Antifeedant,larvicidal and growth inhibitory activities of fractions from Clerodendrum phlomidis Linn. F. against bhendi fruit borer Earias vittella Fab

Antifeedant, larvicidal and growth inhibitory activities of 12 fractions from chloroform extract of Clerodendrum phlomidis Linn. F. were evaluated against Earias vittella. Among the fractions, fraction 5 showed promising antifeedant activity of 86.94% at 1000 ppm followed by 500 ppm concentration with the least LC₅₀ and LC₉₀ values of 120.15 and 1027.92 ppm, respectively, with significant Chi-square values. Fraction 5 had maximum larvicidal activity of 86.38% at 1000 ppm concentration with the least LC₅₀ and LC₉₀ values of 245.42 and 1010.99 ppm, respectively, with significant Chi-square value of 51.33 (p ≤ 0.05). Fractions 5 and 6 reduced the adult emergence to 0% at 1000 ppm concentration. According to our knowledge, this is the first report of fractions from C. phlomidis for activity against E. vittella. The study clearly suggests that the fraction from C. phlomidis could be used to develop a new botanical formulation to manage economically important pests.     

Effects of the IGRs compounds,lufenuron and fenoxycarb on Leptinotarsa decemlineata (Say) (Col.: Chrysomelidae)

In this research work, the susceptibility of egg and four larval instars of Leptinotarsa decemlineata (Say) (Col.: Chrysomelidae) to Insect Growth Regulators (IGRs) compounds (lufenuron 25% EC and fenoxycarb 25% WP) was determined. Different larval instar groups were separated by measuring the head capsule width and were used in all bioassays. The data were analysed with log-probit transformation using the SPSS software. The LC₅₀ for egg was determined by dipping egg masses in different concentration of either compound for 10 s, and LC₅₀ values for each group of larvae was estimated by using treated potato plants. The LC₅₀ values of lufenuron on egg, first, second and third instars of larvae were 682.65, 40.58, 47.83 and 261.38 ppm, respectively, and for fenoxycarb, these were estimated as 897.50, 35.60, 57.91 and 355.23 ppm, respectively. The LD₅₀ values of lufenuron and fenoxycarb on second instar larvae were 139.56 and 228.42 ppm, respectively.     

Biological activity of Hyposidra talaca nucleopolyhedrovirus against all instar stages of a destructive tea pest Hyposidra talaca (Lepidoptera: Geometridae) in India

Hyposidra talaca (Walker) (Lepidoptera: Geometridae) is the most harmful pest of northeastern tea hub of India that devastates the tea production by feasting on the tea leaves. Hyposidra talaca nucleopolyhedrovirus (HytaNPV) is a natural enemy of the aforesaid pest, as it poses great obstruction in the multiplication of the pest by causing significant larval mortality. The study was undertaken to screen the virus activity against first to fifth instar H. talaca larvae. Early instar stages are found more susceptible than the late stages as they tend to reflect highest LC₅₀ value for fifth instar as 4.3 × 10⁷ POB/ml and lowest LC₅₀ value for first instar as 7 × 10⁴ POB/ml within seven days of inoculation. LT₅₀ values vary between 2.47 and 8.45 days for neonates to fifth instar. The high record of virulence of HytaNPV indicates its bright prospect as a useful microbial biopesticide.     

