The red palm weevil (RPW) Rhynchophorus ferrugineus is a main pest of date palm in a number of the Arabian Gulf States which includes Saudi Arabia. This work aimed to evaluate the efficacy of nano chitosan and Spinosad against mortality, some biological aspects, some enzymes & histological, different haemocyte counts and total haemocyte counts of 9^th instar larvae of R. ferrugineus.
    Nano chitosan and Spinosad concentrations of (0.5, 0.1 and 0.05 %) had been tested against these mentioned insects' 9^th instar larvae at different exposure times ranging from 1 to 7 days. The mortality percentage increased with the increase in exposure times at all tested concentrations. The results revealed that LC₅₀ (0.11) for nano chitosan and (0.30) for Spinosad.
     Nano chitosan affects some biological aspects of R. ferrugineus as it led to an increase in the longevity of larvae, pupa and adults (male and female). The female didn't put any eggs so, the sterility was 100% compared with Spinosad and control.
     Nano chitosan decreased changes in enzyme activity of ALP, PO, GPT and GOT recorded (-13.31, -20.88, -10.02 and -35.0%), respectively compared with control. Spinosad decreased changes in enzyme activity of ALP was recorded -35.62% compared with control. While it increased changes in enzyme activity of PO, GPT and GOT were recorded (40.79, 45.05 and 21.43%), respectively compared with the control. As well as, nano chitosan and Spinosad decreased the total protein and total carbohydrates recorded (13.3, 11.67 and 9.03, 10.66 mg/g.b.w.) respectively, in comparison to the control (20.4 and 13.13 mg/g.b.w.), respectively. Results showed that treating 9^th instar larvae of R. ferrugineus with nano chitosan and Spinosad significantly decreased different haemocyte counts and total haemocyte counts when compared to the control. Also, appeared some abnormalities in haemolymph cell morphology.
   The histological changes in the midgut of the 9^th instar larvae of R. ferrugineus showed great abnormalities and destruction compared with the control.