A small deletion in the olive fly acetylcholinesterase gene associated with high levels of organophosphate resistance

Study on the insecticidal activity of entomopathogenic fungi for the control of the fruit fly (Anastrepha obliqua), the main pest in mango crop in Colombia

The aim of this study was to evaluate and select entomopathogenic fungi that produces insecticidal compounds for the control of adults of Anastrepha obliqua Macquart (Diptera: tephritidae) that are the main pest of mango (Mangifera indica L. Bark) in Colombia. Nine entomopathogenic fungi isolates were evaluated, five belonging to the genus Metarhizium and four belonging to the genus Beauveria. One strain of the species Metarhizium robertsii with insecticidal activity was selected. By column fractionation, an active fraction was obtained, which caused mortalities higher than 90% after 48 h of exposure. Through HPLC it was determined that the active fraction is composed of more than 22 metabolites. Identification of the metabolites by UHPLC MS/MS revealed the presence of destruxin in E, D, A and B groups (destruxin E-diol, destruxin D, destruxin D1, destruxin D2, destruxin A2, destruxin A, destruxin A3, dihydrodestruxin A, desmB, destruxin B2, destruxin B and destruxin B1). The evaluation of the insecticidal capacity of the organic fractions obtained by HPLC indicated that the extract obtained from the isolate M. robertsii had a compound with high activity on adults of A. obliqua (destruxin A) causing massive mortality of up to 100%, after 48 h of the treatment administration. Furthermore, two other compounds with medium activity were found (destruxin A2 and destruxin B), showing mortalities between 60.0 and 81.3%, respectively. The extract of the isolate MT008 of M. robertsii showed higher insecticidal activity and a potential source for the control of A. obliqua.

Dimethoate induces genotoxicity as a result of oxidative stress: in vivo and in vitro studies

Dimethoate ([O,O-dimethyl S-(N-methylcarbamoylmethyl) phosphorodithioate]) is an organophosphate insecticide and acaricide widely used for agricultural purposes. Genotoxicity refers to the ability of a chemical agent interact directly to DNA or act indirectly leading to DNA damage by affecting spindle apparatus or enzymes involved in DNA replication, thereby causing mutations. Taking into consideration the importance of genotoxicity induced by dimethoate, the purpose of this manuscript was to provide a mini review regarding genotoxicity induced by dimethoate as a result of oxidative stress. The present study was conducted on studies available in MEDLINE, PUBMED, EMBASE, and Google scholar for all kind of articles (all publications published until May, 2020) using the following key words: dimethoate, omethoate, DNA damage, genetic damage, oxidative stress, genotoxicity, mutation, and mutagenicity. The results showed that many studies were published in the scientific literature; the approach was clearly demonstrated in multiple tissues and organs, but few papers were designed in humans. In summary, new studies within the field are important for better understanding the pathobiological events of genotoxicity on human cells, particularly to explain what cells and/or tissues are more sensitive to genotoxic insult induced by dimethoate.

New Mitochondrial Gene Rearrangement in Psyttalia concolor, P. humilis and P. lounsburyi (Hymenoptera: Braconidae), Three Parasitoid Species of Economic Interest

The family Braconidae consists mostly of specialized parasitoids, some of which hold potential in biocontrol of agricultural pests. Psyttalia concolor, Psyttalia humilis and Psyttalia lounsburyi are parasitoids associated with Bactrocera oleae, a major pest of cultivated olives. The native range of Psyttalia concolor is the Mediterranean, and P. humilis and P. lounsburyi are native to sub-Saharan Africa. This study reports the mitochondrial genomes of the three species, thus laying the foundation for mitogenomic analyses in the genus Psyttalia. Comparative mitogenomics within Braconidae showed a novel gene arrangement in Psyttalia in involving translocation and inversion of transfer RNA genes. The placement of Psyttalia in the subfamily Opiinae was well-supported, and the divergence between Psyttalia and its closest relative (Diachasmimorpha longicaudata) was at ~55 MYA [95% highest posterior density (HPD): 34-83 MYA]. Psyttalia lounsburyi occupied the most basal position among the three Psyttalia, having diverged from the other two species ~11 MYA (95% HPD: 6-17 MYA). Psyttalia concolor and P. humilis were recovered as sister species diverged at ~2 MYA (95% HPD: 1.1-3.6 MYA). This phylogeny combining new sequences and a set of 31 other cyclostomes and non-cyclostomes highlights the importance of a comprehensive taxonomic coverage of Braconidae mitogenomes to overcome the lack of robustness in the placement of several subfamilies.

