Development of Rhodnius prolixus (Hemiptera: Reduviidae) under constant and cyclic conditions of temperature and humidity

Development of Rhodnius prolixus after eclosion until the adult stage was studied at constant temperatures (T), 15, 20, 25, 28, 35ºC, 20/25ºC, 25/35ºC, and relative humidities (RH), 75, 86 and 97 (por cento) and fluctuating (16/8 hr) temperatures, T I/II, 15/28ºC, 25/28ºC and 25/35ºC, and relative humidities, RH I/II, 86/75 (por cento) and 97/75 (por cento). Eclosion or molting were not observed at 15ºC and 86 or 97 (por cento) RH, respectively. At 35ºC and 75 (por cento) RH only few insects molted. By alternating T I/II, 15/28ºC and 25/35ºC, insects developed at high frequency. Cumulating the average lengths of the interphases within independent groups for each instar, R. prolixus reached the adult stage most rapidly (86.7 days) and at highest frequency per instar (mean: 91.8 por cento) at 28ºC and 75 (por cento) RH. Under fluctuating T I/II, development was completed within 100 days or less at 25/28ºC and 20/25ºC (>185 days), and at constant 20ºC (>300 days). Mortality was higher at constant 97 (por cento) RH or fluctuating RH I, 97 (por cento) than at constant or fluctuating 86 (por cento) RH. Refeeding was minimal at optimal conditions of T and RH for development. The most refeeding was observed at a constant 35ºC.

Relative susceptibility of different stages of Rhodinius Prolixus to the entomopathogenic Hyphomycete Beauveria Bassiana

Laboratory bioassays were conducted to determine the relative suscepbility of eggs, 1st-, 3rd-, 5th- instar nymphs and adults of Rhodnius prolixus to one isolate of the entomopathogenic hyphomycete, Beauveria bassiana. Treatments consisted of directly spraying on insects of increasing doses of inoculum (3 x 10* to 3 x 10 (elevated to 5th potency) conidia per cm*). Mortality due to all doses of conidia was very high in the five tested stages of the target insect. Experiments on eggs demonstrated that the fungal isolate was able to kill eggs before they hatched. Both time-mortality and dose-mortality responses showed that the susceptibility of R. prolixus varied according to its stage of development and increased with age. As matter of fact, at the dose of 3 x 10* conidia per cm*, LD50 varied between 11.2 days in 1st-instar nymphs and 6.4 days in both 5th-instar nymphs and adults. Comparison of LD50 permitted to estimate that 1st-instar nymphs were about 700-fold less susceptible than the two oldest stages