A 14-months survey was carried out to identify the species composition of Anopheles mosquitoes from Kampung Bongor, Grik, Perak. Adding to that, a preliminary one month mosquito population screening was done at Kampung Tepin, Serian, Sarawak. Consequently, the insecticide susceptibility status of a pyrethroid was tested against two selected species of Anopheles collected from these two locations in Malaysia. A total of 4,497 Anopheles from 11 species were identified from collections in Kampung Bongor, whereas 2,654 An. letifer were collected from Kampung Tepin. The An. maculatus of Kampung Bongor and An. letifer of Kampung Tepin were then selected and tested using WHO standard diagnostic test kits and impregnated papers with 0.75% permethrin. The response values of KT50 and KT95 for An. maculatus were recorded at 28.09 minutes and 62.98 minutes respectively. Anopheles letifer recorded much slower response values of KT50 and KT95, which was at 35.09 minutes and 73.03 minutes respectively. Both An. maculatus and An. letifer showed 100% mortality after 24 hours holding period. The results indicate that both species were still susceptible to the tested pyrethroid. For effective vector control and resistance management, accurate and periodic insecticide resistance monitoring should be undertaken especially in rural areas with agricultural usage of insecticides.
Anopheles annularis is widely distributed mosquito species all over the country. An. annularis has been incriminated as a malaria vector in India, Sri Lanka, Bangladesh, Myanmar, Indonesia, Malaysia and China. In India, it has been reported to play an important role in malaria transmission as a secondary vector in certain parts of Assam, West Bengal and U.P. In Odisha and some neighbouring countries such as Sri Lanka, Nepal and Myanmar it has been recognised as a primary vector of malaria. This is a species complex of two sibling species A and B but the role of these sibling species in malaria transmission is not clearly known. An. annularis is resistant to DDT and dieldrin/HCH and susceptible to malathion and synthetic pyrethorides in most of the parts of India. In view of rapid change in ecological conditions, further studies are required on the bionomics of An. annularis and its role in malaria transmission in other parts of the country. Considering the importance of An. annularis as a malaria vector, the bionomics and its role in malaria transmission has been reviewed in this paper. In this communication, an attempt has been made to review its bionomics and its role as malaria vector. An. annularis is a competent vector of malaria, thus, due attention should be paid for its control under the vector control programmes specially in border states where it is playing a primary role in malaria transmission.
The objective of this study was to study the possible reproductive adverse effects of the diazinon on rat offspring exposed in utero and during lactation. Dams were gavaged daily (10, 15, and 30 mg/kg) before mating, during mating, and during pregnancy and lactation in separate groups. Reproductive outcome data of dams were examined. Body weight, testis weight, testicular marker enzyme activities (alkaline phosphatase, acid phosphatase, lactate dehydrogenase, and glucose-6-phosphate dehydrogenase), qualitative and quantitative testicular and epididymal histology, and immunohistochemisty for 3-β-hydroxysteroid dehydrogenase (HSD) were examined in male offspring at puberty and adulthood. The 30-mg/kg dose induced significant adverse effects at both puberty and adulthood in offspring. At puberty the male offspring showed a decrease in testicular weight, degenerative changes, and 3-β-HSD. Moreover, an increase in activity of alkaline and acid phosphatase also was observed. At adulthood, there was a decrease in testicular weight and 3-β-HSD with an increase in the levels of testicular marker enzyme. There was evidence of some adverse reproductive effects in male offspring at the 15-mg/kg dose. Most of the adverse effects were irreversible and were evident at both puberty and adulthood in offspring, although a few parameters reverted back to the normal growth pattern. Hence, diazinon is a reproductive toxicant in male offspring, which caused significant damage to the testes when exposed during prenatal and postnatal life.
To evaluate the effectiveness and residual effects of trypsin modulating oostatic factor-Bacillus thuringiensis israeliensis (TMOF-Bti) formulations against Aedes aegypti (Ae. aegypti) (L.) larvae at UKM Campus Kuala Lumpur.
