Lethal and sublethal effects of mineral oils, palizin and buprofezin on predatory ladybeetle, Cryptolaemus montrouzieri (Col.: Coccinellidae)

Citrus, as a critical horticultural product, has a special place in our country's economy. Meanwhile, scale insects such as Planococcus citri and Pulvinaria aurantii are the most important pests of citrus in northern Iran and cause economic damage. To prevent the damage of these pests, various insecticides are recommended. Due to a waxy layer on their bodies, it is difficult to control them chemically. Excessive use of pesticides and repeated spraying can have adverse effects on non-target organisms. In the present study, the effect of three compounds was conducted on some biological and reproductive characteristics of a coccinellid predator, Cryptolaemus montrouzieri. Also, these compounds were grouped according to the criteria of the International Organization for Biological Control (IOBC).

The effect of three compounds at field recommended concentration and half dosage of them in 9 treatments, including: 1, 2: mineral oils, EC, at two concentrations of 5 ml/L and 10 ml/L, 3, 4: mineral oils mayonnaise, at two concentrations of 5 ml/L and 10 ml/L, 5, 6: insecticidal soap palizin 1.25 and 2.5 ml/L, 7, 8: buprofezin 0.25 and 0.5 ml/L and 9: water (control) were investigated on C. montrouzieri. Treatments were done on eggs via dipping method and on the fourth instar larvae and adults via direct spray on mealybug-infested citrus seedling after releasing the ladybeetle.

Mayonnaise oil (10 ml/L) caused a 43.4% reduction on egg hatching compared with that of control. Buprofezin treatment (0.5 ml/L) with 36.6, 35.5 and 40% mortalities on fourth instar larvae, male and female adult respectively, was significantly different compared to the control. In the treated females with buprofezin 0.5 ml/L, mean of longevity and fecundity were 30.9 days and 26.1 eggs compared to the control 87.8 days and 114 eggs, respectively. According to IOBC standard method, mayonnaise (5 ml/L) as harmless (E=24.6, class 1), buprofezin as moderately harmful (E=84.1, class 3), and other compounds as slightly harmful (class 2) were classified. Used compounds at half doses had a low adverse effect on tested parameters compared with field recommended concentration.

Many researchers emphasize the harmlessness of oils to pests' natural enemies. Also, the safety of palizin on them has been reported by some researchers. The use of buprofezin in the larval stage reduced the percentage of adult exit from the pupa, and in the maturing stage, reduced the number of ladybeetle eggs compared to other compounds, so its toxicity is observed to this predator. On the other hand, the effectiveness of mineral oils and palizin in reducing the population of citrus scales has been positively evaluated by researchers. Therefore, these compounds can be used as alternatives to chemical pesticides in the integrated management of citrus pest programs. Also, the mentioned compounds had a less adverse effect on the ladybeetle at the half dosage of the recommended concentrations, which can be used in combination with the ladybeetle to pest control.