Revista Argentina de Microbiologia 20 (SupI): 71-80, 1988. ISSN 0325-754 I Seasonal effects on control strategies of Chagas ‘Disease vectors DAVID E. GORLA Centro de Investigaciones Entomol&icas, Universidad National de C6rdoba, Ve’lez Sarsfieid 299,500O Chioba, Argentina. INTRODUCTION Despite different approaches are using in the searching for an efficient Chagas’ disease con- trol (chemotherapy, vaccination, vector con- trol), the strategies are narrowly associated with vector control through chemical insecticides applications in the short term, and with house improvement and life quality enhancement of affected human rural populations in the long term (2,9,14,16). Although integrated pest management has ._ been successfully used against crop and forest pest, through the combination of chemical in- secticides with other control techniques (natu- ral enemies, male sterilization, etc.), chemical insecticides remain as the main tool in Chagas’ disease vector control, either because it is dif- ficult to combine insecticide application with other strategies or because it could not improve control efficiency (1, 14). However, some-suo- cessful efforts were reached through house im- F rovement or educational campaings or care- ully fitted land management rules (3). . Using insecticides, an optimal strategy could be defined as the one that minimizes insecticide application frequency, maintaining a very low number of infective vector-host encounters during a long time. A control measure should reduce not only infective encounters to the host, but also the infective ones to the vector, to decrease the flow rate of the pathogen het- ween vector and host @fontenegro, pers. comm.). The greatest efficiency of a control measure to reduce a pest population density is reached if the control is applied when the population is represented by individuals with the greatest reproductive value (10). For T. rnfestans popu- lations developed under the natural climatic conditions of Argentine semiarid chaco (with important seasonal thermic fluctuations) this _.. . ~ occurs during the spring, when fecundity of females surviving the winter rises (Figure 1) and 4th and 5th nymphs begin to molt to adult stage (Figure 2) (4). These two fluctuating pro- cess, fecundity and molting to adult stage, mainly affected by thermic fluctuations (Figure 3 B ? produce seasonal changes in vector density ( lgure 4). Also, considering that bug’s food consumption rate is thermodependent (7,8), during the hot summer months great vector numbers with increased energetic re uirements % -will .occur, allowing a hiih chance o host-vec- tor encounters. During the cold winter months vector numbers decrease, because the most im- Portant demoeraphic Process is the loss of indi- sduals by m&taiity, with an almost null input of individuals (fecunditv or recruitment) and with the diminution of “energetic requirehents a low chance of host-vector encounters could be expected. --- ‘An increase on the proportion of infected in- dividuals in the population could be expected towards the begining of the hot season becau- se during the cold season there is an increase on the proportion of individuals at the higher age classes (these classes have the greatest chance of carrying on the parasite because of the accumu- lation of succesive blood intakes). The recruit- ment of new individuals into the population, free of T. crzui, should promote a dilution ef- fect and hence a decrease on the proportion of infected individuals. Recently collected data on domestic populations of T. infestans support that hypothesis (Figure 5) (5). Briefly, in those environments with amde tempera&!% fluctuations (as the semiarid kr- aentine chaco). T. infestans PoPulations should have a fluctuating epidemioiogical importance, with peaks at the begining of the hot seasons and lower values at the cold seasons. Under these seasonally changing conditions, it could be predicted that application of insecti- .____--.--