A one year study was conducted to evaluate the impact of spray application of Bacillus thuringiensis israelensis (Bti), strain AM65-52 on vector populations and dengue transmission in a dengue endemic state in Malaysia. Residential sites with similar populations of Aedes aegypti (L.) and Aedes albopictus Skuse were studied. One site was treated with spray application of Bti into all outdoor target vector habitats, which consisted of natural and artificial containers. The other site was not treated. The impact of spray application was measured with an indoor and outdoor ovitrap index (OI) and epidemiologic data. Significant reductions in both Ae. aegypti and Ae. albopictus, OI were observed both indoors and outdoors, in treated sites compared to untreated sites (p < 0.05). OI reduction was achieved over time in the treated area. The OI was suppressed to below 10%. This was maintained for 4 weeks into the post-treatment phase. The outdoor OI at the untreated site remained at more than 40% for 38 weeks during the evaluation period. One dengue case occurred at the Bti treatment site at the beginning of the treatment phase, but no further cases were detected during the remainder of the treatment phase. However, there was an ongoing dengue outbreak in the untreated area with 15 serologically confirmed cases during weeks 37-54. Intensive fogging operations with pyrethroids at the untreated (Bti) site had a positive impact on Ae. albopictus, but not on Ae. aegypti.
Biweekly ovitrap surveillance (OS) was conducted for a year (August 2007 - September 2008) at two different dengue endemic sites in Shah Alam, Selangor, Malaysia, 50 km from Kuala Lumpur. Aedes aegypti collected from these 2 locations were raised to the F3 stage and subjected to a WHO standard bioassay method to determine lethal time (LT) against pyrethroids (permethrin 0.75%, cyfluthrin 0.15%), organophosphates (malathion 5.0%, fenitrothion 1.0%), carbamates (propoxur 0.1%, bendiocarb 0.1%) and organochlorine (DDT 4.0%). Insecticide susceptibilities were analyzed for one year. Aedes aegypti were resistant to DDT with a mortality range of 0 - 13.3% throughout the year at both sites. Susceptibilities to pyrethroids and carbamates varied throughout the year. In contrast, susceptibilities to pyrethroids and carbamates varied throughout the year: resistant to propoxur, bendiocarb and permethrin with mortality of < 80% in most months; but, showed incipient resistant to cyfluthrin in most months. Mosquitoes were consistently susceptible to malathion and fenitrothion, with complete mortality during most months. They were especially susceptible to malathion with LT50 values of 21.32 - 36.37 minutes, suggesting effectiveness of malathion for control of dengue.
Bioassay test against malathion had been carried out with larval and adult stages of Aedes aegypti. The mosquitoes were under selection pressure against malathion for forty-five consecutive generations. The rate of resistance development was measured by LC(50) and LT(50) values. The larvae and adult females, after subjection to malathion selection for 45 generations, developed high resistance level to malathion, with resistance ratio of 52.7 and 3.24 folds, respectively over control mosquitoes. Cross-resistance towards the same and different groups of insecticides was determined using the F44 and F45 malathion-selected adult females. Insecticides tested were DDT (4.0%), permethrin (0.75%), propoxur (0.1%), fenitrothion (1%), λ-cyhalothrin (0.05%) and cyfluthrin (0.15%). Results indicated that the mosquitoes were highly resistant to DDT and fenitrothion, moderately resistant to propoxur, tolerant to permethrin and λ-cyhalothrin, and very low resistant to cyfluthrin.
Routine surveillance on resistant status of field mosquito populations is important to implement suitable strategies in order to prevent pest outbreaks. WHO test kit bioassay is the most frequent bioassay used to investigate the susceptibility status of field-collected mosquitoes, as it is relatively convenient to be carried out in the field. In contrast, the topical application of active ingredient is less popular in investigating the susceptibility status of mosquitoes. In this study, we accessed the susceptibility status of Aedes albopictus Skuse collected from two dengue hotspots on Penang Island: Sungai Dua and Persiaran Mayang Pasir. Two active ingredients: permethrin and deltamethrin, were used. WHO test kit bioassay showed that both wild strains collected were susceptible to the two active ingredients; while topical application assay showed that they were resistant. This indicated that WHO test kit bioassay less sensitive to low level of resistance compared to topical application assay. Hence, topical application is expected to be more indicative when used in a resistance surveillance programme.
