The Potential for Genetic Suppression 



of Insect Populations 



by Their Adaptations to Climate 



By W. Klassen, J. F. Creech, and R. A. Bell x 



Many of our most serious insect pests have 

 very broad geographical distributions. For 

 example, the codling moth (Carpocapsa pomo- 

 nella (L.)) is distributed from Canada to Ar- 

 gentina, and it occurs in Australia, South 

 Africa, the Mediterranean, and throughout 

 Europe north to the Scandinavian countries 

 (l). 1 Insects with such broad distributions 

 adapt in various ways to climate. 



Many of the reports (2, 3, 5, 6) indicate that 

 genetic differences occur between insect popu- 

 lations within a species with regard to (1) abil- 

 ity to undergo a hibernal diapause, (2) response 

 to diapause-inducing stimuli, (3) duration of 

 diapause, (4) temperature limits of diapause 

 termination, (5) temperature optima for dia- 

 pause termination, (6) ability to develop cold 

 hardiness, (7) thermal constants and tempera- 

 ture threshold for development, (8) choice of 

 hibernal niches and other behavioral traits as- 

 sociated with surviving inhospitable seasons, 

 and (9) ability for aestival diapause, its dura- 

 tion and response to conditions that induce or 

 terminate it. 



Such genetic differences must exist so that 

 adaptations of insects to climate may be appro- 

 priate to their locality. Changes in climate from 

 locality to locality require appropriate changes 

 in adaptations. Insects must synchronize their 

 life cycles with the seasons so that (1) frost- 

 sensitive stages are passed in the frost-free sea- 



1 W. Klassen and R. A. Bell, entomologists, Entomol- 

 ogy Research Division, Agricultural Research Service, 

 and J. F. Creech, graduate student, Department of 

 Electrical Engineering, North Dakota State University. 



2 Italic numbers in parentheses refer to Literature 

 Cited, p. 10. 



son, (2) feeding stages occur when food is avail- 

 able, and (3) no actively developing stages 

 occur in periods of intense heat or drought. 

 Therefore insects must be sensitive to stimuli 

 that portend the change in seasons so that they 

 may prepare for adverse periods. 



If we can genetically disrupt the seasonal reg- 

 ulations or other climatic adaptations of insects, 

 these insects may not survive. For example, 

 if an insect population at Fargo, N. Dak., must 

 respond to a photoperiod of 15 hours in order to 

 enter diapause and be cold hardy in time for 

 dangerous frosts and if we genetically modify 

 the population so that it does not diapause until 

 the day has shortened to 13 hours, then the pop- 

 ulation may be destroyed by the winter. Fur- 

 ther, let us assume that this population must re- 

 main in diapause until early May, when the dan- 

 ger of killing frost is past and when the host 

 plant has again become available. If we geneti- 

 cally shorten the diapause so that the insects 

 resume development in March, then they would 

 be destroyed by frost or lack of food. 



Inappropriate adaptations to climate are lethal 

 at certain times of the year; they are conditional 

 lethal traits. We may use a conditional lethal 

 trait or combination of conditional lethal traits 

 to suppress or eradicate insect populations. The 

 principle of suppressing insect populations by 

 means of their adaptations to climate has been 

 suggested by numerous investigators (-4, 5, 7). 



The purpose of this report is to show that a 

 population may be suppressed by means of con- 

 ditional lethal traits, particularly (1) when the 

 population is held in check by partial sterility 

 while conditional lethal genes are introduced 

 and (2) when the population is held static by 

 conventional means while the conditional lethal 



