The effect of food source on survival and development of Lilioceris cheni (Coleoptera: Chrysomelidae), a biological control agent of air potato (Dioscoreales: Dioscoreaceae).
Freshly picked young air potato leaves and freshly picked brown bulbils and tan bulbils (4-7 cm in diameter) were collected as needed from healthy air potato plants grown in a greenhouse. In a preliminary non-replicated experiment, five 1st, 2nd, or 3rd instar larvae were placed in plastic containers with 1 of the 3 food sources and held at 25 [degrees]C. Survival was recorded daily for 1 wk. No 1st or 2nd instars survived on bulbils of either type, and there was no evidence of feeding damage, whereas 40% of 3rd instars survived on each type of bulbil. Survival on leaves was higher, with 60% of 1st and 2nd instars and 80% of 3rd instars alive after 1 wk.
Based on these results, only 3rd instars were used in a 2nd experiment in which larvae were placed on leaves, brown bulbils, and tan bulbils (6 replicates each) and reared to adult emergence. As in the 1st experiment, young leaves and bulbils (4-7 cm) were freshly picked from air potato plants grown in a greenhouse. Each replicate consisted of 5 larvae placed on each food source, and survival was recorded twice a week. After 1 wk, vermiculate was added to the containers as a substrate for pupation. Digital images were taken of each adult, and ImageJ software (National Institutes of Health, Bethesda, Maryland) (Abramoff et al. 2004) was used to measure adult length and color. Color was analyzed in a 2.5 mm diameter circle located in the center of the right elytron of each insect by using the histogram function of ImageJ. The values were recorded in the red, green, and blue spectra and used a range from 0 to 255. After measurement, each adult was dissected under a microscope to determine sex. The toughness of bulbils and leaves was estimated with a leaf penetrometer constructed from a scale (Pesola Light Line Spring Scale, Pesola AG, Baar, Switzerland) attached to a steel probe with a blunt 0.5 mm diameter point. The amount of pressure in grams required to penetrate the epidermis of bulbils or penetrate a leaf was measured on 10 brown bulbils, 10 tan bulbils, and 46 leaves. Analysis of variance was used for all statistical comparisons (PROC GLM, SAS Institute, 2013) and proportions were arcsin, square root transformed prior to analysis.
Percentage survival to the adult stage was higher on air potato leaves and brown bulbils (45-55%) compared with survival on tan bulbils (10%) (F = 4.63; df = 2, 15; P = 0.027) (Fig. 1). Because very few individuals survived to the adult stage on tan bulbils, they were excluded from the analysis of development time. Development time was nearly 2 d shorter when larvae were fed leaves (23.2 [+ or -] 0.6 d) compared with brown bulbils (25.1 [+ or -] 0.6 d) (F = 5.03; df = 1, 17; P = 0.039) (Fig. 2). There were no significant differences in adult size among sexes (F = 1.61; df = 1, 17; P = 0.225) or food sources (F = 0.13; df = 1, 17; P = 0.722). Elytral coloration of adults reared on leaves and brown bulbils was not different in the red spectrum (F = 2.62; df = 1, 17; P = 0.124) or blue (F = 1.46; df = 1, 17; P = 0.243), but was different in the green spectrum (F = 10.45; df = 1, 17; P = 0.005). Visually, beetles reared on leaves appeared a darker red than beetles reared on brown bulbils. The amount of pressure required to penetrate brown and tan bulbils was not different (700 [+ or -] 47 g and 677 [+ or -] 23 g, respectively), but was much higher than the pressure required to penetrate leaves (7.7 [+ or -] 1.7 g) (F = 799; df = 2, 63; P < 0.0001).
Several dietary factors may have affected the performance of L. cheni. Food toughness is known to influence the size of meals, the speed at which food passes through the gut, and the efficiency of nutrient assimilation in insects (Clissold et al. 2009). The epidermal layer of bulbils was much tougher than leaves, which may explain why only older larvae, with larger mandibles, were able to survive on bulbils. Another influential factor may have been the nutritional value of the food sources. The protein-to-carbohydrate ratio, although not quantified, was undoubtedly much higher for leaves than bulbils, which are composed almost entirely of starch (23-33%) and water (63-66%) (Coursey 1967). A number of studies have shown a relationship between plant nutritional quality and development time, with increased nitrogen often resulting in decreased development time (Scriber 1984). Finally, the concentration of defensive compounds may have varied between leaves and bulbils, and between brown and tan bulbils, which may explain the poor survival on tan bulbils.
