, and prey preference of adult N. oculatus , were studied in the laboratory. Daily consumption of eggs of B. argentifolii by N. oculatus was evaluated at six different densities to obtain functional response curves for all active stages of the coccinellid. Bemisia argentifolii eggs were offered to N. oculatus on collard leaf disks in Petri dish arenas over a 24-h period at 26.7 ∀ 2°C: and a photoperiod of 14:10 (L: D) h. Linear relationship were observed between percentage prey consumed and prey density, with r ² values between 0.82–0.99 for all stages except for the fourth instar that had a smaller r² value (0.64). Functional response curves of prey consumption by N. oculatus against density of B. argentifolii eggs fitted the type II model of Holling's disc equation for all larval stages and both the male and female adults. Adult females consumed more prey than adult males. The maximum theoretical number of prey consumed per day increased with larval development. The fourth instar was the most effective larval predator, followed by the third instar, the second instar, and finally, the first instar. Based on the functional response parameters, a maximum of 321, 312, 237, 229, 73, and 34 B. argentifolii eggs could be attacked by an adult female, a fourth instar, an adult male, a third instar, a second instar, and a first instar of N. oculatus , respectively. Nephaspis oculatus adults strongly preferred collard to tomato, soybean, eggplant or sweet-potato for oviposition and foraging. Nephaspis oculatus did not deposit any eggs on soybean and tomato.     

Amino acid and protein changes in the haemolymph of developing fourth instar Chironomus tentans

The concentration of free amino acids, total soluble protein, and haemoglobin in the haemolymph of fourth instar Chironomus tentans was investigated.The concentration of the free amino acid pool increases between the early (15.7 mM/l) and mid-(33.9 mM/l) fourth larval stages followed by a decline during the late (16.9 mM/l) fourth larval period. Alanine, serine, and the amides of aspartic acid and glutamic acid are the predominant free amino acids at all stages. Physiological fluid analysis of late fourth instar haemolymph detected 32 ninhydrin positive components including 18 common amino acids plus homoarginine, ornithine, citrulline, β-alanine, α-aminoadipic acid, α-aminoisobutyric acid, and sarcosine.The concentration of total soluble protein steadily increases during fourth instar larval development to a maximum of $\text{9.3}\text{g}\text{100}\text{ml}$ followed by a decline during the pharate pupal period. A similar pattern of variation occurs in haemoglobin content which comprises from 51 to 66% of Chironomus tentans haemolymph protein.The mM percentage of individual amino acids of total haemolymph protein varies little during the fourth instar. At all stages alanine and aspartic acid are the predominant amino acids.     

Myelin deposition in the optic tectum of trout as monitored by enzymatic and morphometric analyses

The activity of arylsulfatase A and 23-cyclic nucleotide 3-phosphohydrolase was studied in the brain of trout in parallel to the structural differentiation of tissue from early larval stages into adulthood. Whereas in the optic tectum, phosphodiesterase activity could not be detected before the second month after hatching in brainstem, the enzyme had already reached 80% of adult level. In tectum it was from the fourth to the seventh month that this enzyme dramatically increased, thereby reaching about the adult level. The developmental profile of arylsulfatase A was profoundly different, since 1) considerable activity was found in tectum at early larval stages and 2) the activity showed a peak between two and six months and then dropped markedly.Morphometric analysis of the two myelinated layers of trout tectum support and extend the biochemical results leading to the conclusion that the phosphodiesterase activity reflects the prevailing degree of myelination, whereas the developmental profile of the sulfolipid-metabolizing enzyme indicates the rate of myelin accumulation.     

