Plant Protection Quarterly Vo\.15(3) 2000 95 information on its biology and effective ness as a biological control agent. Growth of alligator weed (Alternanthera philoxeroides Several years after its release (Mart.) Griseb. (Amaranthaceae» and population A. hygrophila had failed to effectively con trol alligator weed in some areas (Roberts development of Agasicles hygrophila Selman & Vogt el al. 1984). Comparisons of climate data (Coleoptera: Chrysomelidae) in northern New and temperature requirements of A. hygro phila (Stewart el al. 1995, 1996) suggested Zealand that temperatures in New Zealand were less than optimal for development, par AC A ticularly in areas south of the Northland Carol A. Stewart , R. Bruce Chapman and Chris M.A. Frampton' region. Port Waikato (Lat. 37' 24·5 Long. A Ecology and Entomology Group, PO Box 84, Lincoln University, Canterbury, 174'43·E) is the southern-most limit of New Zealand. A. hygrophila distribution in this country ·Centre for Computing and Biometrics, PO Box 84, Lincoln University, (c. Stewart unpublished survey). The Canterbury, New Zealand. only site in New Zealand where A. hygro c Current address: 25 Goring Road, Balmoral, Auckland 1003, New Zealand. phila was known to be present each sum mer and autumn in sufficient numbers to cause visible damage and defoliation of alligator weed is at Whatatiri, Northland Summary (Lat. 35' 47"5 Long. 174' 04·E) . Alligator weed (Alternanthera phil 1906). It is currently distributed from This study investigated the changes in oxeroides) is a problem aquatic weed in North Cape to the Waikato Ri ver in the temperature, the growth of alligator weed New Zealand. Little is known about the North Island and appears to be spreading and the distribution and development of population ecology of its introduced bio southwards, albeit at a slow rate (Stewart A. hygrophi/a populations in New Zealand. logical control agents, Agasicles hygro el al. 1995). Alligator weed grows in a A further aim was to estimate the quantity phila and Arcola malloi. A study of alli range of ecosystems from almost arid con of heat units available for A. hygrophila de gator weed and A. hygropllila popula ditions to swampy areas but it grows pri velopment in one season at Whatatiri. tions conducted at a Northland site in marily as an emergent aquatic plant New Zealand found that alligator weed rooted in the substrate below shallow wa Methods dry weights peaked in late January 1994 ter Oulien 1995). In aquatic habitats, alli· Site descriplion and late December 1994 and declined as gator weed forms large floating mats of The study was conducted on one of a a result of feeding by increasing popula interwoven hollow stems which ex tend number of man-made ponds at Whatatiri tions of A. hygrophila. Aquatic alligator over the surface of the water. Terrestrial in the Whangarei District. The study site weed was present throughout the 1994 plants can establish on very thick weed (approximately 1800 m') was loca ted at winter. Internal stem diameters probably mats and this may accelerate succession the western end of the southern-most did not limit A. hygropllila pupation, as and turn enclosed water bodies into pond which had the greatest area of the majority of stem diameters measured swamps. Alligator weed is categorized as aquatic alligator weed floating on its sur were above 1.21 mnl, the width required a 'National Surveillance Plant Pest' which face. for female pupation within the stem. means it is unlawful to knowingly propa Alligator weed extended from the Peak A. hygrophila populations occurred gate, distribute, spread or sell this plant in edges of the pond in large mats and the during February but the density of A. New Zealand (Vervoort and Hennessy density and spatial distribution of the Itygrophila was too low or the damage 1996). mats varied between the seasons and too late in the growing season to provide From 1960 to 1974 biological control years. During winter months, flood wa control, despite considerable defoliation. agents for alligator weed control were se ters from the Wairua River washed alliga It was concluded that A. hygrophila is lected from searches made in South tor weed and debris into the ponds. The unlikely to cause a reduction in alligator America by the United States Department pond was surrounded by stop banks weed in New Zealand even in conjunc of Agriculture (Coulson 1977). Two of which were covered in pasture and scrub tion with Arcola malloi. A. Izygrophila these, Agasicles hygrophila Selman and species, including Ulex europaeus L., Lepto was estimated to have a requirement of Vogt (Coleoptera: Chrysomelidae) and sperntllnt scopariunt J.R. & G.Forst. and Ru 277 degree days above the I3.3°e