We thank the Florida Department of Agriculture and Consumer Services and the Florida Fish and Wildlife Conservation Commission for providing financial support for this study.
Abramoff MD, Magalhaes PJ, Ram SJ. 2004. Image processing with ImageJ. Biophotonics International 11: 36-42.
Center TD, Rayamajhi M, Dray FA, Madeira PM, Witkus G, Rohrig E, Mattison E, Lake E, Smith M, Zhang J, Purcell M, Konstantinov A, Schmitz D. 2013. Host range validation, molecular identification and release and establishment of a Chinese biotype of the Asian leaf beetle Lilioceris cheni (Coleoptera: Chrysomelidae: Criocerinae) for control of Dioscorea bulbifera L. in the southern United States. Biocontrol Science and Technology 23: 735-755.
Clissold FJ, Sanson GD, Read J, Simpson SJ. 2009. Gross vs. net income: how plant toughness affects performance of an insect herbivore. Ecology 90: 3393-3405.
Coursey DG. 1967. Yams. An Account of the Nature, Origins, Cultivation and Utilisation of the Useful Members of the Dioscoreaceae. Tropical Agricultural Series. Longmans, Green and Co. Ltd. London, United Kingdom.
Croxton M, Andreu M, Williams D, Overholt W, Smith J. 2011. Source and diversity of air-potato (Dioscorea bulbifera) in Florida. Invasive Plant Science and Management 4: 22-30.
EDDMapS. 2015. Early Detection and Distribution Mapping System. University of Georgia, Center for Invasive Species and Ecosystem Health, https://www. eddmaps.org/ (last accessed 12 Aug 2015).
Hammer RL. 1998. Diagnosis: Dioscorea. Wildland Weeds 1: 8-10.
Nehrling H. 1944. My Garden in Florida, Volume I. American Eagle, Estero, Florida.
Overholt WA, Markle L, Meisenberg M, Raz L, Wheeler G, Pemberton R, Taylor J, King M, Schmitz D, Parks GR, Rayamajhi M, Rohrig E, Lake E, Smith M, Hibbard K, Center TD, Manrique V, Diaz R, Dray FA. 2014. Air Potato Management Plan. Florida Exotic Pest Plant Council, http://www.fleppc.org/Publications/Air_potato_Management_ Planv8_ updatedFeb2014Version_corrected_Oct_2014_.pdf (last accessed 12 Aug 2015).
Pemberton RW, Witkus GL. 2010. Laboratory host range testing of Lilioceris sp. near impressa (Coleoptera: Chrysomelidae)--a potential biological control agent of air potato, Dioscorea bulbifera (Dioscoreaceae). Biocontrol Science and Technology 20: 567-587.
Schmitz DC, Simberloff D, Hofstetter RH, Haller W, Sutton D. 1997. The ecological impact of non-indigenous plants, pp. 39-61 In Simberloff D, Schmitz DC, Brown TC [eds.], Strangers in Paradise: Impact and Management of Nonindigenous Species in Florida. Island Press, Washington, District of Columbia.
Schultz GE. 1993. Element Stewardship Abstract for Dioscorea bulbifera. The Nature Conservancy, http://www.invasive.org/weedcd/pdfs/tncweeds/diosopp.pdf (last accessed 10 Sep 2015).
Scriber JM. 1984. Host-plant suitability, pp. 159-202 In Bell WJ, Carde RT [eds.], Chemical Ecology of Insects. Chapman and Hall, London, United Kingdom.
Koushal Rao (1), Veronica Manrique (2), and William A. Overholt (2) *
(1) Lincoln Park Academy, Fort Pierce, Florida 34950, USA
(2) Biological Control Research and Containment Laboratory, Indian River Research and Education Center, University of Florida, Fort Pierce, Florida 34945, USA
* Corresponding author; E-mail: email@example.com
Caption: Fig. 1. Percentage survival (mean [+ or -] SE) of Lilioceris cheni from 3rd instar to adult when reared on leaves, brown bulbils, or tan bulbils of air potato.
Caption: Fig. 2. Development time (mean [+ or -] SE) of Lilioceris chenifrom 3rd instar to adult when reared on leaves or brown bulbils of air potato.
Please note: Some tables or figures were omitted from this article.
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|Author:||Rao, Koushal; Manrique, Veronica; Overholt, William A.|
|Date:||Mar 1, 2016|
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