Sterile Insect Technique for Suppressing and Eradicating Insect Population: 55 Years and Counting

The sterile insect technique (SIT) has a long, interesting, but. controversial history. The concept, operation, and outcomes of SIT programs have been criticized heavily and acceptance of this areawide approach to insect management is minimal. These criticisms are examined in general and specifically with regard to Mediterranean fruit fly, Ceratitis capitala (Weidemann), and screwworm, Cochliomyia hominivomx CoquereL The chief objections reviewed included evolutionary responses to SIT, the occurrence of sibling species, the role of weather in causing pest suppression and outbreaks during SIT programs, and the occurrence of undetected pest populations where eradication has been claimed. There is a paucity of data relating sterile fly releases to sterile mating rates in target populations and sterile roatings to target population dynamics. The overkill strategy should be updated, especially in experimental efficacy trials. Despite the carping, it is concluded that SIT is a highly effective method for insect population management. This environmentally benign method of insect pest suppression and eradication is underutilized even though using SIT has eradicated screwworm populations on a continental scale and many tephritid fruit fly infestations throughout the world. It would lend credibility to the efficacy of SIT if sterile mating frquencies were estimated in challenged populations and correlated with target population densities

Population structure of the tsetse fly Glossina pallidipes estimated by allozyme, microsatellite and mitochondrial gene diversities

Diversities at nuclear and mitochondrial loci were examined in eleven natural populations of Glossina pallidipes from east and southern Africa. Alleles in each class of loci are assumed to be selectively neutral. Allozyme gene diversities (heterozygosities) averaged over eight loci were 0.146 among seven Kenya populations and 0.201 among four southern African populations. Microsatellite diversity averaged over three loci was 0.250 in Kenya and only 0.218 in southern Africa. Mitochondrial diversities averaged 0.504 in Kenya and only 0.156 in southern Africa. Mitochondrial and microsatellite diversities in the populations were strongly correlated with each other, but uncorrelated with allozyme diversities. In contrast to the allozyme diversities, mitochondrial and microsatellite variation indicated a severe and prolonged reduction in population size in southern Africa. Genetic distances among populations increased with the geographical distances between them. Allozyme diversities in southern populations were conserved. Genetic differentiation at allozyme loci among populations was greatly damped when compared with the other markers. The foregoing can be explained if allozyme diversities were maintained by balancing selection. Three main points emerged: genetic data confirm the historical evidence that southern G. pallidipes populations experienced a severe and prolonged bottleneck; allozyme variation was conserved in the bottlenecked populations; and gene flow among populations is surprisingly restricted

Aggregations of male screwworm flies, Cochliomyia hominivorax (Coquerel) in South Texas (Diptera: Calliphoridae)

Noted, for the first time, is the occurrence of aggregations of males of the screwworm fly, Cochliomyio hominivorax (Coquerel). The continuous presence of males in each of two sites in south Texas was independent of the presence of cattle or of female screwworm flies. Males captured in autumn 1975 proved to be wild; those captured in spring 1976 were released, sterile insects. The behavior of males, wild or sterile, included vigorous conspecific and interspecific interactions. There was evidence of territoriality and competition for favored perching sites. The observations are consistent with an hypothesis that the male screwworm aggregations were mating assemblies similar to those known among other cyclorrhaphan Diptera. The significance of male aggregation to sterile fly liberations is discussed

Genetic diversity and gene flow in morsitans group tsetse flies

The question of how to achieve effective levels of tsetse fly control at financially and environmentally acceptable costs is perennial and contentious. Even though tsetse flies are slow to reproduce, populations seem to recover sooner or later after control measures are relaxed. A great capacity and propensity to disperse is said to be characteristic of tsetse flies, and many experts suggest that area-wide control measures and eradication are unobtainable for this reason alone. Others contend that area-wide methods, including the sterile insect technique, can be used successfully to achieve a high degree of control. Can a study of tsetse fly population genetics add anything to the ongoing debate? I believe it can. Here’s why

Characterization of microsatellite markers in the tsetse fly, Glossina pallidipes

Glossina pallidipes is a vector of African trypanosomiasis. Here we characterize eight new polymorphic microsatellite loci in 288 G. pallidipes sampled from 12 Kenya populations. The number of alleles per locus ranged from four to 36 with a mean of 20.5 ± 10.1. Expected single locus heterozygosities varied from 0.044 to 0.829. Heterozygosity averaged 0.616 ± 0.246. No linkage disequilibrium was found. We also report results in eight other tsetse species estimated by using the primers developed in G. pallidipes. The primers worked best in G. swynnertoni and G. austeni and worst in G. m. morsitans and G. m. submorsitans

Tsetse fly evolution, genetics and the trypanosomiases - A review

This reviews work published since 2007. Relative efforts devoted to the agents of African trypanosomiasis and their tsetse fly vectors are given by the numbers of PubMed accessions. In the last 10 years PubMed citations number 3457 for Trypanosoma brucei and 769 for Glossina. The development of simple sequence repeats and single nucleotide polymorphisms afford much higher resolution of Glossina and Trypanosoma population structures than heretofore. Even greater resolution is offered by partial and whole genome sequencing. Reproduction in T. brucei sensu lato is principally clonal although genetic recombination in tsetse salivary glands has been demonstrated in T. b. brucei and T. b. rhodesiense but not in T. b. gambiense. In the past decade most genetic attention was given to the chief human African trypanosomiasis vectors in subgenus Nemorhina e.g., Glossina f. fuscipes, G. p. palpalis, and G. p. gambiense. The chief interest in Nemorhina population genetics seemed to be finding vector populations sufficiently isolated to enable efficient and long-lasting suppression. To this end estimates were made of gene flow, derived from FSTand its analogues, and Ne, the size of a hypothetical population equivalent to that under study. Genetic drift was greater, gene flow and Ne typically lesser in savannah inhabiting tsetse (subgenus Glossina) than in riverine forms (Nemorhina). Population stabilities were examined by sequential sampling and genotypic analysis of nuclear and mitochondrial genomes in both groups and found to be stable. Gene frequencies estimated in sequential samplings differed by drift and allowed estimates of effective population numbers that were greater for Nemorhina spp than Glossina spp. Prospects are examined of genetic methods of vector control. The tsetse long generation time (c. 50 d) is a major contraindication to any suggested genetic method of tsetse population manipulation. Ecological and modelling research convincingly show that conventional methods of targeted insecticide applications and traps/targets can achieve cost-effective reduction in tsetse densities