亚致死浓度氯虫苯甲酰胺可降低亚洲玉米螟的种群增长

为了探讨氯虫苯甲酰胺对亚洲玉米螟Ostrinia furnacalis (Guenée)的抗性风险评估, 为科学使用氯虫苯甲酰胺防治亚洲玉米螟提供理论基础, 本研究在实验室条件下采用饲料混毒法测定了新型杀虫剂氯虫苯甲酰胺对亚洲玉米螟的毒力, 利用生命表技术研究了氯虫苯甲酰胺对亚洲玉米螟 3龄幼虫的亚致死效应。结果表明： 氯虫苯甲酰胺对亚洲玉米螟3龄幼虫的LC₁₀, LC₄₀ 和LC₅₀分别为0.038, 0.098 和0.123 mg a. i. /L。以氯虫苯甲酰胺LC₁₀和LC₄₀剂量分别处理亚州玉米螟3龄幼虫后, 幼虫和蛹的发育历期明显延长, 成虫寿命缩短, 产卵量也显著降低, 但对蛹重（雌： P=0.337, 雄： P=0.121）、卵孵化率（P=0.087）和性比（P=0.379）无显著影响。处理种群的净增值率（R₀）、内禀增长率（r_m）和周限增长率（λ）显著低于对照种群（P<0.0001）。结果提示, 氯虫苯甲酰胺的亚致死浓度可降低亚洲玉米螟的种群增长。     

Insecticide susceptibility and resistance of Culex tritaeniorhynchus (Diptera: Culicidae) larvae collected from Gwangju,Republic of Korea

The susceptibility of Culex tritaeniorhynchus collected from Gwangju, Jeollabuk Province, Republic of Korea (ROK) to insecticides was evaluated under laboratory conditions using ten insecticides (7 pyrethroids and 3 organophosphates) that are currently applied by local public health centers in the ROK. Based on the values of median lethal concentration (LC₅₀), Cx. tritaeniorhynchus larvae were most susceptible to chlorpyrifos (0.006 ppm), fenitrothion (0.022 ppm), fenthion (0.035 ppm) and bifenthrin (0.038 ppm), and were least susceptible to esbiol (1.722 ppm). In comparative resistance tests, the resistance ratios (RRs) of seven insecticides were compared among each other using two strains of Cx. tritaeniorhynchus that were collected from the same locality during 1992 and 2010. Culex tritaeniorhynchus demonstrated significantly increased RRs to pyrethroids over time, while demonstrating decreased RRs among the organophosphates. Among the pyrethroids, permethrin had the highest RR values of 182.1‐ and 833.3‐fold differences, followed by etofenprox with RRs of 138.4‐ and 224.1‐fold differences in values of LC₅₀ and concentration that produced 90% mortality (LC₉₀), respectively. Culex tritaeniorhynchus strains demonstrated the least amount of change in susceptibility to the organophosphates, chlorpyrifos, fenitrothion and fenthion with 0.020‐, 0.019‐ and 0.001‐fold differences in resistance ratios (RRLC₅₀), respectively.     

Transformation of the naturally occurring frog skin peptide, alyteserin-2a into a potent, non-toxic anti-cancer agent

Alyteserin-2a (ILGKLLSTAAGLLSNL.NH₂) is a cationic, amphipathic α-helical cell-penetrating peptide, first isolated from skin secretions of the midwife toad Alytes obstetricans. Structure–activity relationships were investigated by synthesizing analogs of alyteserin-2a in which amino acids on the hydrophobic face of the helix were replaced by l-tryptophan and amino acids on the hydrophilic face were replaced by one or more l-lysine or d-lysine residues. The Trp-containing peptides display increased cytotoxic activity against non-small cell lung adenocarcinoma A549 cells (up to 11-fold), but hemolytic activity against human erythrocytes increases in parallel. The potency of the N15K analog against A549 cells (LC₅₀ = 13 μM) increases sixfold relative to alyteserin-2a and the therapeutic index (ratio of LC₅₀ for erythrocytes and tumor cells) increases twofold. Incorporation of a d-Lys¹¹ residue into the N15K analog generates a peptide that retains potency against A549 cells (LC₅₀ = 15 μM) but whose therapeutic index is 13-fold elevated relative to the native peptide. [G11k, N15K] alyteserin-2a is also active against human hepatocarcinoma HepG2 cells (LC₅₀ = 26 μM), breast adenocarcinoma MDA-MB-231 cells (LC₅₀ = 20 μM), and colorectal adenocarcinoma HT-29 cells (LC₅₀ = 28 μM). [G11k, N15K] alyteserin-2a, in concentrations as low as 1 μg/mL, significantly (P < 0.05) inhibits the release of the immune-suppressive cytokines IL-10 and TGF-β from unstimulated and concanavalin A-stimulated peripheral blood mononuclear cells. The data suggest a strategy of increasing the cationicity while reducing the helicity of naturally occurring amphipathic α-helical peptides to generate analogs with improved cytotoxicity against tumor cells but decreased activity against non-neoplastic cells.     

