Laboratory studies utilizing radioisotopic techniques were conducted to determine the adsorption, desorption, and mobility of endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxanthiepin3-oxide) and methamidophos (O,S-dimethyl phosphorothioate) in sandy loam and clay soils of the Cameron Highlands and the Muda rice-growing area, respectively. High Freundlich adsorption distribution coefficients [Kads(f)] for endosulfan (6.74 and 18.75) and low values for methamidophos (0.40 and 0.98) were obtained in the sandy loam and clay soils, respectively. The observed Koc values for endosulfan were 350.85 (sandy loam) and 1143.19 (clay) while Koc values of 20.92 (sandy loam) and 59.63 (clay) were obtained for methamidophos. Log Kow of 0.40 and 1.25 were calculated for endosulfan as well as -1.96 and -1.21 for methamidophos in the sandy loam and clay soils, respectively. Desorption was common to both pesticides but the desorption capacity of methamidophos from each soil type far exceeded that of endosulfan. Soil thin layer chromatography (TLC) and column studies showed that while methamidophos was very mobile in both soils, endosulfan displayed zero mobility in clay soil.
The use of chemical insecticides has had many adverse effects. This study reports a novel perspective on the application of insect-based compounds to repel and eradicate other insects in a controlled environment. In this work, defense fluid was shown to be a repellent and insecticide against termites and cockroaches and was analyzed using gas chromatography-mass spectrometry (GC-MS). Globitermes sulphureus extract at 20 mg/ml showed the highest repellency for seven days against Macrotermes gilvus and for thirty days against Periplaneta americana. In terms of toxicity, G. sulphureus extract had a low LC50 compared to M. carbonarius extract against M. gilvus. Gas chromatography-mass spectrometry analysis of the M. carbonarius extract indicated the presence of six insecticidal and two repellent compounds in the extract, whereas the G. sulphureus extract contained five insecticidal and three repellent compounds. The most obvious finding was that G. sulphureus defense fluid had higher potential as a natural repellent and termiticide than the M. carbonarius extract. Both defense fluids can play a role as alternatives in the search for new, sustainable, natural repellents and termiticides. Our results demonstrate the potential use of termite defense fluid for pest management, providing repellent and insecticidal activities comparable to those of other green repellent and termiticidal commercial products.
We report the first comprehensive insecticide susceptibility status ofAedes aegypti (L.) larvae from Singapore. The study indicated that Ae. aegypti is susceptible to temephos, although resistance (RR50 = 1.29-4.43-fold) couldbe developing. Of high concern is the detection of moderate to high resistance to permethrin (RR50 = 29-47-fold) and etofenprox (RR50 = 14-34-fold). Biolarvicide Bacillus thuringiensis israelensis (Bti) remains effective. The insecticide susceptibility profile of Ae. aegypti larvae was found to be homogenous among the different sites studied across the island city. The addition of synergists piperonyl butoxide, S,S,S,-tributyl phosphorotrithioate, and triphenyl phosphate generally failed to enhance the toxicity of the insecticides investigated, suggesting an insignificant role of metabolic-based resistance, and a possible involvement of target site resistance. Further biochemical investigation of specific metabolic enzyme activities suggested that detoxifying enzymes, mono-oxygenases, esterases, glutathione S-transferases, and altered acetylcholinesterases, generally did not contribute to the resistance observed. This study clearly demonstrated that pyrethroid resistance is widespread among Ae. aegypti population and lowered susceptibility to organophosphates is developing.
The insecticide chlorpyrifos is extensively used in the humid tropics for insect control on crops and soils. Chlorpyrifos degradation and mineralization was studied under laboratory conditions to characterize the critical factors controlling the degradation and mineralization in three humid tropical soils from Malaysia. The degradation was fastest in moist soils (t1/2 53.3-77.0 days), compared to dry (t1/2 49.5-120 days) and wet soils (t1/2 63.0-124 days). Degradation increased markedly with temperature with activation energies of 29.0-76.5 kJ mol(-1). Abiotic degradation which is important for chlorpyrifos degradation in sub-soils containing less soil microbial populations resulted in t½ of 173-257 days. Higher chlorpyrifos dosages (5-fold) which are often applied in the tropics due to severe insects infestations caused degradation and mineralization rates to decrease by 2-fold. The mineralization rates were more sensitive to the chlorpyrifos application rates reflecting that degradation of metabolites is rate limiting and the toxic effects of some of the metabolites produced. Despite that chlorpyrifos is frequently used and often in larger amounts on tropical soils compared with temperate soils, higher temperature, moderate moisture and high activity of soil microorganisms will stimulate degradation and mineralization.
