Life-history traits of Aedes aegypti (Linnaeus) distributed across a latitudinal range of 23 °N-6 °S.

The growth and associated traits of Aedes aegypti (L.) mosquitoes may adapt and evolve in response to the costs associated with body size in relation to latitudinal variation. We analyzed the life-history traits and energy reserves of field-collected mosquitoes from Taiwan, Thailand, and Indonesia along a latitudinal range spanning from 23°N to 6°S. A U-shaped relationship between body size and latitude was observed. Our study demonstrated the role of latitudinal temperature variations in determining the body size patterns of Ae. aegypti. Notably, the body size of the northern populations (from Taiwan) was significantly larger than those of the tropical populations from Thailand and Indonesia. Models have demonstrated that regional precipitation levels may contribute to body trait variations in certain high-latitude populations in Thailand. However, Indonesian populations have high development rates and large body sizes, indicating the involvement of other physiological traits in determining mosquito body size. The reproductive output of the adult females in this study was positively correlated with body size, but our measure of longevity did not covary significantly with the body size. By contrast, the reproductive output of mosquito-tested populations was in inverse proportion to longevity. Additionally, the mean teneral glycogen levels in the Indonesian and Thai populations were 2.5 times higher than those in the Taiwanese populations. The Indonesian and Thai populations had low mean generation and doubling times, resulting in a high intrinsic rate of increase compared with that of the Taiwanese populations, despite the Taiwanese populations having the highest net reproduction rate.

Ovitrap surveillance of dengue vector mosquitoes in Bandung City, West Java Province, Indonesia.

Larval surveillance is the central approach for monitoring dengue vector populations in Indonesia. However, traditional larval indices are ineffective for measuring mosquito population dynamics and predicting the dengue transmission risk. We conducted a 14-month ovitrap surveillance. Eggs and immature mosquitoes were collected on a weekly basis from an urban village of Bandung, namely Sekejati. Ovitrap-related indices, namely positive house index (PHI), ovitrap index (OI), and ovitrap density index (ODI), were generated and correlated with environmental variables, housing type (terraced or high-density housing), ovitrap placement location (indoor or outdoor; household or public place), and local dengue cases. Our results demonstrated that Aedes aegypti was significantly predominant compared with Aedes albopictus at each housing type and ovitrap placement location. Ovitrap placement locations and rainfall were the major factors contributing to variations in PHI, OI, and ODI, whereas the influences of housing type and temperature were subtle. Indoor site values were significantly positively correlated to outdoor sites' values for both OI and ODI. OI and ODI values from households were best predicted with those from public places at 1- and 0-week lags, respectively. Weekly rainfall values at 4- and 3-week lags were the best predictors of OI and ODI for households and public places, respectively. Monthly mean PHI, OI, and ODI were significantly associated with local dengue cases. In conclusion, ovitrap may be an effective tool for monitoring the population dynamics of Aedes mosquitoes, predicting dengue outbreaks, and serving as an early indicator to initiate environmental clean-up. Ovitrap surveillance is easy for surveyors if they are tasked with a certain number of ovitraps at a designated area, unlike the existing larval surveillance methodology, which entails identifying potential breeding sites largely at the surveyors' discretion. Ovitrap surveillance may reduce the influence of individual effort in larval surveillance that likely causes inconsistency in results.

Effects of piperonyl butoxide synergism and cuticular thickening on the contact irritancy response of field Aedes aegypti (Diptera: Culicidae) to deltamethrin.