The bioefficacy of Piper aduncum L. essential oil formulated in aerosol cans was evaluated against Aedes aegypti and Aedes albopictus in a simulated room. The aerosol spray test was based on the Malaysian test standard for aerosol (MS 1221:1991UDC 632.982.2 modified from WHO 2009 methodology) and examined the knockdown effect within 20 minutes of exposure. Mortality rate after 24 hour of holding period was also determined. A commercial aerosol spray (0.09% prallethrin 0.05% d-phenothrin) was also tested as a comparison. Our results showed that the knockdown effect of the commercial aerosol spray and P. aduncum essential oil spray (8% and 10% concentrations) was significantly higher in Ae. albopictus adult females, when compared with that of Ae. aegypti adult females (P<0.05). There was a significant difference in knockdown between commercial aerosol spray and essential oil spray for both Aedes spp. (P<0.05). The essential oil induced significantly higher mortality in Ae. aegypti (80%) than in Ae. albopictus (71.6%) (P<0.05). The commercial aerosol spray caused 97.7% and 86.5% mortality against Ae. aegypti and Ae. albopictus respectively (P<0.05). Based on these data, P. aduncum essential oil has the potential to be used as an aerosol spray against Aedes spp.
Five formulated insecticides (lambda-cyhalothrin at 10 mg m⁻², bifenthrin at 50 mg m⁻², fipronil at 10 mg m⁻², fenitrothion at 50 mg m⁻², imidacloprid at 5 mg m⁻²) and one active ingredient (DDT at 500 mg m⁻²) were evaluated using a surface contact method against early and late instars and adults of two strains of the tropical bed bug, Cimex hemipterus (F.). Synergism of lambda-cyhalothrin and fipronil using piperonyl butoxide (PBO) was also assessed.
To evaluate the mosquito larvicidal potential of the native Bacillus thuringiensis isolate BtReXO2, which was isolated from a tropical rain forest ecosystem in Malaysia. This study also aimed at determining the phenotypic and biochemical characteristics of the isolate.
Seasonal population of the fruit-piercing moths Eudocima spp. was monitored throughout the citrus growing seasons in a citrus orchard and in site adjacent to secondary forest from July 2007 to June 2009. The moth was detected practically throughout the year with activity lowest during the wet months (September-February) when fruits are still available and while highest during the dry months (May-June) which also coincided with the main fruiting season. The effects of an nC24 horticultural mineral oil (HMO) on the citrus fruit damage caused by fruit-piecing moths was also determined. The percent fruit damage was significantly lowest (P≤0.05) in HMO-treated plots (8.4), followed by Dimethoate-treated plots (11.6) and untreated plots (22.5). However, there was no significant difference between HMO and Dimethoate treated plots indicating HMO is effective in reducing percent fruit damage.
The susceptibility status of field-collected Aedes aegypti (L.) from a dengue endemic area to Bacillus thuringiensis israelensis (Bti) and temephos was determined. Since August 2007, biweekly ovitrap surveillance (OS) was conducted for 12 mo in 2 sites, A & B, in Shah Alam, Selangor. Site A was treated with a Bti formulation, VectoBac® WG at 500 g/ha, from December 2007 - June 2008 while Site B was subjected to routine dengue vector control activities conducted by the local municipality. Aedes aegypti larvae collected from OS in both sites were bred until F3 and evaluated for their susceptibility. The larvae were pooled according to 3 time periods, which corresponded to Bti treatment phases in site A: August - November 2007 (Bti pre-treatment phase); December 2007 - June 2008 (Bti treatment phase); and July - September 2008 (Bti post-treatment phase). Larvae were bioassayed against Bti or temephos in accordance with WHO standard methods. Larvae collected from Site A was resistant to temephos, while incipient temephos resistant was detected in Site B throughout the study using WHO diagnostic dosage of 0.02 mg/L. The LC50 of temephos ranged between 0.007040 - 0.03799 mg/L throughout the year in both sites. Resistance ratios (LC50) indicated that temephos resistance increased with time, from 1.2 - 6.7 folds. The LC50 of Ae. aegypti larvae to Bti ranged between 0.08890 - 0.1814 mg/L throughout the year in both sites, showing uniform susceptibility of field larvae to Bti, in spite of Site A receiving 18 Bti treatments over a period of 7 mo. No cross-resistance of Ae. aegypti larvae from temephos to Bti was detected.
