Population fluctuation, immature mortality and adult longevity of Spartocera dentiventris (Berg) (Hemiptera: Coreidae) on Nicotiana tabacum (Solanaceae)

Abstract

The population fluctuations, mortality in the immature phases and longevity of the Spartocera dentiventris (Berg) adults were studied in an experimental plot of Nicotiana tabacum (Solanaceae) at the Faculdade de Agronomia - Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil (30[degree] 05' S and 51[degree] 13' W). From November 1996 to March 1997, 30 sampling occasions were carried out: 23 plants were inspected and the number of eggs and nymphs per instar counted and adults marked/recaptured. Mortality in immature bugs was estimated by the difference between the population peaks in successive instars per plants. Parasitism was evaluated based on the egg colour. Two generations developed through the cycle of the crop, the various instars overlapping in both generations. The mortality rates for immature phase were 93.6[plus or minus]3.19% and 99.8[plus or minus]0.20% for the first and second generations respectively. The highest rates of mortality occurred in young nymphs and eggs. Egg parasitization rates were 8.9[plus or minus]8.48% and 36.2[plus or minus]3.63% for the first and second generations respectively. Sex ratio was 0.42 and minimum average longevity for adults was 19.2[plus or minus]1.00 days in the first and 12.6[plus or minus]2.52 days in the second generation. Population growth was dramatically limited by mortality factors; amongst these, the parasitoids Gryon gallardoi (Brethes) and Neorileya ashmeadi Crawford account for much of the eggs losses and it is suggested that the reduvid Cosmoclopius nigroannulatus Stal plays an important role preying upon nymphs.