Feeding Preference of Conotrachelus retentus on Black Walnut Tissues

Black walnut curculios (Conotrachelus retentus) were collected in a mature black walnut repository at New Franklin, MO, on 2, 9, 10, and 15 May 2012. A total of 138 female and 150 male curculios were collected and used for feeding preference trials. Insects were provided water, but food was withheld for 24 h before the feeding trial. For this test, four types of plant material were placed in each quadrant of a 140 mm-diameter by 25 mm-deep petri dish lined with moist filter paper. Plant material included a pistillate flower (≈ 2 cm-long), a similar length of a catkin, and a 2 cm x 1 cm section of a black walnut or pin oak leaf. One insect was placed in the center of each petri dish lined on a laboratory bench in a lighted room at 0900 HR and the occurrence of feeding on any plant material was recorded after 15, 30, 45, 60, 75, 90, 105, 120, 180, 240, 300, 360 min.  After this time, lighting was eliminated until 0800 HR the next morning when data were recorded again at hourly intervals for 4 h. Insects were removed from petri dishes and the number of eggs within each ovipositional scar on each pistillate flower was recorded. Male and female curculios had similar feeding preferences. Both sexes were observed feeding on catkins most often and female flowers to a lesser extent. The probability of females and males feeding on the catkins was 3.0 and 4.7 times greater, respectively, than that of feeding on pistillate flowers during the trial. Insects were never seen feeding on walnut or oak leaves. Pistillate flowers had the greatest number of ovipositional scars on May 9 and the fewest on May 15.  Also, females oviposited an average of five eggs per pistillate flower on May 9 and less than one per flower on May 15.