Effects of four host plants on susceptibility of Spodoptera litura (Lepidoptera: Noctuidae) larvae to five insecticides and activities of detoxification esterases

BACKGROUND: The tobacco cutworm, Spodoptera litura (F.), is one of the most destructive polyphagous pests worldwide. The susceptibility of S. litura larvae reared on tobacco, Chinese cabbage, cowpea and sweet potato to phoxim, chlorfenapyr, methomyl, fenvalerate and emamectin benzoate under laboratory conditions was determined. RESULTS: Spodoptera litura larvae reared on tobacco were most tolerant to all insecticides, whereas those that fed on sweet potato were most susceptible. When larvae were reared on each host plant for three generations, the susceptibilities to phoxim of larvae that fed on Chinese cabbage and cowpea were similar, whereas the susceptibility of larvae that fed on sweet potato decreased by the third generation, and on tobacco the susceptibility decreased in each consecutive generation. When nicotine was added to their diet for three consecutive generations, the tolerance of larvae to phoxim increased twofold, and to emamectin benzoate 3.1‐fold, but the tolerance of larvae to fenvalerate and chlorfenapyr did not change. The acetylcholinesterase activities of the larvae that fed on sweet potato and cowpea were greater than the activities of those that fed on Chinese cabbage and tobacco. In contrast, the carboxylesterase activities of the larvae that fed on tobacco and Chinese cabbage were greater than the activities of those that fed on sweet potato and cowpea. The glutathione S‐transferase activities of larvae were highest when they fed on tobacco, followed by Chinese cabbage and cowpea, and the lowest activities were observed when larvae fed on sweet potato. CONCLUSION: Feeding on tobacco or with nicotine added to the diet, the larvae became more tolerant to insecticides, especially to phoxim and emamectin benzoate. Copyright © 2010 Society of Chemical Industry     

The effects of azadirachtin and nucleopolyhedrovirus on midgut enzymatic profile of Spodoptera litura Fab. (Lepidoptera: Noctuidae)

The effects of azadirachtin (AZA) and nucleopolyhedrovirus (NPV) on midgut enzyme activity in Spodoptera litura Fabricius (Lepidoptera: Noctuidae) (Tobacco cutworm) were evaluated. Gut enzyme activities were decreased by AZA and NPV individually and in combination. When S. litura larvae were fed a diet of castor leaves treated with AZA and NPV in bioassays, gut enzyme—acid phosphatases, alkaline phosphatases, adenosine triphosphatases, and lactate dehydrogenase—activities were decreased. There were statistically significant differences (P ? 0.05) in enzyme activities between combined and individual treatment. A synergistic effect of botanical insecticides and virus was found when combined in low doses. These effects are most pronounced in early instars. Maximum weight loss (59-72%) occurred, when AZA and NPV were combined.     

Antifeedant activity of a novel 6-(4,7-hydroxy-heptyl) quinone? from the leaves of the milkweed Pergularia daemia on the cotton bollworm Helicoverpa armigera (Hub.) and the tobacco armyworm Spodoptera litura (Fab.)

The effects of crude extracts and an isolated compound from the leaves of milkweed, Pergularia daemia (Forssk) Choiv., on the antifeedant activity against two important lepidopteran pests, Helicoverpa armigera (Hub.) and Spodoptera litura (F.), were studied. Maximum antifeedant activity was recorded in ethyl acetate crude extract against H. armigera (70.3%) and S. litura (71.82%) at 1% concentration. Ethyl acetate crude extract was further subjected to column chromatography, which was performed using hexane as initial solvent and then by increasing the polar strength using ethyl acetate. Fractions collected at hexane and ethyl acetate (80:20) yielded 6-(4,7-hydroxy-heptyl) quinone, a novel compound which showed significant antifeedant activity against H. armigera (80.22% at 2000 ppm) and S. litura (68.31% at 2000 ppm).     