BACKGROUND: Exploiting indoor-resting mosquitoes' innate behavioral responses to commonly used insecticide is crucial in vector control programs. Indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) treated with pyrethroids have become widely used for controlling dengue fever vectors. The present study tested the effects of piperonyl butoxide (PBO) synergism and cuticular thickening on the contact irritancy response of field A. aegypti (Diptera: Culicidae) to deltamethrin in Taiwan and Thailand. RESULTS: The escape response of field mosquitoes treated with PBO was significantly elicited, with an escape percentage increase between 2- and 10-fold. In addition, the escape time was significantly lower in PBO-pretreated mosquitoes compared with field mosquitoes treated with deltamethrin alone. PBO-pretreated mosquitoes from seven out of 11 field strains exhibited a knockdown percentage of 11.23-54.91%, significantly higher than that of mosquitoes in corresponding strains treated with deltamethrin only. The Annan, Zhongxi, Sanmin, and North strains exhibited weak knockdown responses (≤3.75%). The mortality of PBO-pretreated field mosquitoes increased 2- to 75-fold compared with those treated with deltamethrin alone (mortality: 0-6.70%). Furthermore, the effect of cuticular thickness on the escape response of field mosquitoes was significant, that is, the escape response marginally increased inversely to cuticular thickness. By contrast, cuticular thickness was not significantly associated with knockdown or mortality percentage. CONCLUSION: Irritant behavior in mosquitoes was significantly elicited by PBO synergism. PBO incorporating deltamethrin IRS or LLINs may be effective for controlling dengue fever vectors. © 2021 Society of Chemical Industry.

Effect of body lipid content is linked to nutritional adaptation in the acclimation responses of mesic-adapted Paederus to seasonal variations in desiccation stress.

Desiccation stress causes mesic-adapted arthropods to lose their body water content. However, mesic-adapted Paederus beetles can survive over prolonged periods under dry field conditions, suggesting that these beetles adopt an array of water conservation mechanisms. We investigated the water balance mechanisms of field-collected Paederus adults over a 14-month sampling period. We also assessed their nutritional adaptations by performing a stable isotope analysis to examine their diet. The water loss rate (WLR) of the beetles was significantly associated with the rice crop cycle and saturation deficit. The cuticular permeability (CP) of adult beetles was maintained at < 30 µg cm-2h-1 mmHg-1; however, CP increased significantly with the WLR. This result indicates that CP might play a minor role in reducing excessive water loss in beetles. The beetles' body water content and percentage total body water content increased when the WLR was high. Trehalose, glucose, and glycogen did not appear to play a central role in enhancing the water reserves in the insects. The body lipid content ranged from 0.22 ± 0.06 to 0.87 ± 0.07 mg and was negatively associated with the WLR. This association indicates that the increase in internal metabolic water was mediated by lipid catabolism. Stable isotope analysis results revealed that the Paederus beetles shifted their diet to carbohydrate-rich plants when the saturation deficit increased and the associated WLR reached its peak; otherwise, they consumed a high amount of staple carbohydrate-poor herbivore prey. The accumulation of energy reserves in the form of lipids through seasonal dietary shifts may exert major effects on the survival and population success of mesic-adapted Paederus beetles.

Repellency and Contact Irritancy Responses of Aedes aegypti (Diptera: Culicidae) Against Deltamethrin and Permethrin: A Cross-Regional Comparison.

Control strategies exploiting the innate response of mosquitoes to chemicals are urgently required to complement existing traditional approaches. We therefore examined the behavioral responses of 16 field strains of Aedes aegypti (L.) from two countries, to deltamethrin and permethrin by using an excito-repellency (ER) test system. The result demonstrated that the escape percentage of Ae. aegypti exposed to pyrethroids did not vary significantly between the two countries in both contact and noncontact treatment despite the differing epidemiological patterns. Deltamethrin (contact: 3.57 ± 2.06% to 31.20 ± 10.71%; noncontact: 1.67 ± 1.67% to 17.31 ± 14.85%) elicited relatively lower responses to field mosquitoes when compared with permethrin (contact: 16.15 ± 4.07% to 74.19 ± 4.69%; noncontact: 3.45 ± 2.00% to 41.59 ± 6.98%) in contact and noncontact treatments. Compared with field strains, the mean percentage of escaping laboratory susceptible strain individuals were significantly high after treatments (deltamethrin contact: 72.26 ± 6.95%, noncontact: 61.10 ± 12.31%; permethrin contact: 78.67 ± 9.67%, noncontact: 67.07 ± 7.02%) and the escaped individuals spent significantly shorter time escaping from the contact and noncontact chamber. The results indicated a significant effect of resistance ratio on mean escape percentage, but some strains varied idiosyncratically compared to the increase in insecticide resistance. The results also illustrated that the resistance ratio had a significant effect on the mortality in treatments. However, the mortality in field mosquitoes that prematurely escaped from the treated contact chamber or in mosquitoes that stayed up to the 30-min experimental period showed no significant difference.

