Host range testing and life history of the defoliator Hymenomima nr. memor: an unsuitable biological control agent for Schinus terebinthifolia in the U.S.A.

Host range of larvae of Hymenomima nr. memor (Lepidoptera: Geometridae) was examined in quarantine to evaluate its suitability as a biological control of Brazilian peppertree, Schinus terebinthifolia. Brazilian peppertree, S. terebinthifolia is an environmental and agricultural weed from South America that had invaded many subtropical and tropical areas of the world including Florida and Hawaii, USA. Laboratory life history and quarantine host range studies of H. memor were conducted with no-choice feeding tests. These tests included eight species of the Anacardiaceae and one species of Sapindaceae. Larvae of H. memor had five to six instars with each head capsule width increasing by 1.68-X. Development time from neonate to adult was 46.7?±?2.2 days. In host range tests, neonates completed development to the adult stage on all non-target species, except Toxicodendron radicans. Moreover, developmental times were delayed and pupal weights were reduced for larvae fed Spondias purpurea leaves. Due to the broad host range exhibited by H. memor larvae, this species will not be considered as a biological control agent of S. terebinthifolia in the continental U.S.A.     

Life history and host range of Sauris nr. purpurotincta,an unsuitable biological control agent for Chinese tallowtree

Foreign surveys in China discovered a defoliating insect species feeding on the leaves of Chinese tallowtree (Triadica sebifera), an invasive weed of the southeastern U.S.A. The life history of this species, Sauris nr. purpurotincta (Lepidoptera: Geometridae), was examined and larval no-choice and adult multiple-choice host range tests were conducted in quarantine to evaluate their suitability for biological control of Chinese tallowtree. The results indicated that the larvae have five instars and require approximately 22 days to complete development to the adult stage. Host range tests indicated that the larvae could not feed and complete development on most species tested. However, 40% of the larvae survived when fed leaves of Hippomane mancinella, a state-listed endangered species in Florida, and all larvae survived when fed Morella cerifera, a common native species of the southeastern U.S.A. Multiple-choice oviposition tests indicated eggs were laid on leaves of both a south Florida native plant Gymnanthes lucida and Chinese tallowtree. Considering this broad host range, this species will not be considered further for biological control of Chinese tallowtree in the U.S.A.     

Life history and host range of Oxydia vesulia transpeneus,an unsuitable biological control agent of Brazilian peppertree

The suitability of Oxydia vesulia transpeneus (Cramer) (Lepidoptera: Geometridae) was assessed as a potential biological control agent of the invasive weed Brazilian Peppertree Schinus terebinthifolia Raddi. Larvae were collected in Brazil feeding on the plant in its native range and colonised in quarantine where life history and host range studies were conducted (27?±?2°C; 50RH). Development time from neonate to adults when fed Brazilian peppertree leaves was 48.0 (±2.2) days for females and 51.0 (±1.3) days for males. Larvae generally required five (occasionally six) instars to reach the adult stage. Females had greater pupal weights 1004.1 (±45.9) mg compared with males 668.5 (±19.7) mg. Larvae were tested on seven non-target plant species from Florida natives, ornamentals, to economic species. Larvae completed development on all but one of these valued plant species. These results suggest that the host range of O. vesulia is not sufficiently specific for release as a biological control against Brazilian peppertree in the USA.     

Life history and laboratory host range of Stenopelmus rufinasus, a natural enemy for Azolla filiculoides in South Africa

