Influence of Tillage on Adult and Immature Pea Leaf Weevil (Coleoptera: Curculionidae) Densities in Pea

Abstract

The pea leaf weevil, Sitona lineatus (L.) (Coleoptera: Curculionidae), has been a major pest of pea, Pisum sativum L., in eastern Washington and northern Idaho since its introduction to the region in the early 1970s. Eggs are deposited in the spring on the soil surface and first instars hatch and move to pea root nodules, where larvae feed before they pupate and adults emerge in mid- to late summer. No-tillage practices are known to reduce pea leaf weevil colonization in pea, but the effects of tillage on larval densities and subsequent adult emergence have not been examined. During 2005, 2006, and 2007, we compared densities of colonizing adult and immature pea leaf weevils on pea plots grown using conventional tillage and no-tillage. In 2005 and 2006, emergence of adult pea leaf weevil was monitored in the same plots. Densities of colonizing adult and immature pea leaf weevil were significantly higher in conventional tillage plots. Larvae in conventional tillage were further along in development than larvae in no-tillage plots during June and July. Densities of emerging adult pea leaf weevil were significantly greater from conventional tillage than no-tillage plots. Based on densities of colonizing and subsequent emerging adults, survival of weevils from egg through adult was greater in conventional tillage plots. Soils under no-tillage are cooler, resulting in later emergence of the pea crop and delayed root nodule development, possibly affecting the ability of first-instar pea leaf weevil to locate host plant roots. Our results indicate no-tillage fields are less suitable for pea leaf weevil colonization and survival than conventional tillage fields.

Tillage affects the activity‐density, absolute density, and feeding damage of the pea leaf weevil in spring pea

“…This suggests that differences in pitfall catches were due to differences in weevil abundance rather than activity, although mark‐recapture experiments would have to be performed in the same year as the pitfall study to confirm this. Moreover, linear‐meter row sampling at Kambitsch detected significantly fewer PLW in NT than in CT, which is consistent with Hanavan et al. (2008, 2010), who detected lower PLW population densities in NT than CT during the colonization period.…”

“…(2008), although the methods (linear‐meter vs. visual‐counts per plot) and the study years differed between the two studies. This study and Hanavan et al. (2008, 2010) taken together form robust evidence that NT provides a pest suppression benefit during the crop establishment period in pea.…”

“…Once PLW larvae emerge, which likely occurred in mid‐ to late May in our studies, first instars move through the rhizosphere in search of food, boring into root nodules, and eventually feeding on the entire nodule. During the approximately 40 days until the adults emerge (Fisher, 1977), immature PLW are subject to mortality factors including limited food availability, predation, desiccation, and fungal attack, all of which potentially differ between tillage treatments (Hanavan et al., 2010).…”

“…Pitfall trapping might be ineffective, however, for sampling emerging adults, because subsequent studies at Kambitsch using flight‐emergence traps found (1) increased PLW survival in CT compared to NT plots, and (2) greater emergence of adult PLW in CT than NT during the late season (Hanavan et al., 2010). Adults begin to disperse almost immediately after emergence, and pitfall traps might be poorly suited to quantify such behavior if ground‐activity is only marginally affected.…”

“…The different conditions of microclimate and habitat created by CT and NT systems provide possible mechanisms to explain observed differences in PLW abundance and feeding damage between tillage treatments. Higher crop residue levels in NT during the early season can moderate soil moisture concentrations and temperature (Saxton, 1991; Hatten et al., 2007a), potentially slowing seedling germination (Saxton, 1991), crop growth, and weevil immigration and colonization (Hanavan et al., 2008, 2010). However, no effect of tillage on seedling emergence and growth (as measured by number of seedlings per plot and nodes per plant) was detected during our studies.…”