Interpopulation variations in life history traits and reproductive tactics in Aedes aegypti: A test on populations 50 km apart.

The interpopulation variation in life history traits of a species reflects evolutionary adaptation in response to a local environment regime. We examined the life history traits of Aedes aegypti populations from 2 cities in southern Taiwan separated by 50 km. Results revealed a high level of trait differentiation in immature developmental time and survival of Ae. aegypti between the 2 cities. The Kaohsiung populations exhibited total pupation of 40%-60% on day 8; this was significantly lower than that of the Tainan populations and laboratory-reared KHsm mosquitos, which exhibited a pupation rate of 70%-90%. The slow immature development of the Kaohsiung populations was reflected in the low percentage of adult emergence (22%-26%) on day 10. The prolonged immature development did not select larger adults with longer life spans because the Kaohsiung populations had a shorter life span (≈37 d) than that of the Tainan populations (≈42 d). By contrast, immature development and longevity did not differ between populations within each region, indicating weak local differentiation. Three field populations exhibited male-bias sex ratio because of differential mortality of female immatures. The effect of female size on adult life history was nonsignificant. Two reproduction tactics were detected, representing the balanced-mortality hypothesis and the bet-hedging hypothesis. Despite their differential life history strategies and reproductive tactics, these mosquito populations apparently counterbalanced any shortcomings in traits to produce similar population growth. Maintaining optimal population density is essential for Aedes mosquitos to increase the probability of encountering mates and reduce the Allee effect.

Effects of larval diets and temperature regimes on life history traits, energy reserves and temperature tolerance of male Aedes aegypti (Diptera: Culicidae): optimizing rearing techniques for the sterile insect programmes.

BACKGROUND: Producing high quality sterile males is vital in Aedes aegypti rear-and-release birth control strategies. Larval diets, rearing temperatures, and their interactions determine the accumulation rates of essential nutrients in larvae, but these factors have been understudied in relation to mass-rearing techniques for producing eminent males. METHODS: We compared the effects of two larval diets, a cereal-legume-based diet (Khan's diet) and a standard larval diet developed in the FAO/IAEA Insect Pest Control Laboratory (IAEA 2 diet). Diets were tested at selected temperatures for both larval and male adult life history traits, adult extreme temperature tolerance, and mating capacity relative to energy reserves of reared male adult Ae. aegypti. RESULTS: Khan's diet resulted in shorter immature development time at each test temperature (except for 25 °C) than an IAEA 2 diet. Larvae reared at 28 °C and 32 °C with Khan's diet demonstrated low pupation rates (c.80%). We accounted for these phenomena as secondary sex ratio manipulation, because a higher proportion of male adults emerged at 28 °C and 32 °C than that for the IAEA 2 diet. In general, the pupal development time shortened as temperature increased, resulting in higher teneral energy reserves in male mosquitoes. High energy reserves allowed male mosquitoes reared with Khan's diet to have higher adult longevity (5-6 days longer when sugar-fed and 2-3 days longer when water-fed) and tolerance of heat stress than those fed on the IAEA 2 diet. The IAEA 2 diet produced larger male mosquitoes than Khan's diet did: mosquitoes fed on Khan's diet were 1.03-1.05 times smaller than those fed on the IAEA 2 diet at 28 °C and 32 °C. No evidence indicated reduced mating capacity for small mosquitoes fed on Khan's diet. CONCLUSIONS: Larvae reared at 28 °C and 32 °C with Khan's diet were characterized by shorter immature development time compared with those fed on the IAEA 2 diet. Adult mosquitoes produced from that larval rearing condition exhibited a significant male bias, long lifespan, and better endurance against extreme temperatures relative to energy reserves. Thus, the larval diet at rearing temperature of 28 °C and 32 °C optimized rearing techniques for the sterile insect programmes. However, mating competitiveness and flight performance of adult males require further investigation.

