Performance and Impact of the Biological Control Agent Xubida

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 waterhyacinth 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 produced 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,

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. insect treatments, 8 tubs, four of each nutrient level, were Harvests for the high-nutrient treatment were made on randomly selected and Wlled with waterhyacinth plants and the 12th and 13th February 1996 (37 and 38 d after the the remaining 12 tubs received potted pickerelweed. The introduction of the insects) and for the low-nutrient treat- pickerelweed was grown from cuttings in a 50:50 washed ment on the 19th and 20th February 1996 (44 and 45 d after river sand to soil mix. On this date, 1 g of ferrous sulphate introduction of the insects). Harvests occurred when ‘exit was added to all pots and 2 g of a slow-release fertiliser windows’ were Wrst noticed in petioles indicating that at (Osmocote® 4) to the high-nutrient pickerelweed treatment. least some of the larvae were entering the pupal stage. These extra nutrients were added to the pickerelweed pots Dry weights of the plants were determined for the lami- to compensate for its reduced access to the nutrient solu- nae, petioles and root material of the main plants (those of tion compared to the free-Xoating waterhyacinth. Both the 12 original plants starting the experiment) and for the plant species were grown for one month under their respec- new shoots (secondary or daughter plants). The number of tive nutrient treatments prior to the introduction of the secondary shoots produced by each main plant was insect. One day before introducing insects, the plants were recorded. The rate of leaf production was determined by thinned to 12 main plants per tub and secondary shoots recording the change in the position of the Wrst fully removed. Secondary shoots are vegetative oVshoots, often expanded leaf (tagged) each week from the 16th January to referred to as daughter plants or ramets, produced from harvest. axillary buds on the parent plant. Six of the plants removed from each tub during thinning 2.5. Insect records were dried and weighed to obtain an approximate biomass of the 12 initial experimental plants. The pickerelweed At harvest, all the plants were removed from each tub established in the high-nutrient solution had a main shoot and dissected to Wnd larvae and pupae. The cages were also dry weight of 16.1 g and was 73 cm tall (2nd fully expanded searched for any adults that might have emerged. The num- leaf). The pickerelweed under low nutrients was 13.1 g and ber and stage of surviving insects were recorded for each 55 cm tall. The high-nutrient waterhyacinth started the cage. The sex of pupae was determined, and then pupae experiment with a main shoot weight of approximately were weighed and paired with others from the same plant 14.6 g and height of 44 cm. For the low-nutrient treatments species and nutrient treatment, to determine the fecundity the waterhyacinth started the experiment at 12.5 g and of females. Eggs were too diYcult to count directly because height of 27 cm. they are embedded within a cement-like matrix so fecundity was determined by counting larvae upon hatching. 2.3. Insect treatments 2.6. Statistical analysis Newly hatched larvae were introduced at four densities of 0, 1, 2 or 3 larvae per plant, i.e. 0, 12, 24 or 36 larvae per Analysis of variance was conducted using means per tub tub. These were distributed evenly by placing 1, 2, or 3 lar- (mean of 12 plants) as the smallest independent unit and vae onto the youngest petioles of each plant (only 1 to a using the three-factor interaction, with nonsigniWcant two petiole). All larvae were introduced on 6th and 7th January factor interactions, as the error term. Where necessary the 1996 within 12 h of hatching and without prior feeding. All data were transformed but untransformed means are insects were derived from laboratory cultures produced on reported for clarity. SigniWcance levels apply to the trans- waterhyacinth. formed analysis. In the 2 £ 2 £ 4 factorial analyses of plant and insect 2.4. Plant records variables the sum of squares for insect levels were parti- tioned into a linear eVect and deviations from linear and The initial nitrogen and phosphorus content of the the linear interaction with other terms tested. The percent- plants were determined by collecting the youngest fully age surviving insects and the percentage of larvae reaching expanded leaf from six of the plants that were removed the pupal stage at harvest were similarly analysed as a from each of the 20 tubs during thinning. Nitrogen and 2 £ 2 £ 3 factorial, i.e. removing the