Influence of three diets on susceptibility of selected insecticides and activities of detoxification esterases of Helicoverpa assulta (Lepidoptera: Noctuidae)

The oriental tobacco worm, Helicoverpa assulta Guenée, is one of the most destructive pests of tobacco and peppers in China. We determined the susceptibility of H. assulta reared on an artificial diet, chili pepper and tobacco to four insecticides (fenvalerate, phoxim, methomyl, indoxacarb) under laboratory conditions associated with the activities of acetylcholinesterase (AChE), carboxylesterase (CarE) and glutathione S-transferase (GST) in its larvae. H. assulta larvae that were fed with chili pepper were more susceptible to fenvalerate, indoxacarb, and phoxim than those that were fed with tobacco and the artificial diet, but not to methomyl. The larvae that were fed with chili pepper were 3.65-, 2.49-, 1.92- and 2.44-fold more susceptible to fenvalerate, phoxim, methomyl, and indoxacarb than those fed with tobacco, respectively. The AChE activities of H. assulta larvae that were fed with chili pepper and tobacco were 2.12 and 1.07 μmol mg⁻¹ 15 min⁻¹, respectively, almost 2-fold difference. The CarE activity of H. assulta larvae that were fed with chili pepper, tobacco and the artificial diet was 4.12, 7.40 and 7.12 μmol mg⁻¹ 30 min⁻¹, respectively. Similarly, the GST activities of H. assulta larvae that were fed with chili pepper, tobacco and the artificial diet was 52.02, 79.37 and 80.02 μmol mg⁻¹ min⁻¹, respectively. H. assulta larvae that were fed with chili pepper were more resistance to the tested insecticides. The low activities of AChE and the high activities of CarE and GST lead to H. assulta become more susceptible to the tested insecticides.     

Effect of dihydrodillapiole on pyrethroid resistance associated esterase inhibition in an Indian population of Spodoptera litura (Fabricius)

Resistance in Spodoptera litura (Fabricius) has been attributed to enhanced detoxification of insecticides by increased levels of esterases, oxidases and/or glutathione S-transferases. Enzyme inhibiting insecticide synergists can be employed to counter increased levels of such enzymes in S. litura. Dihydrodillapiole induced synergism of pyrethroid toxicity was examined in the laboratory-reared third instar larval population of S. litura collected in Delhi (susceptible), and Guntur (resistant) region of Andhra Pradesh, India. The Guntur population was found to be 7.04 and 10.19 times resistant to cypermethrin and lambdacyhalothrin, respectively. The activity of cypermethrin, lambdacyhalothrin and profenophos against susceptible and resistance populations of S. litura, was gradually increased when used along with a plant-derived insecticide synergist dihydrodillapiole. The α-naphthyl acetate hydrolysable esterase activity in Delhi population was less as compared to the Guntur population. Resistance associated esterases in Delhi population were inhibited by pre-treatment with dihydrodillapiole. The esterase level in insect was instantly reduced initially, sustained for about 3 h and equilibrated at 4 h post treatment. The esterase activity of Guntur population was increased to 1.28 μmoles/mg/min at 2 h post treatment and subsequently reduced to lower than 0.70 μmoles at 4-12 h post treatment. The variation in esterase activity is suggestive of its homeostatic regulation in test populations. Dihydrodillapiole thus caused significant reduction of resistance in S. litura to cypermethrin, lambda cyhalothrin and profenophos.     

Biochemical,physiological and morfological responses in common carp (Cyprinus carpio L.) after long-term exposure to terbutryn in real environmental concentration

The effects of terbutryn at concentrations of 0.02 (reported concentration in Czech rivers), 0.2, and 2.0 μg l^?1 were assessed in one-year-old common carp (Cyprinus carpio L.) exposed for 90 days. Influence on biometric parameters, hematology, biochemistry, histology, and oxidative stress was investigated. Exposure to 0.02, 0.2 and 2.0 μg l^?1 showed significant differences oxidative stress biomarkers compared to controls but exposure to 0.2 and 2.0 μg l^?1 significantly affected biochemical and hematological profiles. Long-term exposure of terbutryn in carp resulted in slight alterations in internal organs and increased reactive oxygen species formation, resulting in oxidative damage to lipids and proteins and inhibition of antioxidant capacities.     

Carboxylamidases inSpodoptera exigua: properties and distribution in the larval body

Resistance to many insecticides demonstrated by the beet armyworm,Spodoptera exigua (Hübner), can be caused by the action of carboxylamidases. A colorimetric method, based on the hydrolysis of 4-nitroacetanilide to 4-nitroaniline by carboxylamidases, was used for evaluating biochemical properties of these detoxifying enzymes in beet armyworm. The optimum pH and temperature were 7.5 and 38°C, respectively. K_m (Michaelis constant) and V_max (maximal velocity) at 28°C were 2.3 X 10^-4 M and 2.06 nmol min^-1 mg protein^-1, respectively. The enzyme activity was evaluated in several body parts and located mostly (66.2%) in the midgut. The soluble fraction (supernatant of 105,000g) contained the highest enzyme activity relative to the total (69.3%), and exhibited the highest specific activity. Carboxylamidase activity was totally inhibitedin vitro at a concentration of 10^-6 M methomyl. The analysis of thein vitro inhibition kinetics indicated the ability of methomyl and diflubenzuron to inhibit carboxylamidases noncompetitively. Over 95% inhibitionin vivo was obtained when the larvae were fed with castor bean leaves dipped in 250 mgl ^-1 of methomyl. Thein vivo enzyme activity could be reduced to half with a pretreatment of 15 mgl ^-1 diflubenzuron.     

