Potential sources of Frankliniella spp. (Thysanoptera: Thripidae) in Iowa

In Iowa, two possible sources of phytophagous Frankliniella spp. infesting strawberry fields in spring are individuals that overwinter in fields or migrate into fields. In April 2001 and March 2002, soil samples taken to a depth of 5 cm from three strawberry fields in central Iowa were dried in Berlese funnels to determine whether thrips overwintered in these strawberry fields. In 2001, one Frankliniella spp. second instar was collected from 39 soil samples; in 2002, five Frankliniella occidentalis (Pergande) adults were collected from 72 samples. To determine whether thrips were flying into fields, 13 yellow and 13 blue sticky cards (8 x 13 cm) were placed in each of three strawberry fields in central Iowa from April to June 2001 and from March to June 2002. Thrips were first captured on sticky cards during the third week of April 2001 and 2002. In 2001, yellow sticky cards caught significantly higher numbers of thrips in strawberry fields compared with blue sticky cards, whereas in 2002, more thrips were captured on blue sticky cards. On the basis of this field study, we conclude that F. occidentalis overwinters in relatively low numbers in the soil in Iowa strawberry fields. Frankliniella tritici (Fitch) was the most common thrips found on the sticky cards during both years. Pest managers may use sticky cards to monitor early colonization of strawberry fields by F. tritici before flowers start appearing.