Lepidopteran pest populations and crop yields in row intercropped broccoli

Abstract

1 To determine how the presence of non-host plants impact populations of lepidopteran pests and yield of broccoli, Brassica oleracea var. italica L., broccoli was intercropped with tomato, Lycopersicon esculentum Miller, or yellow sweetclover (YSC), Melilotus officinalis L., and compared with broccoli monoculture grown at two densities (high and low). 2 During a 1997 study, numbers of early instar imported cabbageworm, Artogeia rapae L., were greater in broccoli monoculture compared with intercropped plantings. In contrast, late instar A. rapae numbers were significantly higher in intercropped broccoli during most of the season, indicating greater survival of early instar stages in intercropped habitats. 3 Cabbage looper, Trichoplusia ni HuÈ bner, eggs and larvae were more abundant in broccoli monoculture than intercropped broccoli in 1997. In addition, T. ni populations were found at significantly lower levels in broccoli-YSC compared with broccoli-tomato habitat throughout the season. 4 During a 1998 study, numbers of early and late A. rapae instars were greater in intercropped broccoli on most sampling dates. 5 The mean percentages of harvested broccoli heads infested with insects and associated frass were higher in monocultures than intercropped treatments in 1997. Additionally, a significantly lower number of contaminants were found in the crowns of broccoli harvested from broccoli-YSC (YSC) compared with broccoli-tomato (tomato) habitat. However, broccoli heads were significantly smaller in intercropped habitats. 6 Variations in insect responses and challenges to using crop diversification as a management tool are discussed.

Population densities of herbivorous lepidopterans in diverse cruciferous cropping habitats: Effects of mixed cropping and using a living mulch

“…Likewise, fewer T. ni pupae were encountered in broccoli heads in the broccoliÀYSC habitats at season end (Hooks and Johnson, 2001). Similar findings were discovered by Hooks and Johnson (2002), in that fewer eggs were found in broccoliÀYSC than in broccoliÀtomato plantings on a few dates, however, significantly fewer associated larvae were found on broccoli plants throughout the season (Hooks and Johnson, 2002). Thus, from these findings it is reasonable to forecast that T. ni females that lay their eggs on broccoli plants interplanted with YSC will have fewer offspring compared with females that oviposit on broccoli plants in monoculture or intercropped with certain vegetables.…”

“…However, during the summer trial, significantly fewer A. rapae eggs were found in broccoliÀpepper compared with broccoliÀYSC habitats on several dates. Similarly, Latheef and Ortiz (1983) and Hooks and Johnson (2002) found that A. rapae lacked a consistent trend in ovipositional preference over seasons. It is unknown why this irregularity occurs, but changes in host plant quality may exert some influence (Radcliffe and Chapman, 1965).…”

“…Sampling was stratified according to plant stratum. Five upper, 10 middle, and 5 lower positioned leaves per subplot were examined each sampling date (Hooks and Johnson 2002).…”

“…Living mulches are cover crops grown within a marketable cash crop to suppress weeds, reduce erosion, enhance fertility, and promote soil quality (Lanini et al, 1989). Recent experiments have shown that living mulches can help suppress insect pest populations when grown with a cash crop (Vidal, 1997;Hooks et al, 1998;Hooks and Johnson, 2002). Several studies have investigated the population dynamics of insect herbivores in vegetationally diverse Brassica plantings.…”

Herbivorous mites as ecological engineers: indirect effects on arthropods inhabiting papaya foliage

“…Nesticodes that colonized experimental rolls may have come from populations found on (1) the lower surface of rolled leaves, (2) unrolled leaves from the same tree, (3) unrolled leaves from other papaya trees, or (4) other plant species in the habitat. Nesticodes is common in many agricultural systems on Oahu, Hawaii (Hooks and Johnson 2002). Leaf rolling might simply redistribute spiders at the level of the papaya field, or might actually generate an increase in the total population density of Nesticodes.…”