BIOLOGY AND LIFE TABLE PARAMETERS OF THE COCCINELLID PREDATORY INSECT Stethorus gilvifrons (MULSANT) FED ON IMMATURES OF Tetranychus urticae ( KOCH )

Abstract

Biological aspects of the predatory insect Stethorus gilvifrons (Mulsant) fed on nymphs of the twospotted spider mite Tetranychus urticae Koch were studied in laboratory at 25 ± 1 o C and 70 ± 5 % RH., Egg incubation period of eggs lasted 3.87 and 4.07 days for male and female, respectively. The first female larval instar was active stage lived for about 2.93 days, during which it consumed and 7.73 T. urticae individuals with a daily rate of 2.64 preys / day. The same trend was noticed within the second larval instar that lived for a shorter time 2.00 days and consumed 14.80 preys with a daily 7.40 preys. The third larval instar lived for 2.33 and consumed 25.46 with a daily rate of 10.92 preys / day. The fourth instar lasted 4.13 days during which it consumed 69.40 with daily rate of 16.80 prey individuals. Pupal stage lasted for 3.73 and 4.47 days for male and female, respectively. Life cycle durated 17.70 and 19.90 days for male and female , respectively.Average male and female longivety was 24.33 and 36.46 days, respectively. Data showed that adult female of S .gilvifrons, which lived 36.46 days, consumed a total number of T. urticae nymphs 2267.13 prey nymphs / female . Thus, adult female consumed during its oviposition period and longevity nearly 77.0 % and 95 % of the total consumed prey during its whole life span. The mean generation time (T) averaged 30.41days. Net reproductive rate (Ro) was 49.53 and the intrinsic rate of natural increase (r m ) was 0.12 , the finite rate of increase e rm (λ) was 1.13.