The frond-feeding weevil, Stenopelmus rufinasus Gyllenhal, was imported into quarantine for testing as a potential natural enemy for the invasive fern Azolla filiculoides Lamarck in South Africa. Adult S. rufinasus lived for approximately 55 days during which the females produced on average 325 offspring. The developmental period for the immature stages (egg, three larval instars and pupation) was about 20 days indicating the potential for several overlapping generations per year. Both the adults and the larvae caused severe damage to A. filiculoides in the laboratory. Host specificity of this insect was determined by adult no-choice oviposition and larval starvation tests on 31 plant species in 19 families. Adult feeding, oviposition and larval development was only recorded on the Azolla species tested (A. filiculoides, A. pinnata subsp. poss. asiatica R.K.M. Saunders and K. Fowler, A. pinnata subsp. africana (Desv.) R.K.M. Saunders and K. Fowler and A. nilotica De Caisne Ex Mett.). A. filiculoides proved to be significantly the most suitable host for the weevil. The low adult emergence from A. nilotica and A. pinnata subsp. africana would most probably prevent the weevil from establishing on them in the field. A. pinnata subsp. poss. asiatica which supported greater development, is thought to be introduced and has a weedy phenology in South Africa and is thus of low conservation value. Therefore, any damage inflicted on this plant in the field may be an acceptable trade-off for the predicted impact of S. rufinasus on the aggressive exotic weed, A. filiculoides.     

Suitability of five mealybug species (Hemiptera,Pseudococcidae) as hosts for the solitary parasitoid Anagyrus sp. nr. pseudococci (Girault) (Hymenoptera: Encyrtidae)

Anagyrus sp. nr. pseudococci is an endoparasitoid which has been used as a biological control agent of mealybug pests. In this study, we compared the suitability of five mealybugs species with different phylogenetic relationships and geographical origins as hosts of this parasitoid. The selected mealybugs were: (1) a Mediterranean-native species, Planococcus ficus, sharing a long co-evolutionary history with the parasitoid; (2) three exotic species, the Afrotropical Planococcus citri, the Australasian Pseudococcus calceolariae and the Neotropical Pseudococcus viburni, with a recent history; and (3) the Neotropical Phenacoccus peruvianus, with no previous common history with the parasitoid. Host suitability was assessed based on different fitness parameters, such as body size, developmental time, emergence rate and sex ratio. The parasitoid was able to complete development in all mealybug species. Nevertheless, its emergence rate significantly varied among mealybug species, with the highest values observed in Pl. ficus and Pl. citri, intermediate values in Ps. calceolariae and the lowest ones in Ps. viburni and Ph. peruvianus. The body size of adult wasp females varied with host suitability and was positively correlated with other measures of parasitoid fitness, including the emergence rate and the sex ratio. The parasitoid developmental time differed among mealybug species but did not correlate with any other measure of fitness. A female biased sex ratio was found in the parasitoid progeny emerged from all mealybug species, except in Ps. viburni and Ph. peruvianus. There was a direct relationship between the proportion of females in the parasitoid progeny and the emergence rate.     

Insect, not plant, determines gall morphology in the Apiomorpha pharetrata species-group (Hemiptera: Coccoidea)

Abstract  Scale insects of the genus Apiomorpha Rübsaamen (Hemiptera: Coccoidea: Eriococcidae) induce sexually dimorphic galls on Eucalyptus, but the Apiomorpha pharetrata species-group is unusual in that nymphal males aggregate on the surface of the maternal gall where they induce a compound structure. Although originally described as distinct species on the basis of differences in gall morphology, A. pharetrata (Schrader) and A. thorntoni (Froggatt) were subsequently synonymised, primarily because the adult females of the two are morphologically indistinguishable. The two gall types of A. pharetrata sensu lato are allopatric and found on different host eucalypt species. To test the hypothesis that gall morphology may be determined by the host species on which the female feeds, we reared crawlers of field-collected females from both gall types on eucalypts in a glasshouse. Both gall types were induced on the same eucalypt species, with the gall type matching that of the maternal gall from which the crawlers had emerged. This indicates that it is the insect, not the host, that determines the gall morphology in these taxa. In addition, insects from the two gall types were different chromosomally and could be distinguished by one fixed allozyme difference. Thus, Brachyscelis (=  Apiomorpha ) thorntoni (Froggatt) revised status is removed from synonymy with Brachyscelis (=  Apiomorpha ) pharetrata (Schrader), and recognised as a distinct biological species. However, the extent of chromosomal variation among the populations of both A. pharetrata and A. thorntoni suggests that there may be further cryptic species present.     

