Sterile Insect Release Method Research Articles

Genetics and its role in the control of animal diseases: A brief review

Veterinary genetics is an emerging branch of genetics which has strong potential application in the control and prevention of livestock disease. Unlike the other methods, control of animal disease through genetic means would be cost effective and does not require continuous investment. This is due to the fact that once a desirable genetic resource is identified and/or achieved, it can be exploited for several generations without any additional input. In the present review, two general approaches or principles to be considered in the control of livestock disease through genetic means are reviewed. The first one is exploitation of the hosts genetic resource, which could be achieved through selection and propagation of those animals having no genetic defects and naturally resistant to a particular disease. Such animals can be prepared through use of transgenic animal technology in which genes for disease resistance have been incorporated. The second approach is genetic control of pathogens by employing several techniques. This includes control of vectors using conventional sterile insect release method, Y-autosome translocation or use of compound chromosomes, and identification and cloning of genes in pathogens responsible for the production of potent antigens which can be used in vaccine development via the application of recombinant DNA technology. Selecting cattle most resistant to the development of infectious diseases will decrease costs of production and should therefore be included in the overall breeding objective.

Quality control methods for Aedes albopictus sterile male production.

The capacity of the released sterile males to survive, disperse, compete with wild males and inseminate wild females is an essential prerequisite to be evaluated in any area-wide integrated pest management (AW-IPM) programs including a sterile insect release method. Adequate quality control tests supported by standardized procedures need to be developed to measure these parameters and to identify and correct potential inappropriate rearing or handling methods affecting the overall male quality. In this study, we report results on the creation and validation of the first quality control devices designed to infer the survival and mating capacity of radio-sterilized Aedes albopictus males through the observation of their flight capacity under restricted conditions (flight organ device) and after stress treatment (aspirator device). Results obtained consistently indicate comparable flight capacity and quality parameters between untreated and 35 Gy irradiated males while a negative impact was observed with higher radiation doses at all observation time performed. The male flight capacity registered with the proposed quality control devices can be successfully employed, with different predictive capacities and response time, to infer the adult male quality. These simple and cost-effective tools provide a valuable method to detect and amend potentially sub-standard procedures in the sterile male production line and hence contribute to maintaining optimal quality and field performance of the mosquitoes being released.

A reaction–diffusion model of the Darien Gap Sterile Insect Release Method

The Sterile Insect Release Method (SIRM) is used as a biological control for invasive insect species. SIRM involves introducing large quantities of sterilized male insects into a wild population of invading insects. A fertile/sterile mating produces offspring that are not viable and the wild insect population will eventually be eradicated. A U.S. government program maintains a permanent sterile fly barrier zone in the Darien Gap between Panama and Columbia to control the screwworm fly (Cochliomyia Hominivorax), an insect that feeds off of living tissue in mammals and has devastating effects on livestock. This barrier zone is maintained by regular releases of massive quantities of sterilized male screwworm flies from aircraft. We analyze a reaction–diffusion model of the Darien Gap barrier zone. Simulations of the model equations yield two types of spatially inhomogeneous steady-state solutions representing a sterile fly barrier that does not prevent invasion and a barrier that does prevent invasion. We investigate steady-state solutions using both phase plane methods and monotone iteration methods and describe how barrier width and the sterile fly release rate affects steady-state behavior.

On an integro-differential model for pest control in a heterogeneous environment.

Insect pests pose a major threat to a balanced ecology as it can threaten local species as well as spread human diseases; thus, making the study of pest control extremely important. In practice, the sterile insect release method (SIRM), where a sterile population is introduced into the wild population with the aim of significantly reducing the growth of the population, has been a popular technique used to control pest invasions. In this work we introduce an integro-differential equation to model the propagation of pests in a heterogeneous environment, where this environment is divided into three regions. In one region SIRM is not used making this environment conducive to propagation of the insects. A second region is the eradication zone where there is an intense release of sterile insects, leading to decay of the population in this region. In the final region we explore two scenarios. In the first case, there is a small release of sterile insects and we prove that if the eradication zone is sufficiently large the pests will not invade. In the second case, when SIRM is not used at all in this region we show that invasions always occur regardless of the size of the eradication zone. Finally, we consider the limiting equation of the integro-differential equation and prove that in this case there is a critical length of the eradication zone which separates propagation from obstruction. Moreover, we provide some upper and lower bound for the critical length.