lower Arcola malloi (Pastrana) (Lepidoptera: bus fru ticOSIlS L. There were other species temperature development threshold to Pyralidae), were imported into Australia of plants growing amongst the weed mat develop from egg to an ovipositional from the USA in 1976 Oulien 1981). An (Table 1), however, alligator weed was the adult. Three generations of A. hygrophila additional species, Disonycha argentinensis dominant species present. were predicted to occur at Whatatiri in Jacoby (Coleoptera: Chrysomelidae), was the 1994-95 season. imported into Australia from Brazil in Air lemperature and rainfall 1979 Oulien and Chan 1992). Between 1981 Air temperatures were recorded using Introduction and 1988 A. hygrophi/a, A. malloi and D. thermistor sensors and data loggers. The Alligator weed, Alternanlhera phi/oxeroides argentinensis were introduced into New loggers were placed in small airtight plas (Mart.) Griseb. (Amaranthaceae), a plant Zealand from Australia (Roberts and tic containers and each sensor (one sensor of So uth American origin, has become a Sutherland 1989), but D. argenlinensis did per data logger) was attached to an an problem in waterways and pastures in not establish. A. hygropllila was intro chored polystyrene float, covered with a many parts of the world, including the duced into Northland and Auckland in ventilated screen and placed 1-2 m from southern USA, Puerto Rico, Burma, Thai 1982 by the Entomology Division, Depart the pond edge, approximately 4 cm above land, Indonesia, India, China, Australia ment of Scientific and Industrial Re the water surface in the alligator weed and New Zealand Oulien 1981, Julienelal. search (Roberts and Sutherland 1989). The canopy. Air temperatures were recorded 1992). Alligator weed was first recorded beetle established and spread rapidly every 24 minutes for the period IS in New Zealand in 1906 at Aratapu by the throughout Northland (Philip el al. 1988), November 1993 to 25 April 1995. From Northern Wairoa River (Cheeseman however, there is limited quantitative 15 November 1993 to 6 December 1994 96 Plant Protection Quarterly Vo1.15(3) 2000 readings were collected from one logger each season depending on insect activity internodes where internal diameters were and from 7 December 1994 to 25 April and the season. During the first growing measured was recorded. 1995 readings were collected from two season (1993-94), samples were taken fort loggers. Due to seasonal flooding, data nightly. During the 1994 winter (May to Analysis of results stored in logger one were destroyed on 13 October) samples were taken monthly. In Data that were collected on a per shoot to 27 December 1993, 27 May, 25 )uly to 6 the second growing season samples were basis were converted to m' by combining August 1994 and 6 March to 4 April 1995. taken fortnightly in spring and autumn data from individual shoot samples and Readings were destroyed on logger two and weekly during summer (January to the quadrats (number of shoots per from 21 March to 4 April 1995. Rainfall March 1995). The number of insects per quadrat). These provided overall esti measurements were obtained from the unit of shoot tissue and the standing crop mates of the means for A. hygrophila den Wairua Falls (Station AS4701) 3.25 km or shoots of alligator weed perO.l m'were sities, alligator weed dry weight, number from the site. Daily rainfall readings were measured. The number of insects per m2 of shoots and shoot length m'. The summed to produce weekly totals. were estimated from these data. variances were also pooled from the data A shoot sample consisted of a ran for number of insects per shoot and stand Alligator weed shoot and quadrat domly selected stem and its leaf tissue cut ing crop and further pooled over time to samples at water level. When each shoot sa mple give common variances for each param Sampling was carried out by boat without was taken, the numbers of A. hygrophila eter in each season. The standard errors disturbing the weed and at least 3 m from adults, each larval instar and egg batches, were then calculated for each parameter the bank to ensure only floating weed was were counted. In the laboratory, shoot and time using these pooled variances and assessed. Samples were taken over two length was measured and the numbers of the appropriate sample size using the years from November 1993 to April 1995. eggs per batch were counted. Stems were SYSTAT statistical package (Wilkinson The sampling frequency varied during cut open and the pre-pupae, pupae and 1990). teneral adults were counted. Leaves were then removed Degree day (DO) calculations Table 1, Plants found growing in the weed mat from the stems and leaf and Degree days were calculated from re at Whatatiri, stem tissue samples were indi corded temperatures, using a modified -F-alJU--·I-y---P-I-an-t-n-a-m-e------vidually dried to constant Simpson's Rule (Broughton and Ramsay __~ ______weight in a drying oven at 1979). Simpson's Rule is an integration Agavaceae Plwrmium tenax ).R. & G.Forst. 