Walther Enkerlin

MEDFLY AREAWIDE STERILE INSECT TECHNIQUE PROGRAMMES FOR PREVENTION, SUPPRESSION OR ERADICATION: THE IMPORTANCE OF MATING BEHAVIOR STUDIES

Abstract The Sterile Insect Technique (SIT) is amongst the most non-disruptive pest control methods. Unlike some other biologically-based methods it is species specific, does not release exotic agents into new environments and does not even introduce new genetic material into existing populations as the released organisms are not self-replicating. However, the SIT is only effective when integrated on an areawide basis, addressing the total population of the pest, irrespective of its distribution. There has been considerable progress in the development and integrated application of the SIT against the Mediterranean fruit fly (medfly), Ceratitis capitata, as reflected by operational programs for prevention, suppression and eradication of this pest. There is however, considerable scope for improving the efficiency of medfly SIT, an indispensable requirement for increased involvement of the private sector in any future application. One way to achieve this has been the development of genetic sexing strains, making it possible to release only sterile males. Another is improving sterile male performance through a better understanding of the sexual behavior of this insect. Unlike other insects for which the SIT has been successfully applied, medfly has a complex lek-based mating system in which the females exert the mate choice selecting among aggregated and displaying wild and sterile males. With the objective of developing a better understanding of medfly mating behavior, an FAO/IAEA Coordinated Research Project was carried out from 1994 to 1999. Some of the resulting work conducted during this period with the participation of research teams from ten countries is reported in this issue.

Strategic Options in Using Sterile Insects for Area-Wide Integrated Pest Management

The four strategic options, “suppression”, “eradication”, “containment” and “prevention”, in which the sterile insect technique (SIT) can be deployed as part of area-wide integrated pest management (AWIPM) interventions, are defined and described in relation to the contexts in which they are applied against exotic or naturally occurring major insect pests. Advantages and disadvantages of these strategic options are analysed, and examples of successful programmes provided. Considerations of pest status, biology and distribution affecting decision-making in relation to strategy selection are reviewed and discussed in terms of feasibility assessment, and programme planning and implementation. Unrealistic expectations are often associated with applying the SIT, resulting in high political costs to change a strategy during implementation. The choice of strategy needs to be assessed carefully, and considerable baseline data obtained to prepare for the selected strategy, before embarking on an AW-IPM programme with an SIT component.

Area Freedom in Mexico from Mediterranean Fruit Fly (Diptera: Tephritidae): A Review of Over 30 Years of a Successful Containment Program Using an Integrated Area-Wide SIT Approach

Abstract The Mediterranean fruit fly (Ceratitis capitata, Wiedemann; Diptera: Tephritidae) is regarded as one of the most destructive insect pests worldwide. It was first detected in Mexico (border with Guatemala) in 1977 after it had spread throughout the Central American region. By 1982, using an area-wide IPM approach that included the Sterile Insect Technique, the Moscamed Program, established by the federal governments of Mexico, Guatemala and USA, succeeded in eradicating the pest from the areas it had invaded in Mexico. Recurrent pest entries in the form of transient detections and outbreaks continue to occur in the southern-most States of Mexico bordering Guatemala. The pest free area status is maintained by eradication actions whose effectiveness is verified by an extensive and intense surveillance network including 24,760 traps. In terms of the International Plant Protection Convention (IPPC), the Mediterranean fruit fly pest status can be defined for most of Mexico as “Pest Absent” (i.e., no records of the presence of the pest confirmed by surveys in 28 States of the 32 States) and as “Pest Transient” (i.e., pest entries that do not result in establishment after applying appropriate phytosanitary measures for their eradication) for the southern border States of Chiapas, Tabasco and Campeche, and for the northern border State of Baja California. The very significant investment that the Government of Mexico has made in the Moscamed Program for over 30 years has been extremely cost-effective (benefit-cost ratio of 112 to 1), when compared to the multi-billion dollar horticultural industry that has developed during this period. In addition through the years, the program engaged its own scientists and scientists in a number of countries and organizations in innovation and optimization of important technologies. These include production techniques for an only male genetic sexing strain, emergence towers, aerial release machines, organic targeted insecticide baits, long lasting bait stations, Phase IV traps and female biased attractants, and use of global positioning systems for data analysis and forecasting and for routing aerial releases. These tools have led to increased program effectiveness and have been adopted in many countries.