The residual effect of a commercial spray containing 2.0% benzyl benzoate against Dermatophagoides pteronyssinus was evaluated in the laboratory. Filter papers treated with benzyl benzoate were dried for 2 hours and placed in Petri dishes. Adult mites were then added and mortality was assessed following 24 hour contact and at succeeding 4 weeks intervals up to week 28 post-treatment using the same treated filter papers. There was 100% mortality at 24 hours post-treatment, declining progressively to 71% by week 28. Probit analysis estimated a median lethal time (LT50) of 59 weeks.
A nationwide investigation was carried out to determine the current susceptibility status of Culex quinquefasciatus Say populations against four active ingredients representing four major insecticide classes: DDT, propoxur, malathion, and permethrin. Across 14 study sites, both larval and adult bioassays exhibited dissimilar trends in susceptibility. A correlation between propoxur and malathion resistance and between propoxur and permethrin resistance in larval bioassays was found. The results obtained from this study provide baseline information for vector control programs conducted by local authorities. The susceptibility status of this mosquito should be monitored from time to time to ensure the effectiveness of current vector control operations in Malaysia.
The sorption and desorption of cyfluthrin mixture isomers were determined using batch equilibration method and mobility was studied under laboratory conditions, using packed soil column. The soil types used in the study were clayey, clay loam and sandy clay loam obtained from three tomato farms in Cameron Highlands. A low Freundlich adsorption distribution coefficient K(ads(f)) for cyfluthrin was observed for clayey, clay loam and sandy clay loam soils (95.69, 21.64 and 8.99 l/kg, respectively). Results showed that cyfluthrin had high Freundlich organic matter (OM) distribution coefficient K(oc) values of 5799, 2278 and 1635 lkg(-1) for clayey, clay loam and sandy clay loam soils, respectively. These values indicate that cyfluthrin is considered immobile in Malaysian soils with different textures, based on the value of K(oc) by McCall. Adsorption of cyfluthrin was significantly (P < 0.05) affected with soil pH, fertilizer NPK, organic matter content and temperature. It was observed that approximately 95.8%, 93.8% and 91.8% of the adsorbed cyfluthrin remained sorbed after four successive rinses for clayey, clay loam and sandy clay loam soils. Soil column test showed that cyfluthrin was not detected in leachate. Cyfluthrin was detected in topsoil and its concentration decreased with depth. The downward movement of cyfluthrin in sandy clay loam soil was more than that in clay loam and clayey soils. Approximately, 80.9%, 77.8% and 67.3% cyfluthrin was observed at the depth of 0-5 cm (rainfall 350 mm) for clayey, clay loam and sandy clay loam soils respectively. Mobility of cyfluthrin showed that the percentage of cyfluthrin leached into soil was not affected by the amount of rainfall. The result clearly showed that cyfluthrin molecules were bound strongly to all the three Malaysian soil types.
Although rove beetles (Paederus spp.) play a beneficial role as biological control agents to manage crop pests in agro-ecosystems, their high prevalence in human settings has elevated them to pest status in urban areas. Rove beetles neither bite nor sting, but accidental crushing on human skin causes them to release the toxin paederin, which causes dermatitis linearis. This review integrates currently available knowledge about the issues pertaining to Paederus infestation. For instance, the results of life history studies conducted under different food and temperature regimes are summarized, as they indicate how large a population can be in a habitat to cause massive and widespread infestation and illustrate the physiological traits required to maintain the population at the maximum level even under adverse conditions. In contrast to what is generally reported, we speculate that climatic factors do not necessarily result in Paederus dispersal in temperate regions; instead, habitat disturbance and site unsuitability may be the main factors that lead to massive dispersal to human settings. Factors such as whether dispersers are adaptable to xeric conditions in human settings, the probability that dispersed Paederus mate with the opposite sex, and whether dispersers have adequate nutrient intake to reproduce are considered to evaluate their potential to reproduce in human settings. Finally, the effectiveness of current commercial insecticides, challenges faced in managing infestations, and sustainable management practices are discussed to provide information for long-term control programs.
A field trial was carried out to study the effect of lambdacyhalothrin on Anopheles maculatus in trap huts in Jeram Kedah, Negeri Sembilan, Malaysia. Two trap huts were built, of which one was sprayed with lambdacyhalothrin at a dosage of 25 mg ai/m2 and the other served as control. Eight collectors commenced collecting mosquitos from 1900 to 2400 hours, two each indoors and outdoors. Bioassay was also carried out in the treated and control huts to determine susceptibility of adult mosquitos to lambdacyhalothrin. In the treated hut more mosquitos were present during the pre- spraying period. Lambdacyhalothrin gave a mortality of 100% against An. maculatus for 8 months.
Bacillus thuringiensis israeliensis (BTI) against culicine mosquitoes was tried out in cement sullage drains in Kelang municipal area at a dosage of 0.15 ppm. and 0.6 ppm. The results of the trial showed that at 0.15 ppm. the BTI was not effective, but at 0.6 ppm. it was effective giving about 95% kill. There was no residual effect and treatment had to be repeated weekly.
