Carriers and cutters: size-dependent caste polyethism in the tropical fire ant (Solenopsis geminata).

Body size is an important life-history trait in eusocial insects which plays a key role in colony fitness. The division of labour, represented by caste polyethism, correlates with divergent morphological traits. Size polymorphism has been noted in the tropical fire ant, Solenopsis geminata; however, little is known regarding the differences in the size distributions of workers performing foraging tasks. In the present study, task partitioning was observed in the foraging activities of S. geminata. Two subgroups among foraging workers of S. geminata were discovered using the Gaussian mixture model: a large worker group (head width ≥ 0.924 mm) and a small worker group (head width < 0.924 mm). The foraging worker population comprised two distinct groups - 25.64% were large workers and 74.36% were small workers. Larger workers delivered heavier seeds faster than smaller workers, but this difference became less apparent when lighter seeds were being carried. When large prey such as crickets was encountered during foraging, S. geminata partitioned their tasks into cutting and transportation. The large workers were observed to cut cricket prey into fragments with their longer mandibles, and the small workers then transported these fragments back to the nest. These results present evidence of task partitioning among tropical fire ants, with different tasks being performed by ants of different castes.

Morphological allometry and intersexuality in horsehair-worm-infected mantids, Hierodula formosana (Mantodea: Mantidae).

Parasitic castration is a strategy used by parasites to minimize damage to the host by consuming its reproductive system, which results in the morphological alteration of the host. We determined that the forewing shape and density of the antennal sensilla of field-collected adult male mantids (Hierodula formosana), infected by horsehair worms (Chordodes formosanus) was partially feminized (intersexuality), and both male and female mantids infected by horsehair worms exhibited allometric changes in their wings and walking legs. In addition, the testes of most infected male adults disappeared or reduced in size, whereas the number of ovarioles in infected female adults was unaffected. The infection mainly influenced the structures related to host reproduction and locomotion, suggesting unbalanced energy exploitation and the reduction of parasitic virulence. In addition, the intersexuality of infected male adults indicated that sexual differentiation in insects, which researchers have considered to be an autonomous process, was influenced by the infection. The similarity of the antennae of infected male adults with those of last-instar female nymphs suggested that parasitic juvenilization may cause such feminization, but the mechanism of parasitic influence on insect sex characteristics should be studied further.

A Checklist of Chigger Mites (Acari: Trombiculidae and Leeuwenhökiidae) From Taiwan, With Descriptions of Three New Species.

Scrub typhus is a lethal human disease transmitted by larval trombiculid mites (i.e., chiggers) that have been infected with the rickettsia Orientia tsutsugamushi. In total, 21 chigger species are known from Taiwan. We update the checklist of chiggers of Taiwan based on an intensive survey of shrew and rodent hosts in grasslands and agricultural fields in lowland Taiwan, coupled with surveys of forests in one mountainous site and an opportunistic examination of submitted host specimens. Three new species of chiggers, Gahrliepia (Gateria) lieni sp. n., Gahrliepia (Gateria) minuta sp. n., and Gahrliepia (Gateria) yilanensis sp. n., as well as 23 newly recorded chigger species, were discovered. Accordingly, recorded chigger species of Taiwan more than doubled from 21 to 47 species. Two new species and nine newly recorded chigger species were discovered in forests in one mountainous site in northeastern Taiwan, suggesting that many more chigger species may be uncovered, particularly in mountainous Taiwan. Further studies should also investigate O. tsutsugamushi infection in different chigger species to assess its risks to human health.

The genome of the fire ant Solenopsis invicta.