105°C. method which calculates the area under Apiaceae Apium nodiflorum (L.) Lag. Shoot samples were cut at the diurnal temperature curve and above Oenantlle pimpinelloides L. water level from within a 0.1 m2 the lower threshold temperature (Worner Asteraceae Bidens frondosa L. circular quadrats, placed ran- 1988). Where data were missing (11 % of Cirsium vulgare (Savi) Ten. domly on the weed mat within measurements), estimates from the Conyza albida Spreng. 50 cm of accessible edges. Whangarei Airport (Station AS4737, Lat. Hypochoeris radicata L. Shoots were counted per 35°46'5 Long. 174° 22'E), 27 km from Picris echioides L. quadrat and total stem length Whatatiri were inserted. The min-max Senecio esleri C.).Webb (stems and flower stalks) was method of Arnold (1960) was used to cal Cyperaceae Carex ovalis Gooden. measured. Material from quad- culate DD from these data. This method Cyperlls eragrostis Lam. rats was dried to constant was found to be reasonably accurate for Fabaceae Lotus pedul1culatus Cav. weight in a drying oven at data recorded at meteorological sites in Gramineae Glyceria maxima (Hartm.) Holmb. 105°C. northern New Zealand (Womer 1988). Ho[cu s lanatus L. The weed mat edge was di- The total DD requirement for A. hygro Paa trivialis L. vided into five sections, each phila development from egg to adult was Haloragaceae Myriophyllum aquaticum (Velloso) Verde. approximately 30 m long, and calculated by summing the DD values for Juncaceae Juncus ? articulahts L. 20 shoot samples and one 0.1 each life stage. DD for each life stage were llmcus effusus L. m' quadrat were randomly se calculated as DD = 1/(slope of regression luncus ? gregifloTlls L. lected within 50 em from the line). The slopes of the regression lines Onagraceae Ludwigia peploides (Kunth) P.H.Raven edge in each section on each were taken from the linear regressions of Ludwigia palustris (L.) Elliott sampling date. From December development rate of A. hygrophila v. tem Polygonaceae Polygollum ? CJlpilatum D.Don. 1994 to April 1995 an additional perature in Stewart e/ al. (1999a). Polygonum salicifolium Willd. sample of 10 shoots was col The DD required to complete the pre Rubiaceae Galium diva rica tum Lam. lected from each of the five sec ovipositional period for adult females was Salviniaceae Azalla pinnlJta R.Br. tions for stem diameter meas estimated using the pre-ovipositional urements on each sampling times at 20, 25 and 30°C (Stewart et al. Table 2. Estimated lower temperature date. 1999b). Linear regression was used to de development threshold (Stewart et aI, 1999a) Internal stem diameters scribe the development rate (l/days) v. and degree day requirement for Agasicles were measured to determine if temperature relationship. DO were esti hygrophila. they were small enough to re- mated from the equation y = 0.0373x-0.585 -=.::...--'-______strict the pupation of A. hygro- (R' = 60.2). This gave an estimate of 27 DD Lower temperature Degree days phi/a . Measurements were for the pre-oviposition period and when development threshold taken (to the nearest 0.5 mm) at added to the 250 DD calculated in Table 2, (0C) the midpoint of the internode gave 277 DD required for development -E-gg------l-'2-.9-'1------falling within 80 cm of the api- from egg to ovipositional female. This 53.6 cal node. If stems were less than value was' used to estimate the potential 1st instar 16.24 15.9 80 I h . 2nd instar 11 .48 433 cm ong, t e uncut mter- number of generations for A. hygrophila in 3rd instar 15.02 22·3 node furthest away from the the field . 12.58 114:7 apical node was chosen for the The following calculations were made Pupa stem diameter measurement. to estimate the earliest time that over Total 249.8 ______The presence of pupae in the wintered females would begin to lay eggs Plant Protection Quarterly Vo1.15(3) 2000 97 in the field. As A. hygrophila has no appar peaked in late December in the second amounts of leaves and stems throughout ent winter diapause and no obvious bio growing season at 358 m m-2 and then de both seasons (Figure 3). Mean internal logical fix point exists, an alternative ap clined to 16 m m·' by late February. stem diameters ranged from 1_2-3.4 ± 0.34 proach was needed to estimate the DO When sampling began in mid Novem mm. available for A. hygrophila development in ber, plant growth had already commenced Densities of A. hygrophila are shown in the field and to determine the number of and total dry weight was estimated at Figures 4-6. Adults were present in de generations possible. 