Evaluation of the effectiveness of Bacillus thuringiensis ssp. israelensis (B.t.i.) against mosquito larvae dispersed by ultralow volume (ULV) spraying was conducted in simulated field trials. Effectiveness was measured using 3 different indicators: larval mortality, colony-forming unit enumeration, and droplet analysis. B.t.i. was dispersed with a ULV generator using 2 different flow rates: 0.3 and 0.5 liter/min on 2 different days. Based on the results of this study, it can be concluded that an output of 0.3 liter/min is effective for controlling Aedes aegypti. although a dosage of 0.5 liter/min can be used when high residual activity is desired. For Culex quinquefasciatus control, both dosages were effective but with low residual activity. For Anopheles maculatus control, only a discharge rate of 0.5 liter/min was effective with low residual activity. B.t.i. application at both dosages penetrated tires well, indicating that B.t.i. ULV application is an effective method for controlling container-inhabiting mosquitoes. Good coverage of target area and penetration were attributed to satisfactory droplet profiles.
Alphacypermethrin (Fendona) and lambda-cyhalothrin (Icon) were evaluated against sentinel bloodfed adults and 4th-instar larvae of Aedes aegypti in a housing estate in Malaysia. The impact of both pyrethroids on field populations of Ae. aegypti and Aedes albopictus were monitored weekly using oviposition trap samples. Both alphacypermethrin and lambda-cyhalothrin showed adulticidal and larvicidal effects.
Rice brown planthopper, Nilaparvata lugens Stål, is a primary insect pest of cultivated rice, and effective control is essential for economical crop production. Resistance to neonicotinoid insecticides, in particular imidacloprid, has been reported as an increasing constraint in recent years. In order to investigate the extent of resistance, 24 samples of N. lugens were collected from China, India, Indonesia, Malaysia, Thailand and Vietnam during 2005 and 2006. Their responses to two diagnostic doses of imidacloprid (corresponding approximately to the LC(95) and 5 x LC(95) of a susceptible strain) were examined.
The bioefficacy of nine commercial formulations of temephos against Aedes aegypti, Aedes albopictus and Culex quinquefasciatus larvae were evaluated in the laboratory. WHO larval bioassay with operational dosage of temephos at 1 mg/L was performed. The larval mortality was recorded every 5 minutes until complete mortality was achieved. All formulations of temephos exhibited various toxicity level against Ae. aegypti, Ae. albopictus and Cx. quinquefasciatus. Generally, larvae of Cx. quinquefasciatus was susceptible to all formulations of temephos, followed by Ae. aegypti and Ae. albopictus.
The efficacy and residual efficacy of commercial baits, Quick Bayt (0.5% w/w imidacloprid) and Agita (10.0% w/w thiamethoxam) against synanthropic flies were evaluated under field conditions. Efficacy was evaluated based on knockdown percentage (KD %). The bait efficacy and residual efficacy evaluation were conducted for a period of 3 weeks and 6 weeks respectively. Baits were applied onto bait targets and placed on fly-count targets to facilitate the counting of flies. All baits were applied according to the manufacturer's recommended application rate. Three replicate treatments for each type of bait were placed at the study site each week. The number of flies feeding on baits and the knocked down flies were counted and collected. The efficacy of Agita and Quick Bayt did not differ significantly (t-test, P>0.05) over the 3-week period, even though Quick Bayt had a slightly higher KD% than Agita. In the residual efficacy evaluation, the (knockdown) KD% of Quick Bayt was consistent at around 36% for the first five weeks but dropped to 33.8 +/- 0.4% on the sixth week. The KD% for Agita on the first week was 33.6 +/- 12.2% and remained relatively consistent for the first 4 weeks at around 31%. KD% dropped to 16.7 +/- 3.3% on week 5 and to 15.7 +/- 1.2% on week 6. The difference in residual efficacy of the two baits was significant (t-test, p < 0.05).
The bioefficacy of a commercial formulation of temephos, Creek against Aedes aegypti larvae was studied in the laboratory. Earthen jars were filled with 10 L tap water each. One g of temephos (Creek) sand granule formulation was added into each earthen jar as recommended by the manufacturer. The final test concentration of Creek was 1 mg a.i./L. One earthen jar was filled with 10 L tap water and served as a test control (untreated). Thirty late 3(rd) or early 4(th) instar of lab-bred Ae. aegypti larvae were added into each earthen jar. Mortality of the larvae was recorded after 24 hours and percent mortality was calculated. Test was repeated every week. The results showed that complete larval mortality was achieved after 24 hours. The residual effect lasted 15 weeks (105 days), indicating that Creek is effective at the dosage recommended by the manufacturer which is 1 mg a.i./L.