Area-wide Control Programmes Research Articles

Geographic variation in genetic composition, sexual communication and mating compatibility of the False Codling Moth, Thaumatotibia leucotreta for optimisation of area-wide control

Intraspecific variation in sex pheromones is a driver of reproductive isolation and speciation in insects. The False Codling Moth (FCM) Thaumatotibia leucotreta (Lepidoptera: Tortricidae) is a quarantine pest endemic to sub-Saharan Africa (SSA). The currently available precision control measures for FCM use female sex pheromone components to lure males into traps. However, the existing data on the composition of the female sex pheromone, especially the isomer ratios of the main pheromone component (E/Z)-8-dodecenyl acetate, are inconsistent for populations in SSA. This inconsistency led to speculation about possible reproductive isolation between geographically separated FCM populations and the potential need for local adjustment of pheromone-based FCM control tools. This, however, requires a comparative evaluation of geographic variation in FCM sexual communication and inter-population mating compatibility. We therefore investigated genetic isolation and mating compatibility between five geographically isolated FCM populations in South Africa and analysed the ratio of (E)- and (Z)-8-dodecenyl acetate in females from these populations. The five studied populations were found to form three genetically distinct groups with high genetic distances between each other. Mating compatibility tests showed that mating is possible across these groups, however, males preferred females of their own population when given choices; without a choice, males successfully mated with and transferred spermatophores to females from all other populations. The ratio of (E)- and (Z)-8-dodecenyl acetate was similar (c. 4:1) across the populations, indicating that this main female pheromone component does not cause the observed intra-population mating preferences. It remains to be investigated if qualitative/quantitative variation in other sex pheromone components influences intra-population recognition in South African FCM, providing a base for the development of regionally-specific lures for area-wide control programmes.

A spatio-temporal modelling approach to understand the effect of urban fruit fly outbreaks on peri-urban orchards

Urban areas are well-known sources of fruit fly introduction and unmanaged populations pose a high risk of dispersal to surrounding agricultural areas. Although management of urban fruit fly populations is recognised as being important for area-wide control programmes, its relative importance is rarely quantified. Identifying possible sources of fruit fly populations is important to the success of area-wide programs, as well as to on-farm management. We developed a modelling approach to analyse the spatio-temporal connectivity of fruit fly across urban-agriculture boundaries. For a case study, we examine Mediterranean fruit fly, Ceratitis capitata, outbreaks in two fruit growing regions in south-west Western Australia. Connectivity between population sources was defined using a dispersal kernel and routinely collected surveillance data from traps located across urban and agricultural areas. Spatio-temporal Bayesian models were then developed to quantify the extent to which unmanaged urban populations contribute to commercial orchards across each region. Our model results from two fruit growing regions indicate that population connectivity is a strong predictor of urban and commercial orchard Mediterranean fruit fly density. Models demonstrate that unmanaged urban outbreaks can contribute to increased pest pressure in surrounding orchards up to 2 km, but the urban contribution quickly declines over this distance. We also demonstrated that our models provide a means of predicting changes in Mediterranean fruit fly density across a region. Regional scale inference from our models may be particularly useful for sites where surveillance trapping data is unavailable. With an increasing risk of fruit fly incursions from expanding urban areas into agricultural regions, it is important to understand the processes driving population connectivity to target pest management strategies. By modelling surveillance trapping data and population connectivity, we can quantify how unmanaged urban pest infestations can contribute to pest pressure in nearby commercial orchards. Such information can help pest managers quantify the risk posed by unmanaged urban infestations when designing and implementing area-wide management.

Can there be a common, risk-based framework for decisions around live insect trade?

A network of scientists involved in shipment of live insects has met and generated a series of articles on issues related to live insect transport. The network is diverse, covering large-scale commercial interests, government operated areawide control programmes, biomedical research and many smaller applications, in research, education and private uses. Many insect species have a record of safe transport, pose minimal risks and are shipped frequently between countries. The routine shipments of the most frequently used insect model organism for biomedical research, Drosophila melanogaster, is an example. Successful large scale shipments from commercial biocontrol and pollinator suppliers also demonstrate precedents for low-risk shipment categories, delivered in large volumes to high quality standards. Decision makers need access to more information (publications or official papers) that details actual risks from the insects themselves or their possible contaminants, and should propose proportionate levels of management. There may be harm to source environments when insects are collected directly from the wild, and there may be harm to receiving environments. Several risk frameworks include insects and various international coordinating bodies, with experience of guidance on relevant risks, exist. All stakeholders would benefit from an integrated overview of guidance for insect shipping, with reference to types of risk and categories of magnitude, without trying for a single approach requiring universal agreement. Proposals for managing uncertainty and lack of data for smaller or infrequent shipments, for example, must not disrupt trade in large volumes of live insects, which are already supporting strategic objectives in several sectors.