On a reaction–diffusion model for sterile insect release method on a bounded domain

We consider a system of partial differential equations that describes the interaction of the sterile and fertile species undergoing the sterile insect release method (SIRM). Unlike in the previous work [M. A. Lewis and P. van den Driessche, Waves of extinction from sterile insect release, Math. Biosci.5 (1992) 221–247] where the habitat is assumed to be the one-dimensional whole space ℝ, we consider this system in a bounded one-dimensional domain (interval). Our goal is to derive sufficient conditions for success of the SIRM. We show the existence of the fertile-free steady state and prove its stability. Using the releasing rate as the parameter, and by a saddle-node bifurcation analysis, we obtain conditions for existence of two co-persistence steady states, one stable and the other unstable. Biological implications of our mathematical results are that: (i) when the fertile population is at low level, the SIRM, even with small releasing rate, can successfully eradicate the fertile insects; (ii) when the fertile population is at a higher level, the SIRM can succeed as long as the strength of the sterile releasing is large enough, while the method may also fail if the releasing is not sufficient.

On a reaction-diffusion model for sterile insect release method with release on the boundary

We consider a partial differential equation model that describes the sterile insect release method (SIRM) in a bounded 1-dimensional domain (interval). Unlike everywhere-releasing in the domain as considered in previous works [17] and [14] , we propose the mechanism of releasing on the boundary only. We show existence of the fertile-free steady state and prove its stability under some conditions. By using the upper-lower solution method, we also show that under some other conditions there may exist a coexistence steady state. Biological implications of our mathematical results are that the SIRM with releasing only on the boundary can successfully eradicate the fertile insects as long as the strength of the sterile releasing is reasonably large, while the method may also fail if the releasing is not sufficient.

Sterile insect release method as a control measure of insect pests: A mathematical model

Recently non-conventional approaches of pest control are getting much more importance in different parts of the world. The main reason behind this is the long list of side effects of conventional approaches (use of pesticides etc.). The present paper focuses on one such extremely useful method of insect pest control, namely the Sterile Insect Release Method (SIRM), by using a mathematical model. A blend of dynamical behaviours of the model is studied critically, which, in turn, indicates the relevance of the method. The effect of uncertain environmental fluctuations on both fertile and sterile insects is also investigated. Our analytical findings are verified through computer simulation. Some important restrictions on the parameters of the system are mentioned, which may be implemented for a better performance of SIRM.

Efficiency of the sterile insect release method as an eradication measure for the sweet potato weevil, Cylas formicarius(Fabricius)(Coleoptera: Brentidae) in the field.

A small scale experiment was carried out to eradicate the sweet potato weevil, Cylas formicarius (Fabricius) by the sterile weevil release method from 1994 to 1996 on the islet, Kiyamajima, 35 ha, of the Amami Islands, Kagoshima Prefecture, Japan. Weevils were mass-reared with fresh sweet potato roots at 27°C and roots filled with the weevils were irradiated with gamma ray, 80 Gy on the 27th to 28th days after oviposition (newly eclosed adult). Sterile weevils were stained with fluorescent dyes and released by hand on host plant foliages. Monitoring was done by both pheromone traps and root traps throughout the experimental period. From 11 January, 1994 to 19 July, 1994, ca. 32,000 sterile weevils were released every 10 d as a rule all over the island. This trial suggested the necessity of a denser release of sterile weevils for successful eradication. Thus, for intensive release ca. 16,000 sterile weevils were released every 10 d as a rule from 29 July, 1994 to 5 September, 1995 in a restricted area, 13 ha, as the release zone. The wild population in the release zone was controlled to zero or at least nearly to zero after summer in 1995. Only a few unmarked males were captured by pheromone traps for one year after the final release of sterile weevils on 5 September, 1995, which was probably immigrants from outside of the release zone. No weevils were found in the reexamination of root traps and dissection of wild host plants carried out in September in 1996.

Waves of extinction from sterile insect release

Employing theoretical models, we show that the sterile insect release method (SIRM) can give rise to travelling waves of fertile insects. The velocity of these waves depends critically upon the density of sterile insects (and thus upon the rate at which sterile individuals are being released into the environment). When the sterile density is sufficiently low, the travelling wave advances, giving rise to an invasion. However, when the sterile density exceeds a critical threshold, the wave reverses direction, thereby retreating and giving rise to local extinction. Both analytical (regular perturbation) methods and numerical methods are used to determine wave velocities and wave profiles. This is the first time traveling wave solutions have been shown for the SIRM.

Flightless Mutants in the Melon Fly and Oriental Fruit Fly (Diptera: Tephritidae) and Their Possible Role in the Sterile Insect Release Method

Two new mutants that affect adult wing morphology and render the flies incapable of flight-bubble wing( bw ) in the melon fly, Bactrocera cucurbitae (Coquillett), and small wing ( sw ) in the oriental fruit fly, Bactrocera dorsalis (Hendel)-are described. Both mutants have variable expression and are caused by autosomal, recessive genes. We discuss the possible role of these alleles in constructing genetic sex sorting systems to improve the effectiveness and efficiency of the sterile insect release method.

