The Effect of Chemical Composition and Bioactivity of Several Essential Oils on Tenebrio molitor (Coleoptera: Tenebrionidae)

The major chemical components of four essential oils (EOs) extracted from dry leaves of Citrus limonum, Cymbopogon citratus, Litsea cubeba, and Muristica fragrans were analyzed with gas chromatograph-mass spectrometer and their fumigant, contact, and repellent activities against 10th instar and adults of Tenebrio molitor were also assayed. The results indicated that the major constituents of C. limonum and Cy. citrates were D-limonene (38.22%) and 3,7-dimethyl-6-octenal (26.21%), while which of L. cubeba and M. fragrans were (E)-3, 7-dimethyl-2, 6-octadienal (49.78%) and (E)-cinnamaldehyde (79.31%), respectively. Contact activities of L. cubeba and C. limonum with LC₅₀ values of 21.2 and 13.9 µg/cm² at 48 h and repellence activities (>89.0% repellence indexes) (P < 0.05) at 12 h on 10th instar were better than those of the other two EOs. Nevertheless, the fumigation activities of L. cubeba on 10th instar and adults (LC₅₀ = 2.7, 3.7 μl/liter) were stronger than those of C. limonum (LC₅₀ = 10.9, 12.0 μl/liter) at 96 h and significant (not overlapping confidence intervals). The EOs of L. cubeba and C. limonum have clearly elongated the growth and development of larvae, egg, and slightly shorten pupae and adults of T. molitor compared with the control. The mainly active ingredients of L. cubeba and C. limonum, including D-limonene and β-pinene, were demonstrated to coinhibit the actives of AChE and enhance the toxicities on 10th instar of T. molitor. These results indicate that the EOs of L. cubeba and C. limonum could have great potential as botanical insecticides against T. molitor.     

Identification of Nanopillars on the Cuticle of the Aquatic Larvae of the Drone Fly (Diptera: Syrphidae)

Here, we describe a nano-scale surface structure on the rat-tailed maggot, the aquatic larva of the Drone fly Eristalis tenax (L.). Larvae of this syrphid hover fly live in stagnant, anaerobic water-courses that are rich in organic matter. The larvae burrow into fetid slurry and feed on microorganisms which they filter out from the organic material. This environment is rich in bacteria, fungi and algae with the capacity to form biofilms that might develop on the larval surface and harm them. Using transmission and scanning electron microscopy we have identified an array of slender (typically < 100 nm in diameter) nanopillars that cover the surface of the larvae. The high density and dimensions of these spine-like projections appear to make it difficult for bacteria to colonize the surface of the animal. This may interfere with the formation of biofilms and potentially act as a defence against bacterial infection.     

Insecticidal Activity and Insect Repellency of Four Species of Sea Lily (Comatulida: Comatulidae) From Taiwan

The methanol and ethyl acetate (EA) extracts of four species of sea lily (Himerometra magnipinna, Comaster multifidus, Comanthina sp., and Comatella maculata) were evaluated for their insecticidal activity against Yellow-fever mosquito larvae (Aedes aegypti) and their repellency against adult Asian Tiger mosquitoes (Aedes albopictus). The 24-hr minimum inhibition concentration (MIC) data revealed that the extracts from H. magnipinna and the C. maculata were the most active, killing mosquito larvae at 12.5 ppm. The toxicity of the extracts from these four sea lilies in descending order was H. magnipinna (12.5 ppm), C. maculata (12.5 ppm), C. multifidus (100 ppm), and Comanthina sp. (200 ppm). Furthermore, no significant difference in toxicity was found using either EA or methanol as the extraction solvent. The MIC at 12.5 ppm is promising as an insecticide lead. The repellency study results show that EA is a better solvent for one species (H. magnipinna), but the methanol is a better solvent overall. The repellency of these sea lily extracts in descending order was Comanthina sp. MeOH (ED₅₀ at 0.32%), followed by H. magnipinna EA (ED₅₀ at 0.38%), C. multifidus MeOH (ED₅₀ at 0.57%), C. maculata MeOH (ED₅₀ at 0.76%), C. multifidus EA (ED₅₀ at 1.25%), and H. magnipinna MeOH (ED₅₀ at 1.67%). A compound with ED₅₀ <0.5% is considered to be a promising repellant. Among the studied sea lilies, both Comanthina sp. and H. magnipinna have potential to be further developed as mosquito control agents due to their favorable toxicity and repellency.     