Hydrocarbon accumulation and lipid biosynthesis during larval development in the cabbage looper,Trichoplusia ni

Larvae of the cabbage looper, Trichoplusia ni, were analyzed for the accumulation and biosynthesis of cuticular and internal hydrocarbon at closely spaced and accurately timed intervals during the fourth and fifth stadia. Large differences in the incorporation of [1-¹⁴C]acetate into hydrocarbon were observed at different times during larval development. Much higher incorporation was observed during feeding stages as compared to wandering stages, while lowest rates of biosynthesis occurred just prior to ecdysis. Fourth stadia wanderers accumulated increased amounts of internal hydrocarbon, which is apparently used to cover the newly forming cuticle. During the fourth to fifth stadium moult insects lost all cuticular hydrocarbon that was present on the old cuticle (about 8 μg/insect) and had about 8 μg/insect on the surface of the newly exposed cuticle. During the fourth stadium incorporation of [1-¹⁴C]acetate into total lipid declined between feeding and wandering stages from 24% of injected radiolabel to 7%. Similar decreases in lipid biosynthesis were observed between feeders and wanderers in fifth stadium larvae with the greatest decrease found in the triacylglycerol fraction. These results document dramatic changes in the accumulation and biosynthesis of hydrocarbon and other lipids during larval development.     

Impact of third and fourth harmonic laser irradiation at embryonic stage on biocommercial traits of Bombyx mori

In order to study the impact of third and fourth harmonic laser on bio-commercial traits of silkworm Bombyx mori, silkworm eggs of 2, 8, 16 and 24 h old embryos were exposed for varying durations to both third and fourth harmonic lasers. Computation of data is explicit that the third harmonic laser had a positive influence for shorter duration exposures on all traits, like hatching percentage (15% increase), larval weight (14% increase), cocooning percentage (12% increase), cocoon weight (7% increase), shell weight (9% increase), shell ratio (15% increase) and fecundity (11% increase) with significant increases in the batches exposed for shorter durations (up to 90 sec) with respect to their controls. Thereafter levels decreased as the duration of exposure increased. Notably, fourth harmonic laser irradiation reveals the negative effect on all the traits studied in the present study. Surprisingly the filament length was decreased in all irradiated samples for both the third and fourth harmonic laser, expect for 24 h old embryos irradiated for 30 s by the third harmonic laser which showed a 6% increase over the control.     

Photoperiodic induction of larval diapause and temperature-dependent termination in a wild multivoltine bruchid,Kytorhinus sharpianus

A wild bean weevil,Kytorhinus sharpianus Bridwell (Coleoptera: Bruchidae), has a multivoltine life cycle and enters a hibernal larval diapause at the fourth instar under a short daylength (Shimada & Ishihara, 1991). Here, we investigated their diapause incidence under different photoperiods at 24°C and 27°C. The critical photoperiods for diapause induction were 14.5 h at 24°C and 14 h at 27°C. The stages susceptible to diapause-inducing stimuli were estimated by transferring larvae of various instars from long days to short days and vice versa. Then we investigated the incidence of larval diapause. The sensitive stage was estimated to be from the third to early fourth instar. Though larval diapause, which was induced under a short daylength, was terminated only by increasing the daylength, the termination was more synchronized by an exposure to a low temperature followed by increasing temperature, irrespective of photoperiod.     

Life history traits of Aedes caspius (Diptera: Culicidae): a laboratory study of larval stages

The larval survival and development times of Aedes caspius (Diptera: Culicidae) were examined in the laboratory. These life history traits were estimated using life tables constructed for two populations, one of which had been subjected to a long-term larvicide control program. Traits were evaluated for eight different population densities. The effects of population, larval stage and larval density were investigated using a general linear model. Density was positively correlated with larval survival but did not affect development time. The fourth instar and pupae had the lowest larval survival rates. First and fourth instar larvae had the longest development times. These traits were not significantly different between the two populations. The effect of larvicide control on these traits is discussed.     

DNA synthesis in polytenic chromosomes of Anopheles atroparvus

DNA synthesis in polytenic chromosomes of Anopheles atroparvus has been studied during the third and fourth larval stages. The beginning of the replication cycle coincides with the moult. With increasing larval age the frequency of nuclei in synthesis decreases continuously to reach 1 per cent in the fourth instar at 48 hours of age. The beginning of synthesis is characterized by asynchrony both among larvae and among nuclei within the same larva. At the beginning of replication the polytenic chromosomes have a discontinuous labelling pattern. The same pattern was observed at the end of reduplication. Whole nuclei and single chromosomal regions seem to reach their maximum degree of polyteny during the third larval stage.     