288 ± 107.5 g m·' (Figure 3). Dry weight tectable numbers on alligator weed at In the 1994-95 season DD were calcu peaked at 405 ± 107.5 g m·' in late january Whatatiri from mid December to late June lated daily from 24 November 1994 to then decreased to 32 g m·' by the begin in the first season and were found from April 1995 using the estimated lower tem ning of March. During the winter months early December onwards during the sec perature development threshold (13.3°C) dry weight ranged from 25 to 81 g m·' un ond season (Figure 4). During the first sea (Stewart et al. 1999a). To selectthe starting til the beginning of October. During the son, the population started to increase in date for the first generation of eggs laid, second growing season, dry weight began january and peaked at 156 ± 64.5 adults the daily DD available were summed to increase rapidly from October reaching m-2 in early February. During the second backwards from the first date a larva was 646 ± 107.5 g m·' in late December and de season the population of adults started to seen in the field. Summing stopped on the clining to 44 g m·' by late April. Total dry increase in mid January and the first peak date when the DD needed for develop weight consisted of approximately equal of 225 ± 64.5 m'2 occurred in late January. ment of the immature stage was reached. This date (24 November 1994) was re 50 ---maximum corded as the start date of the first genera tion of A. hygrophila. Daily DD were summed for subsequent generations and the date on which 277 DO was reached 40 was recorded.
Results Air tempera ture and rai'ifall Weekly mean, minimum and maximum values for Whatatiri are shown in Figure 1. The mean weekly temperature ranged from 8.3-21.8°C during the study period. Mean weekly minimum temperature ranged from 0.1-16.1°C. Annual rainfall 10 for 1994 measured close to the field site was 1010 mm. Greatest rainfall occurred during winter months (770 mm from May o to October). Periods of high rainfall (177 ND J FMAM J J A SOND J FMAM mm in one week) led to flooding in April 1995. 1993 1994 1995 Month Alligator weed shoots and quadrat Figure 1. Mean, minimum and maximum weekly temperatures from samples temperature logger readings taken at Whatatiri from 15 November 1993 to Floating aquatic alligator weed was 24 April 1995. present at Whatatiri through- out the study period. During the first growing season the 1000 500 mean number of shoots ranged -t:r- number of shoots 900 450 from 578 ± 54.9 to 600 ± 60.6 m' - 0 -· shoot length from mid November through to 800 400 early january (Figure 2). From then on the shoot density de- ~ 700 350 dined and was lowest in early .s ~- April (124 shoots m·'). Thereaf- ~ 600 300 E ter shoot density increased and ~ 500 .s peaked in the second growing '0 , 250 , '"15> season in late December (930 Q) 400 , 200 <= Q shoots m-2) _ Shoot numbers fell ~ --'
~ stem dry weight March and April. 350 Egg batches were present in the first - ~ 'leaf dry weight season from late January until early July 300 (Figure 4) _ The number of egg batches peaked at 179 ± 43.2 batches m-' during ~ 250 late April. Egg batches were present in the .9 second season from late December, ~ 200 peaked at 109 ± 43.2 batches m-' in early 0; February and declined to six in late March, ~ , ~ 150 ¢o , before rising again in April. 0 , During the flrst growing season the I> 100 ,, numbers of the three larval ins tars all fol , lowed similar trends (Figure 5). First 50 ... »--0 instars were present from mid December to mid June and second instars were present from mid November to mid July. NDJ FMAMJJASONDJ FMAM Third instars were present from mid No 1993 1994 1995 vember to mid June. All instar numbers Month peaked in late February (870 ± 222.5, Figure 3. Dry weight (g m-') of Alternanthera phi/oxeroides at Whatatiri 1250 ± 224.9 and 668 ± 169.2 larvae m' for first, second and third instars respec between 15 November 1993 and 26 April 1995. tively). Densities of first and second 300 instars declined by the next sampling ---0--- adults date in early March to 204 and 176 larvae m-' respectively. The denSity of third 250 • • <(J. •• egg batches instars declined to 21 m-' by late April. Low levels of each instar were present during autumn until mid June (first and ~ 200 third instars) and mid July (second instars). 00 ~ During the second season, second . ~ 150 instar larvae were present from early De '15 cember and first and third ins tars from ~ n A late January (Figure 5). Maximum num § 100 '. bers of first (939 ± 222.5 larvae m-') and z t;A::" second (1126 ± 224.9) instars were reached in mid February whereas third instars 50 "-. 