Neonicotinoid resistance and cDNA sequences of nicotinic acetylcholine receptor subunits of the western flower thrips Frankliniella occidentalis (Thysanoptera: Thripidae)

The western flower thrips, Frankliniella occidentalis (Pergande), is difficult to control because of high insecticide resistance. In this study, susceptibility to major insecticides was examined in two Japanese strains (H-1 and KC) and a Chinese strain (BJ) using a leaf-dipping method. All three strains were resistant to permethrin and acetamiprid at agriculturally recommended doses. The median lethal concentration (LC₅₀) for acetamiprid was 1720 ppm in strain H-1, 4780 ppm in strain KC and >6680 ppm in strain BJ. In the presence of piperonyl butoxide, an inhibitor of cytochrome P450 monooxygenases, the LC₅₀ for acetamiprid was 312 ppm in strain H-1, 837 ppm in strain KC and 1250 ppm in strain BJ. These results suggested that metabolism by cytochrome P450 monooxygenases is involved in acetamiprid resistance in these strains, though other factors also seem to play a role. Furthermore, cDNA cloning of the nicotinic acetylcholine receptor (nAChR) subunits was performed using degenerate primers, and the presence or absence of a point mutation in nAChR β1 was confirmed. The R81T mutation that had been reported in Myzus persicae (Sulzer) nAChR β1 was not found in F. occidentalis strains tested in this study.     

氯虫苯甲酰胺对白背飞虱实验种群的亚致死效应

为正确评估防治水稻鳞翅目害虫的新型杀虫剂氯虫苯甲酰胺对非靶标害虫白背飞虱Sogatella furcifera (Horváth)的影响, 本文采取稻茎浸渍法测定了氯虫苯甲酰胺对白背飞虱的毒力, 利用生命表技术研究了氯虫苯甲酰胺对白背飞虱的亚致死效应。结果表明： 氯虫苯甲酰胺对白背飞虱3龄若虫和成虫的LC₅₀分别为19.26 mg/L和19.69 mg/L。以氯虫苯甲酰胺LC₁₀和LC₂₅剂量分别处理白背飞虱3龄若虫后, F₀和F₁代雌虫产卵量及其寿命均降低, 尤其LC₂₅处理与对照间存在显著差异（P<0.05）, F₀和F₁代雌虫寿命分别缩短了1.80 d和2.62 d, F₀和F₁代雌虫产卵量分别减少了52.94粒和78.45粒。药剂处理对F1代各虫态发育历期也有一定影响。根据不同剂量处理后白背飞虱各发育阶段的存活率和成虫的繁殖力, 组建了生殖力生命表, 发现LC₁₀和LC₂₅剂量处理的种群内禀增长率rm分别降低了11.25%和34.41%, 净增殖率R0分别降低了36.56%和74.57%, 而世代平均历期T和种群加倍时间t均延长。结果说明, 氯虫苯甲酰胺LC₁₀和LC₂₅剂量可抑制白背飞虱种群的增长; 大田中使用氯虫苯甲酰胺防治鳞翅目害虫时, 可抑制同时发生的非靶标害虫白背飞虱田间种群增长。     

Resistance to cypermethrin in melon thrips, Thrips palmi (Thysanoptera: Thripidae), is conferred by reduced sensitivity of the sodium channel and CYP450-mediated detoxification

Melon thrips, Thrips palmi Karny, is among the most destructive pests of vegetables in western Japan because of its development of insecticide resistance. To examine its resistance mechanisms against cypermethrin, a pyrethroid, we determined partial nucleotide sequences of the sodium channel gene and compared the deduced amino acid sequences of two strains (the KC and OK strains) of T. palmi. The KC and OK strains showed LC₅₀ values of 3922.9 and 72.1?ppm, respectively. The LC₅₀ values were thus above the agriculturally recommended concentration (60?ppm). Both strains had a resistant amino acid, Ile, at amino acid position 929. The synergist piperonyl butoxide caused 14.1- and 3.0-fold decreases in the resistance ratios of the KC and OK strains, respectively. These results suggest that the basal and differential resistance levels of both strains are conferred by reduced sensitivity of the sodium channel and cytochrome P450-mediated detoxification, respectively.     

