Effect of Sequential Cold Shocks on Survival and Molting Rate in Triatoma infestans Klug

Abstract

Key words: Triatoma infestans -nutritional conditions -cold-shock tolerance -survival -molting rateThe survival, molting incidence and chromatin supraorganization of Triatoma infestans and Panstrongylus megistus, blood-sucking hemipteran vectors of Chagas disease, are affected by stressing agents, including heat and cold shocks (Rodrigues et al. 1991, Dantas & Mello 1992, Mello et al. 1995, Garcia et al. 1999, 2000. These insect species differ in nuclear characteristics (Mello 1971, 1975, Mello et al. 1986) and in their response to heat and cold shocks (Rodrigues et al. 1991, Garcia et al. 1999, with P. megistus being less resistant to prolonged heat (40 o C) and cold (0 o C) shocks than T. infestans (Rodrigues et al. 1991, Garcia et al. 1999.Thermotolerance following sequential heat shocks and tolerance to sequential cold shocks (i.e., an acquired increase in survival and molting incidence) have been reported in P. megistus (Garcia et al. 2001a,b). Cold-shock tolerance in insects has been suggested to involve the synthesis of heat-shock or other proteins, as well as the presence of cryoprotectants and improved use of metabolic energy resources (Clark & Fucito 1998). There is no evidence of cryoprotectant use in blood-sucking hemipterans. However, the synthesis of heat-shock proteins during the cold-shock tolerance response has been suggested for P. megistus (Garcia et al. 2001a Since no generalization can be made about the responses of different species of the same family to temperature shocks (Clark & Fucito 1998), and since T. infestans and P. megistus differ from each other in several aspects, including their responses to heat and cold shocks, it is possible that T. infestans may respond differently to sequential cold shocks compared to P. megistus. This response may be affected by the state of nourishment of the insects (Garcia et al. 1999).In the present study, survival and molting incidence were investigated in T. infestans after sequential cold shocks under different conditions of nourishment and the responses compared to those of P. megistus (Garcia et al. 2001a). MATERIALS AND METHODSFifth instar nymphs of T. infestans Klug (Hemiptera, Reduviidae) reared at 30 o C and 80% relative humidity in the laboratory at Sucen (Mogi-Guaçu, SP) were used. The insects fed once a week on hen blood. Some specimens were fasted for up to 15 days before and up to 30 days after the shocks.Immediately after a shock at 0 o C for 1 h, the nymphs were returned to control conditions and 8 h and 24 h later were subjected to a second shock at 0 o C which lasted 12 h. The temperature of 0 o C was chosen based on a previous report (Rodrigues et al. 1991).Nymphs maintained at 30 o C, a temperature traditionally used for rearing T. infestans in the insect facilities at Sucen since 1980 (Rodrigues et al. 1991)(control #1), as well as nymphs subjected to a single shock at 0 o C for 1 h (control #2) and 12 h (control #3) were used as controls.After the shocks, the nymphs were returned to the control temperature (30 o C) and monitored ...

Changes in nuclear phenotype frequencies following sequential cold shocks in Triatoma infestans (Hemiptera, Reduviidae)

“…Indeed, in terms of insect survival, T. infestans is tolerant to single or sequential shocks at 0ºC, regardless of the nutritional state of the specimens, whereas in terms of molting rate, fasting elicits a protective action, in addition to that induced by cold shocks (Campos et al 2002). Since the specimens of T. infestans analyzed here originated from insects collected in the State of São Paulo and south of the Minas Gerais, their source is concerned with the hypothesis of the species coming from Argentina (Aragão 1971, Silva 1986, Monteiro et al 1999.…”

“…Immediately after a shock at 0ºC for 1 h, the insects were returned to 30°C; 8 h and 24 h later, they were subjected to an additional shock at 0°C which lasted 12 h. A temperature of 0°C was chosen based on previous results (Rodrigues et al 1991, Campos et al 2002. Nymphs subjected to a single shock at 0°C for 1 h or 12 h were controls 1 and 2, respectively.…”

“…Survival, molting rate and chromatin supraorganization in this species are affected by stressing agents such as fasting, gamma-radiation, heavy metals and heat and cold shocks (Álvares-Garcia 1988, Mello 1989, Rodrigues et al 1991, Dantas & Mello 1992, Mello et al 1995, Campos et al 2002.…”

“…infestans is tolerant to a single shock at 0°C for up to 12 h, or to sequential cold shocks, regardless of the nutritional state of the specimens (Campos et al 2002). The molting rate of T. infestans nymphs may be affected by cold shocks, the extent of which depends on the nutritional state of the specimens.…”

“…The molting rate of T. infestans nymphs may be affected by cold shocks, the extent of which depends on the nutritional state of the specimens. Fasting enhances tolerance to sequential cold shocks, compared to the fully nourished state, provided the interval at 30°C between sequential shocks at 0°C is no longer than 8 h (Campos et al 2002). The cold-hardening response in T. infestans may have favoured its survival in areas of South America which experience low temperatures, although this insect relocates predominantly in association with human habitats (Campos et al 2002).…”