POTENTIAL FOR GENETIC SUPPRESSION OF INSECT POPULATIONS 



the Fj offspring was then weighted accordingly. 



The process for determining the numbers of 



d F 4 offspring was identical except that the 



tables containing fractional contributions and 



relative locations were stored on direct-access 



storage dev: 



The final phase was to print the results. The 

 results of the computation process were stored 

 in core memory and were written on the printer 

 only when the Fi, Fj, F3, and F 4 computation 

 processes were completed. Control was then re- 

 turned to the point in the program where com- 

 putations were made based on the previously 

 computed formulas, using a new particular 

 weighting factor. 



All programs written for this study had this 

 same basic form and were executed in a similar 

 manner. The number of genes involved dictated 

 the amount of core storage required, the num- 

 ber of genotypes generated, and the speed of 

 execution of the entire program. 



Using these computational methods, we cal- 

 culated the theoretical population trends (tables 

 3-14) when a native population of 2,000 insects 

 (1:1 sex ratio) was overflooded by partially 

 sterile insects. The native and release strains 

 differed by one to four genes, and in some in- 

 stances one of the four genes was sex-linked. 

 The rate of increase between generations was 

 either fivefold or tenfold. Sterility of both 

 sexes of the release strain was either 80 or 90 

 percent. Four releases were made to coincide 

 with the parental, Fi, F 2 , and F 3 generations. 

 Each release consisted of either 198,000 or 396, 

 000 insects (1:1 sex ratio). Matings between 

 partially sterile males and partially sterile fe- 

 males were assumed to yield either no offspring 

 or a number of offspring proportionate to their 

 level of sterility. 



In tables 3-14 the number of individuals for 

 each genotype is rounded to the nearest whole 

 number. However, the column totals were com- 

 puted before the numbers had been rounded. 



To illustrate how populations may be sup- 

 pressed with genes for conditional lethal traits 

 while the populations are held in check with 

 partial sterility, we derived tables 16-27 from 

 tables 3-14. (Actually the number of individ- 

 uals in tables 16-27 were obtained directly 

 from the computer printout for tables 3-14. In 



this way rounding errors were minimized.) 

 Table 15 gives the interpretations and trans- 

 scriptions and the method required to derive ta- 

 bles 16-27 from tables 3-14. The values in 

 tables 3-14 were obtained by introducing 

 insects with all alleles designated by capital let- 

 ters into populations with all alleles designated 

 by lower case letters. When this was not so, cer- 

 tain transcriptions of lower case letters to capi- 

 tals were made in order to obtain the appropri- 

 ate genotypic frequencies from tables 3-14. 

 Tables 16-27 are summarized in table 28. In 

 establishing table 28, we arbitrarily assumed 

 that complete suppression would be achieved 

 when the population of individuals with viable 

 genotypes was reduced to 30. The eight cases in 

 table 28 are as follows: 





Number 



Sterility 



Rate of 



Case 



released 



(percent) 



increase 



1 \ 





/90 



Fivefold. 



2 ( 





J80 



Do. 



3 



198,000 



)90 



Tenfold. 



4 ) 





1 80 



Do. 



5 





/90 



Fivefold. 



6 





J 80 



Do. 



7 



396,000 



•\90 



Tenfold. 



8 





(80 



Do. 



The following data about complete suppression 

 are indicated in table 28 : 



(1) Polyfactorial inheritance of a conditional 

 lethal trait may be more or less advantageous 

 from the standpoint of complete suppression 

 than when the trait is inherited as a single fully 

 dominant gene, depending on the number of 

 native-type alleles required to prevent expres- 

 sion of the lethal trait. 



(2) The more lethal traits incorporated in the 

 release strain, the greater is the approach to 

 complete suppression. 



(3) Complete suppression cannot be achieved 

 when the number of insects released in each 

 generation is 198,000, sterility is 80 percent, 

 and the rate of increase between generations is 

 tenfold (case 4), except in the F 4 generation 

 when the release strain possesses three lethals 

 (two are dominant autosomals and the third is 

 bifactorial, requiring three native alleles to pre- 

 vent expression) and when matings between 

 partially sterile insects yield offspring propor- 

 tionate to the level of sterility. 