zero level of larval den- phosphorus determinations were also made at the end of sity because this cannot provide information on insect sur- the experiment using six of the youngest expanded leaves vival. For the analysis of the eVect of water level on collected during the Wnal harvests from amongst the twelve pickerelweed, the four corresponding tubs from the low main plants in each tub. Leaves damaged by the larvae were water level treatment were combined with the four high not included in the nutrient sampling to avoid the possibil- water tubs to create a 2 (nutrient levels) £ 2 ity of contamination by their frass and exuviae. Nitrogen (water levels) £ 2 (insect densities) factorial design. If the and phosphorus content was expressed as a percentage of water level did not cause a signiWcant eVect, the four high J.N. Stanley et al. / Biological Control 40 (2007) 298–305 301 water treatments were included in the overall analysis of cinth (F3,7 D 6, P D 0.023). The rate of weight decline with plant and insect variables. Regression analysis was used for increasing insect density was also greater at the higher nitrogen and phosphorus content and for pupal weights. nutrient level. The decrease in the weight of pickerelweed was almost linear with larval density but greater than 12 3. Results larvae per tub was needed to reduce the main shoot dry weight of waterhyacinth (Fig. 2a). 3.1. Nutrient treatments The small experiment addressing water level indicated that the dry weight of pickerelweed daughter plants (sec- There was a clear diVerence in plant nitrogen content ondary shoots) was aVected by water level and the presence between the high- and low-nutrient treatments of larvae under the high-nutrient regime (F1,1 D 592, (F1,32 D165.43, P< 0.001) however nitrogen content of both P D 0.026; F1,1 D 336, P D 0.035). The average dry weight of plants species declined during the experiment (F1,32 D100.46, daughter plants increased from 40.5 to 60.1 g per tub when P< 0.001, Table 2). A signiWcant three-factor interaction larvae were present. The deeper water increased the dry (F1,32 D19.27, P< 0.001) indicated that for the higher nutri- weight of daughter plants from 43.2 to 57.5 g per tub. tion level the decrease in nitrogen was greater for pickerel- The dry weights of daughter plants were substantially W V weed than for waterhyacinth. There was no signi cant e ect heavier for waterhyacinth than pickerelweed (F1,10 D 430.2, of tub position on the nitrogen or phosphorus status of the P < 0.0001, Fig. 1b) and at higher nutrition levels plants within nutrient treatments (PD0.91 for nitrogen and (F1,10 D 100.5, P < 0.0001, Fig. 1b). The number of daughter 0.78 for phosphorus). Overall the two plant species had plants was greater for waterhyacinth and increased with the similar nitrogen content (F1,32 D0.08, PD0.777, Table 2). presence of insects on pickerelweed (F1,7 D 44.6, P < 0.0001, V A di erence in phosphorus content was also established F3,7 D 8.4, P D 0.01, Figs. 1d and 2d). between the nutrient treatments (F1,32 D 33.89, P< 0.001). The dry weight of total shoots (main shoots plus daugh- Waterhyacinth had a greater phosphorus content than pick- ter plant material) gave a similar analysis to that of the V erelweed (F1,32 D216.16, P< 0.001). During the experiment main shoots (Figs. 1c and 2c). Water level had no e ect on the phosphorus content of both species decreased the dry weight of main shoots of pickerelweed. W V (F1,32 D263.97, P<0.001). A signi cant three-factor interac- The dry weight of roots was not a ected by larval den- W tion (F1,32 D12.7, P< 0.001) indicating that for the high nutri- sity but there was a signi cant interaction between nutrition level the decrease was greater for pickerelweed whereas tion level and host plant species (F1,6 D 26.39, P D 0.002, at the lower level the decrease was greater for waterhyacinth Figs. 1f and 2f). Although root weights were similar for (Table 2). There was no eVect of tub position or water level both plant species at low- nutrition, at the high-nutrient on the nitrogen or phosphorus status of plants. level pickerelweed root weight increased while waterhyacinth root weight decreased. Water level had no eVect on 3.2. EVects of nutrients, X. infusella larval density and water the root weight of pickerelweed. level on host plants The leaf production rate was greater for waterhyacinth than pickerelweed (F1,12 D 39.13, P < 0.0001, 5.2 and 3.4 As expected, the higher nutrient treatment produced SED 0.6 Fig. 1e) and was not aVected by nutrition. The greater shoot dry weight for the 12 main plants present presence of larvae reduced the rate linearly (b D¡0.043 SE from the beginning of the experiment (F1,7 D 164, 0.014, F1,12 D 10.53, P D 0.007, Fig. 2e) the same for both P < 0.00001, Fig. 1a). A signiWcant interaction showed that plant species. The leaf production rate of pickerelweed was for low nutrition the dry weight of waterhyacinth main- not aVected by water level. shoots was greater than those of pickerelweed (F1,7 D 24.52, P D 0.002, Fig. 1a). The dry weight of both plant species 3.3. EVects of plant species on insects decreased with X. infusella larval density (F3,7 D 19.3, P < 0.0001, Fig. 2a). Shoot weight loss with increasing larval The percentage of X. infusella surviving to harvest on density was greater for pickerelweed than for waterhya- both plant species was similar (Table 3). However, the

