Residual Effects of Some Conventional and Biorational Pesticides on Ladybird Beetle, Adonia variegata Goeze

MATERIALS AND METHODS

Predator rearing: Unsexed coccinellid adults, Adonia variegata Goeza used in this experiment were collected from the alfalfa field at College of Agriculture and Vet. Med. Research Center, King Saud University, Al-Gaseem Branch, where no pesticides were ever applied and transferred to a rearing cages. They kept on aphid-infested leaves in 50x50x50 cm metal cages. Also, they fed on 10% sucrose solution (w/v), which renewed every other day. Ladybird beetles were left for at least 2 weeks to be adapted to the laboratory conditions.

Pesticides tested: Formulated Pesticides Dursban* 4 (48%, EC), Fenvalerate (20%, EC), Bio-Fly (100%, Beauveria bassiana) and Bio-Neem (Azadirachtin, 0.09%, multipurpose concentrate) were purchased from DowElanco (England), Hockley (England), El-Nasar for Fertilizes and Biopesticides, Sadat City, Egypt and Safer, Inc., a wholly owned subsidiary of Verdant Brands, Inc., respectively.

All the tested pesticides were mixed with water at the ½, 1 and 2 fold of the labeled rates. The labeled rates were 1-1.5 L 1000 L^-1, 100 ml 1000 L^-1, 3 fl oz gallon^-1 and 100 ml 100 L^-1 for Dursban, Fenvalerate, Bio-Neem and Bio-Fly, respectively. For comparison water was used as a control treatment.

Bioassay study: A group of 10 beetles were placed into petri dishes (90 x 15 mm) containing a piece of cotton wetted with sugar solution. There were 3 petri dishes in each treatment for a total of 30 beetles per treatment. Each dish was sprayed with 1 ml of the tested concentrations. The number of dead beetle was checked at 1, 3, 24, 48 and 120 h and percentages of mortality were calculated.

RESULTS AND DISCUSSION

Data presented in Tables 1-4 illustrate the effects of the tested conventional and biorational pesticides on coccinellids survival. Mortality percentages in Dursban treatment ranging from 46.7-50, 50 and 50-55.33 during the period of 1-120 h at ½, 1 and 2 folds of the labeled rates, respectively. Fenvalerate at ½, 1 and 2 folds of the labeled rates caused 10-47.7, 20-50 and 13.33-50% mortality, respectively. However, the recommended and half of the recommended dosages of the biorational insecticide, Bio-Neem had slight effect on coccinellids, but statistically increased coccinellids mortality with 2-folds of labeled rate where 26.7% mortality was obtained after 120 h of treatment. Moreover, the biorational insecticide Bio-Fly was found to be the less one to affect the coccinellids, where the mortality percentage not exceed 10 even when lady beetles were exposed to 2 folds of labeled rate. The maximum mortality was 10% after 120 h of treatment with all the tested dosages.

The present investigation revealed that all the tested biorational pesticides had less effects on survival of lady beetles than the conventional ones especially Dursban which resulted in 50% mortality after a short time. Coccinellid susceptibility to insecticides varies with species and the type of pesticide but the sensitivity of coccinellids to insecticides was often slightly lower than that of pests (Theiling and Croft, 1988). Various pesticides such as carbaryl, malathion, diazinon, deltamethrin, endosulfan, etofenprox and thiamethoxam affected predator populations significantly (Thomas et al., 1990; Roger et al., 1991; Yardim and Edwards, 1998; and Youn et al., 2003). Smith and Krischick (2000) showed that Azatin, an extract from the Neem tree containing azadirachtin caused less mortality to lady beetles than carbaryl, whereas horticultural oil had no effect on beetle survivorship. However, the application of azadirachtin should be careful, especially in high concentration of its obvious insect growth regulator effects (Qi et al., 2001).

Table 1:	Mortality of lady beetle exposed to residue of dursban after the application of different labeled rates

Table 2:	Mortality of lady beetle exposed to residue of fenvalerate after the application of different labeled rates

Table 3:	mortality of lady beetle exposed to residue of bio-neem after the application of different labeled rates

Table 4:	Mortality of lady beetle exposed to residue of bio-fly after the application of different labeled rates
Data are expressed as Mean±SE
Means within the same column followed common letters are not statistically different from each other, p≤ 0.05

Also, BotaniGard, the commercial formulation of the entomopathogenic fungus Beauveria bassiana, was found to reduce survival of coccinellids at 72 h after spraying to levels not statistically different from controls (Smith and Krischick, 2000). Biorational pesticides are usually compatible with natural enemies and minimal risk to the human and environment are preferred for pest management (Steiner and Elliott, 1987, Miller and Uetz, 1998). The toxicity of the conventional pesticides Dursban and fenvalerate for coccinellids indicate the application of the pesticides must be considered carefully for use in IPM programs. It can be concluded that biorational pesticides can be used with natural enemies in IPM programs.