Ants have evolved very complex societies and are key ecosystem members. Some ants, such as the fire ant Solenopsis invicta, are also major pests. Here, we present a draft genome of S. invicta, assembled from Roche 454 and Illumina sequencing reads obtained from a focal haploid male and his brothers. We used comparative genomic methods to obtain insight into the unique features of the S. invicta genome. For example, we found that this genome harbors four adjacent copies of vitellogenin. A phylogenetic analysis revealed that an ancestral vitellogenin gene first underwent a duplication that was followed by possibly independent duplications of each of the daughter vitellogenins. The vitellogenin genes have undergone subfunctionalization with queen- and worker-specific expression, possibly reflecting differential selection acting on the queen and worker castes. Additionally, we identified more than 400 putative olfactory receptors of which at least 297 are intact. This represents the largest repertoire reported so far in insects. S. invicta also harbors an expansion of a specific family of lipid-processing genes, two putative orthologs to the transformer/feminizer sex differentiation gene, a functional DNA methylation system, and a single putative telomerase ortholog. EST data indicate that this S. invicta telomerase ortholog has at least four spliceforms that differ in their use of two sets of mutually exclusive exons. Some of these and other unique aspects of the fire ant genome are likely linked to the complex social behavior of this species.

Genetic and physiological data suggest demographic and adaptive responses in complex interactions between populations of figs (Ficus pumila) and their pollinating wasps (Wiebesia pumilae).

To study interactions between host figs and their pollinating wasps and the influence of climatic change on their genetic structures, we sequenced cytoplasmic and nuclear genes and genotyped nuclear microsatellite loci from two varieties of Ficus pumila, the widespread creeping fig and endemic jelly fig, and from their pollinating wasps, Wiebesia pumilae, found in Taiwan and on nearby offshore islands. Great divergence in the mitochondrial cytochrome c oxidase subunit I (mtCOI) with no genetic admixture in nuclear markers indicated that creeping- and jelly-fig wasps are genetically distinct. Compared with creeping-fig wasps, jelly-fig wasps also showed better resistance under cold (20 °C) than warm (25 and 30 °C) conditions in a survival test, indicating their adaptation to a cold environment, which may have facilitated population expansion during the ice age as shown by a nuclear intron and 10 microsatellite loci. An excess of amino acid divergence and a pattern of too many rare mtCOI variants of jelly-fig wasps as revealed by computer simulations and neutrality tests implied the effect of positive selection, which we hypothesize was associated with the cold-adaptation process. Chloroplast DNA of the two fig plants was completely segregated, with signs of genetic admixture in nuclear markers. As creeping- and jelly-fig wasps can pollinate creeping figs, occasional gene flow between the two figs is thus possible. Therefore, it is suggested that pollinating wasps may be playing an active role in driving introgression between different types of host fig.

An injury equivalency system for establishing a common economic threshold for three species of rice planthoppers (Hemiptera: Delphacidae) in Taiwan.

The economic threshold (ET) for multiple pest species that share the same injury type on host plants (feeding guild) has been proposed for decision-making in integrated management framework of many defoliating insect pests. However, only a few consider agricultural pests with sucking mouthparts. This study presents the first injury equivalency system for the feeding guild made up of three rice (Oryza sativa L.) planthopper (Hemiptera: Delphacidae) species--Nilaparvata lugens (Stål), Sogatella furcifera (Harváth), and Laodelphax striatellus (Fallén)--by using relative amount of honeydew excretion of each species. The intraspecific injury equivalent coefficient was determined; this coefficient provides an exchange rate for different developmental stages in a species. N. lugens was chosen as the standard species to obtain interspecific injury equivalents for other individuals in the guild, allowing estimates of total guild injury feasible. For extension purposes, the injury equivalency was simplified by pooling all nymphs and adults in the guild to mitigate the potential confusion resulting from uncertainty of instars or wing form. A matrix of ETs established on previous studies and incorporating changes of management cost and rice price was used and served as a control decision guide for the guild samples. The validity of the proposed injury equivalency system was tested using several field data sets, and the results are generally promising and meaningfully elevate the accuracy of estimating combined injury and damage to rice, suggesting that the proposed system is a better integrated pest management decision-making system compared with conventional practices.

Rickettsia felis is an emerging human pathogen associated with cat fleas: A review of findings in Taiwan.

