Submitted to: Transactions of the American Entomological Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 6, 2006
Publication Date: March 20, 2007
Citation: Day, W.H. 2007. The effect of rainfall on the abundance of tarnished plant bug [lygus lineolaris (Palisot)] nymphs in alfalfa fields. Transactions of the American Entomological Society. 132:445-450. Interpretive Summary: Considerable variation in tarnished plant bug (TBP) numbers and crop damage from year to year have been observed for over six decades in numerous crops and locations, and rainfall was occasionally suggested as the cause. This 13-year study determined that high May-June rainfall (10.7” total) was responsible for reducing first generation TPB numbers in alfalfa by 50%, compared to low May-June rainfall (6.5”). In addition, rainfall and parasitism proved to be complementary mortality factors; mortality by parasites was high when rainfall was low, and vice versa. This means that years with low spring rainfall would be expected to also have higher TPB numbers and more crop damage, which may warrant corrective measures in areas where the introduced parasite (P. digoneutis) is not yet present.
Technical Abstract: During a 13-year field study in northwestern New Jersey, total May-June rainfall ranged from 6.5 to 10.7 inches (165-272mm). The highest rainfall reduced first generation nymphs of the tarnished plant bug, Lygus lineolaris (Palisot) (Miridae), in alfalfa by 50%. This reduction was likely mechanical (raindrops knocking the mirids off the plants) rather than biotic, because infections by nematodes and a fungus disease were not significantly increased. The rainfall-reduced mirid populations also has less mortality by the introduced parasite Peristenus digoneutis Loan (Braconidae), probably a result of the lower host density (via density dependence). Conversely, in low-rainfall years, parasitism rates were doubled, so the two mortality factors were complementary.