Analysis of importations for biological control of insect pests and weeds in New Zealand

Importations of biological control agents for insect pests and weeds in New Zealand are summarized and factors contributing to the relative success of the programmes are examined. The establishment rate of 30.9% is similar to that achieved worldwide, but is significantly lower than the rate achieved in the island habitat of Hawaii. The pioneering role of New Zealand in biological control is shown by the high proportion of programmes first attempted in this country. Although this novelty has not reduced the establishment rate, introductions against endemic species have not succeeded. Size of release was not a dominant feature in the establishment of agents. Complete or substantial success is recorded for 17 of the 70 target pests, with a relatively high success rate in forestry programmes. Examples of the influence of climate matching and competitive exclusion are also discussed. Changing practices and attitudes to the introduction of biological control agents are documented to show the increasing emphasis on specialists. No adverse effects of introductions are reported. The challenge to practitioners and regulators is to develop systems to evaluate conflicts of interest and develop workable mechanisms to determine which biological control agents are suitable for release.     

Host specificity assessment and potential impact of Megamelus scutellaris (Hemiptera: Delphacidae) on waterhyacinth Eichhornia crassipes (Pontederiales: Pontederiaceae)

The delphacid Megamelus scutellaris Berg was evaluated for host specificity and potential impact as part of a biological control program targeting Eichhornia. crassipes. Survival and development of adults and nymphs were used as metrics with no-choice, two-choice, nymph transfer, and sustainability tests conducted under quarantine conditions. A total of 69 plant species were tested including 12 from the Pontederiaceae (including E. crassipes). Additionally, 27 native and 5 exotic associated wetland species and 11 economic species were tested. Megamelus scutellaris exhibited a high level of oviposition and developmental fidelity to E. crassipes by failing to sustain populations on any non-target test plant past the F₁ generation. Nymph transfer tests which simulated potential spill-over events found that survival was virtually non-existent on associated wetland plants, regardless of taxonomic relatedness, including on Pontederia cordata, an important and widespread native species. Eichhornia crassipes plants exposed to two consecutive generations of feeding produced 66.9% less biomass and 73.4% fewer leaves than those in the controls. We conclude that Megamelus scutellaris is safe to release on E. crassipes in the United States.     

Unsuitability of Charidotis pygmaea for biocontrol of Lantana camara in Africa

The host range of the tortoise beetle,Charidotis pygmaea Klug (Coleoptera:Chrysomelidae), was studied under quarantinelaboratory conditions to evaluate the insect'ssuitability for release as a biological controlagent for the noxious weed, Lantanacamara L. (Verbenaceae) in South Africa.Culturing on the target plant, L. camara,proved problematic with high larvalmortalities. Host-specificity studies showedthat four species in the genus Lantana,and two species in the genus Lippiawere acceptable as host plants. Duringlarval development trials, the insect performedbetter on the indigenous Lantana rugosaThunb. (Verbenaceae) and the introduced,commercially used L. montevidensis(Spreng.) Briq. (Verbenaceae), than on any ofthe weedy South African L. camaravarieties tested. Adult multi-choice trialsindicated that the beetle preferred to ovipositon L. rugosa and L. montevidensis.It is therefore recommended that C.pygmaea not be released against L.camara in Africa.     

Rapid preliminary characterisation of host specificity of leaf-beetles (Coleoptera: Chrysomelidae)

Rapid characterisation of host specificity is important both in biological control of weeds and studies in ecology and evolution. A means for doing this was developed and tested on four species of leaf beetles of interest for biological control of the weed Mimosa pigra (Mimosaceae). We identified the most promising for the more detailed tests necessary to obtain release approval. The impact of time-dependent effects and effects of experience were also investigated as part of this study but were not detected. Short-term host specificity tests on adult feeding accurately predicted the results of longer term trials. The long-term trial showed that survival on a plant species depended on feeding on it. Hence short-term feeding trials can predict the longer term survival of adults on other plant species. Different feeding results were obtained in cut foliage versus entire plants but no consistent pattern was shown: of the two insect species tested, one species ate more of the cut material while the opposite was demonstrated for the second species. Species in order of priority for further consideration as biocontrol agents were Syphrea bibiana, Genaphthona sp., Syphrea sp. and Paria sp. The latter three species were probably not sufficiently specific for release. The tests done here allow the identification of the most likely species upon which to conduct the more laborious and difficult larval developmental tests, saving considerable resources.     