Nippostrongylus brasiliensis: effects of immunity on the pre-intestinal and intestinal larval stages of the parasite

Nippostrongylus brasiliensis: effects of immunity on the pre-intestinal and intestinal larval stages of the parasite. International journal for Parasitology4: 183–191. Migration of the pre-intestinal larval stages of N. brasiliensis was studied in rats undergoing either primary or challenge infections. In rats undergoing a primary infection, more than 67 percent of larvae successfully migrated from the skin to the oesophagus by 70 h after infection, and subsequently over 90 per cent of these larvae became established in the small intestine as sexually mature adults. In immune rats undergoing a second infection, 46 per cent of larvae completed migration to the oesophagus by 70 h and of these, only 1·6 per cent became established in the intestine to produce eggs. These inhibitory effects on the pre-intestinal and intestinal larval stages were even more pronounced in immune rats undergoing a third or fourth infection and in addition, there was a prolonged sojourn and substantial retention of larvae in their lungs. There was no evidence that the immune response had an adverse effect on oesophageal fourth stags larvae as these organisms (obtained from immune donors) were able to establish and develop to maturity when transferred per os to normal animals.Syngeneic transfer of immune mesenteric lymph node cells to normal recipients, caused expulsion of parasites from the intestine but failed to effect migration of pre-intestinal larval stages. The implications of these findings are discussed in the context of current knowledge of the mechanisms of immunity to helminths.     

Complete larval development of the hermit crabs Clibanarius aequabilis and Clibanarius erythropus (Decapoda: Anomura: Diogenidae), under laboratory conditions, with a revision of the larval features of genus Clibanarius

The complete larval development (four zoeae and one megalopa) of Clibanarius aequabilis and C. erythropus, reared under laboratory conditions, is described and illustrated. The larval stages of the two northeastern Atlantic Clibanarius species cannot be easily differentiated. Their morphological characters are compared with those of other known Clibanarius larvae. The genus Clibanarius is very homogeneous with respect to larval characters. All Clibanarius zoeae display a broad and blunt rostrum, smooth abdominal segments and an antennal scale without a terminal spine. Beyond the second zoeal stage, the fourth telson process is present as a fused spine, and the uropods are biramous. In the fourth larval stage all species display a mandibular palp. The Clibanarius megalopa presents weakly developed or no ocular scales, symmetrical chelipeds, apically curved corneous dactylus in the second and third pereiopods, and 5–11 setae on the posterior margin of the telson. Apart from the number of zoeal stages, Clibanarius species may be separated, beyond the second zoeal stage, by the telson formula and the morphology of the fourth telson process.     

Developmental expression of three genes for larval cuticular proteins of the tobacco hornworm, Manduca sexta

Three cDNA clones coding for the 12.8, 13.3, and 14.6 kDa larval cuticular proteins of the tobacco hornworm, Manduca sexta, were isolated and characterized. Hybridization to abdominal epidermal RNA from different stages showed that the genes for the 12.8 and 13.3 kDa proteins were expressed only during larval life. By contrast, the gene for the 14.6 kDa protein was expressed throughout the segment during the feeding, growing larval stages, then only in the flexible intersegmental regions during the deposition of endocuticle in the pharate pupa and adult. Quantitative RNA dot blot hybridizations showed that the RNA for each protein disappeared during the larval molt when the ecdysteroid titer was high, then reappeared during the preecdysial deposition of endocuticle. All disappeared when the epidermis became pupally committed at the onset of wandering. Exposure of the fourth instar epidermis to 20-hydroxyecdysone (20HE) in vitro under conditions that lead to the formation of a new larval cuticle by 48 hr caused the disappearance of these RNAs by 18 hr. Exposure of Day 2 fifth instar epidermis to 20HE in vitro caused a depression of these RNAs which in the case of the RNAs coding for the 12.8 and 13.3 kDa proteins was partially prevented by simultaneous exposure to methoprene, a juvenile hormone (JH) mimic. By contrast, the RNA for the 14.6 kDa protein was suppressed by exposure to methoprene alone. Thus, each of these larval cuticular genes is turned off by high ecdysteroid; the presence or absence of JH determines whether or not this suppression is permanent in some or all cells.