Role of trap crops on harlequin bug, Murgantia histrionica (Hahn), population dynamics and parasitism in broccoli plots

Abstract

Trap crops were evaluated for harlequin bug control in broccoli field plots in 1994 and 1995. Mustard and rape prevented low densities of harlequin bug from reaching broccoli, but at high densities the insect moved from the trap plants into the broccoli. This indicates that harlequin bugs that are attracted to trap plants may damage the protected broccoli if their numbers are not prevented from increasing. Harlequin bugs were shown to have two and a partial third generation a year. Trissolcus murgantiae Ashmead and Ooencyrtus johnsoni Howard, were identified as egg parasitoids. Their combined parasitization levels for the two years were 8% and 37%. T. murgantiae accounted for 87% and 96% of the parasitization, respectively.. When 19.6 cm and 11.9 cm broccoli plants were exposed to five densities of harlequin bug adults a negative correlation between plant mortality and insect density was observed (y = 38.00 - 2.32x, r2 = 0.95 and y = 22.17 - 1.17x, r2 = 0.99, respectively). No correlation was observed in broccoli plants 11.9 tall.. Host plants affected harlequin bug development. Nymphs developed faster when reared on rape in comparison with mustard. The preoviposition time for rape reared nymphs was shorter than mustard reared insects. Fecundity and viability of eggs were not different for harlequin bugs reared at different sex ratios.