Synergist induced susceptibility of tobacco caterpillar, <Emphasis Type="Italic">Spodoptera litura</Emphasis> (Fabricius) from Kerala,India exposed to conventional insecticides

The present study was undertaken to assess the insecticide resistance developed in various field collected population of S. litura and to induce susceptibility by using the synergists. Third-instar larvae collected from three different locations of Kerala viz., Thiruvananthapuram (TVM), Pathanamthitta (PTA) and Alappuzha (ALP) were exposed to conventional insecticides like chlorpyriphos, quinalphos, lambda-cyhalothrin and cypermethrin by leaf dip bioassay and resistance ratios were calculated by using the baseline data generated for respective insecticides using susceptible strain. Resistance ratios recorded were 1965, 840 and 320 against chlorpyriphos, 605, 255 and 59 against quinalphos, 926, 250 and 108 against lambda-cyahlothrin and 2566, 534 and 396 against cypermethrin respectively for TVM, PTA and ALP populations. The effect of selected synergists viz., piperonyl butoxide (PBO), diethyl maleate (DEM) and triphenyl phosphate (TPP) was studied in combination with respective test insecticides against the highly resistant population of S.litura collected from TVM of Kerala. The population was tested with insecticide in combination of the above synergists at different ratios. When PBO, TPP and DEM at ratio of 1:4 were used the synergistic ratio was 8.47, 7.26 and 3.98 for chlorpyriphos, 6.09, 5.26 and 3.05 for quinalphos, 13.37, 4.53 and 7.39 for lambda cyhalothrin and 4.77, 3.36 and 3.40 for cypermethrin respectively. PBO showed highest synergistic activity against both the organophosphates tested followed by DEM and TPP. Highest synergistic activity against synthetic pyrethroids also was shown by PBO, followed by TPP and DEM. The results obtained from the present study revealed that PBO at 1:4 ratio showed higher synergism with the test insecticides against the resistant populations of S.litura and proved to be an effective molecule alternate for breaking the resistance against conventional organophosphates and synthetic pyrethroids.     

红蓼拒食活性组分的分离及其对小菜蛾幼虫消化酶活性的影响

为了进一步评价红蓼（Polygonum orientale L.）的抗虫性,采用液 液分配萃取和硅胶柱层析的方法,从红蓼甲醇提取物中分离获得石油醚、氯仿、乙酸乙酯、正丁醇和水的萃取物,测定了其对小菜蛾（Plutella xylostella）3龄幼虫拒食活性。结果显示, 乙酸乙酯萃取物比其他4种萃取物具有更高的拒食活性,在5.0 mg/mL下,24 h和48 h的拒食率分别为68.42%和62.55%。乙酸乙酯萃取物经硅胶柱层析后,得到13个组分,比较13个组分的拒食活性发现,组分8的活性较高,在浓度为2.5 mg/mL时,24 h和48 h的拒食率分别为77.13%和68.53%。组分8对小菜蛾幼虫体内的蛋白酶、脂肪酶和α 淀粉酶的活性具有一定的抑制作用。     

Insecticidal potential of Bowman-Birk proteinase inhibitors from red gram (Cajanus cajan) and black gram (Vigna mungo) against lepidopteran insect pests

The present study assessed the insecticidal potential of purified Bowman-Birk proteinase inhibitors from red gram (RgPI) and black gram (BgPI) towards lepidopteran insect pests. Both RgPI and BgPI showed remarkable inhibitory activity against midgut trypsin-like proteinases of Achaea janata. While, BgPI showed moderate to low inhibitory activity towards the midgut trypsin-like proteinases of Helicoverpa armigera, Spodoptera litura, Papilio demoleus, Amsacta albistriga, Corcyra cephalonica, Bombyx mori and Daphnis nerii, RgPI showed low to negligible inhibitory activity. The isoinhibitors of RgPI and BgPI were stable in presence of trypsin and chymotrypsin of bovine pancreatic origin, as well as larval midgut proteinases of A. janata, H. armigera and S. litura. The midgut trypsin-like proteinases of A. janata and H. armigera as well as midgut trypsin- and chymotrypsin-like proteinases of S. litura were susceptible to inhibition by RgPI and BgPI. Feeding assays displayed a dose-dependent decrease in body weight and survival rate of these larvae with increasing concentration of inhibitors supplemented in the diet. RgPI displayed significant reduction in body weight and survival rate of A. janata larvae compared with BgPI. Conversely, BgPI showed significant reduction in body weight of S. litura larvae compared with RgPI.     

