Utah Pest News Spring 2010

click here for pdf version

Undergraduate Research in Entomology
 


RASPBERRY HORNTAIL OVERWINTERING BEHAVIOR

Horntail larva parasitized by a wasp.


Raspberry horntail is a cane-boring pest of raspberry causing cane wilt and injury, and yield loss.  We examined raspberry horntail behavior and development from fall through early spring, and larval parasitism in two summer-bearing varieties of raspberry.

‘Killarney’ and ‘Cowichan’ raspberry canes with suspect infestation were collected from a farm in Laketown, Utah in fall 2009.  Canes were dissected to observe horntail larval parasitism, stage of larval development, and status of overwintering chamber construction.  A second set of ‘Cowichan’ canes were exposed to winter-to-spring temperature simulation for 4, 6, and 8 weeks to satisfy insect chilling requirements.

Conclusions:

  •  In September, parasitism of horntail larvae was greater in ‘Killarney’ than ‘Cowichan’ canes.  Seasonal growth of ‘Killarney’ was slower than ‘Cowichan’, which may have resulted in delayed larval development in ‘Killarney’, and thus, greater parasitism in those canes late in the season.  
  • Horntail larvae formed overwintering chambers higher above the base in ‘Cowichan’ than ‘Killarney’ canes, probably due to the faster growth rate and greater height of ‘Cowichan’ canes.  In addition, horntail larvae were larger in ‘Cowichan’ canes, probably because of this variety’s higher nutritional quality and earlier maturity.
  • At least 8 weeks of chilling was required for 10% of the horntail larvae to pupate and develop to the adult stage.  This low rate of overwintering survival suggests that more than 8 weeks is required for horntail development.

Further studies will evaluate overwinter survival following longer chilling exposure, and degree-day requirements for adult emergence to determine optimal timing for prevention of springtime cane infestation.

-Bret Butterfield, USU student, and
Diane Alston, Entomologist


USING KILLING STATIONS FOR CHERRY FRUIT FLY

Cherry fruit fly killing stations are rain-protected, inverted trays lined with the GF-120 solution.


The Western cherry fruit fly (WCFF), Rhagoletis indifferens, is an economically important pest in cherry orchards in Utah.  One of the safest and most effective treatments, an attract-and-kill product (GF-120, containing spinosad), has drawbacks, including multiple application requirements and limited rainfastness.  In collaboration with Dr. Jaime C. Pinero of the University of Hawaii, we sought to determine the effectiveness of GF-120 “killing stations” in various colors and baits.

This project compared GF-120 killing stations in green and yellow, and yellow GF-120 stations with standard ammonium acetate concentrations, and 1x and 2x concentrations.  Fourteen trials were conducted over 4 days, both in the morning and in the afternoon.  The killing stations positions were rotated every 15 minutes over a 120 minute period.  WCFF on the underside of the killing stations were counted and collected prior to rotation. 

Preliminary results showed that WCFF females are more attracted to the color yellow.  Both sexes were more attracted to the higher ammonium acetate concentrations (twice the normal amount in GF-120), and were more active in the early afternoon than morning hours.

Further research is needed to make this information useful to cherry growers, and could focus on the effectiveness of GF-120 after longer field exposure, the necessary killing station density in relation to number of WCFF present in the orchard, and killing station placement in the tree.

-Cammile Adams, USU student, and
Diane Alston, Entomologist