Laura C.H. Jesse

Assessing the impact of Cry1Ab-expressing corn pollen on monarch butterfly larvae in field studies

Survival and growth of monarch larvae, Danaus plexippus (L.), after exposure to either Cry1Ab-expressing pollen from three Bacillus thuringiensis (Bt) corn (Zea mays L.) events differing in toxin expression or to the insecticide, λ-cyhalothrin, were examined in field studies. First instars exposed to low doses (≈22 grains per cm2) of event-176 pollen gained 18% less weight than those exposed to Bt11 or Mon810 pollen after a 5-day exposure period. Larvae exposed to 67 pollen grains per cm2 on milkweed leaves from within an event-176 field exhibited 60% lower survivorship and 42% less weight gain compared with those exposed to leaves from outside the field. In contrast, Bt11 pollen had no effect on growth to adulthood or survival of first or third instars exposed for 5 days to ≈55 and 97 pollen grains per cm2, respectively. Similarly, no differences in larval survivorship were observed after a 4-day exposure period to leaves with 504–586 (within fields) or 18–22 (outside the field) pollen grains per cm2 collected from Bt11 and non-Bt sweet-corn fields. However, survivorship and weight gain were drastically reduced in non-Bt fields treated with λ-cyhalothrin. The effects of Bt11 and Mon810 pollen on the survivorship of larvae feeding 14 to 22 days on milkweeds in fields were negligible. Further studies should examine the lifetime and reproductive impact of Bt11 and Mon810 pollen on monarchs after long-term exposure to naturally deposited pollen.

Bacterial Wilt of Cucurbits: Resurrecting a Classic Pathosystem

Bacterial wilt threatens cucurbit crop production in the Midwestern and Northeastern United States. The pathogen, Erwinia tracheiphila, is a xylem-limited bacterium that affects most commercially important cucurbit species, including muskmelon, cucumber, and squash. Bacterial wilt is transmitted and overwintered by striped and spotted cucumber beetles. Since there are few commercially available resistant cultivars, disease management usually relies on use of insecticides to suppress vector populations. Although bacterial wilt was initially described more than 100 years ago, our knowledge of disease ecology and epidemiology advanced slowly for most of the 20th century. However, a recent wave of research has begun to fill in missing pieces of the bacterial wilt puzzle. This article-the first review of research toward understanding the cucurbit bacterial wilt pathosystem-recounts early findings and updates our understanding of the disease cycle, including pathogen and vector biology. We also highlight research areas that could lead to more efficient and ecologically based management of bacterial wilt.

Testing for Plant-parasitic Nematodes that Feed on Corn in Iowa 2000-2010

The Iowa State University Plant and Insect Diagnostic Clinic analyzes soil and root samples for plant-parasitic nematodes. The results of samples associated with corn that were submitted from 2000 through 2010 were summarized. One or more genera of plant-parasitic nematodes were found in 92% of the samples. Spiral nematode and root-lesion nematode were most commonly found. Other nematodes recovered were dagger, lance, needle, pin, ring, and stunt nematodes. Nematodes recovered at damaging population densities were dagger, needle, ring, and spiral nematodes. An average of 15 samples were submitted per year from 2000 to 2004. Sample numbers increased nearly threefold since 2005, but overall sample numbers were low every year from 2000 through 2010. Samples were received from 53 of the 99 Iowa counties, and most samples were received in June and July, which is the recommended sampling time. Nematodes that have been associated with corn in Iowa in the past that were not recovered from the samples were sheath, sting, and stubby-root nematodes. The methods used to extract the nematodes from soil and roots and how the samples were handled during collection and processing may have affected the species and population densities recovered. Much more frequent and widespread sampling is needed in Iowa for plant-parasitic nematodes that feed on corn.