Efficiency ofHippodamia variegata (Col., Coccinellidae) and sublethal doses of spirotetramat in control of melon aphid, Aphis gossypii Glover (Hem., Aphididae), on two greenhouse cucumber varieties

Zahedi, Abdossamad (2019) Efficiency ofHippodamia variegata (Col., Coccinellidae) and sublethal doses of spirotetramat in control of melon aphid, Aphis gossypii Glover (Hem., Aphididae), on two greenhouse cucumber varieties. Doctoral thesis, University of Mohaghegh Ardabili.

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Abstract

Research Aim: This study aimed was to evaluate the efficiency of Hippodamia variegata Goeze (Col., Coccinellidae) and sublethal concentrations of spirotetramat insecticides in controlling of melon aphid, Aphis gossypii Glover (Hem., Aphididae) on two greenhouse cucumber cultivars. Research method: Experiments were performed in a growth chamber set at 25 ± 2 °C, 65±5 relative humidity, and 16 hours light and 8 hours dark periods. For experiments on the Aphis gossypii Glover life table, a number of adult female aphids were selected from the main colony, and one of them was placed underside of each of the Storm and Khasib cultivars in the leaf cage. After 24 hours, female aphids and all nymphs except one nymph were discarded. For experiments on the life table of H. variegata, 100 eggs were collected from ladybird fed on A. gossypii on each the Storm and Khasib cultivars over a 12-hours and transferred to a 10 cm diameter ventilated plastic petri dish in separate oviparous adult-fed cultivars. After the emersion of insects, the number of eggs laid per day for each of the experimental units was counted and recorded separately until the death of all the ladybirds. Sublethal experiments were performed on adult Aphis gossypii Glover, and H. variegata and their life tables on Storm and Khasib cultivars were prepared separately. Findings: According to the results, the developmental times of H. variegata and A. gossypii was increased by sublethal concentrations of Spirotetramat insecticide on both Storm, and Khasib cultivars and adult longevity and life span were decreased. The fertility of the A. gossypii was decreased on Storm cultivar and increased on Khasib cultivar. Also, the fertility of the aforementioned ladybird above was increased on Storm cultivar and decreased on Khasib cultivar. The intrinsic rate of population increase (rm) of A. gossypii in the control treatment was highest, which decreased with increasing sublethal dose. This trend was repeated for the net reproductive rate (R0) and gross reproductive rate (GRR) of the aforementioned aphids above. In the control treatments between two cultivars for Aphis gossypii, rm, R0, and GRR were higher on Khasib cultivar than on Storm cultivar, while these values were reversed for the mentioned parameters in H. variegata. Conclusion: Based on the results, it can be concluded that the application of relatively resistant Storm cultivar with H. variegata reduces A. gossypii population. Also, using sublethal concentrationsof spirotetramat insecticides against Aphis gossypii on relatively resistant Storm cultivar, while reducing and controlling A. gossypii Glover population, leads to adverse effects of this insecticide on H. variegata. Therefore, due to the high toxicity of this insecticide for the aforementioned ladybird, its use in the form of integrated pest management programs in the cucumber production greenhouse is not recommended.

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