The Toxicity and Detoxifying Mechanism of Cycloxaprid and Buprofezin in Controlling Sogatella furcifera (Homoptera: Delphacidae)

The effects of cycloxaprid (a modified neonicotinoid insecticide) and buprofezin (a thiadiazine insecticide) on mortality of the white-backed planthopper (WBPH), Sogatella furcifera, were determined in laboratory assays. Cycloxaprid killed WBPH nymphs and adults but buprofezin killed only nymphs, and cycloxaprid acted faster than buprofezin. One day after infestation, mortality of third-instar nymphs was >65% with cycloxaprid at 125 mg liter⁻¹ but was <38% with buprofezin at 148 mg liter⁻¹. By the 4th day after infestation, however, control of nymphs by the two insecticides was similar, and cycloxaprid at 125 mg liter⁻¹ caused ≥80% mortality of adults but buprofezin at 148 mg liter⁻¹ (the highest rate tested) caused almost no adult mortality. LC₅₀ values for cycloxaprid were lowest with nymphs, intermediate with adult males, and highest with adult females. Although buprofezin was slower acting than cycloxaprid, its LC₅₀ for nymphs 5 d after infestation was 3.79-fold lower than that of cycloxaprid. Mean carboxylesterase (CarE) specific activity of nymphal WBPH treated with cycloxaprid and buprofezin was higher than that of control, but there was no significant difference between cycloxaprid and control (no insecticide), and it was significantly higher for buprofezin than those of cycloxaprid and control. For glutathione S-transferase and mixed function oxygenase, the specific activity of nymphal WBPH treated with buprofezin was significantly higher than those of cycloxaprid and control, too.     

Developmental Biology of Zeugodacus cucurbitae (Diptera: Tephritidae) in Three Cucurbitaceous Hosts at Different Temperature Regimes

Fruit flies are key pests of cucurbits in many parts of the world, including Tanzania. Developmental biology of Zeugodacus cucurbitae (Coquillett) has been determined across temperature regimes in some cucurbitaceous hosts, in limited geographies. This study was conducted to determine duration and survival rates of immature stages of Z. cucurbitae in three cucurbitaceous hosts, at different temperature regimes. It was hypothesized that temperature and cucurbitaceous hosts influence duration and survival of immature stages of Z. cucurbitae. We conducted experiments in the environmental chamber set at 75 ± 10% RH and a photoperiod of 12:12 (L:D) h, at temperatures of 20, 25, and 30°. Our results showed that duration and survival of immature stages of Z. cucurbitae differed significantly among the temperature regimes but not among the hosts. Egg incubation period as well as larval and pupal stages were significantly longer (P < 0.0001) at low temperature in all three hosts Likewise, survival rate of all immature stages were significantly higher (P < 0.0001) at higher than lower temperatures. The three hosts, cucumber (Cucumis sativus), watermelon (Citrullus lanatus (Thunb.) Matsum. and Nakai), and pumpkin (Cucurbita pepo) did not significantly affect duration or survival rates of immature stages of Z. cucurbitae. The low developmental thresholds were estimated at 15.88, 13.44, and 12.62 for egg, larva and pupa, respectively. These results further confirm that Z. cucurbitae is well adapted to warm climate, which dominates many areas of Tanzania.     