4 : peaked a week later (905 ± 169.2 larvae '4 ' . . m-'). The numbers declined sharply by the t. end of March to 23, 16 and 30 larvae m-l for first, second and third instars respec NDJ FMAMJJASONDJ FMA M tively. 1993 1994 1995 Prepupae were present in stems from Month early January to mid July in the first sea Figure 4. Seasonal occurrence of Agasie/es hygrophi/a adults and egg son and from late December to the end of batches at Whatatui between 15 November 1993 and 26 April 1995. the sampling period in late April in the 1600 second season (Figure 6). In the first sea --0-- 1st instars son, pre-pupal densities increased from 64 .. 0 ·· 2nd instal'S m -l in early January to 311 ± 91.1 in late 1400 - -6- ·3rd instars February and then declined to levels rang ing from 7 to 40 m-l. from April until mid 1200 ~:. 9 July. During the second growing season, ~ pre-pupal densities peaked at 474 ± 91.1 -; 1000 pre-pupae m-l in mid February and then 13 <) 00• declined by mid March to levels between .5 800 '15 9 and 74. ~ : Pupae were present in the first growing n• 600 , E : , ., season from early January until mid July , 9 , :, z :, 9 and in the second season from early Janu 400 ary until the end of sampling. In the first season, numbers peaked in mid February 200 at 279 ± 75_0 pupae m-'. The population decreased to 16 at the beginning of April and continued to levels of 6 to 29 pupae NDJFMAMJJASONDJFM A M July. In the second growing season num 1993 1994 1995 bers peaked at 380 ± 75.0 pupae m-' in mid Month February and then declined to a low level; Figure 5. Seasonal occurrence of Agasie/es hygrophi/a larval instars at by mid March only 10--19 pupae m-' were Whatatiri between 15 November 1993 and 26 April 1995. present. Plant Protection Quarterly VoL15(3) 2000 99 700 1978. One month later the population had ,- 0 ·· pupae declined to 31 adults, 100 pupae, 0 larvae --l!.- ·teneral adults and 15 egg batches m'. From both the 600 Australian and this study it appears --0-- pre-pupae in stems A. hygrophila populations fluctuate mark _ 500 edly in response to available food plant. • The decline in A. hygrophila numbers occurred after alligator weed dry weight g 400 .5'" declined (Figures 3-6). Alligator weed de '0 cline was attributed to damage caused by ~300 A. /Jygrophila and A. malloi. The increase in .0 ,E ' 0 egg batches in autumn of both seasons z (Figure 4) was caused by high numbers of 200 V\ fertile adults present and oviposition was probably stimulated by regrowth (Figure 100 2). Alligator weed grew year round at Whatatiri and during the winter months it grew steadily in the absence of large NDJ FMAMJ J ASOND J FMAM A. hygropllila populations (and presum- 1993 1994 1995 ably A. malloi). While A. hygrophila was Month limited by low temperatures in winter Figure 6. Seasonal occurrence of Agasicles hygrophila prepupae in stems, (Stewart et al. 1999a, 1999b), alligator weed pupae and teneral adults at Whatatui between 15 November 1993 and 26 continued to grow giving it a competitive April 1995. edge as the weed mats regenerated each spring. In Georges River (Sydney) the weed mats were destroyed by A. hygro Table 3. Agasicles hygrophila pupae (total of 67) found in Alternanthera phila Oulien et al. 1992); warm tempera philoxeroides stems (1250 stems sampled) of different internal diameter tures and good nutrition led to high A. (±0.25 mm) as a percentag.e of total pupae found. hygrophila numbers which in turn allowed more damage and high alligator weed Stem diameter (mm) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 control. % of total pupae 0 8.9 28.4 38.8 14.9 6.0 1.5 1.5 There was sparse evidence from this study that A. hygrophila over-wintered as an adult. In the samples that were taken A total of 67 pupae were found in the Degree Day (DD) estimates during winter, no life stages of A. hygro 1250 stems sampled. Pupae were found in Three generations were predicted at phila were found although individual stems with diameters ranging from 1.0 to Whatatiri using DD accumulation (Table adults were seen while sampling was 4.0 mm (Table 3), with the largest percent 4). done in July and October. Maddox (1968) age (38.8%) in stems with diameters of 2.0 suggested adults were the over-wintering mm. Discussion stage and it is quite likely that adults over Low numbers of teneral adults were Alligator weed and A. hygrophila wintered at Whatatiri. Gangstad et al. found each year (Figure 6). In the first sea populations (1975) found few A. hygrophila adults sur son they were found from late January to Aquatic alligator weed was present vived the winter months in Georgia and the end of April (2-17 adults m") and in throughout the year and dry