Fitness cost, cross resistance and realized heritability of resistance to imidacloprid in Spodoptera litura (Lepidoptera: Noctuidae)

Imidacloprid has been used as a key insecticide for controlling sucking insect pests of cotton, whereas Spodoptera litura also has been indirectly exposed to this insecticide in Pakistan. To evaluate the risk of resistance evolution and to develop a better resistance management strategy, a field collected population was selected with imidacloprid in the laboratory. Thereafter, fitness cost, realized heritability and cross resistance of imidacloprid resistance in S. litura were investigated. After 14 generations of selection with imidacloprid, S. litura developed a 137.48-fold resistance to the insecticide. Bioassay revealed that this strain showed cross-resistance to acetamiprid (RR 8.52) and a little to lamdacyhalothrin (1.92) but negative cross-resistance was found to methomyl (−0.19). The resistant strain had a relative fitness of 0.38, with substantially lower rates of larval survival, larval duration, male pupal duration, development time, emergence rate of healthy adults, fecundity, hatchability, and prolonged larval and pupal duration. Mean relative growth rate of the larvae, intrinsic rate of population increase, and biotic potential was lower for the selected populations. The estimated realized heritability (h²) of imidacloprid resistance was 0.15 in the resistant strain of S. litura. Development of the resistance may cost significant fitness for the resistant population. This study provided valuable information for further understanding the impact of imidacloprid resistance on physiological parameters of S. litura and for facilitating the development of resistance management strategies.     

人工饲料对黄带犀猎蝽生长发育、繁殖及捕食效能的影响

为评价人工饲料饲养对广泛分布于我国南方的黄带犀猎蝽Sycanus bifidus的生长发育、繁殖和控害能力的影响,在室内条件下测定取食不同胶囊人工饲料的黄带犀猎蝽若虫生长发育和繁殖的相关生物学参数,并比较取食斜纹夜蛾Spodoptera litura胶囊人工饲料和活虫饲料的黄带犀猎蝽3~5龄若虫对斜纹夜蛾3龄幼虫的捕食功能反应和搜寻效应。结果表明,以斜纹夜蛾胶囊人工饲料饲喂的黄带犀猎蝽若虫可完成完整世代并继续繁殖,其成虫获得率为15.0%,若虫总发育历期为107.6 d,雌、雄成虫体重分别为113.8 mg和84.7 mg,产卵前期为31.3 d,单雌产卵量为117.3粒,卵期为24.5 d,卵孵化率为90.8%;而取食胶囊人工饲料内容物为黄粉虫Tenebrio molitor匀浆液和混合匀浆液的黄带犀猎蝽若虫不能完成完整世代。取食斜纹夜蛾胶囊人工饲料和活虫饲料的黄带犀猎蝽3~5龄若虫的捕食功能反应均符合Holling II型和Holling III型功能反应模型,使用斜纹夜蛾胶囊人工饲料饲养的黄带犀猎蝽对猎物的捕食效果和搜寻效应未受到明显影响,表明该人工饲料可用于黄带犀猎蝽的规模化扩繁。     

氯虫苯甲酰胺和氟虫双酰胺对不同虫态甜菜夜蛾的毒力作用

采用浸叶法、点滴法、夹毒叶片法、成虫药膜法、饲喂毒营养液法测定了氯虫苯甲酰胺、氟虫双酰胺对甜菜夜蛾卵、2~4龄幼虫、成虫的活性和对4龄幼虫的拒食活性,以明确氯虫苯甲酰胺和氟虫双酰胺对不同虫态甜菜夜蛾的毒力作用。结果表明,两种杀虫剂均不具有杀卵活性,但可以明显降低初孵幼虫存活率;氯虫苯甲酰胺、氟虫双酰胺均对2龄幼虫活性最高,分别为3龄幼虫的1.50、6.17倍和4龄幼虫的22.25、44.95倍,对4龄幼虫胃毒活性分别为触杀活性的14.10、8.44倍;氯虫苯甲酰胺对甜菜夜蛾成虫毒力为氟虫双酰胺的25.53~34.19倍。氯虫苯甲酰胺、氟虫双酰胺对甜菜夜蛾幼虫表现出较强的拒食作用, 至处理后48 h拒食率达到最高, 分别为 82.73%、84.15%,显著高于对照药剂甲维盐各浓度处理,处理试虫虫体皱缩、体节缩短,体重增加率明显低于对照和甲维盐各处理。     

