Study on the effect of predator density on demographic parameters of Stethorus gilvifrons
عنوان دوره: دومین کنگره بین المللی حشره شناسی ایران
نویسندگان
چکیده
Stethorus gilvifrons (Mulstant) (Col: Coccinelidae) is an important monophagus lady beetle and is considered as a biological control agent against the Tetranychus urticae (Acari: Tetranychidae) in different agricultural crops. In this study, the effects of two densities of one and five pairs of predatory coccinellid were evaluated on its demographic parameters. In this regard, 120 the same aged eggs of predator (< 24h) were picked randomly from the laboratory colony of S. gilvifrons. Different developmental stage of T. uricae was used for feeding of the predator larvae and adults. The experiments were carried out under laboratory conditions, at 27 ± 1°C temperature, 70 ± 5% RH and a photoperiod of 16L:8D h. For 1-pair density of predator, egg, larvae and pupal stages were kept in container separately. After adult emergence one pair of male and female were matched until death. While, in 5-pair density, all the immature stages (egg, larvae, pupa) and adults were kept inside a transparent plastic rectangular container with dimensions 19Í14Í4.5 cm. The data were analyzed based on the age-stage, two-sex life table theory. According to the results, developmental times of larval period (6.52±0.13 d in single; 5.85±0.20 d in a group of five adult, pupal period (2.98±0.06 d in single; 2.85±0.10 in a group of five adult) and total immature stages (23.26±1.68 d in single; 15.10±1.01 d in a group of five adult) were statistically different between single and a group of five adult densities of predator, respectively. While, incubation period (3.51±0.08 d in single; 3.51±0.05 d in a group of five adult) had no statistically difference between two examined treatments. Moreover, estimated values for intrinsic rate of increase (r), finite rate of increase (λ), mean generation times (T), net reproductive rate (R0) and (GRR) were 0.121d-1; 1.129d-1, 30.23d, 39.92 offspring/individual, and 265.38 offspring in single density, respectively. For a group of five adult density, the values of the same parameters were 0.07 d-1, 1.077 d-1, 23.01d, 5.56 offspring/individual and 51.73 offspring, respectively. According to our findings, density of predators in rearing containers is a main factor affecting their population increase. These findings are useful for improving mass rearing technique of S. gilvifrons.
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