Phylogeography of Organophosphate Resistant ace Alleles in Spanish Olive Fruit Fly Populations: A Mediterranean Perspective in the Global Change Context

The olive fruit fly (olf) Bactrocera oleae is the most damaging olive pest. The intensive use of organophosphates (OPs) to control it, led to an increase in resistance in field populations. This study assesses the presence and distribution of three mutations at the ace gene related to target site insensitivity to OPs in Spain. Samples from other Mediterranean countries were included as external references. Resistance-conferring alleles (from exons IV and VII of the ace gene) reached almost an 80% frequency in olf Spanish populations. In total, 62% of them were homozygous (RR/RR), this being more common in eastern mainland Spain. High frequencies of RR/RR individuals were also found in North Mediterranean samples. Conversely, in Tunisia, only sensitive alleles were detected. Finally, the exon X mutation ∆Q3 had an extremely low frequency in all samples. The high frequency of genotype RR/RR in Spain indicates high fitness in an agroecosystem treated with pesticides, in contrast to ∆Q3. At exon IV all flies carried the same haplotype for the allele conferring resistance. The sequence analysis at this exon suggests a unique origin and fast expansion of the resistant allele. These results provide evidence that OPs appropriate use is needed and prompt the search for alternative methods for olf pest control.

Symbiosis in Sustainable Agriculture: Can Olive Fruit Fly Bacterial Microbiome Be Useful in Pest Management?

The applied importance of symbiosis has been gaining recognition. The relevance of symbiosis has been increasing in agriculture, in developing sustainable practices, including pest management. Insect symbiotic microorganisms' taxonomical and functional diversity is high, and so is the potential of manipulation of these microbial partners in suppressing pest populations. These strategies, which rely on functional organisms inhabiting the insect, are intrinsically less susceptible to external environmental variations and hence likely to overcome some of the challenges posed by climate change. Rates of climate change in the Mediterranean Basin are expected to exceed global trends for most variables, and this warming will also affect olive production and impact the interactions of olives and their main pest, the obligate olive fruit fly (Bactrocera oleae). This work summarizes the current knowledge on olive fly symbiotic bacteria towards the potential development of symbiosis-based strategies for olive fruit fly control. Particular emphasis is given to Candidatus Erwinia dacicola, an obligate, vertically transmitted endosymbiont that allows the insect to cope with the olive-plant produced defensive compound oleuropein, as a most promising target for a symbiosis disruption approach.

A Re-Evaluation of Olive Fruit Fly Organophosphate-Resistant Ace Alleles in Iberia, and Field-Testing Population Effects after in-Practice Dimethoate Use