Adult Paederus fuscipes (Coleoptera: Staphylinidae) Beetles Overcome Water Loss With Increased Total Body Water Content, Energy Metabolite Storage, and Reduced Cuticular Permeability: Age, Sex-Specific, and Mating Status Effects on Desiccation.

The ability of Paederus beetles to resist desiccation stress is vital to their adaptability in various ecological niches. How water relations and their response to desiccation vary among adult beetles of different age, sex, and mating status is unclear. We examined the water relations of adult Paederus fuscipes Curtis and the mechanisms used to reduce desiccation stress. One-day-old beetles had an exceptionally high percent total body water (%TBW) content and tolerated a high level of %TBW loss. Newly emerged beetles contained a high level of trehalose and 40 to 60% lipid content of their total dry mass, which allowed them to endure desiccation. Beetles that were 10 wk old and older exhibited reduced cuticular permeability. Glucose, glycogen, and lipid contents were crucial throughout most of the adult life span, as they helped compensate for water loss via increased water vapor absorption and metabolic water. In particular, the accumulation of lipid after mating was significant and may further confer tolerance to water loss. The effect of melanization on the desiccation tolerance of beetles was not significant. Females had better tolerance in response to desiccation stress compared with males. We suggest that the observed differences between sexes likely were a function of water relations and an effect of energy metabolite reserves. However, the mortality of females at 24-h postdesiccating stage was marginally significant compared with males. These results demonstrate that P. fuscipes adults prevent dehydration using multiple mechanisms that collectively reduce desiccation stress and increase dehydration tolerance.

Effect of imidacloprid exposure on life history traits in the agricultural generalist predator Paederus beetle: Lack of fitness cost but strong hormetic effect and skewed sex ratio.

A trade-off between life history traits in the evolution of insecticide resistance is common in insects because energy acquisition is mainly channeled for detoxification enzyme production. In addition, sublethal exposure to insecticides may have an effect on the physiology and behaviors of surviving insects. Similar to other agricultural pests, pesticide use may have led to insecticide resistance in populations of Paederus fuscipes Curtis. In this study, we determined the median lethal time of 10 field-collected strains in Taiwan for three insecticides that are commonly employed to manage agricultural pests. We determined that the susceptibility of these strains to cyhalothrin and fenitrothion were similar, with resistance ratios (RRs) ranging from 1 to 4; however, significantly different to imidacloprid (RRs: 1-16). The effect of imidacloprid resistance on the life history traits studied of Paederus beetles was limited; only a prolonged egg incubation period, and adult longevity decreased as imidacloprid resistance increased. Regarding sublethal exposure to imidacloprid, adult sex ratios were female biased in most combinations, though nonsignificant. The quality of offspring, particularly the length of eggs significantly decreased. In addition, a hormetic effect was apparent when the individual was exposed to LT25 and LT50; mean fecundity per female increased from 12.80 ±â€¯8.95 (±â€¯standard error [SE]) to 42.70 ±â€¯13.77 eggs compared with that of the control (7.10 ±â€¯1.32). However, the hormetic effect was inconsistent among the tested strains, possibly because of the difference in insecticide resistance levels given that reproductive compensation was absent among the resistant population.

Comparison of Water Relation in Two Powderpost Beetles Relative to Body Size and Ontogenetic and Behavioral Traits.