Area-Wide Control Program in Management of Chinese Citrus Fly, Bactrocera minax (Enderlein) (Diptera: Tephritidae), in Citrus Orchards, Sindhuli, Nepal

Chinese citrus fly, Bactrocera minax (Enderlein) (Diptera: Tephritidae) is one of the important citrus pests in Nepal, India and Bhutan including China where it was originated. Since 2014/15, the problem of B. minax in sweet orange fruit is being faced by citrus growers in Sindhuli, Nepal. To mitigate the problem of B. minax, Chinese citrus fly in the orchards, afield practice of area wide control program (AWCP) was piloted in the selected 231 citrus orchards for the first time in Sindhuli in 2018 which has been adopted by 1153 citrus growers in 2019. The obvious recessions of mean fruit damage percentages due to B. minax in the sweet orange orchards at different locations in 2018 (range: 3.9 ± 1.1% to 29.7 ± 9.6%) and 2019 (range: 2.6 ± 0.8% to 7.5 ± 2.3%) have been achieved by virtue of B. minax management through AWCP with poisonous protein bait component and sanitation measure in the citrus orchards.

Transcribed sex-specific markers on the Y chromosome of the oriental fruit fly, Bactrocera dorsalis

BackgroundThe Oriental fruit fly, Bactrocera dorsalis, is a highly polyphagous invasive species with a high reproductive potential. In many tropical and subtropical parts of the world it ranks as one of the major pests of fruits and vegetables. Due to its economic importance, genetic, cytogenetic, genomic and biotechnological approaches have been applied to understand its biology and to implement the Sterile Insect Technique, currently a part of area-wide control programmes against this fly. Its chromosome complement includes five pairs of autosomes and the sex chromosomes. The X and Y sex chromosomes are heteromorphic and the highly heterochromatic and degenerate Y harbours the male factor BdMoY. The characterization of the Y chromosome in this fly apart from elucidating its role as primary sex determination system, it is also of crucial importance to understand its role in male biology. The repetitive nature of the Y chromosome makes it challenging to sequence and characterise.ResultsUsing Representational Difference Analysis, fluorescent in situ hybridisation on mitotic chromosomes and in silico genome resources, we show that the B. dorsalis Y chromosome harbours transcribed sequences of gyf, (typo-gyf) a homologue of the Drosophila melanogaster Gigyf gene, and of a non-LTR retrotransposon R1. Similar sequences are also transcribed on the X chromosome. Paralogues of the Gigyf gene are also present on the Y and X chromosomes of the related species B. tryoni. Another identified Y-specific repetitive sequence linked to BdMoY appears to be specific to B. dorsalis.ConclusionsOur random scan of the Y chromosome provides a broad picture of its general composition and represents a starting point for further applicative and evolutionary studies. The identified repetitive sequences can provide a useful Y-marking system for molecular karyotyping of single embryos. Having a robust diagnostic marker associated with BdMoY will facilitate studies on how BdMoY regulates the male sex determination cascade during the embryonic sex-determination window. The Y chromosome, despite its high degeneracy and heterochromatic nature, harbours transcribed sequences of typo-gyf that may maintain their important function in post-transcriptional mRNA regulation. That transcribed paralogous copies of Gigyf are present also on the X and that this genomic distribution is maintained also in B. tryoni raises questions on the evolution of sex chromosomes in Bactrocera and other tephritids.