The management of the olive fruit fly (Bactrocera oleae) is traditionally based upon the use of organophosphate insecticides, mainly dimethoate. In this evolutionary arms race between man and pest, the flies have adapted a pesticide resistance, implying two point-mutations of the Ace gene -I214V and G488S- and a 9bp deletion -Δ3Q. We revisited 11 Iberian locations to evaluate this adaptation of organophosphate (OP)-resistant alleles through amplicon sequencing. Screening for populations where the wild type is prevalent allows an identification of hotspots for targeted mitigation measures; we have hence refined the scale to the region with the lowest OP-resistant alleles frequency 71 locations were sampled and individuals checked using a fast and low-cost allele-specific-primer polymerase chain reaction (ASP-PCR) method]. An increase in Ace gene point-mutations was observed, and the Δ3Q mutation remains undetected. The lowest frequencies of the OP-resistant alleles remain in the west, underlining the hypothesis of an introduction of resistance from eastern Mediterranean areas. A field test was performed by sampling the fly population before and after in-practice dimethoate application. A clear reduction in olive fruit fly numbers was observed, with no relevant changes in the genotypic frequencies of the resistance alleles. The findings are discussed in frame of the type and intensity of the selection pressure that has led to the adaptation to resistance and its consequences from the producer perspective.

Identification of a carboxylesterase associated with resistance to naled in Bactrocera dorsalis (Hendel)

Compared to other organophosphate-resistant and -susceptible (S) lines of Bactrocera dorsalis, the carboxylesterase (CBE) BdE5 in the naled-resistant (nal-r) line has been found to possess remarkable quantitative elevation. Our study attempts to identify the role of BdE5 in naled resistance, and we discovered several points of interest. Firstly, activity staining on native PAGE revealed that the percentage of flies with intensive BdE5 bands in the nal-r line was substantially higher than in the S line, indicating that the BdE5 band correlates with naled susceptibility. Secondly, in vitro and in vivo inhibition assays showed that BdE5 was inhibited by naled in both lines; under diagnostic doses of naled, the overall extent of inhibition on CBEs was much greater in the S line than in the nal-r line. Thirdly, NanoLC-nanoESi-MS/MS analysis used the NCBI database to identify and annotate BdE5 as an esterase FE4-like (XP_011200445.1) in B. dorsalis. Fourthly, rapid amplification of cDNA ends was used to obtain the 2012-bp full-length BdE5 cDNA, which contained an open reading frame of 1770bp and encoded a putative protein of 590 amino acid residues. Phylogenetic analysis revealed that BdE5 is a secreted β-esterase (E clade) closely related to CG6414 (NP_570089), a CBE in Drosophila melanogaster. Finally, our relative quantification real-time PCR data showed a significant elevation in transcript levels of the BdE5 gene in nal-r line. Our results confirmed that BdE5 is correlated with naled resistance and provides further understanding about the identification and molecular characteristics of BdE5 in B. dorsalis.

Geographical distribution and frequencies of organophosphate-resistant Ace alleles and morphometric variations in olive fruit fly populations

BACKGROUND

In the Mediterranean basin, organophosphate (OP) insecticides have been used intensively to control olive fly populations. Acetylcholinesterase (Ace) is the molecular target of OP insecticides, and three resistance-associated mutations that confer different levels of OP insensitivity have been identified. In this study, genotypes of olive fly Ace were determined in field-collected populations from broad geographical areas in Turkey. In addition, the levels of asymmetry of wing and leg characters were compared in these populations.

RESULTS

Our study revealed the existence of a genetically smooth stratification pattern in OP resistance allele distribution in the olive fly populations of Turkey. In contrast to earlier findings, the frequency of Δ3Q was found to be lower in the Aegean region, where the populations have been subjected to high selection pressure. Results based on the morphological differences among the samples revealed a similar pattern for both sides and did not demonstrate a clear separation.

CONCLUSION

The frequencies and geographic range of resistance alleles indicate that they were selected in the Aegean coast of Turkey and then spread westward towards Europe. One possible explanation for the absence of morphological asymmetry in olive fly samples might be the presence of modifier allele(s) that compensate for the increase in asymmetry.

