Use of Expanding Foam for Confining Thrips in Cages on Cowpea, Vigna unguiculata (L.) Walp, Flowers

Abstract

Studies on insect biology often require insects to be confined on a plant surface with cages. E. A. Hartley (1923) discussed the use of glass lantern globes for caging insects on plants shortly after the beginning of the 20th century. He devised improvements in cage production that included such things as use of perforated celluloid that provided better air circulation and use of melted paraffin to reduce insect escape. A substantial improvement in cage production was the development of clip cages that enabled small insects to be caged on a small portion of the plant, i.e., branches and foliage (MacGillivary and Anderson, 1957; Guthrie and Bishop, 1960; and Mowry, 1993). These cages, however, are not without their problems. Although clip cages may work well with aphids and whiteflies, they may be unsuccessful in preventing escape of smaller insects like thrips. Further, standard clip cages are not suitable for confining certain plant structures like flowers. Salguero et al (1991) used perforated plastic bags to cage thrips on tomato blooms. Bags were secured with paraffin strips. Although this method successfully confined thrips to small blooms, the process is time consuming and difficult. Thrips are considered a major insect pest of cowpea, Vigna unguiculata (L.) Walp, worldwide with different species attacking either the blooms or foliage of cowpea (Singh and van Emden, 1 979; Jackai and Daoust, 1986). Chalfant (1976) reported Frankliniella tritici (Fitch) to be the most abundant species on cowpea. F. tritici attack cowpea flowers and can cause damage to reproductive portions of blooms resulting in premature senescence (Jackai and Daoust, 1986). The impact of thrips, especially F. tritici, on cowpea is not well defined. Although several studies have correlated F. tritici management with improved cowpea yield (Chalfant and Johnson, 1972; Sweeden et al, 1994) other studies suggest that yield increase may actually be caused by other factors such as insecticides directly inducing plant responses (Hundley, 2004). In order to define the impact of F. tritici on cowpea, known numbers of thrips will need to be confined on cowpea flowers. The objective of this manuscript is to describe a caging system that successfully confines thrips on cowpea flowers. Thrips cages (Fig. 1) were constructed by taking a square of No-Thrip Insect Screen (Green-Tek, Edgerton, WI) measuring approximately 13 cm X 13 cm and rolling it into a tube 3.5 cm in diameter. Duct tape (Duck® Brand, Henkel Consumer Adhesives, Inc., Avon, OH) strips approximately 2.5 cm wide were used to seal inner and outer seams of the rolled mesh. A 29.5 ml plastic cup (Solo Cup Co., Highland Park, IL) was placed bottom-side inward in one end of the tube. Another 2.5 cm wide strip of duct tape was used to secure the cup to the tube and tape was burnished around the juncture to ensure a seal. The end opposing the cup was also taped shut and burnished. The bottom of the cup was then removed with a carpet knife. A hole was punched in the center of the cup lid approximately 0.5 cm in diameter and a slit was created from the hole to the edge of the lid to allow placement over the peduncle of the cowpea