Two performance (efficacy and attractiveness) comparisons of neonicotinoid baits QuickBayt® (imidacloprid) and Agita® (thiamethoxam) against filth flies were conducted under field conditions to determine suitability for use outdoors. The first experiment compared bait performance and the second compared effects of different applications on QuickBayt® performance. Applications compared were: (i) scattered in petri dish (SPD); (ii) wet-down in petri dish (WPD); (iii) scattered on cardboard (SCB) and (iv) painted on cardboards (PCB). Efficacy and attractiveness were assessed based on knockdown percentage (KD%) and number of flies feeding on baits, respectively. The KD% of QuickBayt® (34% ± 3.0%) was not significantly higher than Agita® (29% ± 1.3%) (t-test, P>0.05). Agita® (101 ± 5.7 flies) was significantly more attractive to flies than QuickBayt® (76 ± 4.8 flies) and the sugar solution (49 ± 7.2) (one-way ANOVA, P<0.05). The PCB and SCB applications were significantly more attractive to filth flies than WPD and SPD (One-way ANOVA, P<0.05), however differences in KD% were not significantly different (One-way ANOVA, P>0.05). The two baits provided the same level of efficacy in a wide-open area against filth flies of various species. QuickBayt® was more versatile; efficacy was not significantly affected by different applications. Surface area and moisture affects attractiveness of the bait.
Aedes albopictus was bioassayed to determine resistance development to malathion (OP). Two methods were applied, including WHO larval bioassay to determine the susceptibility to lethal concentration (LC), and adult bioassay to determine lethal time (LT). Larvae from colonies that had undergone selection pressure with malathion to yield 50% mortality were further subjected to selection for subsequent 10 generations. Selection of Ae. albopictus with malathion could relatively induce a consistent resistance ratio of 1.0 throughout 10 generations. It was noted that Ae. albopictus larvae showed less susceptibility to malathion compared to adults. The susceptibility test of adult mosquitoes to diagnostic dosage of 5.0% malathion-impregnated paper showed a variety of susceptibility to malathion when compared to the susceptible strain. Bioassay results indicated that the LT50 values of malathion-selected Ae. albopictus ranged between 11.5 - 58.8 minutes for ten consecutive generations. Biochemical enzyme studies indicated that there was a significant difference (p < 0.05) in esterase level in malathion-selected mosquitoes compared to non-selected control. Electrophoretic patterns of non-specific esterases at different life stages in malathion-selected Ae. albopictus suggested that non-specific esterases do not play a role in resistance of malathion-selected Ae. albopictus.
Thrips are key pests of mango, Mangifera indica (L.), in Malaysia, including the Northern Peninsular. As Penang has year-round equatorial climate and high of rainfall, the populations of thrips may be subject to variations in composition and size. With a goal of developing an appropriate control strategy, a survey was conducted in Penang to determine species composition and abundance in relation to some environmental factors. Sprayed and unsprayed orchards were sampled on weekly basis through two flowering seasons of 2009 using CO(2) collection technique. Larval population falling into the ground to pupate and adults emerging from the soil were investigated in both orchards. Thrips hawaiiensis (Morgan) and Scirtothrips dorsalis (Hood) were the most prevalent species in the sprayed and the unsprayed orchards, respectively. The abundance of thrips was high during the flowering period of the dry season and decreased during the flowering period of the rainy season. This latter period coincided with decreased temperature and increased relative humidity. Percentage of adult emergence from the soil was lower in the rainy season than recorded in the dry season in both orchards. Taken together, these observations suggest that T. hawaiiensis and S. dorsalis are the main thrips species pests of mango panicles in Penang. Direct control with insecticides focusing on these two species may help to reduce cosmetic injuries and other damages on mango fruits.
House flies were collected from April 2007-April 2008 from two poultry farms (Balik Pulau and Juru) in the state of Penang. The resistance level of the first generation offspring was evaluated against DDT, malathion, propoxur, and permethrin using the topical application method. The resistance ratio (RR) of the Balik Pulau strain house flies for propoxur, malathion and DDT ranged from 10.28 to 99.00, 7.83 to 47.01 and 6.05 to 31.10, respectively. Resistance to propoxur and malathion in house fly was attributed to cross resistance to organophosphate insecticides used in the farm. Increased metabolic detoxification might be the mechanism involved in DDT resistance due to excessive application of cypermethrin formulation. The RR of the Juru strain for propoxur, malathion and DDT was in a decreasing pattern throughout the study period, ranging from 5.58 to 83.38, 15.19 to 27.82, and 10.04 to 22.69, respectively. Permethrin appeared to be the most potent insecticide in controlling house fly in both the Balik Pulau (RR=0.50 to 1.96) and Juru poultry farms (RR=0.64 to 2.40). The fluctuations of insecticides resistance in house fly was also found to correlate with climatic factors due to its rapid breeding. Relative humidity exhibited positive correlation indices with the changes in the resistance level for DDT (r=0.481, p<0.05), malathion (r=0.698, p<0.01), and permethrin (r=0.580, p<0.05) in Balik Pulau. Similarly, relative humidity in Juru also showed strong correlation with the RR for DDT (r=0.900, p<0.01), malathion (r=0.762, p<0.05), permethrin (r=0.760, p<0.05), and propoxur (r=0.897, p<0.01).
