The Role of Ground Beetles in Biological Control of Weeds

  • Author / Creator
    Kulkarni, Sharavari
  • Ground beetles (Coleoptera: Carabidae) are important components of temperate agroecosystems, and contribute many ecological services including weed seed predation. Although their role as arthropod predators is well known, their contributions to weed biological control through seed predation and management of weed seedbanks is not fully understood. The goal of this dissertation was to develop insights into aspects of carabid weed seed predation in canola agroecosystems of western Canada, and to investigate factors influencing weed seed predation in those agroecosystems. I investigated carabid weed seed preferences, role of olfactory cues involved in weed seed detection, effects of weed seed burial in seed predation, and field dynamics and the spatial distribution patterns of seed predatory carabids under field conditions. My studies to investigate adult carabid preferences for three brassicaceous weed species (Brassica napus L., considered weedy as volunteers; wild mustard, Sinapis arvensis L.; and field pennycress, Thlaspi arvense L.) in canola revealed that carabids exhibited specific, distinct preferences for weed seeds. Seed consumption among carabids was influenced by several factors, including weed species, the physiological state of seeds, and carabid activity–density. All carabid species preferred seeds of volunteer canola the most and those of field pennycress the least and showed intermediate preference for wild mustard seeds. Beetles highly preferred imbibed seeds of all three weed species. Activity–density of carabids and mean weed seed removal were highly correlated in field plots of canola, with activity–density accounting for 67% of the observed variation in seed removal. I further investigated behavioural responses of carabids to olfactory cues, and whether such responses translated into seed preferences. Results of olfactometer-based bioassays suggested that imbibed volunteer canola seeds were preferred over other weed species by two of the three carabid species tested. Only A. littoralis responded significantly to odours from unimbibed seeds of B. napus. Sensitivity to olfactory cues appeared to be highly specific as all carabid species discriminated between the olfactory cues of imbibed brassicaceous weed seeds, but did not discriminate between weed seeds that were unimbibed. Overall, data suggested that depending on seed physiological state, odours can play an important role in the ability of carabids to find and recognize seeds of particular weed species. Seed burial depth influenced seed consumption rates as demonstrated by a significant interaction between seed burial depth, carabid species, and gender of the carabid species tested. We observed higher seed consumption by females of all species, and greater consumption of seeds scattered on the soil surface compared with seeds buried at any depth. However, there was evidence of seed consumption at all depths and seed burial did not eliminate weed seed predation. My studies to investigate spatial relationship between carabid beetles, weeds, and weed seeds in canola (Brassica napus L) under field conditions using Spatial Analysis by Distance Indices (SADIE) revealed that carabids and weed populations were highly clustered. Moreover, there was significant spatial overlap between activity-density of carabids and patches of high weed density, with an association index, X, ranging between 0.40 and 0.71. Our results suggest that the presence of weedy patches of vegetation in cropped areas may contribute to biodiversity by conserving populations of carabids, which can also increase rates of weed seed predation.

  • Subjects / Keywords
  • Graduation date
    Fall 2017
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.