weights South Carolina in the USA, and feeding the second season they were found from peaked in early summer in both seasons activity was not noticed until the follow early January to late March (3-64 adults and declined as A. hygrophila populations ing summer and autumn, a similar situa m·'). began to build up. Julien et al. (1992) meas tion to that which occurred at Whatatiri. Peak A. hygrophila populations oc ured alligator weed in Australia through In early April 1995 flooding washed curred during February in 1994 and 1995. out the 1977-78 season and found 368-656 large sections of alligator weed mat from During the first growing season, all life stems m-2 fresh at water sites compared to the sampling area and this was replaced stages peaked on the same sampling date 124-930 stems m" at Whatatiri. Dry by alligator weed washed in from further except for eggs and adults which peaked a weight per stem was heavier in Australia upstream. Although the water levels rose fortnight earlier. During the second sea than at Whatatiri, 0.28-1.04 g compared to over one metre above normal, the weed son, clearer differences between the insect 0.08-0.88 g. life stages were observed (possibly due to Julien et al. (1979) measured adult A. the increased frequency of sampling), hygrophila densities over 100 m-2 in the first Table 4. Estimated dates for however, the life stages still peaked within season after release in Australia and ap Agasicles hygrophila females to a short period between late January and proximately 875 adults m" in the follow reach their ovipositional stage for mid February. Pre-pupal numbers peaked ing season. The latter value is three and a each generation using the 277 00 at the same time as second and third half times higher than the highest record requirement (summing ended on 25 ins tars, which suggests these peaks re at Whatatiri and may be attributed to dif April 1995) at Whatatiri, Northland. sulted from different generations. It is ferent environmental factors (e.g. nutri probable that generations of A. hygrophila ents and temperatures) which affected the Generation Immature indicator overlapped. A. hygrophila populations. At another site in Australia (William town), in a drain 1 6 January 1995 with permanent water, a population of155 2 13 February 1995 adults, 674 pupae, 343 larvae and 88 egg 3 27 March 1995 batches m-2 was recorded in December Excess DO 159 100 Plant Protection Quarterly Vo1.15(3) 2000 was probably never submerged as popu low. These predictions suggest three gen that earlier predictions were wrong, al lation levels were not obviously affected. erations per growing season at Whatatiri. though the weed may be actually defoli It is unlikely that many A. hygrophila were Population numbers of A. hygrophila ated in north of New Zealand, overall washed into the ponds because the new were low at the beginning of spring and weed reduction is unlikely. alligator weed had minimal insect dam this was probably due to high mortality age. The results obtained at Whatatiri for aU life stages during winter due to low Acknowledgments were contrary to those expected, based on temperatures. The lower temperature de Project funding, facilities and support the literature reports which stated A. velopment thresholds for A. Jrygrophi/a life were provided by Manaaki Whenua - hygrophila can be adversely affected by stages ranged from 11 to 16' C (Table 1); Landcare Research and Lincoln Univer flooding (e.g. Coulson 1977). temperatures that are commonly experi sity. Rowan Emberson and Pauline Syrett Maddox and Hambric (1970, 1971) sug enced during winter at Whatatiri (Figure provided helpful guidance and comments gested A. hygrophila populations were lim 1) . Results from laboratory experiments on this work. The authors are also grateful ited by nutrient deficient alligator weed (Stewart et af. 1999a) showed there was to Northland Fish and Game Council for with tough, fibrous epidermal tissue and high mortality (94%) of immature stages the use of the Whatatiri site and Bill the absence of hollow internodes. This reared at 15°C. No eggs that were incu McMeikan for assistance during the field would prevent the completion of the life bated at 10' C hatched. It is therefore un sampling. We thank Sue Worner for valu· cycle due to the lack of pupation niches likely that egg laying and development able discussions on degree day theories. and the authors suggested larvae could for A. JrygropJrila will occur during winter. NIW A provided rainfall and temperature not enter the stems at all. Vogt et af. (1979) Clearly A. hygrophila persists from one data and difficult to locate references were indicated that pronotal width (1.21 mm in season to the next. However, there