Appl. Entomol. Zool. 44 (1): 103–113 (2009) http://odokon.org/ Conservation of natural enemies in brassica crops: comparative selectivity of insecticides in the management of Brevicoryne brassicae (Hemiptera: Sternorrhyncha: Aphididae) Leandro BACCI,1,*,† Marcelo Coutinho PICANÇO,1 Jander Fagundes ROSADO,1 Gerson Adriano SILVA,1 André Luiz Barreto CRESPO,2 Eliseu José Guedes PEREIRA3 and Júlio Cláudio MARTINS1 1 Integrated Pest Management Laboratory, Department of Animal Biology, Federal University of Viçosa; 36570–000 Viçosa, Minas Gerais State, Brazil 2 Department of Entomology, University of Nebraska Lincoln; 68503–0816 Lincoln, Nebraska State, USA 3 Entomological Laboratory, Federal University of Viçosa; 38810–000 Rio Paranaíba, Minas Gerais State, Brazil (Received 16 July 2008; Accepted 25 September 2008) Abstract In the present study, we evaluate the toxicity of six insecticides to Brevicoryne brassicae (L.) (Hemiptera: Sternor- rhyncha: Aphididae), predatory coleopterans Cycloneda sanguinea (L.) (Coccinellidae) and Acanthinus sp. (Anthici- dae), and the hymenopteran parasitoid Diaeretiella rapae (McIntosh) (Braconidae, Aphidiinae). Late-instar nymphs of B. brassicae and adults of C. sanguinea, Acanthinus sp. and D. rapae were exposed to nine concentrations of acephate, deltamethrin, dimethoate, methamidophos, methyl parathion and pirimicarb. Selectivity, toxicity, and toler- ance ratios were calculated from LC50 values to determine insecticide toxicity to B. brassicae and natural enemies as well as insecticide tolerance of the natural enemies. Pirimicarb was highly selective to Acanthinus sp., C. sanguinea, and D. rapae. Dimethoate, methamidophos and methyl parathion also showed selectivity to C. sanguinea and Acanthi- nus sp., but not to D. rapae. Methamidophos was the least potent insecticide against B. brassicae exhibiting the high- est LC50 amongst the products tested and was more toxic to the D. rapae relative to the aphid. Overall, the predators Acanthinus sp. and C. sanguinea were more tolerant to the insecticides than was the parasitoid D. rapae. The role of insecticides in IPM systems of brassica crops is discussed based on the toxicity to B. brassicae and selectivity to natu- ral enemies. Key words: Cabbage aphid; physiological selectivity; Cycloneda sanguinea; Acanthinus sp.; Diaeretiella rapae per or by removal or reduction of adverse factors to INTRODUCTION natural enemies (Landis et al., 2000). The most Attack by predators and parasitoids are the most significant factor disrupting biological control in frequent source of mortality for phytophagous most cropping systems is the use of broad spec- arthropods in agroecosystems (Cornell and trum insecticides (Croft, 1990; Naranjo, 2001). Hawkins, 1995), and the conservation of these or- Therefore, the use of insecticides with low toxicity ganisms is an essential component in Integrated to natural enemies is an important component of Pest Management (IPM) programs (Bacci et al., conservation biological control. 2007). Conservation biological control involves the The selectivity of insecticides can be classified management of agroecosystems to enhance fitness as ecological and physiological (Ripper et al., and behavior of natural enemies increasing their 1951). The ecological selectivity is related to the effectiveness against pests. This can be achieved different ways to apply insecticides as a means to through the provision of essential requirements and minimize exposure of natural enemies to the insec- *To whom correspondence should be addressed at: E-mail: [email protected] † Present address: Av. P. H. Rolfs, s/n, Department of Animal Biology, Federal University of Viçosa, 36570–000 Viçosa, Minas Gerais State, Brazil. DOI: 10.1303/aez.2009.103 103 104 L. BACCI et al. ticide (Ripper et al., 1951). The physiological se- the toxicity of an insecticide among several lectivity is based on the use of insecticides that are species, or to determine which insecticide it is more toxic to the target pest than the natural ene- more toxic for one particular organism. Therefore, mies (O’Brien, 1960). concentration-mortality curves can be used to se- The cabbage aphid Brevicoryne brassicae (L.) lect insecticides which are harmless to the natural (Hemiptera: Sternorrhyncha: Aphididae) causes se- enemies, and efficient to manage the pest. rious loss of yield in brassica crop fields and re- The evaluation of selectivity to natural enemies duces its market values (Liu et al., 1994; Costello is limited for insecticides used to manage B. bras- and Altieri, 1995). This insect causes severe dam- sicae in Brassicas (Picanço et al., 1997, 1998). age by sucking the plant sap and injecting toxins Therefore, in the present study, we used concentra- (Bacci et al., 2001). Because of