Toxic effects of pyriproxyfen,neemarin, acetamiprid and Ferula assafoetida essential oil on the common pistachio psylla,Agonoscena pistaciae

The common pistachio psylla, Agonoscena pistaciae, Burckhardt and Lauterer (Hemiptera: Psyllidae) is the key pest of pistachio orchards in Iran. Chemical control is the common method for the control of this pest. In this study, the effects of pyriproxyfen (an insect growth regulator), neemarin (a botanical insecticide), acetamiprid (a neonicotinoid) and Ferula assafoetida essential oil were investigated on the fifth instar nymphs of A. pistaciae. Probit analysis of concentration-mortality data was conducted to estimate the LC₅₀ values. The LC₅₀ values for neemarin, pyriproxyfen, acetamiprid and F. assafoetida essential oil were estimated to be 0.22, 0.52, 290 and 5.62 ppm, respectively. Our results showed that the fifth instar nymphs of A. pistaciae are very sensitive to neemarin and pyriproxyfen.     

Toxicity of parathion-methyl to cells, akinetes and heterocysts of the cyanobacterium Cylindrospermum, sp. and the probit analysis of toxicity

The toxicity of a commercial formulation of the insecticide parathion‐methyl to the N2‐fixing filamentous cyanobacterium (blue‐green alga) Cylindrospermum, sp. was studied. A concentration of parathion‐methyl of 0.5 ppm caused growth increase in liquid growth media. The minimum inhibitory concentration of parathion‐methyl for both types (N₂, fixing and nitrate supplemented) of liquid and solid media was 1.0 ppm. LC₅₀ values were: 4.4 ppm (liquid, N₂, fixing), 5.5 ppm (liquid, nitrate supplemented), 3.3 ppm (agar, N₂‐fixing) and 4.0 ppm (agar, nitrate supplemented). LC100 values for N₂‐fixing liquid and both types of agar media were 10.0 ppm, while for the liquid nitrate supplemented medium the LC₁₀₀ was 12.0 ppm. Both akinete (spore) formation and germination were inhibited below the highest permissive concentration of 8.0 ppm, with the insecticide incorporated in the agar media. In soil, the LC50 and LC100 values for parathion‐methyl were 13.6 and 30 ppm, respectively. Both the dehydrogenase activity of heterocysts (monitored by 2,3,5‐triphenyl tetrazolium chloride reduction) and the nitrogen concentration of cultures (estimated by the micro‐Kjeldahl method) were affected by the insecticide, but the latter (N₂‐fixation) was more sensitive. The Kruskal‐Wallis H test on the numbers of vegetative cells in the filaments revealed that the insecticide significantly affected the division of vegetative cells. The cyanobacterium could detoxify the growth medium containing high levels (30 and 40 ppm) of the insecticide in short‐term exposures at the expense of cell viability.     

Effects of soil-treatment with fungal biopesticides on pupation behaviors,emergence success and fitness of tea geometrid,Ectropis grisescens (Lepidoptera: Geometridae)

