2. Larvicidal activity of IGR insect growth regulator and insecticides:2.1. Insect growth regulator IGR: Bakr, et al. (1984) evaluated certain IGRs Dimilin (25% WP), Bay Sir 8514 (6.5% EC), Altosid (10% EC) and RO-08-9801 (50% EC) against Culex pipiens. The results revealed that all tested compounds inhibited the molting process of third and fourth larval instars with different degrees of morphogenetic changes. Developmental events of Dimilin-dead pupae are not completely out of larval exoskeletons and the larval-pupa intermediate shows 4th instar larval exuviae attached to the thoracic and abdominal region. Adult developmental events died following treatment with Dimilin and Bay Sir 8514. Death occurred before exuviations, just after partial emergence, after incomplete emergence (where nymphal exuviae remain attached to the thorax and to the head region) or after incomplete emergence (where the main trunk exuiates but the rest of the adult body is retained in the pupal exuvia. Generally, the observed morphogenetic effects of the tested insect growth regulators were characterized and varied relative to the type of each compound. The results showed that the sensitivity of the larvae to a given compound varied with age. It depended on the insect species and the compound used. investigated the effectiveness of IGRs-21149, an oxime [O-(2-(4-Phenoxyphenoxy) ethyl propionaldoxime], against 2nd and 4th instar larvae and pupae of An. quadrimaculatus, Ae. aegypti and Cx tarsalis The compounds produced overall mortality or 95% inhibition of adult emergence at 0.0047, 0.0013, and 0.00041 mg/liter in the three species, respectively. LC95 values ​​for another IGR-31183, a pyridine compound, [1-(4-Phenoxyphe...... middle of article......emboonkeat (1987) reported that an aqueous extract of neem seeds was less toxic than petroleum ether and alcohol extracts when tested against Spodoptera litura and Plutella xylostella The addition of 0.1% piperonyl butoxide gave the best result, especially with petroleum ether and alcohol extracts Karr and Coats (1988) evaluated the insecticidal properties of limonene against many insects only when limonene was applied with piperonyl butoxide. Synergy also occurred. Limonene also had some repellent activity and fumigating action. Songkittisuntorn (1989) evaluated the effectiveness of substances extracted from neem oil on the rice leafhopper. increased oil concentration Neem oil reduced nymph populations. Addition of 0.1% piperonyl butoxide as a synergist to neem oil increased mortality..