An emergence trap was developed to test the hypothesis that Dasineura oxycoccana Johnson (Diptera: Cecidomyiidae) adults in cranberry, Vaccinium macrocarpon Aiton (Ericaceae), emerge from overwintering as larvae in soil throughout the spring and summer. The trap was constructed from 2 white plastic cylinders made from buckets, with the inner bucket telescoping into the support bucket. A mesh lid allowed penetration of rain and irrigation water. Wire support pegs and a skirt of landscape cloth anchored the trap to soil to prevent escape of target insects and ingress of others without damaging the mat of woody cranberry vines. Overwintered cranberry tipworms and their parasitoids were trapped on a yellow sticky card suspended inside the emergence trap. In the first year of testing, the trap detected overwintered tipworms every wk from early May to mid Aug, and overwintered parasitoids of 4 genera most wk from late May to mid Aug. It is probable that overwintered insects inside the traps emerged slightly ahead of those outside because temperatures inside traps were warmer than outside. We found that overwintered cranberry tipworms, and their parasitoids, emerge and add to the field population throughout the growing season in British Columbia, Canada.
Dasineura oxycoccana Johnson (Diptera: Cecidomyiidae) is an economically significant pest of cranberry, Vaccinium macrocarpon Aiton (Ericaceae), and highbush blueberry species, including V. corymbosum L., V. corymbosum L. × V. darrowi Camp., and V. virgatum Aiton (all Ericaceae) (Dernisky et al. 2005; Fitzpatrick 2009; Liburd & Averill 2016; Rhodes et al. 2014). Host-associated populations of D. oxycoccana from cranberry (cranberry tipworm) and blueberry (blueberry gall midge) (Cook et al. 2012) are genetically distinct (Mathur et al. 2012), produce different pheromones (Fitzpatrick et al. 2013) and do not interbreed (Cook et al. 2011). The overwintering stage of cecidomyiids is usually the full-grown larva that uses a spatula structure on the prothorax to dig into soil before entering diapause (Gagne 1989). Cranberry tipworm larvae overwinter in leaf litter and soil below the mat of cranberry vines (Eck 1990). Pupation is presumed to occur in early spring before adults emerge, mate, and lay eggs in the apex of growing cranberry shoots. Oviposition begins as cranberry shoots elongate in early spring (Cockfield & Mahr 1994) and increases steadily until mid- or late Jul when fruit have formed and plants are setting buds for the following year (Cook et al. 2012). Eggs laid in early spring are progeny of overwintered individuals. It is not known if eggs laid later in the season are progeny of overwintered or subsequent generations. If cranberry tipworm adults have a prolonged period of emergence from overwintering, as do adults of the swede midge, Contarinia nasturtii (Kieffer) (Diptera: Cecidomyiidae) (Des Marteaux et al. 2015), then a proportion of eggs laid throughout the growing season would originate from overwintered females.
To test the hypothesis that overwintered cranberry tipworms emerge as adults during a prolonged period through spring and summer, we designed an emergence trap similar to the bucket traps evaluated in blueberries (Roubos & Liburd 2010; Hahn & Isaacs 2012; Rhodes et al. 2014), but with some notable differences. Our buckettype emergence trap can be seated snugly onto the soil without damaging the mat of intertwined woody cranberry vines while allowing penetration of rain and irrigation water. Here we describe trap design, report seasonal emergence of overwintered cranberry tipworms, and compare temperature inside and outside the trap during the growing season. In addition, we discovered that our emergence trap detected overwintered hymenopteran parasitoids from the soil beneath infested cranberry plants.
The emergence trap was constructed from 2 white 2.3 L buckets of high density polyethylene (Snap on Lid Pails; Pro-Western Plastics Ltd., St. Albert, Alberta, Canada) (Fig. 1). In order to create a cylinder 16 cm high, the bottom of 1 bucket (the support bucket) was removed with a power saw. The lower edge of the support bucket was fitted with 3 pegs (15 cm long) of plastic-coated wire (0.3 cm diam) spaced equidistantly and attached with cable ties through holes 2.5 cm above the lower rim. A pleated skirt (15 cm long) of black landscape fabric (Vigoro Polyethylene Weed Barrier; Home Depot Inc., Chilliwack, British Columbia, Canada) was attached with weatherproof sealant and black weatherproof electrical tape to the outer surface of the support bucket, 2.5 cm above the lower rim. The second (inner) bucket was cut to create a bottomless cylinder 10 cm high. A circular opening (10 cm diam) was cut in the center of the lid (16 cm diam) of the inner bucket. The opening was covered with a circle (13 cm diam) of white no-seeum mesh (7250NSW; BioQuip Products, Rancho Dominguez, California, USA) glued at the perimeter to the underside of the lid. To hold a double-sided yellow sticky card trap (Silvalure Catch-It Yellow; Terra-Link, Abbotsford, British Columbia, Canada) inside the inner bucket, a length of wooden dowel (0.5 diam × 16.5 cm long) was positioned 1 cm below the top rim and glued at the ends into holes (0.5 cm) cut into the plastic. A 2.5 cm foldback binder clip (Lyreco; Grand & Toy, Vaughan, Ontario, Canada) was clipped around the dowel and oriented so that the handles could be gripped through the no-see-um mesh to attach or release the yellow sticky card.
The trap was assembled by sliding the inner bucket, with the yellow sticky card attached to the clip on the dowel in the lid, into the support bucket (Fig. 1). The trap (20 cm high, 16 cm diam [top], 13 cm diam [bottom]) was seated into the cranberry field by pushing the 3 pegs on the support bucket into soil exposed by parting the cranberry vines, then pushing square-top landscape staples into the fabric skirt to seal the lower rim of the support bucket to the soil. The circular lower rim of the trap enclosed 135 cm2 of soil. Traps were checked weekly by sliding the inner bucket out of the support bucket and squeezing the clip handles to release the used yellow sticky card before installing a fresh one.
Emergence traps were tested in 2015 on 6 cranberry f