Rickettsia felis is an emerging rickettsial agent principally associated with cat fleas (Ctenocephalides felis), formerly discovered in 1990. Since then, clinical cases of R. felis infection have been identified globally by specific DNA sequences in patients with undifferentiated febrile illness, including in Taiwan, but such evidence is limited. R. felis rickettsiosis is self-limiting and easily treated with doxycycline, but its diagnosis remains a challenge. Environmental risk factors for R. felis rickettsiosis have yet to be clearly demonstrated, and its transmission biology is incompletely understood. Cat fleas are naturally infected with R. felis at varying rates, and vector competence in the transmission of R. felis has been demonstrated in animal models, including dogs, which may serve as reservoir hosts. In northern Taiwan, despite ∼20% of cat fleas infesting companion animals consistently found to be infected with R. felis, only a few cases of potential R. felis infection have been identified through a retrospective serological investigation, though without molecular confirmation. Ecological studies have identified divergent R. felis-like organisms in different arthropod hosts, but these strains appear to serve as nonpathogenic endosymbionts. Although its association with disease is limited, we believe cat flea-borne R. felis warrants increased recognition in an aging population due to immunosenescence and the proximity of companion animals to the elderly. Adopting a One Health approach involving collaboration and communication between clinicians, veterinarians, public health practitioners, and environmental scientists will improve our knowledge about this neglected pathogen and promote the prevention and control of vector-borne diseases.

The insecticidal activities of fire ant (Hymenoptera: Formicidae) venoms against Plutella xylostella (Lepidoptera: Plutellidae) larvae.

Although fire ants frequently have negative impacts on agricultural systems and public health, they have additional beneficial insecticidal effects. To evaluate the potential effect of fire ant venoms on agricultural pests, the compositions of the venoms and their insecticidal activities against Plutella xylostella (L.) larvae were evaluated under laboratory conditions. The alkaloids found in Solenopsis geminata (F.) venom are primarily saturated C11, which occur in both cis and trans forms, whereas the venom of S. invicta Buren contains six principal alkaloids (from trans C1, to C17). Moreover, the proportions of unsaturated alkaloids in the venom of polygynous S. invicta were significantly higher than the corresponding proportions in the monogynous S. invicta, as shown by our previous studies. Fire ant venoms were topically applied to the dorsal thoracic region of fourth-instar larvae of P. xylostella. The results of the experiment showed that the larval symptoms induced by fire ant venom include contractile, flaccid paralysis, black coloration and death. P. xylostella larvae were most susceptible to S. geminata venom. The order of the susceptibilities of the larvae to the venoms was as follows: S. geminata > S. invicta (monogyne form) > S. invicta (polygyne form), as measured by the corresponding LT50 values at 24 h.

Prevalence of Rickettsia felis and the first identification of Bartonella henselae Fizz/CAL-1 in cat fleas (Siphonaptera: Pulicidae) from Taiwan.

Cat fleas (Ctenocephalides felis [Bouché]) are the primary ectoparasites of dog and cat populations. In this study, we report the monthly population dynamics of Rickettsia felis and Bartonella spp. (two zoonotic pathogens that can cause human disease) in cat fleas collected from dogs and cats in Taipei, Taiwan, from December 2006 to December 2007. Natural R. felis infection in individual cat fleas was assessed by polymerase chain reaction (PCR) using pRF-, ompB-, and gltA-specific primer pairs. Samples positive by PCR were confirmed with DNA sequencing. R. felis was detected in cat fleas year round, and the average infection rate was 21.4% (90 of 420) in 2007. Cat fleas also play an important role in the transmission of Bartonella between reservoirs and other mammalian hosts. In this study, we used primer pairs specific for the Bartonella gltA and rpoB genes to detect Bartonella infections. Of the 420 cat fleas tested, 38 were positive by PCR for Bartonella. Sequence similarities to Bartonella henselae, Bartonella clarridgeiae, and Bartonella koehlerae were observed in 6.2% (26 of 420), 2.1% (9 of 420), and 0.7% (3 of 420) of the fleas, respectively. Based on the pap31 gene sequence, several amplicons of the B. henselae detected in the cat fleas could be subgrouped into three strains: Fizz/CAL-1 (n = 18), Marseille (n = 5), and Houston-1 (n = 3). These results demonstrate that cat fleas infected with R. felis are endemic to Taiwan, and highlight the role of C. felis in Bartonella transmission between reservoirs and other mammal hosts and demonstrate the genetic variability of B. henselae in Taiwan.