High Performance Thin Layer Chromatography (HPTLC) profile of an insecticidal compound of <Emphasis Type="Italic">Trochus radiatus</Emphasis> and assessment of mucus-associated bacterial extracts

The current study is based on the screening of novel insecticides from new sources that have not being exploited hitherto. The major objectives of this research work were to extract marine molluscs, Lambis lambis, Trochus radiatus and Chicoreus ramosus, from Tuticorin coastal waters using different solvents to test their insecticidal properties and partially purify the active components. The ethyl acetate extracts of L. lambis and T. radiatus showed 100% mortality of Sitophilus oryzae, at a concentration of 200 μg ml⁻¹. The LC₅₀ values for ethyl acetate extracts of L. lambis, T. radiatus and C. ramosus were found to be 67.08, 348.86 and 571.42 μg ml⁻¹, respectively. With regard to bacterial metabolites, at a concentration of 200 μg ml⁻¹ the ethyl acetate extract of A3 was able to elicit an activity of 40% and that of strain A1 – 20%. The LC₅₀ values of the bacterial metabolites were also investigated. Upon chromatographic separation of active ethyl acetate extracts of T. radiatus, the 100% methanol column-purified fraction was found to have an activity of 30% at a concentration of 10 μg against S. oryzae. The purity of the partially pure active compound was observed to be 72.78% on analysis with high pressure thin layer chromatography.     

Nile tilapia (Oreochromis niloticus), liver morphology, CYP1A activity and thyroid hormones after Endosulfan dietary exposure

Endosulfan is a worldwide used insecticide suspected to be highly toxic to aquatic organisms, including fish. Most of the available studies have focused in water exposures, although this pollutant can be transferred through food chain. Therefore, in the present study, the effects of Endosulfan on tilapia (Oreochromis niloticus), when administered through the diet. Fish were fed 21 days with diets containing 1 and 0.5 μg g⁻¹ of Endosulfan, after which qualitative histological liver analysis showed that Endosulfan induced hepatocyte destruction, vessel endothelium rupture and increased melanomacrophages aggregates. To test lower environmentally relevant doses of Endosulfan could induce hepatic damage, as well as other negative effects, such as altered phase I metabolism and plasma thyroid hormone levels. Hence, tilapia were orally exposed to 0.1 and 0.001 μg g⁻¹ for 35 days. Low environmentally realistic doses of Endosulfan were still able to induce liver histopathological damage such as increased hepatocyte vacuolization and increased eosinophil granular cell aggregates. Liver cytochrome P450 1A activity, evaluated through ethoxyresorufin-o-deethylase (EROD), was enhanced in tilapia exposed to 0.001 μg g⁻¹, whereas the highest dose had no measurable effects in this enzyme activity. Fish exposed to 0.1 μg g⁻¹ of Endosulfan had depressed T4 plasma levels. Overall, the results of the present study further demonstrate the toxic effects of Endosulfan in tilapia when administered in the diet at environmentally relevant concentrations, which indicates that in the field food chain transfer may also be an importance source of this pollutant.     

The chemical control of the lesser date moth,Batrachedra amydraula meyr., and residue levels of organophosphate insecticides in dates

Larvae of the lesser date moth (Batrachedra amydraula Meyr.) cause damage to dates in Iraq. A formulation based on a mixture of equal parts of wheat flour and pollen grains and containing either chlorpyrifos, fenitrothion or pirimiphos-methyl (all at 5 mg kg^?l) was dusted (5 g formulation bunch^?1) onto female clusters of dates at the time of pollination. Numbers of larvae, yield of dates and insecticide residues were monitored over a three-month period. Results showed that, by this technique, all three insecticides were effective in controlling the pest but that fenitrothion and chlorpyrifos were better than pirimiphos-methyl.     