this high capacity tion-mortality curves to determine (i) the toxicity for reproduction and dispersion, high population of insecticides to B. brassicae, (ii) the selectivity of densities are easily attained and efforts to suppress insecticides to the predators C. sanguinea and populations using insecticide sprays are often nec- Acanthinus sp. and to the parasitoid D. rapae, (iii) essary (Zhang and Hassan, 2003). the relative toxicity of insecticides to B. brassicae The use of insecticides to manage B. brassicae is and natural enemies, and (iv) the relative tolerance rather complex, and the low efficiency of insecti- of natural enemies to insecticides used to manage cides causes control failure, which also increases B. brassicae. The results provided preliminary in- production costs and environmental contamination. formation regarding insecticides that can be used Because insecticides are likely to remain a major to manage B. brassicae and natural enemies in kale component of pest suppression for B. brassicae, crops. minimizing the effects of insecticides on natural enemies will require more selective approaches for MATERIALS AND METHODS use of broad-spectrum insecticides and per or more selective products. The IPM concept emphasizes Insects. Individuals of B. brassicae were main- the importance of both chemical and biological tained in greenhouse at the Universidade Federal methods to suppress pest population in agricultural de Viçosa (UFV), Viçosa, Minas Gerais State, systems. Therefore, the use of selective insecti- Brazil. To originate the colony, leaves of cabbage cides is necessary for development of sound IPM infested with B. brassicae were collected in fields practices in kale crops (Giles and Obrycki, 1997; free of insecticide applications at the UFV experi- Galvan et al., 2005). mental station. The leaves were inspected for re- Attack by predators and parasitoids are the main moval of other aphid species and parasitoid-in- cause of the declining population of B. brassicae fected nymphs, and then placed onto cabbage (Dixon, 1977; Raworth et al., 1984; Rice and plants inside cages measuring 50ϫ50ϫ50 cm. The Wilde, 1988). Coccinellid and anthicid predators cages were built with wood frame and covered with (Elmali, 1997; Miranda et al., 1998) and braconid organza. Plants were kept free of pests and dis- parasitoids (Chambers et al., 1986) are recognized eases. Cabbage seedlings were transplanted in 3 L as important mortality factors of aphids. Cycloneda plastic containers with 3 parts of soil and one part sanguinea (L.) (Coleoptera: Coccinellidae) and of livestock manure. The old cabbage plants were Acanthinus sp. (Coleoptera: Anthicidae) are often regularly replaced by new plants free of aphids. observed occurring in high density in fields culti- Mummified aphids were periodically removed vated with brassicas (M. C. Picanço, personal com- and transferred to new cages to isolate D. rapae. munication). Similarly, Diaeretiella rapae (McIn- The newly emerged D. rapae were used in bioas- tosh) (Hymenoptera: Braconidae, Aphidiinae) has says to access toxicity of insecticides. Adults of the been reported as an important agent of natural bio- parasitoid D. rapae were also collected daily from logical control of B. brassicae populations in bras- cabbage fields. Similarly, adults of C. sanguinea sica crops (Costello and Altieri, 1995; Desneux et and Acanthinus sp. were collected from cabbage al., 2004). fields. The field collections were performed using Concentration-mortality regression lines ob- plastic containers and aspirators. The natural ene- tained by probit analysis may be used to compare mies were collected in random plants from the Selectivity of Insecticides to Natural Enemies 105 same cabbage fields located at the UFV experimen- opened inside plastic bags to avoid individuals fly tal station. Specimens of insect species were stored away. in 4 mL vials with 70% of alcohol, and sent to tax- Statistical analysis. Concentration-mortality onomists for identification. data were analyzed by probit regression (Finney, Insecticides. Bioassays were conducted with six 1971) using SAEG software (SAEG, 2001) to ob- insecticides including acephate (Orthene 750 BR, tain the regression equation and the insecticide Arysta LifeScience do Brasil, São Paulo, SP), concentration needed to kill 50% of the test popu- deltamethrin (Decis 25 CE, Bayer CropScience, lation (LC50) with their 95% confidence intervals São Paulo, SP), dimethoate (Perfekthion, Basf (Finney, 1971). Mortality was corrected for control S.A., São Bernardo do Campo, SP), methami- mortality using the method of Abbott (1925). We dophos (Tamaron BR, Bayer CropScience), methyl accepted curves which had probability greater than parathion (Folidol 600 CE, Bayer CropScience)