Eggplant-garlic intercrops reduce the density of Tetranychus urticae on eggplant and improve crop yield.

Diversification of cultivation systems plays a critical role in ecosystem functions such as pest control, diversity of beneficial arthropods, and soil fertility. Repellent plants (releasing volatile organic compounds as arthropod repellents and providing alternative prey for natural enemies) may be used in an intercropping system for pest control; however, little is known concerning their relative priority. In this study, the impact of intercropping eggplant (E) (Solanum melongena L.) and garlic (G) (Allium sativum L.) in three designs - with row ratios of 4E:4G, 4E:8G, or 4E:12G - was assessed on the density of the two-spotted spider mite (TSSM) (Tetranychus urticae Koch), the abundance and diversity of predators, and crop yields, compared with the sole crops over two growing seasons of 2019 and 2020. In three intercrops, a significant decrease in the density of TSSM egg and mobile stages was observed compared with the sole eggplant at each growth stage of eggplant. The damage index by TSSM on eggplants was lower in intercrops (8.1-11.5%) compared with sole crop (37.0-40.3%) in the two seasons. The abundance of Stethorus gilvifrons was lower in the three intercrops than in the sole crop on the blooming-initial fruit set and the fruit development stages of eggplant. The density of Orius niger was higher in the three intercrops compared with the sole crop on vegetative growth and flowering to initial fruit set stages of eggplants. The abundance of Chrysoperla carnea was not significant among treatments. Greater values of the Shannon diversity index and the Pielou's evenness index for the construction of TSSM predators were recorded in the three intercrops compared with the sole eggplant over both growing seasons. In addition, a significant improvement in the yield per unit area of eggplant and garlic was obtained in intercrops compared with sole crops. These results indicate intercropping eggplant and garlic was a practical solution for reducing TSSM on eggplant, promoting the abundance of predators, and improving the crop yields of eggplant and garlic compared with the sole crops.

Evaluation of the effect of strip intercropping green bean/garlic on the control of Tetranychus urticae in the field.

In this study, the effect of strip intercropping green bean (GB), Phaseolus vulgaris L., with garlic (G), Allium sativum L., in three row ratios (3GB:5G, 3GB:8G and 3GB:11G) was assessed on two-spotted spider mite (TSSM), Tetranychus urticae Koch, compared with green bean sole crop over two growing seasons, in 2017 and 2018. The results indicated that intercrops reduced the densities of T. urticae eggs and mobile forms on the vegetative growth, the flowering, and the bean expansion stages of green bean plants compared with sole crop. In this study, seven predators of T. urticae including Stethorus gilvifrons (Mulsant), Orius niger (Wolff), Neoseiulus zwoelferi (Dosse), Chrysoperla carnea (Stephens), Geocoris punctipes (Say), Scolothrips sexmaculatus Pergande, and Nabis pseudoferus (Remane) were collected on TSSM-infested green bean plants during the two growing seasons. Among them, S. gilvifrons and O. niger were the main predators of TSSM on green bean plants in the two growing seasons. Furthermore, the densities of O. niger were significantly higher in intercrops on the vegetative growth and the flowering stages of green bean compared with sole crop, whereas no significant difference was observed in the densities of S. gilvifrons between intercrops and sole crop in 2017 and 2018. Moreover, the values of the Shannon diversity index (H') and Pielou's evenness index (J') for the composition of TSSM predators were greater in the three intercrops compared with sole crop for the entire growing seasons 2017/2018. On the other hand, the land equivalent ratio (LER), which is used to assess the yield benefit in intercrops, was greater than one in intercrops, especially in the 3GB:5G ratio (1.29 in 2017 and 1.40 in 2018). These results indicated that strip intercropping green bean with garlic could be effective in the control of T. urticae in green bean fields.

Life-history parameters of the Colorado potato beetle, Leptinotarsa decemlineata, on seven commercial cultivars of potato, Solanum tuberosum.

The Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), is an important pest of potato, Solanum tuberosum L. (Solanales: Solanaceae), crops in the Ardabil region of Iran. In this research, the life-history parameters of L. decemlineata were investigated on seven potato cultivars, namely Agria, Aozonia, Diamant, Cosmus, Kondor, Morene, and Savalan, in a greenhouse at 23 ± 1° C and 55 ± 5% RH under a natural photoperiod. The results indicated that the development time of larvae was longest on Savalan (18.3 days) among the tested potato cultivars. The survival rates (egg to adult) on Savalan and Morene were significantly lower than on the other studied cultivars. L. decemlineata reared on Savalan had the lowest fecundity (286.3 eggs/female) among the tested potato cultivars. The oviposition period of females was significantly shorter on Savalan and Diamant than on Kondor, Aozonia, Morene, Agria, and Cosmus. The values of intrinsic rate of natural increase and population growth rate were lowest on Savalan (0.055 and 1.056, respectively). The generation time and doubling time were significantly longest on Savalan (69.5 and 12.7 days, respectively). Based on these results, it can be concluded that Savalan is the least suitable cultivar for L. decemlineata among the ones tested. These results can be useful in integrated management of L. decemlineata in potato fields.