Heterobostrychus aequalis (Waterhouse) (Coleoptera: Bostrychidae) and Lyctus africanus Lesne (Coleoptera: Lyctidae) are distributed mainly in tropical regions. The primary mechanism allowing these beetles to survive in cold and arid habitats beyond the native tropical region is a reduced water loss rate. This study investigated the water relations of these two beetles in relation to their size, ontogenetic traits, and behavioral characteristics to determine how they can survive in desiccated wood. H. aequalis and L. africanus share similar water characteristic with beetles living in desert and woodlands. They have high percentage total body water (%TBW) content (58.38 ± 1.86% to 63.20 ± 1.38%), but low %TBW loss (4.28 ± 1.02% to 48.26 ± 8.28%) due to their impermeable cuticle (cuticular permeability [CP] value: 0-15.57 ± 4.90 µg cm-2 h-1 mmHg-1) at all life stages. Although the larvae of L. africanus exhibited relatively high %TBW loss, they had relatively shorter development times that minimized prolonged exposure to dry conditions inside the wood. The aggregative behavior of the adult could be responsible for maintaining a low water loss rate to compensate for their small body size. In contrast, the larvae of H. aequalis had larger body size and significantly lower CP values, allowing them to survive in the desiccated wood for a longer period of time. These results demonstrate the remarkably sophisticated strategies that insects employ as a trade-off between body size, ontogenetic development, and insect sociality (aggregative and non-aggregative behavior) to maintain their water balance in xeric environments.

The Effect of Insecticidal Stress on Reproductive Output of Susceptible and Field Strains of Aedes aegypti (Diptera: Culicidae).

The phenomenon of high egg reproduction when mortality risk rises is common in mosquitoes. However, the phenomenon may vary between insecticide susceptible and field-collected strains, due to the latter's decreased energy allocation in reproduction in the presence of insecticide resistance. In this study, we evaluated the effect of chlorpyrifos (CP) and temephos (TP) exposure on the oviposition and survival of Aedes aegypti (Linnaeus) (Diptera: Culicidae) using a susceptible strain (KHsm) and two field strains (KHly and TNnorth). We also dissected the female mosquitoes of each strain on fifth day after the first blood meal to examine the total number of eggs produced. Neither CP nor TP exhibited oviposition deterrent against female mosquitoes of any of the three strains, as the females did not show decreased reproduction activity on the insecticide-treated sites. Of the two insecticides tested, only CP had an adulticidal effect on Ae. aegypti. High mortality was recorded in KHsm after contacting the CP-treated oviposition sites on day 4. Before death, KHsm mosquitoes oviposited significantly more eggs compared to the two field strains. However, the difference of total egg production between susceptible and field-collected strains was subtle. Thus, the decreased reproductive output in field-collected strains might not be directly linked to energy and resource allocation. In this respect, we should consider the possible involvement of biogenic amines in the egg retention in field-collected strains when mortality risk rises. The phenomenon was not observed in nonadulticidal TP treatment.

The effect of remnant forest on insect successional response in tropical fire-impacted peatland: A bi-taxa comparison.

Fire has become a common feature in tropical drained peatlands, and it may have detrimental impacts on the overall biodiversity of the forest ecosystem. We investigated the effect of fire on termite and ant assemblages and the importance of remnant forest in restoring species diversity in fire-impacted tropical peat swamp forests. The species loss of both termites and ants was as high as 50% in some fire-impacted peats compared to remnant forests, but in most cases the species richness for termites and ants was statistically equal along the land uses surveyed. However, a pronounced difference in functional group composition of termites was detected. In particular, sites close to remnant forests contained two additional termite feeding groups so that they shared a similar composition structure with remnant forests but were significantly different from sites distant from remnant forests. In general, ants were resilient to fire, and the similarity index showed a high degree of similarity among ant communities in all land uses surveyed. The Shannon diversity index for termites and ants decreased with increasing distance from the remnant forests and level of ecological degradation. Peat vegetation variables and ecological degradation were important in shaping termite and ant communities in the tropical peatlands, but their relative importance was not significant in fire-impacted peats regardless of distance from the remnant forests. This study highlights the importance of remnant forests as a biodiversity repository and natural buffer that can enhance species diversity and recolonization of forest-adapted species.

The Impact of Tropical Peat Fire on Termite Assemblage in Sumatra, Indonesia: Reduced Complexity of Community Structure and Survival Strategies.