is little provided by the Aquatic Plant Informa females and 1.07 mm in males) deter information on over-wintering survival or tion Retrieval System, Centre for Aquatic mined the minimum internal stem diam fecundity of the survivors. A previous Plants, Florida University. Chris Pugmire eter in which pupation could occur. If study (Stewart et al. 1999a) indicated that (HorHResearch, Auckland) compiled pro stems were too narrow, the pre-pupae the number of frosts at a given location grams to calculate the Simpson's rule and may have enlarged them by chewing, but may influence its suitability for A. hygro the min-max method. Steve Taylor as not ingesting, the internal pithy walls phila development. Egg viability was re sisted with graph formatting. (Vogt el al. 1979). This may have happened duced after adults were chilled overnight. with 9% of stems at Whatatiri that had in This suggests the over-wintering ability of References ternal diameters <1.21 mm and which A. Jzygrophila would be reduced in areas Arnold, c.Y. (1960). Maximum-minimum held pupae. The greatest proportion of which have similar low temperatures and temperatures as a basis for computing pupae (91%) were found in stems with in frosts. heat units. Proceedings of the American ternal diameters which exceeded 1.25 mm Two generations of A. hygrophila at Society for HortiCtlltural Science 76 , (1.5 ± 0.25 mm) (Table 3). Therefore the de Whatatiri were sufficient to provide defo 682-92. velopment of most pupae was not re liation but not alligator weed control. At Broughton, R.L. and Ramsay, A.RD. stricted by stem diameter at Whatatiri Whatatiri, despite predictions for control, (1979) 'Numerical methods', 136 p. because mean internal stem diameters temperatures limit A. hygrophila popula (Eton Press Ltd., Christchurch). were above 1.5 mm except in early March tion increase until it is too late in the grow Cheeseman, T.F. (1906). 'Manual of the 1995 when aUigatorweed had suffered de ing season and they also limit the size of New Zealand Flora', 1199 p. (Govern foliation. the population needed to provide control. ment Printer, Wellington). Vogt et al . (1992) considered that A. The work at Whatatiri was conducted Coulson, j.R (1977). Biological control of hygrophila populations in the United States some years after release when field alligatorweed, 1959- 1972. A review were overlapping, however, they were not populations of the insect were well estab and evaluation. United States Depart measured. In this study no clear peaks al lished compared with Australian data that ment of Agriculture Technical Bulletin lowed discrimination of generations. included the first summer peak of A. No. 1547, 98 p. hygrophila after its release (d uring the pre Gangstad, E.O., Blackburn, RD., Durden, Degree days and development vious autumn) and the second summer W.c., Center, T.D., Balcuinas, J., Inglis, The DD analysis suggests that at any site peak. A. hygropJrila numbers were three A., Davis, E.L., Seaman, D.E. and where less than 554 DD are accumulated times higher than those at Whatatiri and Steenis, j.H. (1975). Integrated program (allowing two generations), A. hygrophila resulted in permanent reduction of for alligator weed management. Tech populations are unlikely to be large aquatic mats on Georges River Oulien et nical report la, Army Engineer Water· enough to defoliate alligator weed. 1n this al. 1979). Considering that Whatatiri is a ways Experiment Station, 120 p. study, one method of determining the most favourable site in New Zealand for julien, M.H. (1981). Control of aquatic number of generations were used. Exactly A. hygropJri/a, it is unlikely that this beetle AIternanthera philoxeroides in Australia; when DD summing should begin is diffi will provide control of alligator weed in another success for Agasic/es hygrophila . cult to determine and will vary between New Zealand even in conjunction with A. Proceedings of the V International years. The method used assumed the first malloi . Symposium on Biological Control of inunature A. hygrophila life stage seen be Stewart et al . .(1995) predicted that A. Weeds, Brisbane 1980, pp. 583-8. longed to the first generation. DD were hygrophila could only control alligator julien, M.H. (1995). Alternanlhera phil counted backwards to predict when eggs weed from Auckland to Northland and in oxeroides (Mart.) Griseb. In 'The biology were laid, thus giving the start date. There several coastal areas in the North Island of Australian weeds, volume I', eds are disadvantages when using this where optimum temperatures for the in RH. Groves, RC.H. Shepherd and RG. method, as accuracy may be affected by sect are only sustained for a short period Richardson, pp. 1-12 (R.G. and F.j. the length of the time intervals between of time (Stewart et al . 