Lethal and sublethal effects of ten insecticides, used in date palm production in Saudi Arabia, on the parasitoid Trichogramma cacoeciae

Lethal and sublethal effects of ten insecticides commonly used in date palm production in Saudi Arabia were assessed in the laboratory against adults of Trichogramma cacoeciae, an important egg parasitoid of the dried fruit moth Ephestia calidella. Bioassays were conducted according to the standard protocol of the International Organization for Biological Control IOBC/WPRS/Working Group ‘Pesticides and Beneficial Organisms’. Our results showed that cypermethrin, deltamethrin, malathion, phenthoate, methomyl, and carbosulfan were moderately harmful (IOBC Class 3) to the parasitoid. The botanical insecticides azadirachtin and matrine were moderately harmful (IOBC Class 3) and slightly harmful (IOBC Class 2), respectively. The insect growth regulator pyriproxyfen was slightly harmful, whereas bistrifluron was harmless (IOBC Class 1). Regarding sublethal effects, the parasitism ratios compared to control were reduced by pyriproxyfen and azadirachtin to 49.0% and 58.0%, respectively; hence they are classified as slightly harmful insecticides (IOBC Class 2). Bistrifluron and matrine were harmless (IOBC Class 1) as parasitism ratios were reduced by 9.2% and 27.6%, respectively. Longevity of adults exposed to bistrifluron and matrine (3.6 and 3.3 days, respectively) and to pyriproxyfen and azadirachtin (1.7 and 1.3 days, respectively) was significantly lower than that in control (4.67 days). In semi-field tests, residues of most insecticides on leaves of tomato, a common host plant of lepidopteran pests parasitized by T. cacoeciae, were considered moderately harmful to harmful based on parasitoid mortality at 24 h post-treatment whereas they were slightly harmful at 7 and 14 days post-treatment