Table 2 The nitrogen and phosphorus content of waterhyacinth and pickerelweed in the high- and low-nutrient treatments at the beginning and end of the experiment expressed as a percentage of dry weight with SE in parenthesis Nutrient treatment Host plant Nitrogen (% dry weight) Phosphorus (% dry weight) Beginning Final Beginning Final Low Waterhyacinth 1.69 (0.08) 1.12 (0.11) 0.54 (0.009) 0.30 (0.029) Low Pickerelweed 1.67 (0.07) 1.24 (0.06) 0.36 (0.012) 0.20 (0.010) High Waterhyacinth 2.39 (0.13) 2.18 (0.12) 0.59 (0.025) 0.46 (0.028) High Pickerelweed 2.88 (0.10) 1.65 (0.08) 0.43 (0.013) 0.21 (0.008) Each sample included six leaves (i.e. the youngest fully expanded leaf from six plants from each tub, petiole plus lamina). For waterhyacinth n D 4 and for pickerelweed n D 6, (SE). 302 J.N. Stanley et al. / Biological Control 40 (2007) 298–305

Fig. 1. The average growth of waterhyacinth and pickerelweed at low (lightly shaded columns) and high (darkly shaded columns) nutrient levels for: (a) main shoot dry weights (g/tub), (b) daughter plant shoot dry weights (g/tub), (c) total shoots dry weight (g/tub), (d) daughter plants (number/tub), (e) leaf production (leaves/plant) and (f) root dry weight (g/tub). Bars are Standard Errors. percentage that developed to the pupal stage by harvest emergence from the low-nutrient treatments was too pro- time, averaged over both nutrient levels, was greater on tracted for males and females to coincide. The females waterhyacinth than on pickerelweed (38% on waterhya- from pickerelweed produced signiWcantly fewer hatch- cinth and 10.9% on pickerelweed, F1,7 D 12.34 P <0.01). lings, 194 per female compared to 326 from waterhyacinth SigniWcantly heavier pupae were produced on waterhya- (P <0.001). cinth than on pickerelweed (F1,57 D 14.09, P <0.001, Table Similar numbers of insects survived at each plant nutri- 4). Female pupae were heavier than males and greater in ent level but the rate of development of larvae was delayed the high-nutrient treatment but a signiWcant interaction at least 6 d by low nutrition. The smaller proportion of shows that females increase with nutrition more than the insects that had reached the pupal stage by the collection V males (F1,57 D 4.47, P < 0.05). Matings were only possible date under low nutrition suggests that the di erence between adults from the high-nutrient treatments because exceeded 6 d (Table 3). J.N. Stanley et al. / Biological Control 40 (2007) 298–305 303

Fig. 2. The average growth of waterhyacinth (᭹) and pickerelweed (ؠ) at four X. infusella densities for: (a) main shoot dry weights (g/tub), (b) daughter plant shoot dry weights (g/tub), (c) total shoots dry weight (g/tub), (d) daughter plants (number/tub), (e) leaf production (leaves/plant), and (f) root dry weight (g/tub).

4. Discussion sue concentrations of approximately 1.4% for the low and 2.3% for the high treatments in this experiment repre- Mean nitrogen contents of the second youngest leaves sented low and average Weld nitrogen levels, respectively of waterhyacinth in the Weld have been determined as: (Table 2). Records of nitrogen content for Weld grown 2.75%, Center and Wright (1991); 2.0% range 0.98–4.80%, pickerelweed have not been determined but levels M. Purcell (unpublished data); and 1.74%; range 0.88– similar to those of waterhyacinth were achieved in this 3.46%, M. H. Julien (unpublished data). Therefore, the tis- experiment. 304 J.N. Stanley et al. / Biological Control 40 (2007) 298–305

