The red palm weevil Rhynchophorus ferrugineus is the most important insect pest for the date palm trees in the middle east and Gulf states. The objective of this study was to investigate the pathogenicity of sublethal doses of a natural plant extract (neem) and a synthetic insect growth regulators (IGRs) (flufenoxuron) on the ultrastructure of testis of the red palm weevil. Prepupae were grouped and treated with neem extract (Neem J, 50 ppm) and a synthetic insect growth
regulator (flufenoxuron, 0.05 ppm). Ultrastructure observations of spermatogenesis confirm the histopathological findings and suggest that the two IGRs act at the cellular level. Collectively, these investigation suggest that IGRs alter germ cells functions in Rhynchophorus ferrugineus by acting at one or more stages of maturation pathway during spermiogenesis in male. In spermatozoa, IGRs induced aberration in acrosomal development which causes failure in
acrosomal reaction and egg envelope penetration and consequently in fertilization process. Also, inhibition of chromatin condensation, mitochondrial degeneration and disorganization of flagellar elements resulted from IGRs treatment perturb the function, viability and mortality of spermatozoa.