The role of intercrops of eggplant and cowpea on the control of Leucinodes orbonalis guenee (Lepidoptera: Crambidae)

The eggplant fruit and shoot borer (EFSB), Leucinodes orbonalis Guenee (Lepidoptera: Crambidae) is the major pest of eggplant, Solanum melongena L., in Iran. Influences of intercropping eggplant (E) with cowpea (C), Vigna unguiculata L. Walp., in the three patterns: 4E:2C, 4E:4C and 4E:8C (row ratios) and sole eggplant were assessed on the densities of EFSB, the efficacy of enemies, and the crop yield. Our experiments we conducted in a trial farm through the two consecutive cropping seasons 2019 and 2020. Moreover, sole cowpea plots were just established to evaluating the yield benefit in intercrops. The densities of EFSB eggs and larvae per plant were fewer in intercrops on the vegetative growing (0.4–1.5 eggs per plant and 0.2 -0.75 larvae per plant), the blooming and initial fruit set (9.6–13.9 eggs per plant and 2.4–5.1 larvae per plant), and the fruit development (14.8–22.7 eggs per plant and 3.3–7.7 larvae per plant) stages of eggplant, especially in the 4E:8C pattern at the later growth stages than in sole eggplant (4.1–39.4 eggs per plant and 2.6–20.3 larvae per plant over two seasons) (P ≤ 0.05). Chrysoperla carnea (Stephans) as the main predator of EFSB eggs and larvae were more frequent in all intercrops on the blooming (3.7–4.7 larvae per plant) and the fruit development (5.5–7.9 larvae per plant) stages of eggplant than sole eggplant (2.7–3.4 larvae per plant) in two years. Trichogramma brasicae Bezdenko and Bracon hebetor Say were the prevalent parasitoids of EFSB eggs and larvae, respectively. The rates of eggs and larval parasitism were higher in all intercrops compared with sole eggplant on the blooming and the fruit development stages of eggplant. The values of land equivalent ratio (LER) in intercrops ranged from 1.14 to 1.41 for 4E:2C and 4E:8C, respectively that indicate the yield benefit of intercrops compared with the sole crops. Therefore, intercropping eggplant and cowpea, particularly in the 4E:8C pattern, is more profitable in the management of L. orbonalis in eggplant farms.