Tropical peat swamp forests in Southeast Asia account for approximately 72% of global peatland. However, extensive forest exploitation following peat drainage for agricultural expansion has been leading to catastrophic peat fires. In this study, we compared the termite assemblage in burnt and unburnt peats in Sumatra, Indonesia. We also identified which taxonomic group is particularly resistant to fire disturbance and the traits that correlate with its persistence in fire-impacted peatlands. Overall, the termite species richness in fire-impacted peats was up to 40% lower than that of the total species found in peat swamp forests. Although the estimated species richness values in fire-impacted peats and peat swamp forests were not significantly different, fire changed termite community structure significantly. Only termites of the family Rhinotermitidae survived in the fire event, whereas members of the Termitidae that were reportedly resilient to fire and open habitats elsewhere disappeared during the fire events. The rhinotermitids found in the burnt sites were exclusively wood nesters. This suggests that the desiccation tolerance of termites in open habitat is not the simple underlying survival strategy, but tree branches and barks might have provided a refuge from heat during fire. The result also suggests that the high similarity in species composition in recently burnt peats and long burnt peats implies low species turnover. Thus, regardless of how much time had passed since the fire-impacted peats were abandoned or cultivated, the increase in habitat complexity did not favor colonization by the forest-dependent group.

Paederus Outbreaks in Human Settings: A Review of Current Knowledge.

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.

Effect of diet quality on survival and reproduction of adult Paederus fuscipes (Coleoptera: Staphylinidae).

The survival and reproduction of the beetle Paederus fuscipes Curtis on diets that differed in macronutrient composition were investigated in the laboratory. The sex organs of females fed each test diet were dissected to evaluate the ovarian development over time. Adults fed on a carbohydrate-rich diet lived longer than adults fed the other diets, but this diet provided insufficient nutrients for reproduction. Females fed on a protein-rich diet had high fecundity; however, the mean longevity of reproductive adult P. fuscipes significantly was shortened by 20-30 d compared with longevity of 60-70 d for adults fed a carbohydrate-rich diet. In contrast, adults that were provided lipid-rich diet had low survival and fecundity. Overall, the development ofprevitellogenic follicles was significantly affected by diet regime and days since starting a particular diet. The follicle size of females given protein-rich diet increased 0.5-fold 2 wk after beginning the diet. In contrast, the development of the follicles was slow in females given the carbohydrate-rich diet and the follicles degenerated in females given the lipid-rich diet. In terms of ovarian maturation, females fed on a protein-rich diet contained mostly vitellogenic and chorionated follicles. In contrast, the ovarioles of females on the carbohydrate-rich diet were largely occupied with previtellogenic and vitellogenic follicles, whereas for a lipid-rich diet, the follicles remained at the previtellogenic stage throughout the experiment.

Dispersal pattern of Paederus fuscipes (Coleoptera: Staphylinidae: Paederinae) in relation to environmental factors and the annual rice crop cycle.

Paederus fuscipes Curtis, a dermatitis linearis causing agent, has received increasing attention from the public, as it poses a serious health threat after mass dispersal into human-dominated areas. Preventive measures against this insect have so far been unsuccessful partly because of limited knowledge about its dispersal pattern. In this study, the dispersal activity of P. fuscipes was studied at infestation-prone residential buildings in Mainland Penang, Malaysia. The dispersal activity of P. fuscipes showed two peaks, that is, from February to April and August to October. Overall, there was no statistical significant correlation between dispersal and climatic parameters, that is, temperature, relative humidity, total rainfall, at all sampling localities. However, dispersal was primarily caused by human activities in rice fields, which accounted for >60% of the variability in dispersal. Particularly, rice harvesting, including straw burning, and cultivation were the major factors triggering P. fuscipes dispersal. These activities presumably disrupted the habitat and normal activities of P. fuscipes and rendered the rice fields unfavorable refuges. In addition, the beetles might also face food shortages after the disturbance of their prey base in the crop fields. The current study provides a predictive tool of P. fuscipes flight periods to ensure insecticide residual spraying is timed in the infestation-prone residential areas before the onset of infestation.

Influence of temperature on survival and water relations of Paederus fuscipes (Coleoptera: Staphylinidae).

