Taste sensitivity of the cotton leafworm, Spodoptera littoralis, to chemicals

Threshold values of acceptance and rejection for 16 sugars and 12 electrolytes were measured. Most pentoses, hexoses, di- and tri-saccharides are stimulating. Compounds with α-linkage are superior stimuli. Substitution in the sugar molecule causes an obvious change in its stimulating characteristic. The rejection thresholds of the larvae to electrolytes showed a higher stimulating effectiveness for either acids or hydroxides than for neutral inorganic salts. The cations in a uniform anion combination stimulated in an order which was mostly correlated to their ionic mobilities. The stimulating efficiency of aliphatic alcohols was found to increase with the increase of molecular weight. An inverse relation was found between the stimulating efficiency and the vapour pressure of the alcohols tested. The line describing the relation between the rejection thresholds and the chain length of alcohols showed an inflection near butanol with a molecular weight of 74.     

Molecular characterization and expression pattern of Spodoptera litura (Lepidoptera: Noctuidae) vitellogenin, and its response to lead stress

Vitellogenin (Vg) cDNA from Spodoptera litura Fabricius was cloned and sequenced. The open reading frame (ORF) of Vg cDNA was 5247 nucleotides in length (GenBank Accession no. EU095334), which encoded for a protein of 1748 amino acids. S. litura Vg comprised three conserved regions (Vitellogenin-N domain, DUF1943 and von Willebrand factor type D domain (VWD)), a 17 amino-acid signal peptide and a RXXR cleavage signal (RTIR). The highly conserved GL/ICG motif, the DGXR motif and cysteine residues were found in the C-terminus of the Vg. Vg mRNA was found specifically in the female fat body. Vg expression was first transcribed in 6th day female pupae and levels increased with insect development. The maximum level of Vg mRNA appeared in 24-h-old adults. When S. litura larvae were exposed to lead (Pb) (25-200 mg Pb/kg), there was a significant inhibition in Vg of female adults. The start of Vg expression was advanced ahead by Pb, from 6th day pupae to 3rd day or 4th day pupae. Low levels of Vg in male adults were also induced by low concentrations of Pb (12.5 and 25 mg Pb/kg). These data show that Pb stress elicits an important Vg response in S. litura.     

Clock-controlled rhythm of ecdysteroid levels in the haemolymph and testes, and its relation to sperm release in the Egyptian cotton leafworm, Spodoptera littoralis

In Spodoptera littoralis, testicular sperm release occurs in a daily rhythm, which is controlled by endogenous circadian oscillator located in the male reproductive system. Although this rhythm is essential for male fertility, factors that initiate and maintain daily sperm release are not understood. In this study, we investigated a modulatory role for ecdysteroids in the sperm release rhythm and identified the source of ecdysteroids in adult males. We found that the onset of sperm release occurs two days pre-eclosion and coincides with a significant decrease in haemolymph ecdysteroids levels. 20-HE injection into the pupae prior to the first sperm release delayed its initiation and disrupted the developing rhythm in a dose dependent manner. 20-HE injection into adults depressed the number of sperm bundles leaving the testes. A day before the initial sperm release, ecdysteroid levels in the haemolymph and testes begin to oscillate in a circadian fashion. Ecdysteroid rhythms continue throughout imaginal life and correlate with the rhythm of sperm release. In each cycle, testicular sperm release coincides with a trough in testicular ecdysteroid concentration. Rhythmic changes in ecdysteroid levels are regulated by an endogenous circadian oscillator that continues to function in decapitated males. The generation of a complete cycle of ecdysteroid release by testes cultured in vitro indicates that this oscillator is located in the gonads. The haemolymph ecdysteroid levels are significantly lower and arrhythmic in males with removed testes, indicating that the testes are an important ecdysteroid source that may contribute to oscillations in haemolymph ecdysteroid levels.     

Peripheral modulation of olfaction by physiological state in the Egyptian leaf worm Spodoptera littoralis (Lepidoptera: Noctuidae)

Insects show behavioural plasticity based on their physiological state. Deprivation from a resource will normally make them more responsive to it or to perform behaviour increasing the probability of encountering such a resource. Modulation of the olfactory system has been shown mainly in the central nervous system, but also in the periphery. In this study, antennal sensitivity of females of the Egyptian cotton leaf worm Spodoptera littoralis to different plant and sex pheromone odours was measured using electroantennography (EAG). Different mating status, age, and feeding status were used to investigate peripheral changes in olfactory responses. Virgin females were found to be more sensitive to plant odours and sex pheromone compared to mated females. Age also had an impact on antennal sensitivity, 2 and 4 days old females being more sensitive than just-emerged ones. Such an increase in sensitivity could be explained by maturation of olfactory receptor neurons after emergence or by an increase in motivation as the available expected life time remaining decreases. Finally, feeding status did not modify the antennal sensitivity of females. A peripheral modulation could thus be demonstrated in the olfactory system of female Spodoptera littoralis at certain life stages.     