Present status and future prospects to safeguard Nepali citrus industry against Chinese citrus fly (Bactrocera minax Enderlein)

Unlike other Tephrid flies, the Chinese citrus fly (Bactrocera minax Enderlein) is univoltine and oligophagous species strictly restricted to citrus fruits. It has been a serious threat to the citrus industry in China, Bhutan, India and Nepal causing up to 100% of fruit drop before the harvest. Citrus groves, especially tight-skinned cultivars, sweet orange (Citrus sinensis L. Osbeck) in mid-hill districts like Ramechhap, Sindhuli, Dolakha, Kavre, Syangja, Gulmi, etc. have been threatened while in some pockets, lemon, acid lime, and mandarin have vanished due to the Chinese citrus fly (CCF). The driver behind the spread of this invasive pest seems to be poor research works on the phenology of the pest, ill-equipped management practices, flying nature of adult fly and easy movement of infested fruits. Therefore, with reviewing published data, this study aimed to figure out the most appropriate management technology for curbing the CCF and make comprehensive material for safeguarding the citrus industry in the future. Since Area-Wide Integrated Pest Management (AW-IPM) or Area-Wide Control Program (AWCP) was found to be an effective tool to control the CCF, individual practices are crucial to incorporate. Monitoring the pest with the lure of protein hydrolase (PH) and subsequently killing adults with attractive protein baits of 25% hydrolyzed protein + insecticide as lethal dinner is mentioned exceptionally better. In AWCP domestic practice: orchard sanitation is not so effective if the orchards are sloppy while shallow tillage adds less to the natural enemy mechanism of CCF pupae in the soil. Equally, we conclude that Sterile Insect Technology (SIT) is not so economical and the boons of natural enemies, parasitoid and entomo-pathogens against CCF, is yet to be exploited.

Area-Wide Control Program of Chinese Citrus Fly Bactrocera minax (Enderlein) in Sindhuli, Nepal

Citrus plays a significant role in providing nutrition to people and generating income for the citrus farmers in Nepal. Among various biotic problems in citriculture, Chinese Citrus Fly (CCF), Bactrocera minax (Enderlein) (Diptera: Tephritidae) has become a major threat to the production of the tight skin citrus fruits, viz. sweet orange, lemon and lime in recent years. This invasive species originated in China and seems to have entered into north-eastern Nepal through Bhutan and Sikkim (India). The damage to sweet orange (Citrus sinensis (L.) Osbeck) by CCF has shown a yearly increasing pattern since 2014 in the central hilly citrus orchards in the districts of Sindhuli and Ramechhap. Sindhuli district holds the first position in terms of sweet orange acreage and its production in Nepal. Conventional pest control measures including pesticide cover spray seemed to have resulted in limited effect in controlling CCF. Thus, as a pilot program, an Area-Wide Control Program (AWCP) of this pest was conducted in 40 ha of sweet orange orchards at Golanjor Rural Municipality-4, Tinkanya in Sindhuli, Nepal to minimize the fruit damages by maggots of B. minax. AWCP focused on the life cycle based management strategy of this pest, targeting the female adult fly population. Formulated protein bait (Great Fruit Fly Bait) containing 25% protein hydrolysate and 0.1% Abamectin was used as spot application underside of the 0.5 to 1 m2 leaf for 10 times at a weekly interval from May to July 2018 as per the protocol developed by Ecoman Biotech, China. The result revealed that the leaf underside spot treatment with the protein bait was highly efficient to minimize the sweet orange fruit losses from 56.7 to 10.9%. Coordination among stakeholders along with sound technical aspect and managerial function seemed essential for the successful implementation of B. minax AWCP.

Growers' risk perception and trust in control options for huanglongbing citrus-disease in Florida and California

Citrus huanglongbing disease (HLB) is an acute bacterial disease that threatens the sustainability of citrus production across the world. In the USA, the Asian citrus psyllid (ACP) is the vector responsible for spreading the disease. Successful suppression of HLB requires action against ACP at large spatial scales, i.e. growers must cooperate. In Florida and California, the citrus production regions have been split into vector-management areas and growers are encouraged to coordinate spraying of insecticide across these (to achieve area-wide control). We surveyed growers from Florida and California, obtaining samples of opportunity at grower meetings, to assess the consensus of opinions concerning issues that influence HLB management. Our results show that a grower's perception of the risk of disease infection and their trust in control options are central to the decision on whether to join an area-wide control program. Growers' perceptions on risk and control efficacy were found to be influenced by information networks and observations about the state of the HLB epidemic and psyllid populations. Within the growers' information networks, researchers and extension agents were reported to have the largest influence on perceptions. Differences in opinion between California and Florida growers as to the efficacy of treatments could be explained as a function of experience: growers from areas with lower densities of ACP were associated with rating insecticide control more positively than those where psyllids population density was higher. Thirty percent of growers identified the expected lack of participation by other growers as a reason why they themselves would not participate in area-wide control.

Seasonality of the Mediterranean Fruit Fly (Diptera: Tephritidae) on Terceira and Sao Jorge Islands, Azores, Portugal.

