The simultaneous use of a parasitoid wasp, Lysiphlebus fabarum and pirimicarb insecticide to control Aphis gossypii, in greenhouse conditions

Background and Objectives The melon or cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is hazardous to many agricultural crops. Melon aphid is a highly polyphagous pest, feeding on more than 320 plant species including cucumber. Melon aphids physically damage plants by directly sucking their phloem sap, resulting in premature leaf drop, wilting, and desiccation of host plants. Application of insecticides is usually considered as the most common method to control this pest. As a result of the widespread use of these chemical compounds, this pest has become resistant against several classes of synthetic insecticides. Therefore, in this study, sub-lethal concentrations of pirimicarb, and a parasitoid wasp, Lysiphlebus fabarum (Marshall) (Braconidae: Aphidiinae) were simultaneously used to control melon aphid on cucumber, as part of a comprehensive study for the integrated pest management. Materials and Methods In this research, first, bioassay of pirimicarb was performed with third instar of A. gossypii to calculate lethal concentrations of pirimicarb and then, another experiment was conducted to determine stability of pirimicarb, and also its effects on survival of a parasitoid wasp adult, L. fabarum. In the following, the effects of simultaneous releasing of L. fabarum with applying sub-lethal concentration (LC50) of pirimicarb on cucumber were investigated by determining population dynamics A. gossypii, every 5 days. In the first treatment, as a control treatment; the plants were sprayed with the recommended field concentration, at the beginning of the experiment, without releasing of the parasitoid wasp. In the second and third treatments, 40 male and female parasitoid wasps were released every 3 days on each plant. In the fourth and fifth treatments, 60 male and female parasitoid wasps were released. In all the last four treatments, at the beginning of the experiment, and in the third and fifth treatments on the 15th day, the plants were sprayed with LC50 of pirimicarb. After 30 days, the experiment was ended and the total number of alive aphids and total number of the mummified aphids were counted on each plant.   Results Mean lethal concentration (LC50) of pirimicarb was equal to 212.6 µg/L for the third nymphal instar and due to low stability of this concentration of pirimicarb; it was possible to release the wasps 3 days after spraying. The results of releasing different densities of wasp showed that higher density of wasps (60 wasps per release) did not have a highly significant effect, and low density of wasps (40 wasps) was able to control aphids. After a significant reduction in aphid population due to pesticide use, the parasitoid wasp was able to prevent growth of aphid population, but if necessary, spraying can be repeated by sub-lethal concentration (LC50)of the pirimicarb, after 15 days. Discussion Findings of the present study suggested that lethal concentration (LC50) of pirimicarb can be applied as a suitable insecticide, simultaneously with L. fabarum, for the integrated pest management of melon aphids.