Genetic variation in the Old World screw-worm fly,Chrysomya bezziana(Diptera: Calliphoridae)

AbstractThe Old World screw-worm fly,Chrysomya bezzianaVilleneuve, occurs in Africa, the Middle East, Malaysia, Indonesia and Papua New Guinea, but it is not found in Australia. Introduction into Australia from any of these source areas would threaten the viability of much of the grazing industry in the northern part of the continent. Proposed control by the sterile insect release method (SIRM) would be compromised by the existence of sibling species withinC. bezziana.This study examines the degree of genetic differentiation throughout the extensive range of the fly to assess if the degree of geographic differentiation indicates the existence of sibling species and, allows identification of the source of any introduced flies. Electrophoretic analysis of 23 loci from samples collected in southern Africa, the Middle East, Malaysia, Indonesia, and Papua New Guinea revealed 11 polymorphic loci. Overall, populations show remarkably little divergence given the geographic distribution of sample sites. None of the populations sampled were fixed for alternative electromorphs. There is no evidence from this study for the presence of sibling species withinC. bezziana.

A Genetic Sexing System to Improve the Sterile Insect Technique against the Mediterranean Fruit Fly

The autosomal recessive allele v wing (v) in the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), produces flies that when reared at 30 degrees C have stubby wings. The mutant was used to construct a translocation-based genetic sexing system in an attempt to improve the efficiency and effectiveness of the sterile insect release method for field control.

The screw‐worm fly Chrysomya bezziana villeneuve (Diptera: Calliphoridae) in a sterile insect release trial in Papua New Guinea

SummaryThe feasibility of the sterile insect release method (SIRM) was tested against natural populations of the Old World screw‐worm fly, Chrysomya bezziana in the Musa Valley, Papua New Guinea. Sterile mating frequencies were determined from egg masses laid by native females on wounded, sentinel cattle. The aerial release of sterilised puparia resulted in low frequencies of sterile matings and few trap recaptures of released material. The release of chilled adult flies resulted in higher frequencies of sterile matings and many trap recaptures. The mean density of males released was 230 males per km2 per week over a target area of 361 km2 (48% of the valley). Sterile masses were first detected 2 weeks after the release of chill flies commenced, reaching a weekly peak of 33% after 5 weeks of releases with 15% of egg masses found to be sterile during the final month. The levels of sterile matings achieved in this trial were similar to comparable SIRM studies made in the USA, Mexico and Guatemala to control the New World screw‐worm fly, Cochliomyia hominivorax.

Radiosensitivity of different larval stage duration pupae of the Mediterranean fruit-fly, Ceratitis capitata Wied

The sensitivity of different larval stage duration pupae of Mediterranean fruit-fly, Ceratitis capitata to gamma irradiation, was tested by exposing pupae, 1 day before adult eclosion, to various gamma ray doses (60, 80 and 100 Gy). The treated pupae were biologically different in their larval span (5, 7 and 9 days). The pupae of med-fly having shorter larval period (5 days) were more resistant to sterilizing effects of gamma irradiation than those having longer larval period (9 days). The longevity of sterilized females developing from irradiated pupae, which had 5-and 7-day larval span, was increased considerably. Treatment of pupae which had 5-day larval span with a dose of 80 Gy, resulted in females which lived 84.3 days, but laid only 2.33 eggs as compared with their control females which lived 51.4 days and laid 976.71 eggs. In general, irradiation of pupae of different larval stage duration with a dose of 60 Gy or greater did not adversely affect the longevity of emerging adults. It is concluded that 60 Gy-irradiation of pupae having long larval span (9 days) should be used in the sterile insect release method for population suppression of Ceratitis capitata .

Relationship between Sperm Competition and Copulation Duration in the Mediterranean Fruit Fly (Diptera: Tephritidae)

Newly identified genetic markers in the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), have been employed to analyze sperm use in multiple-mated females. The sperm of second mating males predominates over that of the initial male in offspring from multiple-mated females. These results are significant for the basic study of the evolution of mating behavior, and for such applied research as the sterile insect release method for field control.

Two Artificial Larval Diets for Rearing Dacus latifrons (Diptera: Tephritidae)

Malaysian fruit fly, Dacus latifrons (Hendel), has been reared on artificial diet for the first time. A carrot and a wheat larval diet were used. Larval recovery for both diets was >50%. Fastest development, highest fecundity, and highest fertility were obtained with the wheat diet. Although reproductive parameters for the wheat diet were less than those for a preferred natural larval host, pepper, Capsicum annuum L. variety jalapeño, scarcity of quality peppers in markets favors use of a wheat artificial diet for mass production of D. latifrons. Results are discussed in relation to mass production of insects for attractants/screening and sterile insect release method (SIRM) programs.