Population dynamics studies are very important for any area-wide control program as they provide detailed knowledge about the relationship of Medfly [Ceratitis capitata (Wiedemann)] life cycle with host availability and abundance. The main goal of this study is to analyse seasonality of C. capitata in Terceira and Sao Jorge Islands (Azores archipelago) using field and laboratory data collected during (2010–2014) CABMEDMAC (MAC/3/A163) project. The results from Sao Jorge Island indicate significantly lower male/female ratio than on Terceira Island. This is an important finding specially regarding when stablishing the scenario parameters for a sterile insect technique application in each island. The population dynamics of C. capitata are generally linked with host fruit availability and abundance. However, on Terceira Island fruit infestation levels are not synchronized with the trap counts. For example, there was Medfly infestations in some fruits [e.g., Solanum mauritianum (Scop.)] while in the nearby traps there were no captures at the same time. From this perspective, it is important to denote the importance of wild invasive plants, on the population dynamics of C. capitata, as well important to consider the possibility of having different densities of traps according to the characteristics of each area in order to improve the network of traps surveillance’s sensitivity on Terceira Island.

Developing a mass-rearing system for Anastrepha fraterculus (Diptera: Tephritidae) in north-eastern Brazil

Fruit fly pests in north-eastern Brazil include several species of the genus Anastrepha and the Mediterranean fruit fly Ceratitis capitata (Wiedemann). The most common species are Anastrepha zenildae Zucchi, the South American fruit fly Anastrepha fraterculus (Wiedemann), the West Indian fruit fly Anastrepha obliqua (Macquart) and Anastrepha sororcula Zucchi. In this study, attempts were made to mass-rear A. zenildae and A. fraterculus. The objective was to adapt local populations to laboratory conditions and develop mass-rearing systems for further utilization in integrated area-wide control programmes. Small colonies initially fed on guava fruits were developed in the laboratory. Adults were fed a diet made of brown sugar (60%), hydrolysed corn protein (26%), brewer’s yeast (5%) and honey (9%). Adult diets with other combinations of ingredients were also tested. The colonies of A. zenildae and A. fraterculus achieved mating and egg hatch rates of 32 and 39%, respectively. The best diets for adults, resulting in good egg hatch, were as follows: diet B — brown sugar (60%), hydrolysed corn protein (26%), brewer’s yeast (5%) and honey (5%); diet C — hydrolysed corn protein and white sugar (1:3); and diet D — soybean protein and white sugar (1:3). The best larval diet was based on 18% sugarcane bagasse and 9% protein. Adult mortality during the first 15 days was still high, over 50%. Adult recovery from pupae was over 70%. The best oviposition substrate was an agar-coated glass bottle. Mating compatibility was highest for A. fraterculus from the state of Sao Paulo. Mating between A. fraterculus and A. zenildae yielded no viable eggs.

A New Threat Looming over the Mediterranean Basin: Emergence of Viral Diseases Transmitted by Aedes albopictus Mosquitoes

A New Threat Looming over the Mediterranean Basin: Emergence of Viral Diseases Transmitted by Aedes albopictus Mosquitoes

Functional Morphology of the Mouthparts of the Adult Mediterranean Fruit Fly,Ceratitis capitata

Food-based attractants incorporating an insecticide are an important component of area-wide control programmes for the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). This study was carried out to understand the feeding mechanism of adults of this species. Mouthparts of C. capitata are similar in general structure to those of another Tephritid genus, Bactrocera, and have specific structural modifications that determine what adult flies can ingest. The labellum has a series of fine tube-like structures, called pseudotracheae, on its inner surface. Each pseudotrachea leads from the outer margin of the labellum and ends at the prestomum to the oral opening. The pseudotracheae contain fine micropores about 0.5µm in size. During feeding, the oral opening is never exposed to the feeding substrate but the portions of the opposing labellar lobes proximal to the oral opening are flexed against each other and distal portions of the opposing labellar lobes are opened and pressed flat against the feeding substrate or surface. The prestomal spines at the base of each pseudotrachea interlock to form a barrier across the oral opening. Thus entry of large particles directly into the crop and gut through the oral opening is prevented by flexure of the opposing labellar lobes against each other and the interlocking prestomal spines across the oral opening. Only liquids and suspended particles less than 0.5µm in size are sucked through the micropores into the lumen of the pseudotracheae and then pass into the food canal and into the crop and gut. The pseudotracheae of adult C. capitata, particularly along the middle portion of the labellum, have prominent blade-like projections that Bactrocera do not have. These projections are probably an ancestral condition as they were not observed to use them to abrade the plant or feeding surface as has been reported for species in the Tephritid genus, Blepharoneura.

