Postdispersal Predation of Velvetleaf (Abutilon theophrasti) Seeds

Abstract

Studies were conducted from 1989 to 1993 in continuous no-tillage and moldboard plow corn fields to describe rates of velvetleaf seed predation with time and with seed density, and to identify principal seed predators. Rates of seed loss from the soil surface averaged 1 to 57% day−1and were equivalent in the two tillage systems. Predator populations were the same in no-tillage and moldboard plow fields. The predation rate was generally low in winter months, increased in mid-summer, and declined in late summer. In 2 of the 4 yr, predation increased in October and November. The predation rate was described by an exponential decay function of seed density, with high rates of seed loss at low densities and leveling off to a nearly constant level at densities above 600 seeds m−2. Predation was highest where seed access was not restricted, and exclosures of 6.5 and 1.6 cm2reduced predation up to 15 and 52%, respectively. Mice were important predators in the field. In laboratory feeding studies, the carabid beetleAmara cupreolata, the slugsArion subfuscusandDeroceras reticulatum, and cutworms (Agrotis ipsilon) consumed imbibed velvetleaf seeds.Amara cupreolataand A.subfuscuswere the only predators to damage unimbibed velvetleaf seeds.

The strength of seeds and their destruction by granivorous insects

“…Laboratory feeding observations revealed that imbibing the unpreferred seeds (e.g., morning glory) in water for 24 h, or mechanically removing the seed coat rendered them susceptible to attack by G. pennsylvanicus (J. G. L., unpublished data). These observations are supported by literature on post-dispersal granivory by other insects as well (Cardina et al 1996;Pausch and Pausch 1980;Ready and Vinson 1995), and lend credence to the idea that the seed coat is obstructing granivory. Perhaps phytochemical constituents of the seed coat are more important in restricting granivory of small seeds by insects than the physical strength of the covering itself.…”

Weed Problems, Ecology, and Management Options in Conservation Agriculture: Issues and Perspectives

“…Predation of S. faberi seeds by invertebrates was higher in maize and soybean compared to triticale-alfalfa and alfalfa and there were higher predation rates in RT soybean (O'Rourke et al, 2006). In contrast to all the above findings, Cardina et al (1996a) could not detect any measurable variation in predator populations between NT and moldboard plough in corn suggesting that soil disturbance might not affect the weed seed predator community rather crop diversification in terms of monocrop heterogeneity and intercropping enhanced carabids (Kromp, 1999).…”

“…In laboratory studies, the carabid beetle Amara cupreolata, the slugs Arion subfuscus and Deroceras reticulatum, and cutworms (Agrotis ipsilon) consumed imbibed velvetleaf seeds (Cardina et al, 1996a).…”

Are irrigation and grazing effects transferred, accumulated, or counteracted during plant recruitment?

“…Several mechanisms may explain this effect of nullifying the summer drought. Irrigation during summer may (a) favour seed mortality by a wider group of soil organisms (e.g., moulds) (Cardina et al 1996); (b) increase the activity of invertebrates that feed on or harvest seeds (Fenner 2000); and (c) promote a greater abundance of latesummer species (e.g., Conyza canadensis), the seeds of which would not be present at the time of sampling because for these species the seed rain occurs later. Additional studies are needed to analyse the relevance and mechanisms of these detrimental effects of All-year irrigation Individuals / 100 cm 2 (e) Fig.…”