Isolation,Characterization, Kinetics,and Enzymatic and Nonenzymatic Microbicidal Activities of a Novel c-Type Lysozyme from Plasma of Schistocerca gregaria (Orthoptera: Acrididae)

A protein, designated as Sgl, showing a muramidase lytic activity to the cell wall of the Gram-positive bacterium Micrococcus lysodeikticus was isolated for the first time from plasma of Escherichia coli-immunized fifth instar Schistocerca gregaria. The isolated Sgl was detected as a single protein band, on both native- and SDS-PAGE, has a molecular weight of ∼15.7 kDa and an isoelectric point (pI) of ca 9.3 and its antiserum has specifically recognized its isolated form. Fifty-nine percentage of Sgl lytic activity was recovered in the isolated fractions and yielded ca 126-fold increase in specific activity than that of the crude. The partial N-terminal amino acid sequence of the Sgl has 55 and 40% maximum identity with Bombyx mori and Gallus gallus c-type lysozymes, respectively. The antibacterial activity against the Gram-positive and the Gram-negative bacteria were comparatively stronger than that of the hen egg white lysozyme (HEWL). The detected Sgl poration to the inner membrane that reach a maximum ability after 3 h was suggested to operate as a nonenzymatic mechanism for Gram-negative bacterial cell lysis, as tested in a permease-deficient E. coli, ML-35 strain. Sgl showed a maximal muramidase activity at pH 6.2, 30–50°C, and 0.05 M Ca²⁺ or Mg²⁺; and has a K_m of 0.5 μg/ml and a V_max of 0.518 with M. lysodeikticus as a substrate. The Sgl displayed a chitinase activity against chitin with a K_m of 0.93 mg/ml and a V_max of 1.63.     

Investigation into the Effect of Altitude on the Differential Hemocyte Count of Circulating Plasmatocytes and Granulocytes of Larval Stage of Antheraea assama (Lepidoptera: Saturniidae)

Differential hemocyte count of circulating plasmatocytes (PL) and granulocytes (GR) of fifth-instar larvae of Muga Silkworm Antheraea assama Westwood (Lepidoptera: Saturniidae) reared at four different sericulture farms situated at different altitudes, viz, Khanapara State Sericulture Farm, Assam, altitude 55.5 m above sea level (ASL); Nongpoh (Central Silk Board farm), Meghalaya, altitude 464 m ASL; Tura (Central Silk Board farm), West Garo Hills, Meghalaya, 657 m ASL; and Kalimpong (Central Silk Board farm), West Bengal, altitude 1,247 m ASL, were calculated and compared to investigate the effect of altitude on the number of PL and GR per mm³ of larval hemolymph. The investigation showed that the mean circulating PL and GR were highest at Khanapara (55.5 m ASL) located at the lowest altitude, whereas their numbers gradually decreased with increase in altitude at Nongpoh (464 m ASL), Tura (657 m ASL), and Kalimpong (1,247 m ASL). This may be attributed to the average environmental temperatures observed at different altitudes, which may affect the overall hemocyte load of larval stages reared at those altitudes.     

Identification and Characterization of Bacillus cereus SW7-1 in Bombyx mori (Lepidoptera: Bombycidae)

The bacterial diseases of silkworms cause significant reductions in sericulture and result in huge economic loss. This study aimed to identify and characterize a pathogen from diseased silkworm. SW7-1, a pathogenic bacterial strain, was isolated from the diseased silkworm. The strain was identified on the basis of its bacteriological properties and 16S rRNA gene sequence. The colony was round, slightly convex, opaque, dry, and milky on a nutrient agar medium, the colony also exhibited jagged edges. SW7-1 was Gram-positive, without parasporal crystal, and 0.8–1.2 by 2.6–3.4 µm in length, resembling long rods with rounded ends. The strain was positive to most of the physiological biochemical tests used in this study. The strain could utilize glucose, sucrose, and maltose. The results of its 16S rRNA gene sequence analysis revealed that SW7-1 shared the highest sequence identity (>99%) with Bacillus cereus strain 14. The bacterial strain was highly susceptible to gentamycin, streptomycin, erythromycin, norfloxacin, and ofloxacin and moderately susceptible to tetracycline and rifampicin. It exhibited resistance to other antibiotics. SW7-1 had hemolytic activity and could produce extracellular casease, lipase, and amylase. SW7-1 could reproduce septicemia-like symptoms with high mortality rate when re-fed to healthy silkworm. .The median lethal concentration (LC₅₀) was 5.45 × 10⁴ cfu/ml. Thus, SW7-1 was identified as B. cereus, which is a pathogen for silkworm and human infections are possible.     

