Role of Egg Density on Establishment and Plant-to-Plant Movement by Western Corn Rootworm Larvae (Coleoptera: Chrysomelidae)

Abstract

The effect of egg density on establishment and dispersal of larvae of the western corn rootworm, Diabrotica virgifera virgifera LeConte, was evaluated in a 3-yr field study. Implications of these data for resistance management plans for Bt crops are discussed. Viable egg levels of 100, 200, 400, 800, and 1600 eggs per infested plant were evaluated in 2000, 2001, and 2002. A 3200 viable egg level was also tested in 2001 and 2002. All eggs were infested on one plant per subplot in a field that was planted to soybean, Glycine max (L.), in the previous year. For each subplot, the infested plant, three plants down the row, the closest plant in the adjacent row of the plot, and a control plant at least 1.5 m from any infested plant (six plants total) were sampled. In 2000, there were five sample dates between egg hatch and pupation, and in 2001 and 2002, there were six sample dates. On each sample date, four replications of each egg density were sampled for both larval recovery and plant damage. Initial establishment on a corn plant seemed to not be density-dependent because a similar percentage of larvae was recovered from all infestation rates. Plant damage and, secondarily, subsequent postestablishment larval movement were density-dependent. Very little damage and postestablishment movement occurred at lower infestation levels, but significant damage and movement occurred at higher infestation rates. Movement generally occurred at a similar time as significant plant damage and not at initial establishment, so timing of movement seemed to be motivated by available food resources rather than crowding. At the highest infestation level in 2001, significant movement three plants down the row and across the 0.76 m row was detected, perhaps impacting refuge strategies for transgenic corn.

Increased survival of western corn rootworm on transgenic corn within three generations of on-plant greenhouse selection

“…Although we only have one colony per treatment, our data suggest that selection for resistance may be minimal when neonate larvae are exposed to Bt corn but development is completed on isoline corn (the Neonate-exposure colony was not significantly different from the Control colony for any parameter of resistance). However, in a scenario where initial development occurs on grassy weeds and the weeds are then sprayed with herbicide, or in a seed-mix scenario where isoline food resources are significantly depleted forcing larvae to move (24), resistance might be expected to evolve, given that survival of the Lateexposure colony on Bt corn relative to isoline survival was significantly (3.8-fold) greater than the Control colony in the field.…”

“…Temperatures in such a greenhouse in late June in Missouri are often 50 -65°C. Under these conditions, larvae leave the hot and drying soil in search of a more suitable environment (12,24). Larvae were captured in water pans below each root ball, and were transferred to 95% ethanol at least twice daily.…”

Influence of drought on plant performance through changes in belowground tritrophic interactions

“…Western corn rootworm survival was evaluated by suspending the plant roots and surrounding soil in mesh bags (New cabbage, USA) over water filled pans (6.65 L) in a greenhouse at day 68, causing the fall of soil‐dwelling invertebrates (Hibbard, Higdon, Duran, Schweikert, & Ellersieck, 2004). WCR larvae were counted twice a day for 12 days.…”

Modeling Evolution of <I>Diabrotica virgifera virgifera</I> (Coleoptera: Chrysomelidae) to Transgenic Corn With Two Insecticidal Traits

“…However, to permit reasonable comparison with seed mixture studies in the future, we include the probability of leaving a nontransgenic plant, Z, the probability of leaving a transgenic plant, V, and the proportion surviving dispersal as neonates, SM, in the model. The data of Hibbard et al (2004) observed 66% of neonates on the initially infested roots. Therefore, we set Z ϭ 0.5 and SM ϭ 0.5 (Onstad 2006).…”