Genotype to phenotype, the molecular and physiological dimensions of resistance in arthropods

The recent accumulation of molecular studies on mutations in insects, ticks and mites conferring resistance to insecticides, acaricides and biopesticides is reviewed. Resistance is traditionally classified by physiological and biochemical criteria, such as target-site insensitivity and metabolic resistance. However, mutations are discrete molecular changes that differ in their intrinsic frequency, effects on gene dosage and fitness consequences. These attributes in turn impact the population genetics of resistance and resistance management strategies, thus calling for a molecular genetic classification. Mutations in structural genes remain the most abundantly described, mostly in genes coding for target proteins. These provide the most compelling examples of parallel mutations in response to selection. Mutations causing upregulation and downregulation of genes, both in cis (in the gene itself) and in trans (in regulatory processes) remain difficult to characterize precisely. Gene duplications and gene disruption are increasingly reported. Gene disruption appears prevalent in the case of multiple, hetero-oligomeric or redundant targets.

Detection and geographical distribution of the organophosphate resistance-associated Δ3Q ace mutation in the olive fruit fly, Bactrocera oleae (Rossi)

BACKGROUND

The olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae), is the most important pest of olives. Its control is based mostly on organophosphate (OP) insecticides, a practice that has led to resistance development. OP resistance in B. oleae has been associated with three mutations in the acetylcholinesterase (AChE), the product of ace gene. The current study presents new diagnostic tests for the detection of the ace mutations and aims at monitoring the frequency of the Δ3Q mutation, which appears associated with resistance at higher OP doses in natural olive fly populations.

RESULTS

An allele-specific polymerase chain reaction (PCR), a PCR-RFLP (restriction fragment length polymorphism) and a Taq-Man test were developed for the Δ3Q mutation detection and a new duplex quantitative PCR assay was designed for the G488S and I214V mutations. Moreover, the frequency of Δ3Q mutation was examined in ten populations of eight countries around the Mediterranean basin. The highest frequencies (10%) were found in Greece and Italy, whereas a gradual decrease of Δ3Q frequency towards the western Mediterranean was noted.

CONCLUSION

Robust tests for insecticide resistance mutations at their incipient levels are essential tools to monitor the increase and geographical spread of such mutations. Three different tests were developed for AChE-Δ3Q that indicated its association with OP applications across the Mediterranean.

Analysis of the Olive Fruit Fly Bactrocera oleae Transcriptome and Phylogenetic Classification of the Major Detoxification Gene Families

The olive fruit fly Bactrocera oleae has a unique ability to cope with olive flesh, and is the most destructive pest of olives worldwide. Its control has been largely based on the use of chemical insecticides, however, the selection of insecticide resistance against several insecticides has evolved. The study of detoxification mechanisms, which allow the olive fruit fly to defend against insecticides, and/or phytotoxins possibly present in the mesocarp, has been hampered by the lack of genomic information in this species. In the NCBI database less than 1,000 nucleotide sequences have been deposited, with less than 10 detoxification gene homologues in total. We used 454 pyrosequencing to produce, for the first time, a large transcriptome dataset for B. oleae. A total of 482,790 reads were assembled into 14,204 contigs. More than 60% of those contigs (8,630) were larger than 500 base pairs, and almost half of them matched with genes of the order of the Diptera. Analysis of the Gene Ontology (GO) distribution of unique contigs, suggests that, compared to other insects, the assembly is broadly representative for the B. oleae transcriptome. Furthermore, the transcriptome was found to contain 55 P450, 43 GST-, 15 CCE- and 18 ABC transporter-genes. Several of those detoxification genes, may putatively be involved in the ability of the olive fruit fly to deal with xenobiotics, such as plant phytotoxins and insecticides. In summary, our study has generated new data and genomic resources, which will substantially facilitate molecular studies in B. oleae, including elucidation of detoxification mechanisms of xenobiotic, as well as other important aspects of olive fruit fly biology.