Table 3 plant (i.e. 12 larvae per tub) reduced total and main shoot Percentage survival of X. infusella to the Wnal harvest (survival) and the biomass of pickerelweed, whereas, two or more larvae were percentage of those that had developed to the pupal stage (pupae) on required to reduce the biomass of waterhyacinth. pickerelweed and waterhyacinth at diVerent nutrient levels and infestation densities (larvae/tub) Many plants respond to damage or herbivory by increasing production of secondary shoots, e.g. S. molesta Initial Low nutrient High nutrient density (Julien and Bourne, 1986). For pickerelweed, the larvae Waterhyacinth Pickerelweed Waterhyacinth Pickerelweed stimulate a substantial increase in the number of secondary Survival Pupae Survival Pupae Survival Pupae Survival Pupae shoots and the weight of those shoots was very low. Similar 12 25 8 75 0 58 58 83 42 tunnelling by larvae in the crown of waterhyacinth did not 24 54 25 29 4 79 58 71 33 stimulate nearly so great a response although damage to 36 56 22 50 6 33 14 44 22 waterhyacinth caused by larvae of the noctuid Bellura Average 45 18 47 5 57 43 66 32 densa Walker has been observed to cause production of supernumerary shoots in Florida, USA (TDC, personal Table 4 observations). In our experiment, waterhyacinth produced Average pupal weights of male and female X. infusella that developed on a greater number of daughter plants than pickerelweed, waterhyacinth or pickerelweed at two nutrient levels with or without larval feeding, and those daughter plants Pupal weight (g) n reached a substantial size. Host E. crassipes 0.133a 38 A reduction in the rate of leaf production by main plants P. cordata 0.107b 24 was a dominant detrimental inXuence on the growth of Female Low nutrient 0.117a 8 waterhyacinth measured in this experiment. Rapid leaf pro- High nutrient 0.155b 23 duction was considered by Center (1985) to be a major Male Low nutrient 0.089a 6 requirement for recovery of waterhyacinth from insect High nutrient 0.103a 25 attack. The considerable reduction measured here, even in Entries followed by the same letter are not signiWcantly diVerent the high-nutrient treatment, shows potential for X. infusella (P < 0.05). to contribute to the control of waterhyacinth. However, the reduction of a greater proportion of total leaf production in X. infusella performed better on waterhyacinth than on pickerelweed shows the potential for a greater impact on pickerelweed. Survival was similar on both plant species pickerelweed. but insects reared from waterhyacinth were heavier. The Overall, waterhyacinth exhibited a greater capacity to ensuing adults also produced 70% more progeny than those maintain biomass and produce new plants and leaves than from pickerelweed. These diVerences may be caused by the pickerelweed and could therefore be expected to persist nutrient status of the plants rather than the host species per longer than pickerelweed during X. infusella feeding and se because the pickerelweed grown with high nutrient recover faster when released from the pressure of these inputs did not retain the high nitrogen status of the water- herbivores. hyacinth throughout the experiment (Table 2). Neverthe- It is important to appreciate that this experiment only less, the adult insects that developed from pickerelweed explores the impact of certain densities of X. infusella over a produced a considerable number of progeny, 194 newly single and synchronised generation of feeding when conWned hatched larvae per female on average. On plants of similar on each host plant. The greater impact on pickerelweed than nutrient status, fecundity of X. infusella may be similar for waterhyacinth predicted by this experiment may not occur in both plant species. the Weld if X. infusella prefers to oviposit on or near waterhy- Heavier and/or faster developing insects with greater acinth. Oviposition preference remains unknown because of fecundity produced on higher nitrogen diets have been extensive laying on cages rather than the host plants in labo- commonly reported (White, 1993). This eVect of nutrition ratory trials (DeLoach et al., 1980). Location of substantial has implications for the implementation of biological con- populations of X. infusella on pickerelweed in the native trol. Insects developing on high-nutrient plants are likely to range of the insect (DeLoach et al., 1980; H. Cordo, personal have greater population increase giving a better chance of communication, USDA/ARS South American Biological establishment and causing greater impact. For example, Control Laboratory, 1996) suggests that any preference, even providing nitrogen fertilizer is thought to have assisted if experimentally determined, could not be interpreted as a establishment of Cyrtobagous salviniae Calder and Sands high degree of protective host speciWcity in support of a (Coleoptera: Curculionidae) on Salvinia molesta D. S. decision to release. Mitchell (Salviniaceae) (Room and Thomas, 1985) and The likelihood of a substantial impact on pickerelweed improved rate of control (Room et al., 1989). The faster must be considered in a risk assessment on the release of development rates and greater fecundity on higher nutrient X. infusella in countries where pickerelweed is a native and/or plants suggests that sites with high nutrient status would