Biology and Trapping of Stable Flies (Diptera: Muscidae) Developing in Pineapple Residues (Ananas comosus) in Costa Rica

Pineapple production in Costa Rica increased nearly 300-fold during the last 30 yr, and >40,000 hectares of land are currently dedicated to this crop. At the end of the pineapple cropping cycle, plants are chopped and residues incorporated into the soil in preparation for replanting. Associated with increased pineapple production has been a large increase in stable fly, Stomoxys calcitrans (L.), populations. Stable flies are attracted to, and oviposit in, the decomposing, chopped pineapple residues. In conjunction with chemical control of developing larvae, adult trapping is an important control strategy. In this study, four blue-black fabric traps, Nzi, Vavoua, Model H, and Ngu, were compared with a white sticky trap currently used for stable fly control in Costa Rica. Overall, the white sticky trap caught the highest number of stable flies, followed by the Nzi, Vavoua, Model H, and Ngu. Collections on the white sticky trap increased 16 d after residues were chopped; coinciding with the expected emergence of flies developing in the pineapple residues. During this same time period, collections in the blue-black fabric traps decreased. Sex ratio decreased from >7:1 (females:males) 3–7 d after chopping to 1:1 at 24–28 d. White sticky, Nzi and Vavoua traps collected similar numbers of colonizing flies 3–7 d after residues were chopped. However, white sticky traps collected more flies once emergence from the pineapple residues began. Although white sticky traps collected more flies than fabric traps, they remain labor intensive and environmentally unsound because of their disposable and nonbiodegradable nature.     

Histopathological Changes in Third-Instar and Adult Anastrepha ludens (Diptera: Tephritidae) After in vitro Heat Treatment

The Mexican fruit fly, Anastrepha ludens Loew (Diptera: Tephritidae), is one of the most harmful pests of mango causing direct damage by oviposition on the fruit pulp. Mango for export is subjected to hydrothermal treatment as a quarantine method for the control of this pest, but exposure to heat for long periods of time reduces considerably the quality and shelf-life of treated fruit. The aim of this work was to study morphological changes of third-instar larvae and adults of A. ludens after in vitro exposure to high temperature at sublethal times. A heating block system was used to expose larvae at 46.1°C for 19.6 and 12.9 min, producing 94.6 and 70% mortality, respectively. Treated larvae were processed for optical microscopy. A fraction of surviving treated larvae was separated into containers with artificial diet to allow development into adults. Adult sexual organs were dissected and processed for transmission electron microscopy analysis. Results showed that 94.6% of the treated larvae died at 46.1°C for 19.6 min and none of the surviving larvae eclosed to adulthood, as they developed as malformed puparia. For the in vitro treatment at 46.1°C during 12.9 min, 70% of the treated larvae died and only 3.75% reached the adult stage, but ultrastructural damage in the male testes and in the female ovaries was observed. Additionally, 11.1% of the adult flies from the in vitro treatment also showed wing malformation and were incapable of flying. The analysis showed that surviving flies were unable to reproduce.     