A Conceptual Model for Assessing the Minimum Size Area for an Area-Wide Integrated Pest Management Program

A conceptual model was developed based on the two basic spatial elements of area-wide integrated pest management (AW-IPM), a core area and a buffer zone, to determine the minimum size of the protected area for the program to be technically feasible and economically justifiable. The model consisted of a biological part (insect dispersal) and an economic part. The biological part used random walks and diffusion equations to describe insect dispersal and to determine the minimum width of the buffer zone required to protect the core area from immigration of pests from outside. In the economic part, the size of the core area was calculated to determine the point at which the revenues from the core area equal the control costs. This model will need to be calibrated and validated for each species and geographic location. Tsetse flies and the Mediterranean fruit fly are used as case studies to illustrate the model.

Sterile males of Ceratitis capitata (Diptera: Tephritidae) as disseminators of Beauveria bassiana conidia for IPM strategies

Sterile Mediterranean fruit fly, Ceratitis capitata (Wied.), males were evaluated as vectors to spread Beauveria bassiana (Bals) conidia to wild C. capitata populations under field conditions. The inoculated sterile males were released by air, using the chilled adult technique over 7000 ha of coffee growing in Chimaltenango, Guatemala, Central America. The impact of releases was determined using dry traps baited with a food attractant. The effects of these releases on Apis mellifera, Linnaeus (honey bee), Hypothenemus hampei, Ferrari (coffee berry borer) and the parasitic mite Varroa destructor (Oudeman) were also evaluated. Inoculated sterile males were able to transmit fungal spores to 44% of the wild C. capitata flies captured in traps, which likely were infected through intra- and intersexual interactions during leks, mating or mating attempts. There was no transmission of the fungal spores to non-target insect species such as coffee berry borer, honey bees or varroa. We conclude that sterile males of Mediterranean fruit fly inoculated with B. bassiana can act as effective vectors of conidia to wild populations, constituting a safe, environmentally friendly and selective alternative for suppressing the medfly under a Sterile Insect Technique-based IPM approach.

Estimation of Populations and Sterility Induction in Anastrepha ludens (Diptera: Tephritidae) Fruit Flies

ABSTRACT The relationship between different release densities of sterile flies and fly trap captures, expressed as flies per trap per day, in the monitoring of Anastrepha ludens (Loew) populations was evaluated in mango orchards. The induction of sterility in fertile females was evaluated using different ratios of sterile: fertile males under field cage conditions. A direct relationship between recaptured flies and densities of release sterile flies was found. However, trap efficiency, expressed as percentage of recaptured flies, decreased as the density of released flies increased. Sterility induction was positively correlated to the ratio of sterile: fertile flies. A significant difference in egg fertility among treatments was observed. The trajectory of sterility induction slowed down after a sterile: wild ratio of 30:1, which suggests that this ratio could be appropriate in an sterile insect technique program with A. ludens. Sterility induction was greater when only sterile males were released than when releasing both sterile males and females, but the differences were not significant. Our findings contribute to a better interpretation of fly captures obtained from the field trapping networks, and to an improvement in the efficiency of sterile insect technique against A. ludens fruit flies, through the implementation of more rational sterile fly release densities.

Pathogenicity of three formulations of Beauveria bassiana and efficacy of autoinoculation devices and sterile fruit fly males for dissemination of conidia for the control of Ceratitis capitata

This study reports the pathogenicity of three formulations of Beauveria bassiana (Balsamo) Vuillemin (Hypocreales) – Bb‐ET, GHA, and Bb‐AES – and their application in panel‐type and cylinder‐type autoinoculation devices, and using sterile males as vectors for the control of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) in coffee‐producing areas of the Central Highlands of Guatemala. Using sterile adults of C. capitata under laboratory bioassays, mean lethal concentrations (LC50) of 1.4 × 107, 2.4 × 106, and 8.2 × 105 conidia ml−1, and median survival times of 4.1 ± 0.1, 4.2 ± 0.1, and 3.8 ± 0.1 days, were recorded for the strains GHA, Bb‐AES, and Bb‐ET, respectively. These values indicate that the three strains were sufficiently pathogenic and that their period of biological activity was considered adequate for using sterile flies as vectors of the inoculum. Observed percentages of sporulated wild C. capitata flies were 57.3, 44.7, and 44.3% for sterile fly vectors, panel devices, and cylinder devices, respectively. The total population reduction at the end of the study period was over 90% for the three treatments. Our results show that sterile males used as vectors or disseminator devices may represent a new control method for area‐wide integrated management of Mediterranean fruit flies. The potential of this new approach and its integration with other control methods, including the sterile insect technique, is discussed.