A new species of Nosema from Hylobittacus apicalis (Insecta: Mecoptera: Bittacidae)

An undescribed Nosema was found infecting adults of the mecopteran Hylobittacus apicalis. This microsporidium is described herein as the first record of a microsporidium from the order Mecoptera. The slightly pyriform spores measured 4.5 × 2.4 μm. Mature spores had 9.5–10 polar filament coils irregularly grouped in the posterior end. The life cycle and ultrastructure of the developmental stages were described, and were typical of other Nosema spp. This microsporidium was regularly recorded from adult Hylobittacus apicalis populations over a 10-year period and tbe incidence of infection increased during the summer.     

Inheritance of Bacillus thuringiensis Cry1C resistance in Egyptian cotton leafworm,Spodoptera littoralis (Lepidoptera: Noctuidae)

A field strain of Spodoptera littoralis Biosduval was selected against Cry1C toxin derived from Bacillus thuringiensis entomocidus for 10 subsequent generations under laboratory conditions. Selection pressure resulted in a 29‐fold resistance ratio compared with the susceptible strain. Inheritance of Cry1C resistance was partially dominant and autosomal on the basis of bioassay response to Cry1C toxin in a reciprocal cross between male and/or female F₁. Consistent with earlier findings, resistance was recessive at high concentrations of Cry1C toxin. However, the dominance of resistance increased as the concentration of Cry1C decreased. Analysis of survival and growth of progeny from a backcross (F₁ × resistance strain) suggested that resistance was controlled by either a single or a few loci in cotton leafworm.     

Sex-specific differences in nutrient regulation in a capital breeding caterpillar, Spodoptera litura (Fabricius)

Nutrient requirements by male and female insects are likely to differ, but relatively little is known regarding how sexes differ in their regulation of macronutrient acquisition. The present study reports the results from a laboratory experiment in which behavioural and physiological components of nutrient regulation were compared between male and female caterpillars of Spodoptera litura (Fabricius). When provided with choices between two nutritionally complementary foods (one is a protein-biased diet and the other a carbohydrate-biased diet), both males and females adjusted their food selection to defend an intake target. However, the composition of diet preferred by the two differed, with females selecting significantly more protein than males with no difference in carbohydrate intake between the two. When confined to single diets with varying mixtures of protein and carbohydrate [P:C ratios, expressed as the percentage of diet by dry mass: protein 42%:carbohydrate 0% (p42:c0), p35:c7, p28:c14, p21:c21, p14:c28, p7:c35], females consumed more macronutrients than did males across on all P:C diets except the extremely carbohydrate-biased diet (p7:c35). Under both choice and no-choice feeding condition, such sex differences in nutrient intake were not expressed until late in the feeding stage of the final stadium. Sexes also differed in post-ingestive utilization of ingested nutrients. Females utilized ingested protein for body growth with greater efficiency compared to males, presumably reflecting provisioning their adult needs for protein to develop eggs, whereas males were more efficient at depositing lipids from carbohydrate intake than females.     

Effects of insect growth regulators on the tobacco cutworm, Spodoptera litura: Rectal prolapse

Prolapse of the rectum was observed when ZR-515 (isopropyl 11-methoxy-3,7,11-trimethyl-2,4-dodecadienoate) was applied to the 6th instar larva of the tobacco cutworm, Spodoptera litura. It was induced by an administration of ZR-515 in the middle of the 6th instar larval stage, and either by a dose higher than required for the induction of larval-pupal intermediates or by a dose lower than the dose that produces extra larvae. Larvae with a rectal prolapse appeared only on the 3rd day after treatment. These larvae did not survive for more than 1 to 2 days because the prolapsed rectum ruptured, leading to haemorrhage.Rectal prolapse was also induced by other two IGRs, ZR-512 (ethyl 3,7,11-trimethyl-2,4-dodecadienoate) and ZR-619 (ethyl 11-methoxy-3,7,11-trimethyl-2,4-dodecadienethiolate).     

Quadriflagellar primary spermatocytes in the cotton leafworm,Spodoptera littoralis (Boisd.) (Noctuidae,Lepidoptera)

Summary The surface morphology of primary spermatocytes from testicular cysts of the last instar larvae of Spodoptera littoralis was examined by scanning electron microscopy (SEM). At this stage, each primary spermatocyte possesses four developing flagella, directed towards the lumen of the cyst. The identical length of flagella in all primary spermatocytes from a single cyst indicates that the initiation and rate of flagellar growth are synchronized. Some asynchrony can, however, be observed in the translocation of flagella to secondary spermatocytes during the first meiotic division.     