Modeling of Preferential Mating in Areawide Control Programs That Integrate the Release of Strains of Sterile Males Only or Both Sexes

Understanding the principles that govern the mating behavior of insects that are the target of areawide integrated pest management (AW-IPM) programs by using the sterile insect technique (SIT) is a prerequisite to ensure optimal efficiency of such programs. Models were constructed to assess the effect of mating preference of insects, which display a female- or male-choice mating system, on the efficiency of SIT programs that release males only or programs that release both sexes. The model on preferential mating indicated that in a male choice mating system [e.g., screwworm, Cochliomyia hominivorax (Coquerel)], overcoming the discrimination of wild males against mating with sterile females would require a doubling of the number of sterile males compared with male-only releases. The model on female choice was incapable of distinguishing between reduced sterile male competitiveness and female preference for wild males and implied, in addition, that the release of both sexes and male-only releases required the same sterile to wild male overflooding ratio. Operational SIT projects have, however, shown a significant benefit with male-only releases against insects which have a female-choice mating system [e.g., Mediterranean fruit fly, Ceratitis capitata (Wiedemann)], and models were constructed to assess the potential effect of sterile female presence or absence on some parameters, i.e., reduced sterile sperm quantity with remating, reduced sterile sperm quality with aging and incomplete redistribution of the sterile males with the wild insects. The model suggests that in all three cases, male-only releases result in relatively more efficient sterile insects compared with programs releasing both sexes. The results of the models are discussed in relation to data available from operational screwworm and Mediterranean fruit fly AW-IPM programs with an SIT component.

Macrogeographic population structure of the tsetse fly, Glossina pallidipes (Diptera: Glossinidae).

Tsetse flies are confined to sub-Saharan Africa where they occupy discontinuous habitats. In anticipation of area-wide control programmes, estimates of gene flow among tsetse populations are necessary. Genetic diversities were partitioned at eight microsatellite loci and five mitochondrial loci in 21 Glossina pallidipes Austin populations. At microsatellite loci, Nei's unbiased gene diversity averaged over loci was 0.659 and the total number of alleles was 214, only four of which were shared among all populations. The mean number of alleles per locus was 26.8. Random mating was observed within but not among populations (fixation index FST=0.18) and 81% of the genetic variance was within populations. Thirty-nine mitochondrial variants were detected. Mitochondrial diversities in populations varied from 0 to 0.85 and averaged 0.42, and FST=0.51. High levels of genetic differentiation were characteristic, extending even to subpopulations separated by tens and hundreds of kilometres, and indicating low rates of gene flow.

Microsatellite diversities and gene flow in the tsetse fly, Glossina morsitans s.l.

Tsetse flies occupy discontinuous habitats and gene flow among them needs to be investigated in anticipation of area-wide control programs. Genetic diversities were estimated at six microsatellite loci in seven Glossina morsitans submorsitans Newstead (Diptera: Glossinidae) populations and five microsatellite loci in six G. m. morsitans Westwood populations. Nei's unbiased diversities were 0.808 and 76 alleles in G. m. submorsitans and 0.727 and 55 alleles in G. m. morsitans. Diversities were less in three laboratory cultures. Matings were random within populations. Populations were highly differentiated genetically. Populations were strongly subdivided, as indicated by fixation indices (F(ST)) of 0.18 in G. m. morsitans and 0.17 in G. m. submorsitans. 35% of the genetic variance in G. m. submorsitans was attributed to differences between populations from The Gambia and Ethiopia. All available genetic evidence suggests that genetic drift is much greater than gene flow among G. morsitans s.l. populations.

Constraints to the implementation of IPM programs in the U.S.A.: A course outline

To develop and implement the pest management programs of the future, students in crop protection should be educated about the economic, social and institutional contexts in which these programs will operate. To this end, an overview of selected constraints to the implementation of IPM in the U.S.A. is presented. A broad range of constraints is addressed, including institutional conflicts, cosmetic standards, the lack of incentive to develop and use alternatives to chemical control, difficulties in communication and acceptance by growers, risk-aversion, difficulties in organizing area-wide control programs and the complexity of agroecosystems.