Fitness costs of an insecticide resistance and their population dynamical consequences in the oriental fruit fly.

Naled is a commonly used insecticide for controlling populations of the oriental fruit fly, Bactrocera dorsalis (Hendel), in Taiwan and other countries. B. dorsalis has developed resistance to the insecticide, and the resistance management is an important issue. Ecological effects (e.g., fitness costs) of the resistance, when fully understood, can be used for the resistance management. This study examined the effects of the insecticide resistance on important life history traits (i.e., survival rates, stage durations, and fecundity) of the oriental fruit fly by comparing the traits of insecticide resistant individuals and susceptible individuals. Population dynamical properties were also examined using a stage-structured matrix model that was parameterized with the empirical data. The results revealed that susceptible individuals had shorter stage durations (e.g., grew faster) and reproduced more than resistant individuals. The average longevity of sexually mature susceptible adults was longer than that of sexually mature resistant adults. The matrix population model predicted that a population of the susceptible individuals would grow faster than a population of the resistant individuals in the absence of the insecticide. The sensitivity analysis of the model suggests that the sexually immature adult stage is a good candidate for controlling B. dorsalis populations.

Species identification of Ixodes granulatus (Acari: Ixodidae) based on internal transcribed spacer 2 (ITS2) sequences.

To investigate the genetic specificity of Ixodes granulatus ticks collected from Taiwan, the genetic identities and phylogenetic relationships were analyzed by comparing the sequences of the internal transcribed spacer 2 (ITS2) region obtained from 27 strains of ticks representing twelve species of Ixodes. Five major clades can be easily distinguished by neighbour-joining analysis and were congruent by maximum-parsimony method. All these I. granulatus ticks collected from Taiwan and Japan were genetically affiliated to a monophyletic group with highly homogeneous sequences (95.8-99.5% similarity), and can be discriminated from other species and subgenera of Ixodes ticks with a sequence divergence ranging from 13.6% to 62.9%. Moreover, interspecific analysis revealed that four distinct lineages are evident between Ixodes ticks, and all these I. granulatus ticks collected from Taiwan and Japan belong to the same lineage. Our results provide the first investigation on the genetic specificity of I. granulatus ticks, and demonstrate that all these I. granulatus ticks represent a unique lineage distinct from other species and subgenera of Ixodes ticks. The feasibility of ITS2-based genetic analysis for species-specific identification of I. granulatus ticks around East Asia was highly anticipated.

Molecular detection of Borrelia valaisiana-related spirochetes from Ixodes granulatus ticks in Taiwan.

Borrelia valaisiana-related spirochetes were detected for the first time in Ixodes granulatus ticks collected in Taiwan. The genetic identities of these detected spirochetes were determined by analyzing the gene sequences amplified by a genospecies-specific polymerase chain reaction assay based on the outer surface protein A (OspA) gene of B. burgdorferi sensu lato. Phylogenetic relationships were analyzed by comparing the sequences of OspA gene obtained from 35 strains of Borrelia spirochetes representing six genospecies of Borrelia. Eight major clades can be easily distinguished by neighbour-joining analysis and were congruent by maximum-parsimony method. Except one strain (KH-74), all these Borrelia spirochetes of Taiwan were genetically affiliated to the same clade with highly homogeneous sequences (97.8-100% similarity), and can be discriminated from other groups of B. valaisiana and other genospecies of Borrelia spirochetes with a sequence divergence ranging from 3 to 19.6%. Moreover, intraspecific analysis also revealed that three distinct groups are evident between the same species of B. valaisiana spirochetes detected in Taiwan. Our results provide the first evidence of B. valaisiana spirochetes detected in I. granulatus ticks collected in Taiwan and demonstrate that all these B. valaisiana spirochetes of Taiwan represent three major groups distinct from the European group of B. valaisiana spirochetes.