Hormonal regulation of phase polymorphism and storage-protein fluctuation in the common cutworm, Spodoptera litura

Three storage proteins are synthesised by Spodoptera litura last-instar larvae as detected by an antiserum against pupal fat body proteins. The putative pupal storage proteins 1 and 2, appear in the haemolymph of the last-instar larvae 36 h after ecdysis under crowded rearing conditions: they appear 1 day later in isolated conditions. The appearance of these proteins in the haemolymph is prevented by juvenile hormone treatment and enhanced by allatectomy. Injection of 20-hydroxyecdysone into ligatured larvae does not induce appearance of these 2 proteins. Accumulation of protein 3 that reacts with Bombyx mori arylphorin antiserum is not blocked by juvenile hormone and is similar in both phases. It also accumulates to a small extent in the haemolymph during the moult to the final-larval instar and then disappears at ecdysis. One-hundred ng/ml ecdysteroid caused the sequestration of these proteins by the fat body, but a higher concentration of ecdysteroid (200 ng/ml) produced pupal cuticle in the isolated abdomens, suggesting that different ecdysteroid concentrations are necessary for these two events.     

Bioefficacy of cadmium and lead on cotton leafworm Spodoptera littoralis (Lepidoptera: Noctuidae) larvae

The sensitivity of Spodoptera littoralis second and fourth instar larvae to the heavy metals cadmium (Cd) and lead (Pb) was investigated under laboratory conditions. Both Cd and Pb, even, at very low concentrations, had relatively high toxic effects on S. littoralis larvae. Cd was more toxic to S. littoralis larvae than Pb. In addition, the mean percentage feeding deterrence (FDI%) of Cd and Pb was concentration-dependent. The nutritional indices (consumption index, growth rate, efficiency of converted ingested and digested food, and approximate digestibility) of S. littoralis second and fourth instar larvae were more affected in Cd-treatments compared with those of Pb-treatments. Therefore, the presence of such heavy metals in the environment would exert an adverse impact on S. littoralis larvae and their development.     

Effects of juvenile hormone on some phase characteristics in the common cutworm, Spodoptera litura

Phase characters of the common cutworm, Spodoptera litura, were influenced by different rearing densities from the 4th-larval instar. Primarily the final feeding period of isolated larvae was 1 day longer than that of crowded larvae causing an increase in pupal weight. Applications of juvenile hormone I, II, or methoprene to crowded larvae caused an increased feeding period similar to that of isolated larvae when the juvenile hormones were applied within 1 day after the last-larval ecdysis. Allatectomy of isolated Spodoptera during the moult to the final-larval instar decreased the duration of the final feeding period to that of intact crowded larvae. These results suggested that one of the characters of phase variation, pupal weight, is influenced by the differences in the regulation and activity of the corpora allata during the last-larval instar. Other characteristics of phase variation such as behaviour (feigned death) and colour were not affected by alteration in juvenile hormone levels after the last larva ecdysis.     

Influence of a baculovirus infection on molting and food consumption by Spodoptera litura

The effect of a baculovirus (nuclear polyhedrosis virus) infection on molting, neurosecretory activity, and food consumption of the tobacco leaf eating caterpillar. Spodoptera litura, is studied. The virus was administered by allowing the larvae to feed on castor leaves contaminated with purified polyhedral suspension (5.57 × 10⁸/ml). Host larvae failed to molt more than once after infection. Infected last-instar larvae failed to pupate and had prolonged larval stage. Activity of median neurosecretory cells (MNC) of brain increased during disease development. However, the larval—pupal molt was inhibited, possibly due to lack of release of neurosecretion from the MNC. The surface area of corpus allatum of last-instar larvae increased during infection indicating high activity. Infected larvae continued to feed almost until death. The indices of digestion and utilization were significantly lowered due to disease development.     

Characterization of an extracellular lipase from the biocontrol fungus, Nomuraea rileyi MJ, and its toxicity toward Spodoptera litura

An extracellular lipase from Nomuraea rileyi MJ was purified 23.9-fold with 1.69% yield by ammonium sulfate precipitation followed by Sephacryl S-100 HR column chromatography. By mass spectrometry and SDS-polyacrylamide gel electrophoresis, the molecular weight of the homogenous lipase was 81 kDa. The N-terminal sequence was determined as LeuSerValGluGlnThrLysLeuSerLysLeuAlaTyrAsnAsp and it showed no homology to sequences of known lipases. The optimum pH and temperature for activity were 8.0 and 35 °C, respectively. The enzyme was stable in the pH range 7.0-9.0 and at 15-35 °C for 1 h. Higher activity was observed in the presence of surfactants, Na⁺, NH₄⁺ ions, NaN₃ and ethylenediaminetetraacetic acid (EDTA), while Co²⁺ and Cu²⁺ ions, cysteine and dithiothreitol (DTT) strongly inhibited activity. The purified lipase hydrolyzed both synthetic and natural triglycerides with maximum activity for trilaurin and coconut oil, respectively. It also hydrolyzed esters of p-nitrophenol (pNP) with highest activity for p-nitrophenyl caprate (pNPCA). The purified lipase was found to promote N. rileyi spore germination in vitro in that germination reached 98% in conidial suspensions containing purified lipase at 2.75 U. Moreover, it enhanced toxicity of N. rileyi toward Spodoptera litura larvae with mortality via topical application reaching 63.3% at 4-10 days post-treatment which calculated to be 2.7 times higher than the mortality obtained using conidial suspensions alone.     