Genomic structure, organization and localization of the acetylcholinesterase locus of the olive fruit fly, Bactrocera oleae

Acetylcholinesterase (AChE), encoded by the ace gene, is a key enzyme of cholinergic neurotransmission. Insensitive acetylcholinesterase (AChE) has been shown to be responsible for resistance to OPs and CBs in a number of arthropod species, including the most important pest of olives trees, the olive fruit fly Bactrocera oleae. In this paper, the organization of the B. oleae ace locus, as well as the structural and functional features of the enzyme, are determined. The organization of the gene was deduced by comparison to the ace cDNA sequence of B. oleae and the organization of the locus in Drosophila melanogaster. A similar structure between insect ace gene has been found, with conserved exon-intron positions and junction sequences. The B. oleae ace locus extends for at least 75 kb, consists of ten exons with nine introns and is mapped to division 34 of the chromosome arm IIL. Moreover, according to bioinformatic analysis, the Bo AChE exhibits all the common features of the insect AChE. Such structural and functional similarity among closely related AChE enzymes may implicate similarities in insecticide resistance mechanisms.

Biochemical and molecular characterisation of acetylcholinesterase in four field populations of Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

BACKGROUND

The oriental fruit fly, Bactrocera dorsalis, is a major pest that infects fruits and agricultural products worldwide. The latest resistance monitoring of B. dorsalis from mainland China has identified high levels of resistance to insecticides. In this study, the biochemical and molecular characteristics of acetylcholinesterase (AChE) in four field populations of B. dorsalis are investigated.

RESULTS

Among the four populations, the DG population and its purified AChE were found to be the least susceptible to malathion and five inhibitors, whereas the KM population and its purified AChE were the most susceptible. The highest catalytic activity of purified AChE was found for the KM population, and the catalytic activity of the DG population was the lowest. Among developmental stages, the AChE purified from larvae was found to be the most insusceptible to inhibitors, but its catalytic activity was the highest. Sequence analysis of the cDNA encoding AChE showed that some residue differences existed. However, no significant differences in expression levels of the AChE gene among populations and developmental stages were detected.

CONCLUSION

The results suggest that the decrease in susceptibility of B. dorsalis was mainly caused by decrease in AChE activity, and they provide a broad view on the relation between AChE and resistance.

Polymorphism in the acetylcholinesterase gene of Musca domestica L. field populations in Turkey

Acetylcholinesterase (AChE), encoded by the Ace gene, is the primary target of organophosphates (OPs) and carbamates (CBs) in insects. Ace mutations have been identified in OP and CB resistant strains of Musca domestica. In this study, the Ace gene was partially amplified and sequenced at amino acid positions 260, 342, and 407 to determine the frequencies of these mutations in housefly samples collected from farms and garbage disposal sites of 16 provinces in the Aegean and Mediterranean regions of Turkey. In addition, the percent remaining AChE activities in these samples were assayed by using three OPs (malaoxon, paraoxon, and dichlorvos) and one CB (carbaryl) compound as inhibitors. In all the analyzed samples, 13 different combinations at the three amino acid positions were identified and the L/V260-A/G342-F/Y407 combination was found in the highest frequency. No susceptible individual was detected. The highest mean percent remaining AChE activities were detected in the individuals having the L260-A/G342-F/Y407 genotype when malaoxon and paraoxon were used as inhibitors and in the individuals with the L260-A342-F/Y407 combination when dichlorvos and carbaryl were used as inhibitors. The obtained data were heterogeneous and there was no exact correlation between the molecular genetic background and the resistance phenotypes of the flies. The findings of this study at the molecular and biochemical levels indicate the presence of significant control problems in the field.

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.