Ectropisgrisescens Warren (Lepidoptera: Geometridae) is one of the most severe defoliating pests of tea plants. Synthetic pesticides have been widely applied to control this pest in tea plantations, but pesticide residues may decrease the quality and safety of tea products. In the present study, we hypothesized that soil treatment with the two commercial biopesticides (Shuiguxin^®) based on Metarhizium anisopliae (Metchnikoff) Sorokin and Beauveria bassiana (Balsamo) could reduce the survivorship and fitness of E. grisescens. Wandering larvae of E. grisescens were allowed to pupate in soil treated with each biopesticide, and the concentrations of M. anisopliae (Shuiguxin^®) and B. bassiana (Shuiguxin^®) that produced the 50% mortality values (LC₅₀) were 2.9 × 10⁶ and 1.6 × 10⁷ conidia/g soil, respectively. Artificial burying the pupae using soil treated with M. anisopliae (Shuiguxin^®) and B. bassiana (Shuiguxin^®) (1 × 10⁸ or 1 × 10⁹ conidia/g soil for both biopesticides) also significantly reduced emergence success of E. grisescens. In addition, choice tests showed that soil treated with the high concentration of M. anisopliae (Shuiguxin^®) or B. bassiana (Shuiguxin^®) had repellent effects on pupating E. grisescens. However, sublethal concentrations (LC₂₅ and LC₅₀) of both biopesticides did not significantly affect fecundity, fertility and longevity of post-emerged adults. Our study showed that soil treatment with the two commercial biopesticides caused direct mortality of pupating E. grisescens, but may not effectively suppress E. grisescens populations at sublethal concentrations. The realistic application of the fungal dosage in fields should be determined in future studies     

Relationship between susceptibility to neonicotinoids and population dynamics of cotton aphid,Aphis gossypii Glover (Hemiptera: Aphididae)

Efficiency of imidacloprid and thiametoxam on population growth parameters of Aphis gossypii Glover (Hemiptera: Aphididae) was assessed using three bioassay methods including; residual, starvation and FAO dip methods. Aphids were assayed under laboratory conditions at 23 ± 2°C, photoperiod of 16:8 (L:D) and 70% relative humidity. Aphids were transferred to sprayed leaves and Petri dishes in residual and starvation methods, respectively. There was no feeding for the aphids in starvation method. In FAO dip method, insects were dipped for 5 s in pesticide solutions and then transferred to fresh leaves. Results revealed that LC₅₀ values calculated with the starvation and residual methods were respectively 15 and 11% more than FAO dip method (for imidacloprid) and 22 and 18% (for thiametoxam). The LC₅₀ value in starvation method was 3% more than the residual method. Calculated LC₅₀ in starvation and residual methods with imidacloprid respectively caused 160 and 34% increase in intrinsic rates of increase (r _m) and net reproductive rate (R ₀) in comparison with FAO dip method. Generation time (T) and doubling time (DT) were respectively 59 and 62% less than those in FAO dip method. In contrast, thiametoxam (LC₅₀ concentration) in starvation and residual method lead to 9 and 67% increase in r _m and R ₀ parameters compared to FAO dip method. However T and DT were respectively 65 and 92% less than mentioned parameters in FAO dip method. There was not any significant difference between life table parameters calculated by residual and starvation bioassay methods.     

Investigation of the contribution of RyR target-site mutations in diamide resistance by CRISPR/Cas9 genome modification in Drosophila

Diamide insecticides are used widely against lepidopteran pests, acting as potent activators of insect Ryanodine Receptors (RyRs) and thus inducing muscle contraction and eventually death. However, resistant phenotypes have recently evolved in the field, associated with the emergence of target site resistance mutations (G4946E/V and I4790M). We investigated the frequency of the mutations found in a resistant population of Tuta absoluta from Greece (G4946V ~79% and I4790M ~21%) and the associated diamide resistance profile: there are very high levels of resistance against chlorantraniliprole (9329-fold) and flubendiamide (4969-fold), but moderate levels against cyantraniliprole (191-fold). To further investigate functionally the contribution of each mutation in the resistant phenotype, we used CRISPR/Cas9 to generate genome modified Drosophila carrying alternative allele combinations, and performed toxicity bioassays against all three diamides. Genome modified flies bearing the G4946V mutation exhibited high resistance ratios to flubendiamide (91.3-fold) and chlorantraniliprole (194.7-fold) when compared to cyantraniliprole (5.4-fold). Flies naturally wildtype for the I4790M mutation were moderately resistant to flubendiamide (15.3-fold) but significantly less resistant to chlorantraniliprole (7.5-fold), and cyantraniliprole (2.3-fold). These findings provide in vivo functional genetic confirmation for the role and relative contribution of RyR mutations in diamide resistance and suggest that the mutations confer subtle differences on the relative binding affinities of the three diamides at an overlapping binding site on the RyR protein.     