Instructional Simulation: Sterile Insect Release Method with Spatial and Random Effects

A simulation model of the sterile insect release (SIR) method of population suppression was developed as a modeling exercise by advanced students of integrated pest management (IPM). Objectives were to create an instructional model that would demonstrate the principles and operation of the SIR technique to undergraduate IPM students, and allow users to see the effects of relaxing or violating various assumptions of the basic model. In particular, the influence of dispersal, spatial distribution of wild and sterile insects, uncertainty about the initial population density, and stochastic processes can be examined by simulation. Ease of changing the qualitative structure of the model and quantitative values of parameters, along with rapid execution and graphic display on a microcomputer, enhance the instructional value of the model. Simulations show that adjustment of the number of sterile males released can generally compensate for variations in competitiveness of sterile males and uncertainty about the survival rate, fecundity and sex ratio of wild insects. However, dispersal and spatial heterogeneity of the target population place more severe demands on the technique. Release of sterile males in a buffer zone surrounding an isolated population is necessary whenever dispersal is likely, but high mobility of the target species and economic and practical considerations may limit the feasibility and success of this approach. Release ratios that greatly exceed expected necessary levels may fail to ensure eradication due to variations in local pest density and sampling errors. Inadequate detection methods may add to the difficulty of eradicating mobile pests. Knowledge of emigration probabilities and dispersal distances, carefully designed sampling and release programs that take spatial heterogeneity of density into account, and efficient detection methods are all essential to success of the SIR technique.

Mortality, Stadial Duration, and Weight Loss in Three Species of Mass-reared Fruit Fly Pupae (Diptera: Tephritidae) Held with and without Vermiculite at Selected Relative Humidities

Mediterranean fruit fly, Ceratitis capitata (Wiedemann); melon fly, Dacus cucurbitae Coquillett; and oriental fruit fly, Dacus dorsalis Hendel, pupae were held with and without a pupation medium (vermiculite) at 20°C and 90, 60, and 40% RH. For all three species of fruit flies, pupae held with vermiculite were significantly heavier than those held without vermiculite. Storage of pupae in boxes of vermiculite significantly reduced mortality at both 60 and 40% RH. For pupae held without vermiculite, lowest mortality, shortest stadial duration, and highest weight occurred at 90% RH for all three species. At 90% RH, mortality of pupae held without vermiculite did not differ significantly from mortality of those held with vermiculite. Results are discussed with respect to selection of holding procedures for mass-produced fruit fly pupae for programs involving the sterile insect release method.

Suppressive action of Samorin on the cyclical development of pathogenic trypanosomes in Glossina morsitans centralis.

Male Glossina sexually sterilized by gamma-irradiation are as efficient vectors of trypanosomiasis as fertile males. An attempt was made, using isometamidium chloride (Samorin), to interfere with the cyclical development of trypanosomes in sterile males, destined for use in the sterile insect release (SIR) method of tsetse eradication. The infection rate with mature Trypanosoma congolense Broden was effectively reduced in sterile male Glossina morsitans centralis Machado, when the flies were fed on an infected goat 2 days after they were fed as tenerals on an in vitro bloodmeal containing 8 micrograms Samorin/ml blood. The infection rates with mature T.vivax Ziemann and T.brucei brucei Plimmer & Bradford were completely suppressed at this drug dose. Whensterile teneral males were fed on a bloodmeal containing 12 micrograms/ml Samorin and given the infected bloodmeal 10 days later, infections by mature T.vivax, T.congolense and T.b.brucei were completely suppressed. Hence in the management of a tsetse eradication programme utilizing the SIR method, it is recommended that the sterile teneral male tsetse should, prior to release, be given a bloodmeal containing Samorin at 12-15 micrograms/ml blood. This will effectively suppress future disease transmission.

Models of sterile insect releases for populations under attack by parasitoids

Five host-parasitoid models are presented to determine the effects of: (a) host stage parasitized, and (b) position of density-dependent population regulation on the efficiency and dynamics of the sterile insect release method for pest control. Previous models indicate a catastrophic decline of the pest population when sterile releases are above a certain threshold. The five models incorporating parasitoids presented here indicate that this catastrophic decline will usually not occur, but rather the parasitoids will be driven extinct whereupon the system reverts to the one-species dynamics. In this situation, either a population explosion or extinction of the pest species will generally follow, depending on the level of sterile releases and on chance events. The models predict that the behavior of the system is similar regardless of whether the parasitoids parasitize host larvae or host adults. The system dynamics do depend, however, on whether density-dependent population regulation is effective in the hosts or the parasitoids. If population regulation is in the hosts, then the parasitoids may or may not reduce the sterile release rate required for eradication; usually the existence of the parasitoids will substantially reduce this sterile release rate. If population regulation is via the parasitoids, then the sterile release rate required for eradication is greatly reduced over that with no parasitoids; however, the possibility of a major population explosion during the release program is more likely than if population regulation is in the hosts. Model stability was much greater with population regulation in the parasitoids than in the hosts.