Altered GPI modification of insect AChE improves tolerance to organophosphate insecticides

The olive fruit fly Bactrocera oleae is the most destructive and intractable pest of olives. The management of B. oleae has been based on the use of organophosphate (OP) insecticides, a practice that induced resistance. OP-resistance in the olive fly was previously shown to be associated with two mutations in the acetylcholinesterase (AChE) enzyme that, apparently, hinder the entrance of the OP into the active site. The search for additional mutations in the ace gene that encodes AChE revealed a short deletion of three glutamines (Δ3Q) from a stretch of five glutamines, in the C-terminal peptide that is normally cleaved and substituted by a GPI anchor. We verified that AChEs from B. oleae and other Dipterans are actually GPI-anchored, although this is not predicted by the "big-PI" algorithm. The Δ3Q mutation shortens the unusually long hydrophilic spacer that follows the predicted GPI attachment site and may thus improve the efficiency of GPI anchor addition. We expressed the wild type B. oleae AChE, the natural mutant Δ3Q and a constructed mutant lacking all 5 consecutive glutamines (Δ5Q) in COS cells and compared their kinetic properties. All constructs presented identical K(m) and k(cat) values, in agreement with the fact that the mutations did not affect the catalytic domain of the enzyme. In contrast, the mutants produced higher AChE activity, suggesting that a higher proportion of the precursor protein becomes GPI-anchored. An increase in the number of GPI-anchored molecules in the synaptic cleft may reduce the sensitivity to insecticides.

Frequencies of organophosphate resistance-associated mutations in the acetylcholinesterase gene of field collected olive fly (Bactrocera oleae) populations under different insecticide regimes

In the present study, the frequencies of three organophosphate (OP) resistance-associated mutations in acetylcholinesterase gene of Bactrocera oleae (BoAce) populations collected from 8 different important olivegrowing areas in the west part of Turkey were determined. Populations were sampled from the areas that have been treated with only the pyrethroid α-cypermethrin; pyrethroids plus OPs; deltamethrin with pheromone eco-traps, and no insecticide treatment applied areas for many years. For Ile214Val and Gly488Ser point mutations PCR-RFLP and for Δ3Q deletion mutation PCR diagnostic tests were carried out. Seventy-two percent of the total individuals analyzed in the study were exhibited heterozygous genotype (RS) for both Ile214Val and Gly488Ser point and homozygous susceptible genotype (SS) for Δ3Q deletion mutations. This RS/RS/SS combination together with RS/RR/SS with the frequency of 13% were the most common two combinations observed in all of the populations under different insecticide regimes, even in the populations under no insecticide pressure for many years. Independent evaluation of the three mutations resulted in 0.450, 0.534 and 0.037 frequency values for the resistant alleles of 214Val, 488Ser and Δ3Q mutations, respectively. Among the studied populations, the frequencies of resistant alleles for the positions of 214 and 488 were not differed from each other. However, in 3 of the populations the frequency of the R allele of Δ3Q was zero and it changed between 0.025 and 0.100 in the remaining five populations. Results of this study contributed to the distribution pattern of the two point mutations in Europe and a pattern for Δ3Q mutation was determined for the first time in the field collected olive fly samples.

Isolation, annotation and applications of expressed sequence tags from the olive fly, Bactrocera oleae

The olive fruit fly, Bactrocera oleae, is the major pest of the olive tree. Despite its importance, very little genetic and molecular knowledge is available. The present study is a first attempt to identify and characterize B. oleae expressed sequence tags (ESTs). One hundred and ninety-five randomly selected cDNA clones were isolated and the obtained sequences were annotated through BLASTX similarity searches. A set of 159 unique putative transcripts were functionally assigned using Gene Ontology terms in broad categories of biological process, molecular function and cellular component based on D. melanogaster matches. Moreover, the cytogenetic location of 35 ESTs was determined by in situ hybridization to B. oleae polytene chromosomes. The resulting low-resolution EST map more than doubles the available entry points to the insect's genome and can assist syntenic comparisons with other distant species. The deduced codon usage of the isolated ESTs suggested a conserved pattern of B. oleae with its closest relatives. Additionally, the comparative analysis of B. oleae ESTs with the homologous D. melanogaster genes led to the development of 17 nuclear EPIC-PCR markers for the amplification of intron sequences of 11 Tephritidae species. Sequencing analysis of several cross-amplified intron sequences revealed a high degree of conservation among Bactrocera species and a varying transferability of the generated markers across the examined genera, suggesting that this method can provide a useful tool for the clarification of phylogenetic relationships among different species, particularly in cases of species complexes.