转Cry1Ac/1Ab基因棉花对棉铃虫的控制效果及对甜菜夜蛾和斜纹夜蛾生长发育的影响

为评估转Cry1Ac/1Ab基因棉花对棉铃虫Helicoverpa armigera的抗性及对非靶标害虫甜菜夜蛾Spodoptera exigua和斜纹夜蛾S.litura生长发育的影响,采用室内生测法测定其对棉铃虫的抗性及对甜菜夜蛾和斜纹夜蛾不同龄期幼虫存活率、营养代谢及中肠酶活性的影响。结果表明,转Cry1Ac/1Ab基因棉花对棉铃虫第2代幼虫的抗性程度最高,幼虫校正死亡率达91.33%,但对甜菜夜蛾和斜纹夜蛾的抗性程度较低,幼虫校正死亡率分别为15.33%和13.33%。甜菜夜蛾和斜纹夜蛾各龄期幼虫取食转Cry1Ac/1Ab基因棉花后,其存活率与取食常规棉花对照无显著差异;甜菜夜蛾对转Cry1Ac/1Ab基因棉花叶片的相对取食量、近似消化率分别为16.68和93.12%,均高于取食常规棉花对照的10.72和92.00%,但差异不显著,而斜纹夜蛾取食转Cry1Ac/1Ab基因棉花后的各项营养指标均低于取食常规棉花对照,差异也不显著。取食转Cry1Ac/1Ab基因棉花后,甜菜夜蛾的过氧化物酶活性为0.02 U/mg prot,显著低于取食常规棉花的0.05 U/mg prot;斜纹夜蛾的酸性磷酸酶活性为0.15 U/mg prot,高于取食常规棉花的0.10 U/mg prot,但差异不显著,其它中肠酶活性均低于对照,亦无显著差异。     

Inhibition on brown rot disease and induction of defence response in harvested peach fruit by nitric oxide solution

Nitric oxide (NO) is an important signal molecule involved in numerous plant responses to biotic and abiotic stresses. The effect of nitric oxide (NO) solution on pathogen infection and defence response of peach (Prunus persica (L.) Batsch) fruit against brown rot disease caused by Monilinia fructicola was investigated. The results showed that 15 μmol l^?1 NO solution did not significantly inhibit spore germination, germ tube length or pathogenicity of M. fructicola, but significantly reduced disease incidence and lesion areas in the fruit. Although 100 μmol l^?1 NO solution effectively inhibited the spore germination, germ tube elongation and pathogenicity of M. fructicola, the high concentration of NO solution caused damage to the fruit. Moreover, 15 μmol l^?1 NO enhanced the activities of chitinase (CHI) and β-1,3-glucanase (GNS) in the fruit. RT-PCR analysis showed that the expression of four genes, CHI, GNS, pathogenesis-related protein 1 and 10 genes (PR-1, PR-10) all increased after NO treatment. Conversely, pretreatment with 100 μmol l^?1 NO scavenger, 2-4-carboxyphenyl-4,4,5,5- tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), rendered the fruit relatively susceptible to pathogen infection and inhibited the defence response of the fruit. These results suggest that NO solution treatment can protect peach fruit from pathogen infection by inducing the activities of the defence enzymes and the expression of PR genes.     

Synthesis and insecticidal activities of pyridine ring derivatives of podophyllotoxin

In an attempt to find the biorational pesticides, we synthesized 12 pyridinyl derivatives of podophyllotoxin (PPT) and 4′-demthylepipodophylltoxin (4′-DMEP) in this study. Their structures and the α/β substitution at C-4 were confirmed by ¹H NMR, IR, MS spectral analyses and elemental analysis. The insecticidal activities were tested against fifth-instar larvae of Pieris rapae and the third-instar larvae of Cullex pipiens pallens at concentrations of 250 and 10 μg ml⁻¹. Four derivatives of PPT, 4.1, 4.2, 4.3 and 4.5, showed higher insecticidal activities against P. rapae than PPT, while three derivatives of PPT, 4.4, 4.5 and 4.6, displayed higher mosquito larvicidal activity than PPT, with LC₅₀ values of 1.66, 3.96 and 1.54 mg l⁻¹, respectively. Interestingly, we also found that the pyridine ring derivatives of PPT showed delayed insecticidal activity, which is different from traditional neurotic insecticides. The results suggest that 4′-OCH₃ in the PPT derivatives is essential to keep the insecticidal activity and the insecticidal activities of pyridine ring derivatives of PPT are higher than that of the derivatives of 4′-DMEP, supporting PPT has the potential to be a lead structure of semi-synthetic insecticides.