A rapid insect species identification system using mini-barcode pyrosequencing.

BACKGROUND: Rapid and accurate species identification is not only important for biodiversity studies and pest quarantine and management, but in some cases may also influence the results of international trade negotiations. In this study, we developed a rapid species identification system for insects. RESULTS: A universal DNA mini-barcode primer pair was designed to target ∼ 120 bp of the mitochondrial 16S rDNA gene. This primer set can amplify the targeted region from all 300 species of 26 insect orders tested as well as other classes of Arthropoda. Although we found no within-species variation in this region, it provided enough information to separate closely related species or species complexes, in particular Thrips spp. and Bemisia spp. By combining a quick DNA extraction method with pyrosequencing, we were able to generate DNA sequences and complete species identification within 5 h. CONCLUSION: Mini-barcode pyrosequencing of 16S rDNA coupled with the GenBank database provides a rapid, accurate, and efficient species identification system. This system is therefore useful for biodiversity discovery, forensic identification, and quarantine control and management. © 2019 Society of Chemical Industry.

Investigation of Ctenocephalides felis on domestic dogs and Rickettsia felis infection in the Democratic Republic of Sao Tome and Principe.

Rickettsia felis is an obligate intracellular Gram-negative bacterium which causes flea-borne spotted fever in humans. In the past decades, R. felis has been detected worldwide in Ctenocephalides felis fleas and various other arthropods. However, due to its shared symptoms with other common vector-borne diseases, human infection is prone to be underestimated or misdiagnosed, especially in the malaria-endemic areas including sub-Saharan Africa, where confirmatory laboratory diagnoses are not usually available. In this study, a 'One Health' approach was adopted to explore potential vector-borne and zoonotic pathogens in the Democratic Republic of Sao Tome and Principe (DRSTP), an island nation in the Gulf of Guinea. By collaborating with local veterinarians, 1,187 fleas were collected from 95 domestic dogs across the country and later identified as Ct. felis using taxonomic keys. A cytochrome oxidase gene-based phylogenetic analysis revealed that all collected fleas belonged to a single haplotype and were identical to isolates from Ivory Coast and Brazil that clustered into a clade of tropical distribution. Additional samples of 14 chigoe fleas (Tunga penetrans) were collected from the surrounding environment of the dogs' resting spots. Rickettsia felis infection in fleas was examined by molecular methods targeting the citrate synthase (gltA)- and outer membrane protein A (ompA)-coding genes as well as the R. felis-specific pRF plasmid. The bacterial DNA was detected in 21.01% (146/695) of cat fleas but none of the chigoe fleas. Microimmunofluorescence assay was then performed to assess pathogen exposure of the residents. Of 240 dried blood spots from participants with dog contacts, 8 (3.33%) exhibited R. felis antibodies. Our findings demonstrated the presence of R. felis in DRSTP. Further extensive epidemiological studies regarding its prevalence and its role in causing febrile illness while the nation is entering pre-elimination stage of malaria will be carried out.

A new millipede-parasitizing horsehair worm, Gordius chiashanus sp. nov., at medium altitudes in Taiwan (Nematomorpha, Gordiida).