Spinosad resistance development in wild olive fruit fly Bactrocera oleae (Diptera: Tephritidae) populations in California

BACKGROUND

Among target pests of the insecticide spinosad is the olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae). In Cyprus, spinosad has been sporadically used since its registration in 2002, whereas in Greece its use has been very limited since its registration in 2004, particularly in biological olive cultivars in Crete. By contrast, in California it has been the only insecticide used against the olive fruit fly since its registration in 2004. This study aimed at examining the resistance status of the olive fruit fly to spinosad.

RESULTS

Populations from California, Greece and Cyprus, plus a laboratory population, were tested. Bioassays were performed by oral or topical application of different concentrations of the insecticide. Cypriot populations demonstrated no resistance as compared with that of the laboratory population. Among the Greek populations, only one from Crete demonstrated a fourfold increase in resistance, whereas five populations from California demonstrated a 9-13-fold increase.

CONCLUSION

The observed resistance increase was associated with spinosad applications in the respective areas. These values are relatively low and do not yet pose a serious control problem in the field. However, the observed variation documents that spinosad tolerance has increased in areas where the insecticide has been more extensively used.

Olive fruit fly: managing an ancient pest in modern times

Olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae), is the major pest of commercial olives worldwide. Various aspects of its biology, ecology, management, and impact on olive production are highlighted. With the discovery of insecticidal resistance in some populations frequently treated with organophosphates, old and new control options are being investigated. The potential of biological control is examined. Surveys suggest that a small group of braconids in the Opiinae subfamily best represent the primary parasitoids attacking olive fruit fly in its native range. These species include Psyttalia lounsburyi, P. dacicida, P. concolor, P. ponerophaga, and Utetes africanus. Bracon celer, another braconid but in the Braconinae subfamily, is also reared from the fruit fly in its native range. The potential of these and other natural enemies is discussed with respect to olive fruit fly biology, commercial olive production, and biological constraints that may limit their success. We suggest that numerous species exist that should be further investigated as control agents for olive fruit fly in the many climatic regimes where the pest is found.

Molecular cloning and characterization of an acetylcholinesterase cDNA in the brown planthopper, Nilaparvata lugens

A full cDNA encoding an acetylcholinesterase (AChE, EC 3.1.1.7) was cloned and characterized from the brown planthopper, Nilaparvata lugens Stål (Hemiptera: Delphacidae). The complete cDNA (2467 bp) contains a 1938-bp open reading frame encoding 646 amino acid residues. The amino acid sequence of the AChE deduced from the cDNA consists of 30 residues for a putative signal peptide and 616 residues for the mature protein with a predicted molecular weight of 69,418. The three residues (Ser242, Glu371, and His485) that putatively form the catalytic triad and the six Cys that form intra-subunit disulfide bonds are completely conserved, and 10 out of the 14 aromatic residues lining the active site gorge of the AChE are also conserved. Northern blot analysis of poly(A)+ RNA showed an approximately 2.6-kb transcript, and Southern blot analysis revealed there likely was just a single copy of this gene in N. lugens. The deduced protein sequence is most similar to AChE of Nephotettix cincticeps with 83% amino acid identity. Phylogenetic analysis constructed with 45 AChEs from 30 species showed that the deduced N. lugens AChE formed a cluster with the other 8 insect AChE2s. Additionally, the hypervariable region and amino acids specific to insect AChE2 also existed in the AChE of N. lugens. The results revealed that the AChE cDNA cloned in this work belongs to insect AChE2 subgroup, which is orthologous to Drosophila AChE. Comparison of the AChEs between the susceptible and resistant strains revealed a point mutation, Gly185Ser, is likely responsible for the insensitivity of the AChE to methamidopho in the resistant strain.