The Complete Mitochondrial Genome of Brachmia macroscopa (Lepidoptera: Gelechiidae) and Its Related Phylogenetic Analysis

The sweet potato leaf folder, Brachmia macroscopa, is an important pest in China. The complete mitogenome, which consists of 13 protein-coding genes (PCGs), 22 transfer RNA genes, two ribosomal RNA genes, and an A + T-rich region, was sequenced and found to be 15,394 bp in length (GeneBank no. KT354968). The gene order and orientation of the B. macroscopa mitogenome were similar to those of other sequenced lepidopteran species. All of the PCGs started with ATN as the canonical start codon except for cox1, which started with CGA. In regard to stop codons, most PCGs stopped at TAA except for cox2, which stopped at TA, and nad4, which stopped at a single T. Thirteen PCGs of the available species (33 taxa) were used to demonstrate phylogenetic relationships. The ditrysian cluster was supported as a monophyletic clade at high levels by using maximum likelihood and Bayesian methods. The apoditrysian group, covering the Gelechioidea, formed a monophyletic clade with a bootstrap value of 88% and a posterior probability of 1.00. The superfamily Gelechioidea was supported as a monophyletic lineage by a posterior probability of 1.00.     

Potential of two entomopathogenic fungi,Beauveria bassiana and Metarhizium anisopliae (Coleoptera: Scarabaeidae), as biological control agents against the June beetle

The aim of this study was to evaluate the effectiveness of the entomopathogenic fungi (EPF), Beauveria bassiana (Bals.) Vuill. (Deuteromycotina: Hyphomycetes) strain PPRI 5339 [BroadBand, an emulsifiable spore concentrate (EC) formulation] and Metarhizium anisopliae (Metsch.) Sorokin (Hypocreales: Clavicipitaceae) strain F52 [Met52, both EC and granular (GR) formulations] against the larvae of Polyphylla fullo (L.) (Coleoptera: Scarabaeidae). Larvicidal bioassays were performed in foam boxes (100 by 75 by 50 cm; length by width by height), containing moist soil medium with some humus and potato tubers as food. Although the B. bassiana product (min. 4 × 10⁹ conidia/ml) was applied at 100, 150, and 200 ml/100 l water; M. anisopliae strain F52 was applied at 500, 1,000, and 1,500 g/m³ of moist soil medium for GR (9 × 10⁸ cfu/g) and 75, 100, and 125 ml/100 l water for EC (5.5 × 10⁹ conidia/ml) formulation. Both fungi were pathogenic to larvae of the pest; however, young larvae (1st and 2nd instars) were more susceptible to infection than older ones (3rd instar). Mortality rates of young and older larvae varied with conidial concentration of both fungi and elapsed time after application. The B. bassiana product was more effective than both of the formulations of the M. anisopliae product, causing mortalities up to 79.8 and 71.6% in young and older larvae, respectively. The highest mortality rates of young and older larvae caused by the M. anisopliae product were 74.1 and 67.6% for the GR formulation, 70.2 and 61.8% for the EC formulation, respectively. These results may suggest that both fungi have potential to be used for management of P. fullo.     

Geographic Variation of Diapause and Sensitive Stages of Photoperiodic Response in Laodelphax striatellus Fallén (Hemiptera: Delphacidae)

Large numbers of the small brown planthopper Laodelphax striatellus (Fallén) (Hemiptera: Delphacidae) occur in temperate regions, causing severe losses in rice, wheat, and other economically important crops. The planthoppers enter diapause in the third- or fourth-instar nymph stage, induced by short photoperiods and low temperatures. To investigate the geographic variation in L. striatellus diapause, we compared the incidence of nymphal diapause under various constant temperature (20 and 27°C) and a photoperiod of 4:20, 8:16, 10:14, 12:12, 14:10, and 16:8 (L:D) h regimes among three populations collected from Hanoi (21.02° N, 105.85° E, northern Vietnam), Jiangyan (32.51° N, 120.15° E, eastern China), and Changchun (43.89° N, 125.32° E, north-eastern China). Our results indicated that there were significant geographic variations in the diapause of L. striatellus. When the original latitude of the populations increased, higher diapause incidence and longer critical photoperiod (CP) were exhibited. The CPs of the Jiangyan and Changchun populations were ∼12 hr 30 min and 13 hr at 20°C, and 11 hr and 11 hr 20 min at 27°C, respectively. The second- and third-instar nymphs were at the stage most sensitive to the photoperiod. However, when the fourth- and fifth-instar nymphs were transferred to a long photoperiod, the diapause-inducing effect of the short photoperiod on young instars was almost reversed. The considerable geographic variations in the nymphal diapause of L. striatellus reflect their adaptation in response to a variable environment and provide insights to develop effective pest management strategies.     