Gordius chiashanus sp. nov., a newly described horsehair worm that parasitizes the Spirobolus millipede, is one of the three described horsehair worm species in Taiwan. It is morphologically similar to G. helveticus Schmidt-Rhaesa, 2010 because of the progressively broadening distribution of bristles concentrated on the male tail lobes, but it is distinguishable from G. helveticus because of the stout bristles on the mid-body. In addition, a vertical white stripe on the anterior ventral side and areoles on the inside wall of the cloacal opening are rarely mentioned in other Gordius species. Free-living adults emerged and mated on wet soil under the forest canopy in the winter (late November to early February) at medium altitudes (1100-1700 m). Mucus-like structure covering on the body surface, which creates a rainbow-like reflection, might endow the worm with high tolerance to dehydration. Although Gordius chiashanus sp. nov. seems to be more adaptive to the terrestrial environment than other horsehair worm species, cysts putatively identified as belonging to this hairworm species found in the aquatic paratenic host, Ephemera orientalis McLachlan, 1875, suggest the life cycle of Gordius chiashanus sp. nov. could involve water and land. The free-living adults emerged from the definitive hosts might reproduce in the terrestrial environment or enter an aquatic habitat by moving or being washed away by heavy rain instead of manipulating the behavior of their terrestrial definitive hosts.

Analysis of Recent Interception Records Reveals Frequent Transport of Arboreal Ants and Potential Predictors for Ant Invasion in Taiwan.

We uncovered taxonomic diversity, country of origin and commodity type of intercepted ants at Taiwanese borders based on an 8 year database of 439 interception records. We found intercepted ants arrived predominantly via timber, a pattern likely reflecting the high domestic demand for foreign timber in Taiwan. The most frequently intercepted species were either arboreal or wood-dwelling ants, raising a concern of these ants constituting a next wave of ant invasion in Taiwan. Further analyses indicate that the taxonomic composition of intercepted ants does not match that of established non-native ant species, suggesting that interception data alone fails to provide adequate power to predict the establishment success of ants. Yet, interception frequency and selected life-history traits (i.e., flexible colony founding mode and general nesting habits) were shown to jointly serve as a practical predictor of the establishment risk of non-native ants. Consistent with other border interception databases, secondary introduction (i.e., species arriving from their introduced ranges instead of their native ranges) also represents a major pathway for transport of invasive ants into Taiwan, suggesting its role in shaping the global invasion of ants. Our findings offer baseline information for constructing a prediction framework for future ant invasions and assist in the decision-making process of quarantine authorities in Taiwan.

Rapid identification of the Mediterranean fruit fly (Diptera: Tephritidae) by loop-mediated isothermal amplification.

The Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), ranks as one of the world's most destructive agricultural pests. This pest is also widespread and highly invasive; thus, it is a high priority for pest detection and quarantine programs. Although Mediterranean fruit fly adult and third-instar larvae can usually be identified and distinguished from other species by morphological keys, it is often difficult or impossible to identify or distinguish this species from other tephritids by using material from other stages of development. In such situations, use of a molecular technique known as loop-mediated isothermal amplification (LAMP) would be valuable as a rapid and robust alternative species diagnostic tool. This method uses isothermal conditions and requires only relatively inexpensive equipment. In this study we have developed a simple and rapid procedure that combines a Chelex-based DNA extraction procedure with LAMP to rapidly detect the presence of Mediterranean fruit fly DNA and discriminate it from other species, by using material from different stages of development. Amounts of DNA as little as that recovered from a single egg were shown to be adequate for the analysis, and LAMP itself required only 45 min to complete.

Molecular analysis of Ixodes granulatus, a possible vector tick for Borrelia burgdorferi sensu lato in Taiwan.