Larvicidal Efficiency of Certain Seed Extracts Against Anopheles Stephensi,with Reference to Azadirachta indica

The toxicity of seed extracts of three Indian medicinal plants, Azadirachta indica, Momordica charantia and Ricinus communis, was evaluated for their larvicidal efficacy against Anopheles stephensi. The methanol extract of A. indica exhibited potent larvicidal activity with LC₅₀ 15.25 and 12.70 ppm and LC₉₀ 46.79 and 45.56 ppm after 24 and 48 hrs, respectively, followed by methanol extract of R. communis with LC₅₀ 54.95 and 23.06 ppm and LC₉₀ 251.03 and 144.54 ppm after 24 and 48 hrs of post treatment, respectively. In case of M. charantia, the carbon tetrachloride extract possess potential larvicidal efficacy with LC₅₀ values 87.00 and 57.53 ppm and LC₉₀ 301.20 and 262.21 ppm after 24 and 48 hrs of exposure period. The results indicate that A. indica methanol extract was most potential mosquito larvicide and can be use as alternate potential to synthetic insecticides.     

Efficacy of Beauveria bassiana (Blas.) Vuill. against cabbage aphid Brevicoryne brassicae L. (Hem.: Aphididae) in laboratory condition

In order to replace the conventional chemical pesticides, extensive researches have been done on entomopathogenic fungi. Entomopathogenic fungus Beauveria bassiana is an important biocontrol agent against major economic pests and is being employed in Integrated pest management (IPM) along with synthetic pesticides. Cabbage aphid Brevicoryne brassicae L. is one of the important pests of Brassicaceae family. Therefore, in this research, the virulence isolate of B. brassicae (IRAN 429C) was investigated on adults of cabbage aphid under laboratory conditions. The experiments were conducted at 25 ± 2 °C, 60 ± 10 R. H. and a photoperiod of 16:8 (L: D). After preliminary experiments, the adult aphids were treated with fungal concentrations of 1 × 10³ to 1 × 10⁷ spores/ml. Probit analysis was conducted to calculate LC₅₀ and LC₉₅ values for the isolate. Positive correlation was observed between concentrations and pest mortality. LC₅₀ and LC₉₅ values calculated for IRAN 429C isolate are 2.04 × 10⁵ and 1.82 × 10⁸, respectively. The mortality was counted one day after the treatment and then continued for 14 days. Cumulative mortality for 14 days after treatment varied from 54% for IRAN 429C at low concentration (10³ conidia/ml) to 83% at high concentration (10⁷ conidia/ml). The lowest LT₅₀ was obtained at 7.67 days for IRAN 429C isolate at concentration 1 × 10⁷ spore/ml. According to the insecticidal activity of mentioned fungi on cabbage aphid, it can be used in biocontrol programmes of B. brassicae.     

Evaluation of the toxicity of different phytoextracts of Ocimum basilicum against Anopheles stephensi and Culex quinquefasciatus