Population Dynamics of Empoasca fabae (Hemiptera: Cicadellidae) in Central Iowa Alfalfa Fields

Adults and nymphs of Empoasca fabae Harris (Hemiptera: Cicadellidae) and adults of predatory species in the families Coccinellidae, Anthocoridae, Nabidae, Chrysopidae, and Hemerobiidae were sampled in Iowa alfalfa fields from June to September in 1999 and 2000. The relationship between each predatory taxa and E. fabae was examined using regression analysis. In 2000, all predators were found to be positively correlated with the presence of E. fabae during all periods sampled and most likely contributed to mortality. Orius insidiosus (Say) (Hemiptera: Anthoridae) was the most numerous insect predatory species; population numbers ranged from 0 to 1 and 0.1 to 3.7 adults per 0.25 m² in 1999 and 2000, respectively. Partial life tables were constructed for E. fabae nymphs for two alfalfa-growing periods. Nymphs were grouped into three age intervals: first and second, third and fourth, and fifth instars. For the first alfalfa growing period examined, E. fabae nymphal mortality was 70% in 1999 and 49% in 2000. During the last growing period of each season (August–September), total nymphal mortality was relatively low (<25%). Adult E. fabae density ranged from 5.4 to 25.6 and 1.4–9.2 per 0.25 m² in 1999 and 2000, respectively. E. fabae population peaks were similar for each age interval in all growing periods. This study provides further information on the population dynamics of E. fabae and its relationship with select predatory species in Iowa alfalfa fields.     

The Distribution of Dragonfly Larvae in a South Carolina Stream: Relationships With Sediment Type,Body Size,and the Presence of Other Larvae

Dragonfly larvae were sampled in Little Creek, Greenville, SC. The distributions of five common species were described relative to sediment type, body size, and the presence of other larvae. In total, 337 quadrats (1 m by 0.5 m) were sampled by kick seine. For each quadrat, the substrate was classified as sand, sand-cobble mix, cobble, coarse, or rock, and water depth and distance from bank were measured. Larvae were identified to species, and the lengths of the body, head, and metafemur were measured. Species were distributed differently across sediment types: sanddragons, Progomphus obscurus (Rambur) (Odonata: Gomphidae), were common in sand; twin-spotted spiketails, Cordulegaster maculata Selys (Odonata: Cordulegastridae), preferred a sand-cobble mix; Maine snaketails, Ophiogomphus mainensis Packard (Odonata: Gomphidae), preferred cobble and coarse sediments; fawn darners, Boyeria vinosa (Say) (Odonata: Aeshnidae), preferred coarse sediments; and Eastern least clubtails, Stylogomphus albistylus (Hagen) (Odonata: Gomphidae), preferred coarse and rock sediments. P. obscurus and C. maculata co-occurred more frequently than expected by chance, as did O. mainensis, B. vinosa, and S. albistylus. Mean size varied among species, and species preferences contributed to differences in mean size across sediment types. There were significant negative associations among larval size classes: small larvae (<12 mm) occurred less frequently with large larvae (>15 mm) than expected by chance, and large larvae were alone in quadrats more frequently than other size classes. Species may select habitats at a large scale based on sediment type and their functional morphology, but small scale distributions are consistent with competitive displacement or intraguild predation.