This study assessed the effectiveness of a biorational control approach using 2% hydramethylnon gel bait on German cockroaches, Blattella germanica (L.) in some residential and hospital buildings in South Western Iran. In total, three buildings consisting of 150 apartment units and 101 hospital units were monitored weekly via sticky trap for German cockroach infestations over a period of eight months. These infested units were randomly subjected to intervention and control treatments. Pamphlets and posters were provided and lectures were given to support the educational programmes as a tactic of the biorational system. Survey on cockroach index for intervention units showed 67-94% recovery to achieve clean level of infestation for intervention units of the residential buildings and 83% for the hospital. Mean percentage reductions for treatment groups throughout the 15-week treatment period were 76.8% for the residential buildings and 88.1% for the hospital, showing significant differences compared to the control groups. Linear regression of infestation rates were recorded weekly after treatment and their negative slope for treatment groups substantiated significant reductions for interventions. The results of this study showed that biorational control method, using gel bait, educational programmes and sanitation, is an effective way to manage German cockroach infestation.
The resistance profiles of 22 field-collected populations of the German cockroach, Blattella germanica (L.) (Dictyoptera: Blattellidae), from various localities in Singapore were determined by topical bioassay against novel and conventional insecticides from six classes: (1) pyrethroid (beta-cyfluthrin, deltamethrin), (2) carbamate (propoxur), (3) organophosphate (chlorpyrifos), (4) phenyl pyrazole (fipronil), (5) neonicotinoid (imidacloprid), and (6) oxadiazine (indoxacarb). Compared with a laboratory susceptible strain, resistance levels ranged from 3.0 to 468.0x for the pyrethroids, from 3.9 to 21.5x for the carbamate, from 1.5 to 22.8X for the organophosphate, from 1.0 to 10.0X for phenyl pyrazole, and were absent or low for the neonicotinoid (0.8-3.8x) and the oxadiazine (1.4-5.3x). One strain demonstrated broad-spectrum resistance to most of the insecticides. Synergism studies using piperonyl butoxide (PBO) and S,S,S-tributylphosphorotrithioate (DEF) in combination with a discriminating dose (LD99) of selected insecticides were conducted to test for possible resistance mechanisms. Resistance to pyrethroid was reduced with PBO and DEF, suggesting the involvement of P450 monooxygenase and esterases in conferring resistance. Propoxur resistance also was suppressed with PBO and DEF, and coadministration of both synergists resulted in complete negation of the resistance, indicating the involvement of both P450 monooxygenase and esterase. In six B. germanica field strains evaluated, esterases were found to play a role in chlorpyrifos resistance, whereas the P450 monoxygenase involvement was registered in three strains. Additional resistance mechanisms such as kdr-type and Rdl mutation contributing toward pyrethroid and fipronil resistance, respectively, also may be involved in some strains in which the resistance levels were not affected by the synergists. We conclude that insecticide resistance is prevalent in field German cockroach populations in Singapore.
Here, we describe the biology of a relatively new pest cockroach species in Southeast Asia, Symploce pallens (Stephens) (Dictyoptera: Blattellidae). S. pallens collected from Penang Island, Malaysia, were used for the biological parameter studies and were observed for molting and reproduction events. Nymphal development took 118.2 +/- 1.7 d, with a mean of 9.5 +/- 0.1 molts. The oothecal incubation period was 36.1 +/- 0.2 d. Females produced a mean of 16.0 +/- 10.2 oothecae, with mean 17.6 +/- 0.1 nymphs per ootheca. Nymphal survivorship per ootheca was 90.4%, and 90.7% of nymphs achieved adulthood. The sex ratio did not deviate from 1:1. The mean longevity of adult males and females was 309.3 +/- 7.6 and 322.6 +/- 14.8 d, respectively. In general, S. pallens exhibited higher oothecal production and longer nymphal development and longevity compared with the German cockroach, Blattella germanica (L.).