The effects of four temperatures (15, 23.5, 28, and 35 degrees C) on the biological characteristics of the rove beetle Paederus fuscipes Curtis were studied, and its cuticular permeability also was measured. Specimens successfully developed to adulthood at each temperature tested, but development time of each preadult stage significantly decreased with increasing temperature. Both egg and L1 stages required at least 80 degree days above a threshold of approximately 10 degrees C to develop to the subsequent stage. The lengthy development time and high survival rate of preadults at 15 degrees C suggests that P. fuscipes can survive in a harsh environment during cold weather by hibernating, and this ability could allow preadults to succeed ecologically in temperate countries. However, adult longevity was short, and no fecundity was recorded at 15 degrees C. At 28 degrees C, P. fuscipes exhibited a high survival rate of adults, which had a longer life span and high fecundity; thus, the population had the highest intrinsic rate of increase (0.0788 +/- 0.0051 d(-1)) and the shortest mean generation time (48.57 +/- 1.43 d) at 28 degrees C. At this temperature, the population might reach a size that could facilitate invasion into residential areas. However, in the absence of a hygric environment, P. fuscipes was unable to survive despite favorable temperature. Unlike in adults and pupae, high cuticular permeability values were found in the larval stages. This indicates that larvae are highly susceptible to desiccation, and it explains why the distribution of P. fuscipes is restricted to moist habitats.

Contact toxicity and residual effects of selected insecticides against the adult Paederus fuscipes (Coleoptera: Staphylinidae).

The contact toxicity of four insecticide formulations (deltamethrin, fipronil, fenitrothion, and imidacloprid) applied on three different substrates (tile, plywood, and concrete) against the adult rove beetle, Paederus fuscipes Curtis, was evaluated. The relative order of speed of killing effects was as follows: deltamethrin > imidacloprid > fipronil > fenitrothion. Although deltamethrin showed the fastest action against P. fuscipes, the recovery rate of rove beetles at 48 h posttreatment was moderate (approximately 25%) on the tile surface to high (approximately 80%) on the plywood surface. Thus, it is likely that the insects did not pick up the lethal dose especially on porous surfaces. In contrast, fipronil demonstrated delayed toxicity that might promote maximal uptake by the insects. More than 80% mortality was registered for tile and plywood surfaces up to 4 wk after exposure. High mortality (almost 100%) was recorded for imidacloprid-exposed P. fuscipes at 48 h posttreatment, but only on the tile surface. Among the four insecticides tested, fenitrothion was the least effective against P. fuscipes because low percentage to no mortality was recorded in the fenitrothion treatment.

Life table of Paederus fuscipes (Coleoptera: Staphylinidae).

The life history characteristics of the rove beetle Paederus fuscipes Curtis were studied under laboratory conditions using three field strains from Malaysia: Desa Wawasan (DW), Sri Pinang (SP), and Ampang Jajar (AJ). The total development time of immature stages differed significantly among the three strains, especially between DW (17.43 +/- 0.16 d), SP (18.60 +/- 0.19 d), and AJ (18.68 +/- 0.22 d). Adult females and males from DW also exhibited a shorter life span, although the difference among strains was not significant. In terms of fecundity, the numbers of eggs laid per female for DW, SP, and AJ were 121.28 +/- 15.98, 127.30 +/- 18.01, and 147.45 +/- 17.12, respectively. Additionally, because of the shorter life span in DW strain, two apparent peaks in age-stage specific fecundity were detected. The beetles compensated for their shorter life span by increasing their reproductive activity to sustain the progeny in the population. The intrinsic rates of increase (r) of P. fuscipes from DW, SP, and AJ were 0.0773 +/- 0.0046 d(-1), 0.0788 +/- 0.0051 d(-1), and 0.0873 +/- 0.0054 d(-1), respectively; and the net reproduction rates (R0) were 40.09 +/- 7.39 offspring, 45.29 +/- 8.74 offspring, and 42.34 +/- 8.25 offspring, respectively. The mean generation time of P. fuscipes from AJ was 43.08 +/- 1.07 d, which was significantly higher than that from DW (47.95 +/- 1.36 d) and SP (48.57 +/- 1.43 d). The total immature development time of P. fuscipes in this study was shorter than values reported in previous studies.