1999a, New Zealand Richardson, Melbourne). sampling dates and ability to detect indi Meteorological Service 1983). This study Julien, M.H., Bourne, A.S. and Low, viduals in a small population. Where sam shows that the low winter temperatures V.H.K. (1992). Growth of the weed pling intervals are long (>3 weeks) it is «15°C) in winter limits over winter sur Alternanthera philoxeroides (Marti us) possible to miss a generation, especially vival and prevents significant population Grisebach, (alligator weed) in aquatic during the spring when alligator weed is increase before mid-summer, even at the and terrestrial habitats in Australia. rapidly growing and insect numbers are most suitable site, Whatatiri. This suggests Plant Protection Quarterly 7, 102-8. Plant Protection Quarterly Vo1.15(3) 2000 101 julien, M.H., Broadbent, j.E. and Harley, hygrophila, (Coleoptera: Chryso- K.L.S. (1979). The current status of bio melidae): implications for biological logical control of Altemant/tera phil control in New Zealand. Proceedings of oxeroides in Australia . Proceedings of the IX International Symposium on the 7th Asian-Pacific Weed Science S0- Biological Control of Weeds, Stellen- ciety Conference, Sydney, pp. 231-5. bosch, pp. 393-8. julien, M.H., Chan, R.R (1992). Biological Stewart, C.A., Julien, M.H. and Worner, control of alligator weed: unsuccessful S.P. (l995). The potential geographical attempts to control terrestrial growth distribution of alligator weed (Alternan using the flea beetle Disonycha thera philoxeroides) and a biological con argentinensis [Col.: Chrysomelidae]. trol agent, Agasie/es hygrophila, in New Entomophaga 37, 215-21. Zealand. Proceedings of the 48th New Maddox, D.M. (1968). Bionomics of an Zealand Plant Protection Conference, alligatorweed flea beetle, Agasicles sp. pp.270-5. in Argentina. Annals oj the Entomologi Vervoort, L. and Hennessy, C. (l996). Na cal Society oj America 61, 1299-305. tional Surveillance Plant Pests. Auck Maddox, D.M. and Hambric, R.N. (1970). land Regional Council, 38 p. Use of alligatorweed flea beetle in Vogt, G. B., McGuire, j.U. and Cushman, Texas: an exercise in environmental A.D. (1979). Probable evolution and biology. Proceedings of the 23rd morphological variation in South Southern Weed Science Society, pp American Disonychine flea beetles 2-286. (Coleoptera: Chrysomelidae) and their Maddox, D.M. and Hambric, RN. (1971). Amaranthaceous hosts. United States A current examination of the alligator Department of Agriculture Technical weed flea beetle in Texas. Proceedings Bulletin Number 1593, 148 p. of the 24th Southern Weed Science So Vogt, G.B., Quimby, P.c. and Kay, S.H. ciety, pp. 343-8. (1992). Effects of weather on the bio New Zealand Meteorological Service logical control of aUigatorweed in the (1983). 'Summaries of climatological Lower Mississippi Valley region, 1973- observations to 1980', 172 p. (New Zea 83. United States Department of Agri land Meteorological Service Miscella culture Technica.l Bulletin Number neous Publication 177). 1766,143 p. Philip, B.A., Winks, Cj., joynt, P.w. and Wilkinson, L. (1990). 'SYSTAT: The sys Sutherland, O.R. W. (1988). Current sta tem for statistics'. (SYSTAT INC., tus of biological control of alligator Evanston, IL). weed in New Zealand. Proceedings of Worner, S.P. (1988). Evaluation of diurnal the 41st New Zealand Weed and Pest temperature models and thermal sum Control Conference, pp. 61-5. mation in New Zealand. Journal of Eco Roberts, L.I.N. and Sutherland, O.RW. nomic Entomology 81, 9-13. (1989). Altemanthera philoxeroides (C. Martius) Grisebach, alligator weed (Amaranthaceae). In 'A review of bio logical control of invertebrate pests and weeds in New Zealand 1874 to 1987', pp. 325-30. (CAB Intemationallnstitute of Biological Control, Wallingford). Roberts, L.l.N., Winks, c.j., Sutherland, O.RW. and Galbreath, RA. (1984). Progress of biological control of alliga tor weed in New Zealand. Proceedings of the 37th New Zealand Weed and Pest Control Conference, pp. 50-4. Stewart, C.A., Chapman, RB., Barrington, AM. and Frampton, C.M.A (1999b). Influence of temperature on adult lon gevity, oviposition and fertility of the leaf beetle Agasie/es hygrophila Selman & Vogt (Coleoptera: Chrysomelidae). New Zealnnd JOllrnal oJZoology 26,191-7. Stewart, C.A, Chapman, RB., Emberson, RM., Syrett, P. and Frampton, C.M.A (1999a). The effect of temperature on the development and survival of Agasie/es hygrophila Selman & Vogt (Coleoptera: Chrysomelidae). New Zea lalld Joumal oj Zoology 26, 11-20. Stewart, C.A , Emberson, RM. and Syrett, P. (1996). Temperature effects on the al ligator weed flea-beetle, Agasie/es