Submitted to: Journal of Entomological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2004
Publication Date: 1/31/2005
Citation: Gourdine, J.S., Simmons, A.M., McCutcheon, G.S., Leibee, G.L. 2005. Floral Nectars and Honey Enhance Survival of Iadegma Insulare (Hymenoptera: Ichneumonidae), A Parasitoid of the Diamondback Moth (Lepidoptera: Plutellidae). Journal of Entomological Science. 40:96-99. Interpretive Summary: The diamondback moth is a major pest on cole crops. The application of insecticide is the primary method of control this insect. A native beneficial parasitic wasp, Diadegma insulare, has been demonstrated to be effective against this pest. Flowers of various types of plants may serve as a potential food source for enhancing populations of this parasite. A study was conducted to determine the effect of selected food sources on the survival and parasitism of Diadegma insulare. The test consisted of three varieties of cultivated ('Vates) and ornamental ('Nagoya' and 'Frizzy') kale, red clover, white clover, wild radish, tansy, 15% honey, and water. In the field, the parasitoids survived significantly longer when allowed to feed on floral nectars of 'Nagoya' kale or 'Vates' kale, or on 15% honey as compared with parasitoids that were allowed to feed on flowers of the other plants or on water. Parasitoids that were provided flowers of 'Frizzy' kale survived longer compared with those that were provided flowers of white clover or tansy. An additional field test further supported that white clover is a poor food source for the survival of the parasitoid, although this plant is common throughout the southeastern U.S. No differences among the food sources for rate of parasitism were detected. This study demonstrates that several Brassica plant species can enhance the survival of this beneficial insect. The inclusion of nectar-producing plants as a food source in crop systems may reduce the need for insecticides by growers.
Technical Abstract: Diadegma insulare (Cresson) is a parasitoid of the diamondback moth, Plutella xylostella (L.), a serious pest of Brassica crops. Tests were conducted to determine the effect of floral nectars of three varieties of cultivated ('Vates') and ornamental ('Nagoya and 'Frizzy') kale (Brassica oleracea var. acephala L.), red clover (Trifolium pratense L.), white clover (T. repens L.), wild radish (Raphanus raphanistrum L.), tansy (Phacelia tanacetifolia Benth.), and 15% honey on survival and parasitism by D. insulare. In the field, the parasitoids survived significantly longer when allowed to feed on floral nectar of 'Nagoya' kale (mean = 3.1 days), 'Vates' kale (mean = 3.0 days), 'Vates' kale plus water (mean = 2.5 days), or 15% honey (mean = 2.5 days) compared with parasitoids that were allowed to feed on flowers of the other plants (less than 1.5 days) or on water (mean = 0.8 days). Parasitoids that were provided flowers of 'Frizzy' kale survived significantly longer compared with those that were provided flowers of white clover or tansy. An additional field test further supported that white clover is a poor food source for the survival of D. insulare. No significant differences among treatments for mean percent parasitism were detected. As demonstrated with 'Vates' and 'Nagoya' kale, floral nectars of some plants, such as Brassica, can enhanced longevity of D.insulare, and may help in diamondback moth management if these plants are integrated in cropping systems.