Susceptibility of early larval stages of Pseudaletia unipuncta and Spodoptera exigua (Lepidoptera: Noctuidae) to the entomogenous nematode Steinernema feltiae (Rhabditida: Steinernematidae)

Early stages (neonate to 7- or 8-day-old larvae) of Spodoptera exigua and Pseudaletia unipuncta were exposed to the entomogenous nematode, Steinernema feltiae, at concentrations of 0, 10, 25, 60, 100, or 200 nematodes per larva. Larvae of both species were susceptible to nematode infections. However, neonate larvae of S. exigua were significantly less susceptible to nematode infection than 3- or 8-day-old larvae at or above 50 nematodes per larva. Mortalities of neonate larvae exposed to 50 or more nematodes ranged from 68 to 74% while mortalities of 3- and 8-day-old larvae ranged from 91 to 100%. The results with P. unipuncta showed similar trends as described for S. exigua, albeit at a lower mortality level and usually with no statistical differences. Mortalities of neonate larvae exposed to 50 or more nematodes ranged from 34 to 44% while mortalities of 7-day-old larvae ranged from 32 to 91%.     

The preservation of infective spores of Nosema necatrix (Protozoa: Microsporida) in Spodoptera exempta (Lepidoptera: Noctuidae) by lyophilization

Cadavers of Spodoptera exempta infected with Nosema necatrix were lyophilized. The lyophilized material was tested against a standard spore preparation 1 day after lyophilization and retested 2 yr later. There was some loss of spore viability. The feasibility of using dose-mortality experiments to estimate the loss in viability is discussed.     

Ovule morphology, embryogenesis and seed development in three Hylocereus species (Cactaceae)

Pre-embryonic and embryonic stages and seed developments were studied in the diploids Hylocereus monacanthus and Hylocereus undatus and the tetraploid Hylocereus megalanthus. Ovule morphology was similar among species except for micropyle entrance. H. monacanthus had the thickest and most robust suspensor. Embryo developmental time, measured from fertilization to maturity, was significantly more prolonged in H. megalanthus. Typical to Cactaceae, the seed coat was formed by one layer of sclerenchymatous cells, but was more lignified in H. megalanthus. Morphological features common to all species included (1) cellular type endosperm with independent patterns of development in the chalazal and micropylar zones, forming a haustorium layer from the chalazal zone to the embryo; (2) an endothelial layer surrounding the embryo sac almost complete; (3) a nucellar summit growing into the micropyle; and (4) a placental obturator and a funicle connecting the ovarian tissue to the ovule. Seed development was typically endospermic (exendospermic orthodox seeds). Anomalies included two egg cells in the same embryo sac, two embryos developing in the same ovule, and embryos developing from the chalazal pole region. Total seed number and seed viability were significantly lower in H. megalanthus than in the other two taxa. Embryos at different developmental stages were observed in aborted H. megalanthus seeds.     

Morphological and molecular studies of a microsporidium (Nosema sp.) isolated from the thee spot grass yellow butterfly, Eurema blanda arsakia (Lepidoptera: Pieridae)

A microsporidium possessing molecular and morphological characteristics of the genus Nosema was isolated from larvae of the thee-spot grass yellow butterfly, Eurema blanda arsakia. The complete rRNA gene sequences of the E. blanda isolate contained 4,428 base pairs (GenBank Accession No. EU338534). The organization of the rRNA genes is LSU rRNA-ITS-SSU rRNA-IGS-5S, which corresponds with that of Nosema species closely related to Nosema bombycis. Phylogenetic analysis based on rRNA gene sequences show that this isolate is closely related to Nosema bombycis, Nosema plutellae, Nosema spodopterae, and Nosema antheraeae. The ultrastructure of all developmental stages of this microsporidium confirmed its placement in the genus Nosema. The isolate was successfully propagated in cell lines IPLB-LD652Y (Lymantria dispar) and NTU-LY (Lymantria xylina) and, in the in vitro system, it was frequently found to develop in the nuclei of the host cells, a circumstance that seldom occurs in other Nosema species. An extra-cellular vegetative stage of this microsporidium was also observed in the culture medium after 14 days of infection. The ECMDFs might be released from disrupted host cells.