The Moscamed Regional Programme: review of a success story of area‐wide sterile insect technique application

The Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), is considered one of the most important pests worldwide because of its direct damage to fruit and vegetable production, and restrictions imposed to commercialization of horticultural commodities by countries free of the pest. It was introduced to Brazil in 1901 and to Costa Rica in 1955, from where it spread across the Central American region, reaching Guatemala and Mexico in 1976 and 1977, respectively. In response, the governments of Guatemala, Mexico, and the USA joined efforts to (1) contain further northward spread of the pest, (2) eradicate it from the areas it had invaded in southern Mexico, and (3) in the longer term eradicate it from Guatemala and eventually from the rest of Central America. To this effect, cooperative agreements were subscribed between the three countries and also between the USA and Belize. This allowed regional cooperation against the Mediterranean fruit fly and the creation of the Moscamed Programme. The programme was the first area‐wide large‐scale application of the sterile insect technique (SIT) against this pest. By 1982, the Programme had achieved its first two objectives with the containment of the northward advance of the pest, and its eradication from the areas it had invaded in the states of Chiapas and Oaxaca in southern Mexico. Furthermore, by 1985 the Mediterranean fruit fly had been eradicated from areas in Guatemala located at the border with Mexico. Since then, the programme has had years with significant territorial advances in the eradication of the pest from areas within Guatemala, combined with years when it had setbacks resulting in losses of the territorial gains. Nevertheless, during 4 decades, the programme has effectively served as an effective containment barrier maintaining the Mediterranean fruit fly‐free status of Belize, Mexico, and the USA. It has also protected and increased the Mediterranean fruit fly‐free areas in Guatemala. As a result, it has protected the assets of horticultural producers and contributed during this period to the development of multibillion dollar export industries in these countries. This paper provides an historical review of the programme and describes briefly how technological innovations and decision‐making tools have contributed to programme efficiency. It also discusses how non‐technical and external factors have limited the eradication process and further programme advance within the Central American region.

Population Fluctuation of Ceratitis capitata (Diptera: Tephritidae) as a Function of Altitude in Eastern Guatemala.

Abstract Population fluctuations of Ceratitis capitata (Wiedemann) were evaluated over a period of 12 mo in four altitudinal strata (400–750, 750–1,100, 1,100–1,450, and 1,450–1,800 meters above sea level, masl) in Eastern Guatemala. Within each altitudinal range, sampling plots were established in coffee plantations and adjacent areas, in which Jackson traps were set and baited with Trimedlure. Coffee berries and other host fruits were collected. Population density was lowest at the 400–750 masl stratum and highest at 1,450–1,800 masl. At every altitudinal range, the fluctuations of the pest were associated mainly with the availability of ripe coffee berries as a primary host. From 750–1,450 masl, the pest was also associated with the availability of sweet orange and mandarins in commercial and backyard orchards. The highest densities of the pest were recorded in the dry season. Citrus were the main alternate host where ripe coffee berries were not available. This knowledge on population dynamics of C. capitata will contribute to develop more effective area-wide pest management strategies including the use of sterile insects, natural enemies, and bait sprays.

Modeling diffusive movement of sterile insects released along aerial flight lines

ABSTRACT The redistribution of insects that are released from an airplane is described using a diffusion equation to derive optimal spacing of flight lines and time interval between flights to achieve a reasonably uniform spatial distribution of released insects and to minimize costs. This optimization is done based on relative costs of sterile males and of flying time. An example is presented using data on the Mediterranean fruit fly, Ceratitis capitata (Weidmann), from the Moscamed program in Guatemala. For the parameter values used, the cost (sterile males plus flights) is minimized when insects are released at intervals of approximately every 2 days (for daily mortality μ = 0.24) to 10 days (for μ = 0.04) and flights are spaced at 300 m (for μ = 0.24) to 600 m (for μ = 0.04) apart, depending on daily medfly mortality estimates, which vary widely in the literature. A simpler approximate method of optimization is then presented based on a relationship observed in the optimization results between flight-line separations and the standard deviation of the distribution.