Scientific Notes: Insect (Neuroptera: Lepidoptera) Clogging of a Microsprinkler Irrigation System in Florida Citrus

The use of subcanopy irrigation, including microsprinkler systems, has been steadily increasing over the past 15 years by the Florida citrus industry (Smajstrla et al. 1992). Reduced water volume, more efficient delivery of irrigation water to the tree roots, limited water application to competitive weeds all provide the grower with incentives to use these systems (Parsons 1989, Zekri & Parsons 1988, 1989). This technology is especially important to growers because of freeze protection. Various insect and mammal problems have been identified in recent years in association with irrigation systems in Florida. Fire ant colonies, mainly Solenopsis invicta Buren (Hymenoptera: Formicidae), have been observed by the first author to utilize the solar heating potential of the black polyethylene tubing to maintain their eggs and developing young. The eggs and immature ants are found along the underside of feeder lines that run parallel to tree rows in Florida citrus groves. Fire ant species in Florida have caused occasional localized problems by clogging tubing and individual emitters (L. R. Parsons, University of Florida, IFAS, Citrus Research and Education Center, personal communication). Secondary nests of the Argentine ant, Iridomyrmex humilis Mayr, have been found in sprinkler heads in California citrus groves (Haney 1984). Mature larva of Selenisa sueroides (Guenee) (Lepidoptera: Noctuidae) have damaged microsprinkler irrigation systems in several citrus groves in central and southwest Florida since 1987 (Brushwein et al. 1989). The mature larvae leave their host plants (i.e., Aeschynomene spp., Sesbania spp. and Macroptilium lathyroides (L.)) prior to pupation in October and November, climb nearby irrigation sprinklers and chew holes in the flexible pvc tubing. The larvae then enter the tubing and pupate. The level of damage caused by Selenisa sueroides was shown to be related to the abundance and distribution of certain legume host plants, larval population levels, sprinkler type and grove cultural practices (Brushwein et al. 1989). Damage to sprinklers and connecting tubing averaged $797 per site in 1987 (Brushwein et al. 1989). Four species of rodents including the house mouse, Mus musculus L., the cotton mouse, Peromyscus gossypinus palmarius Bangs, the rice rat, Oryzomys palustris natator Chapman and the hispid cotton rat, Sigmodon hispidusfiordanus A. H. Howell were associated with damaged sections of irrigation tubing in tomato fields in southwest Florida (Stansly & Pitts 1990). The rodents had chewed on irrigation tubing resulting in leaks. Of 45 leaks observed in the field, eight were found to be caused by mice and 37 by the two rat species. Most of the damage occurred on 4 mil tubing compared with damage on the 15 mil irrigation tubing. A 52.6-ha citrus grove was planted southeast of Arcadia in DeSoto County during the first 3 weeks in July, 1991. The trees were set at 3.05 x 7.62 m (= 430.5 trees per ha). The citrus varieties included 'Hamlin' orange on Bittersweet rootstocks and 'Rohde Red Valencia' orange on Swingle rootstocks. Japanese millet, Setaria italica (L.) Beauvois, was planted throughout the citrus grove about 1 June 1991.