Biological Control 40 (2007) 298–305 www.elsevier.com/locate/ybcon Performance and impact of the biological control agent Xubida infusella (Lepidoptera; Pyralidae) on the target weed Eichhornia crassipes (waterhyacinth) and on a non-target plant, Pontederia cordata (pickerelweed) in two nutrient regimes John N. Stanley a,¤, Michael H. Julien b, Ted D. Center c a School of Rural Science and Agriculture, The University of New England, Armidale, NSW 2351, Australia b CSIRO Entomology, 120 Meiers Road, Indooroopilly, Qld 4068, Australia c USDA-ARS, Aquatic Plant Control Research Unit, 3205 College Avenue, Fort Lauderdale, FL 33314, USA Received 22 February 2006; accepted 12 December 2006 Available online 20 December 2006 Abstract Xubida infusella (Walker) (Lepidoptera: Pyralidae) is potentially a useful biological control agent targeting Eichhornia crassipes (waterhyacinth) in the USA but many regions infested with waterhyacinth are also inhabited by an alternative native host, Pontederia cordata (pickerelweed). Experiments were conducted in Australia to assess the impact of X. infusella on pickerelweed compared to water- hyacinth where both these plants were available and X. infusella had already been released. Overall X. infusella had a greater impact on pickerelweed than on waterhyacinth. More than one larva per plant was required to reduce the total shoot dry weight of waterhyacinth but only one larva per plant reduced the total shoot dry weight of pickerelweed. Insect feeding caused the number of secondary shoots (daughter plants) of pickerelweed to double whereas the number of daughter plants produced by waterhyacinth remained unchanged. We suggest this indicates a considerable impact on pickerelweed rather than eVective compensation for insect damage because the shoots pro- duced were very small. Waterhyacinth produced a constant number of daughter plants when fed on by up to three larvae per plant. Higher nitrogen status of both species of host plant increased the rate of larval development and pupal weight of X. infusella. The weight and fecundity of X. infusella reared on pickerelweed were lower than those reared on waterhyacinth but large numbers of progeny were produced on both plant species. This experiment demonstrates a considerable impact of X. infusella on pickerelweed suggesting this plant is at risk from this agent if released in the USA where pickerelweed is present. The considerable impact on waterhyacinth demonstrates the potential for this insect to contribute to waterhyacinth control in countries where risk assessment favours release. © 2006 Elsevier Inc. All rights reserved. Keywords: Xubida infusella; Acigona infusella; Eichhornia crassipes; Pontederia cordata; Pickerelweed; Waterhyacinth; Cage trials; Biological control; Nutrients 1. Introduction in its native range in South America. The absence of absolute host speciWcity has delayed its consideration as a Xubida infusella (D Acigona infusella) (Walker) (Lepi- biological control agent for waterhyacinth in the US, doptera: Pyralidae) was considered by DeLoach (1975) to although it was released in Australia. X. infusella can be the most damaging insect found attacking waterhya- develop on at least six plant species in the Weld in South cinth, Eichhornia crassipes (Mart.) Solms, (Pontederiaceae), America; E. crassipes, Eichhornia azurea (Sw.) Kunth, Eich- hornia heterosperma Alexander, Eichhornia paniculata (Spr- eng.) Solms-Laub, Pontederia cordata L. and Pontederia * Corresponding author. Fax.: +11 2 6773 3238. rotundifolia L. (Silveira-Guido, 1971; DeLoach et al., 1980). E-mail address: [email protected] (J.N. Stanley). All are members of the freshwater aquatic plant family, 1049-9644/$ - see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.biocontrol.2006.12.008 J.N. Stanley et al. / Biological Control 40 (2007) 298–305 299 Pontederiaceae, which includes about 25 species of Xoating parallel rows of Wve down a sloping site of approximately or rooted emergent plants in nine genera throughout the 10% grade, downhill to the southeast. Each tub was 2 m new world, and one genus Monochoria native to the Old away from the next in its row and 2.5 m from the tub in the World (Leach and Osborne, 1985). next row across. Sixteen of these tubs were used to produce Xubida infusella can complete its life cycle on the two a 2 £ 2 £ 4 factorial design. The three factors were the two plant species investigated in this study E. crassipes (water- plant species, high- and low-nutrient levels, and four insect hyacinth) and P. cordata (pickerelweed). Egg masses are densities (0, 12, 24 and 36 insects per tub). laid within white, frothy cement in folds and crevices A high-nutrient solution Xowed from a supply tank amongst the leaves of host plants. Egg masses collected in down through two rows of Wve tubs and into a collection laboratory cultures contained 82–225 eggs and required 