a beneWcial species. However, in countries where pickerel- favour establishment and performance by X. infusella. weed is not present or considered important relative to the In this experiment the impact of X. infusella was greater waterhyacinth problem, X. infusella may be useful. This on pickerelweed than on waterhyacinth. One larva per experiment has demonstrated a considerable impact by low J.N. Stanley et al. / Biological Control 40 (2007) 298–305 305 densities of X. infusella larvae over a single larval generation. J.L. (Eds.), Proceedings of a Symposium on Water Quality Manage- What remains to be seen is whether the insect will exhibit the ment Through Biological Control, pp. 45–50. numerical response or repeated damage necessary to success- DeLoach, C.J., Cordo, H.A., Ferrer, R., Runnacles, J., 1980. Acigona infusella, a potential biological control agent for waterhyacinth: observa- fully reduce rapidly growing waterhyacinth infestations. tions in Argentina (with descriptions of two species of Apanteles by L.D. Santis). Ann. Entomol. Soc. Am. 73, 138–146. Acknowledgments Johnson, A.D., Simons, J.G., Hansen, R.W., Daniel, R.A. 1985. Chemical procedures for the analysis if plant material: multi-element, oil, sugars Technical assistance was provided by Michael Day, and gum. CSIRO Division of Tropical Crops and Pastures Agronomic Technical Memorandum No. 40. Teresa Finley, Michael Hand, Dalio Mira, and Shaun Julien, M.H., Bourne, A.S., 1986. Compensatory branching and changes in Winterton. Anne Bourne assisted the statistical analysis. nitrogen content in the aquatic weed Salvinia molesta in response to Collection and shipment of Xubida infusella from South disbudding. Oecologia 70, 250–257. America was conducted by Mr. Hugo Cordo of the Julien, M.H., Harley, K.L.S, Wright, A.D., Cilliers, C., Hill, M., Gunter, T., United States Department of Agriculture (USDA) South Cordo, H., Confrancesco, A. 1996. International co-operation and linkages in the management of water hyacinth with emphasis on biological control. American Laboratory in Argentina. This work was par- Proceedings of the Ninth International Symposium on Biological Control tially funded by the United States Department of Agricul- of Weeds. In: Moran, V.C, HoVman, J.H. (Eds.), Stellenbosch, South ture (SCA No. 58-6629-4-F135), the Florida Department Africa, University of Cape Town, 19–26 January 1996, pp. 273–282. of Environmental Protection, and the United States Army Julien, M. Stanley, J. 1999. Recent research on biological control for water Corps of Engineers (Jackson District) and the Common- hyacinth in Australia. Proceedings of the First IOBC Global Working W Group Meeting for the Biological and Integrated Control of Water wealth Scienti c and Industrial Research Organisation Hyacinth, Harare, Zimbabwe, November 1998, pp. 52–61. (CSIRO), Australia. Leach, G.J., Osborne, P.L., 1985. Freshwater Plants of Papua New Guinea. The University of Papua New Guinea Press, Port Moresby. Melton, F., Sutton, D.L., 1991. Pickerelweed. Aquatics 13, 3–7. References Room, P.M., Julien, M.H., Forno, I.W., 1989. Vigorous plants suVer most from herbivores: latitude, nitrogen and biological control of the weed Center, T.D. 1985. Leaf life tables: a viable method for assessing suble- Salvinia molesta. Oikos 54, 92–100. thal eVects of herbivory on waterhyacinth shoots. In: Delfosse, E.S. Room, P.M., Thomas, P.A., 1985. Nitrogen and establishment of a beetle (Ed.), Proceedings of the VI International Biological Control of for biological control of the Xoating weed Salvinia in Papua New Weeds, Vancouver, Canada, 19–25 August 1984. Agriculture Can- Guinea. J. Appl. Ecol. 22, 139–156. ada, pp. 511–524. Sands, D.P.A., Kassulke, R.C., 1983. Acigona infusella (Walker) (Lepidop- Center, T.D., Wright, A.D., 1991. Age and phytochemical composition tera: Pyralidae), an agent for biological control of waterhyacinth (Eich- of waterhyacinth (Pontederiaceae) leaves determine their acceptabil- hornia crassipes) in Australia. Bull. Ent. Res. 73, 625–632. ity to Neochetina eichhorniae (Coleoptera: Curculionidae). Environ. Silveira-Guido, A., 1971. Datos preliminares de biologÂ´a y espediWcidad Entomol. 20, 323–334. de Acigona ignitalis Hamps. (Lep. Pyralidae) sorbre el hospedero Eich- Center, T.D., Frank, J.H., Dray Jr., F.A., 1995. Biological invasions: stem- hornia crassipes (Mart.) Solms-Laubach (Pontederiaceae). Revta. Soc. ming the tide in Florida. Flor. Entomol. 78, 45–55. Ent. Argent. 33, 137–145. DeLoach, C.J. 1975. Evaluation of candidate arthropods for biological White, T.C.R., 1993. The Inadequate Environment: Nitrogen and the control of waterhyacinth: studies in Argentina. In: Brezonik P.L., Fox, Abundance of Animals. Springer-Verlag, Berlin.