The larvicidal effect of the crude carbon tetrachloride, methanol and petroleum ether leaf extracts of a widely grown medicinal plant, Ocimum basilicum, against Anopheles stephensi and Culex quinquefasciatus was evaluated. Petroleum ether extract was found to be the most effective against the larvae of both mosquitoes, with LC₅₀ values of 8.29, 4.57; 87.68, 47.25 ppm and LC₉₀ values of 10.06, 6.06; 129.32, 65.58 ppm against A. stephensi and C. quinquefasciatus being observed after 24 and 48 h of treatment, respectively. The efficacy of petroleum ether was followed by that of the carbon tetrachloride and methanol extracts, which had LC₅₀ values of 268.61, 143.85; 446.61, 384.84 ppm and LC₉₀ values of 641.23, 507.80; 923.60, 887.00 ppm against A. stephensi after 24 and 48 h, respectively, and LC₅₀ values of 24.14, 17.02; 63.48, 53.77 ppm and LC₉₀ values of 295.38, 204.23; 689.71, 388.87 ppm against C. quinquefasciatus after 24 and 48 h of treatment, respectively. These extracts are highly toxic against mosquito larvae from a range of species; therefore, they may be useful for the management of mosquito larvae to control vector borne diseases.     

Laboratory assessment of acaricidal activity of Cymbopogon winterianus,Vitex negundo and Withania somnifera extracts against deltamethrin resistant Hyalomma anatolicum

Larval packet test was used for detection of resistance levels against cypermethrin and deltamethrin, the most commonly used synthetic pyrethroids, in the multi-host tick Hyalomma anatolicum collected from district Moga, Punjab (India). Results indicated the presence of level I resistance against deltamethrin (RF = 2.81), whereas the tick isolate was susceptible to cypermethrin (RF = 0.2). The aqueous and ethanolic extracts of leaves of Cymbopogon winterianus, Vitex negundo and Withania somnifera along with roots of Vitex negundo were assessed for their acaricidal activity against the larvae of deltamethrin resistant H. anatolicum. The efficacy was assessed by measuring per cent larval mortality and determination of LC₅₀ values. The various ethanolic extracts produced a concentration dependent increase in larval tick mortality, whereas the aqueous extracts exhibited a much lower mortality. The highest mortality (93.7 ± 0.66 %) was observed at the 5.0 % concentration of ethanolic extract of leaves of C. winterianus and the lowest LC₅₀ value (0.011 %) was recorded for ethanolic extracts of leaves of V. negundo. The results indicated that these plant extracts have potential to be developed as herbal acaricides.     

Toxic effects of juncusol,a marsh plant phenolic extract,on estuarine fish and shrimp

Juncusol, a phenolic compound, was isolated from the black needlerush, $\text{Juncus roemerianus}$. Different concentrations of this extract were tested for toxicity against selected species of estuarine fish and grass shrimp. Juncusol was ten times more toxic to the various species of fish than to grass shrimp. At 2.0 ppm concentration all fishes tested were killed within 36 hr. One hundred per cent mortality in the grass shrinmp occured at 20 ppm during 95 hr exposure. The LC₁₀, LC₅₀, and LC₉₀ concentration for juncusol were calculated for grass shrimp and for juvenile sailfin molly.     

Chemical composition and larvicidal activity of Piper capense essential oil against the malaria vector,Anopheles gambiae

Hydro-distilled essential oil from Kenyan Piper capense (Piperaceae) was analysed by gas chromatography mass spectrometry (GC–MS) and evaluated for larvicidal activity against the malaria vector, Anopheles gambiae. The oil consisted mainly of sesquiterpene hydrocarbons which accounted for 43.9% of the oil. The major sesquiterpenes were δ-cadinene (16.82%), β-bisabolene (5.65%), and bicyclogermacrene (3.30%). The oil also had appreciable amounts of monoterpene hydrocarbons (30.64%), including β-pinene (7.24%) and α-phellandrene (4.76%), and arylpropanoids (8.64%), including myristicin (4.26%). The oil showed larvicidal activity against third instar larvae of A. gambiae, with LC₅₀ and LC₉₀ values of 34.9 and 85.0 ppm, respectively. Most of the larvae died within the first few hours. The high larvicidal activity of this oil was indicated by the fact that over 80% mortality was observed at a concentration of 100 ppm after 24 h. These results compared favourably with the commercial larvicide pylarvex® which had LC₅₀ and LC₉₀ values of 3.7 and 7.8 ppm, respectively. Application of this oil or of products derived from it to larval habitats may lead to promising results in malaria and mosquito management programmes.