6– sump where it was pumped back up to the supply tank. An 7 days at 25 °C for incubation (Sands and Kassulke, 1983). identical system supplied the other 10 tubs with a low- After hatching, larvae disperse and burrow into laminae or nutrient solution. Rectangular, aluminium cages (1.5 m petioles and tunnel downwards, often girdling a petiole high) screened with Wbreglass Xyscreen were sealed onto which causes death of the distal leaf portions. Larvae con- each tub to exclude predators, parasitoids and other herbi- tinue to tunnel extensively throughout the petioles and vores, especially the waterhyacinth weevils, Neochetina rootstock causing considerable damage and may exit one eichhorniae Warner and Neochetina bruchi Hustache (Cole- plant to feed on another nearby. At 25 °C, the larvae optera: Curculionidae). The water level in the tubs contain- require about 48 days to develop and grow to about 20 mm ing pickerelweed was maintained at the soil surface level in in length (Silveira-Guido, 1971; Sands and Kassulke, 1983). the pots. Potted pickerelweed was also placed in the four Before pupating, larvae excavate an exit tunnel up a petiole remaining tubs, but the water level in these was maintained and across to the outer surface. A very thin ‘exit window’ of at 6 cm above the soil surface to produce a high water level plant epidermis is left to cover the tunnel opening but if the treatment. Two of the high water level treatments were in epidermis is breached, the larva repairs the hole with web- the high and two in the low-nutrient side of the system with bing. Exit windows can appear at any point up the petiole. insect levels of 0 and 12 per cage. Water level in tubs The larvae back down the exit tunnel to pupate. On com- containing waterhyacinth is of no consequence because it pleting pupation, the pupa winds its way up the exit tunnel Xoats. The trial was conducted in summer between 6th and pushes through the window to allow the adult moth to December and 20th February 1995/6 at Long Pocket emerge outside the plant. Pupal exuviae often protrude Laboratories in Brisbane, Australia (27 °58Ј S; 153°01Ј E). from these windows after the moths have emerged. Adult moths live for about 5 days. The life cycle requires 64 days 2.2. Nutrient treatment at 25 °C (Sands and Kassulke, 1983). Increasing waterhyacinth problems worldwide have Nutrients were added to the sump tanks twice weekly rekindled interest in X. infusella despite the breadth of its to produce a modiWed 10% Hoagland and Arnon’s solution host range (Julien et al., 1996; Julien and Stanley, 1999). No. 2 throughout both sides of the system (Table 1). High- Waterhyacinth is an important Xoating weed in the south- and low-nutrient treatments were established by adjusting ern states of the USA where it has invaded wetlands inhab- the quantities of nitrogen (N) and phosphorus (P) (Table 1). ited by the native plant, pickerelweed (Center et al., 1995). Pickerelweed is a perennial, erect, and emergent plant that, Table 1 The concentrations of nutrients in water supplied to plants in high unlike waterhyacinth, is rooted into the substrate. Pickerel- and low nitrogen and phosphorus treatments (a modiWcation of 10% weed grows to a height of 1 m and has smooth, glossy, Hoagland and Arnon’s solution No.2) broad laminae on long petioles. It has ecological impor- Plant nutrient Source of the Nutrient concentration tance as food and shelter for Wsh and wildfowl. It is also nutrient (ppm) valuable for shoreline erosion mitigation, riverbank resto- Added to both high- and low-nutrient treatments ration, and roadside drain re-vegetation (Melton and Sut- Calcium (Ca) CaSO4·2H2O50 ton, 1991). Magnesium (Mg) MgSO4 10 We report the impact of X. infusella on pickerelweed rel- Potassium (K) K2SO4 50 ative to waterhyacinth so that an informed risk assessment Iron (Fe) FeSO4 2.0 Manganese (Mn) MnSO4·7H2O0.1 can be made on the safety of X. infusella as a biological Molybdenum (Mo) (NH ) Mo 0.0015 control agent for use in the USA. 4 6 7 Boron (Bo) H3Bo3 0.1 Zinc (Zn) ZnSO4·7H2O0.016 2. Materials and methods Copper (Cu) CuSO4·5H2O0.01 Added to the high-nutrient treatment 2.1. Experimental design Nitrogen (N) KNO3 1.6 Phosphorus (P) KH2PO3 1 Potted pickerelweed and Xoating waterhyacinth plants Added to the low-nutrient treatment were grown in 20, rectangular, 280 l Wbreglass tubs Nitrogen (N) KNO3 0.1 (900 £ 700 £ 450 mm deep). The tubs were arranged in four Phosphorus (P) KH2PO3 0.02 300 J.N. Stanley et al. / Biological Control 40 (2007) 298–305 Every 2 weeks both systems were Xushed with tap water dry weight determined using the Kjeldahl procedure (John- and the nutrient solution replaced to prevent accumulation son et al., 1985). Analysis was performed on the combined of salts. harvests to detect diVerences and changes in the nitrogen On 6th December 1995, 1 month before the start of the and phosphorus status.