The genetic identity of Ixodes granulatus ticks was determined for the first time in Taiwan. The phylogenetic relationships were analyzed by comparing the sequences of mitochondrial 16S ribosomal DNA gene obtained from 19 strains of ticks representing seven species of Ixodes and two outgroup species (Rhipicephalus sanguineus and Haemaphysalis inermis). Four major clades could be easily distinguished by neighbour-joining analysis and were congruent by maximum-parsimony method. All these I. granulatus ticks of Taiwan were genetically affiliated to a monophyletic group with highly homogeneous sequences (92.2-99.3% similarity), and can be discriminated from other Ixodes species and other genera of ticks with a sequence divergence ranging from 11.7 to 30.8%. Moreover, intraspecific analysis revealed that two distinct lineages are evident between the same species of I. granulatus ticks collected from Taiwan and Malaysia. Our results demonstrate that all these I. granulatus ticks of Taiwan represent a unique lineage distinct from the common vector ticks (I. ricinus complex) for Borrelia burgdorferi spirochetes.

Detection of Male Oriental Fruit Fly (Diptera: Tephritidae) Susceptibility to Naled- and Fipronil-Intoxicated Methyl Eugenol.

Naled-intoxicated methyl eugenol (ME) is commonly used to control oriental fruit flies, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), in Taiwan. However, non-responsiveness to ME and pesticide resistance in oriental fruit flies may reduce control efficacy. In this study, mark-recapture experiments were used to analyze the effects of naled-intoxicated ME on field and naled-resistant fly strains. ME non-responsiveness was tested in field, naled-resistant, and susceptible strains and pyrosequencing techniques were used to detect frequencies of point mutations on organophosphate resistant alleles in field strains. Finally, the effects of fipronil-intoxicated ME were analyzed to determine whether control efficiency could be enhanced through the use of alternate pesticides. Control efficiency of naled-intoxicated ME was found to be significantly lower in the field and resistant strains compared to the susceptible strain. ME non-responsiveness was found to be 1.7-1.9% in our lab-reared strains (both naled-resistant and susceptible) and 3.4-4.3% in field strains. Results of our pyrosequencing study found frequency of resistant alleles in captured male field flies to be significantly lower than that of the original population, indicating that it is highly probable that resistant flies may escape from traps. Finally, capture rates of naled-resistant flies increased when naled was replaced with fipronil in attractants, showing that use of pesticides with different modes of action could possibly increase control efficiency of intoxicated ME attractants.

Alterations of the acetylcholinesterase enzyme in the oriental fruit fly Bactrocera dorsalis are correlated with resistance to the organophosphate insecticide fenitrothion.

Alterations of the structure and activity of the enzyme acetylcholinesterase (AChE) leading to resistance to organophosphate insecticides have been examined in the oriental fruit fly, Bactrocera dorsalis (Hendel), an economic pest of great economic importance in the Asia-Pacific region. We used affinity chromatography to purify AChE isoenzymes from heads of insects from lines showing the phenotypes of resistance and sensitivity to insecticide treatments. The AChE enzyme from a strain selected for resistance to the insecticide fenitrothion shows substantially lower catalytic efficiency for various substrates and 124-, 373- and 5810-fold less sensitivity to inhibition by paraoxon, eserine and fenitroxon, respectively, compared to that of the fenitrothion susceptible line. Using peptide mass fingerprinting, we also show how specific changes in the structure of the AChE enzymes in these lines relate to the resistant and sensitive alleles of the AChE (ace) gene characterized previously in this species (described in Hsu, J.-C., Haymer, D.S., Wu, W.-J., Feng, H.-T., 2006. Mutations in the acetylcholinesterase gene of Bactrocera dorsalis associated with resistance to organophosphorus insecticides. Insect Biochem. Mol. Biol. 36, 396-402). Polyclonal antibodies specific to the purified isoenzymes and real-time PCR were also used to show that both the amount of the isoenzyme present and the expression levels of the ace genes were not significantly different between the R and S lines, indicating that quantitative changes in gene expression were not significantly contributing to the resistance phenotype. Overall, our results support a direct causal relationship between the mutations previously identified in the ace gene of this species and qualitative alterations of the structure and function of the AChE enzyme as the basis for the resistance phenotype. Our results also provide a basis for further comparisons of insecticide resistance phenomena seen in closely related species, such as Bactrocera oleae, as well as in a wide range of more distantly related insect species.