Biology and host range of the stem-boring beetle Aphanasium australe, a promising agent for the biological control of Hakea sericea in South Africa

The invasive Australian shrubHakea sericea Shrader is a majorenvironmental weed in the Western and EasternCape Provinces of South Africa. Dense,impenetrable thickets severely threaten theunique endemic vegetation of the Cape FloristicKingdom, increase fire hazards and reduce wateryields in catchments. Biological control,initiated in the 1970s, is largely confined tothe use of seed-feeding insect agents. Becausenone of these agents reduce the density ofexisting hakea populations, a stem-boringbeetle, Aphanasium australe (Boisduval) (Cerambycidae),was imported into quarantine in South Africa in1975. During multichoice oviposition tests,involving 12 Australian and six South Africanproteaceous species, in a walk-in cage, A. australe only oviposited on four species ofHakea and two exotic species of Grevillea. However, culturing difficultiesresulted in the suspension of host-specificitytesting after three years. Testing was resumedfollowing re-importations in 1995, also becauseA. australe also attacks Hakeagibbosa (Sm.) Cav., which is not attacked byany of the existing biocontrol agents. Duringno-choice survival tests, involving 66test plant species from 15 families, A. australe only developed on H. sericea, H. gibbosa and one exoticspecies of Grevillea. The contention thatA. australe is confined to the genus Hakea was confirmed by host records andsurveys in Australia which provided no evidenceof attacks on crop, pasture or related plants.The regulatory authorities accepted theseresults and A. australe was cleared forrelease in South Africa during 2001.     

Host range of the European,rhizome-stem feeding scale Rhizaspidiotus donacis (Hemiptera: Diaspididae), a candidate biological control agent for giant reed,Arundo donax (Poales: Poaceae) in North America

The armored scale Rhizaspidiotus donacis (Leornardi) was evaluated as a potential biological control agent of the invasive reed grass Arundo donax in North America. No-choice tests, native range field surveys and non-target host exposures were used to determine the fundamental host range of the scale collected from Caloma, Spain and Perpignan, France. Thirty-five species, including two genotypes of A. donax and seven ecotypes of Phragmites australis, along with closely related grasses, economic grasses and habitat associates were tested. In quarantine no-choice testing using releases of 200 crawlers per plant, normal development of R. donacis was observed on A. donax and A. formosana, with very limited survival to the adult stage on Spartina alterniflora and Leptochloa spp. In follow-up studies using 1000 crawlers per plant, 10 live adult females were found on Leptochloa virgata, and one adult female on Spartina alterniflora, but average adult female abundance per plant was (2580%) 26-times lower on L. virgata and over (39,090%) 100-times lower on S. alterniflora than on A. donax. Field surveys were conducted at five locations in Spain and France at which A. donax infested with R. donacis, co-occurred with two non-target species of concern and R. donacis was only found on A. donax. Six-month field host exposures in Spain using potted Leptochloa plants entwined with heavily infested A. donax confirmed that R. donacis is specific to Arundo under field conditions. Based on our results, the scale R. donacis appears to be specific to the genus Arundo and is unlikely to harm native or cultivated plants in the Americas.     

Arid-adapted Mexican leafhopper, Barela parvisaccata (Hemiptera: Cicadellidae), unsuitable for biocontrol of Lantana camara (Verbenaceae) in South Africa

A host specificity study conducted in South Africa between 2000 and 2004 showed that the leafhopper, Barela parvisaccata Young, performed as well on some of the indigenous Lippia spp. as on the target weed Lantana camara L. During adult no-choice tests, B. parvisaccata reproduced on eight species of the two closely related genera, Lantana and Lippia. Although B. parvisaccata has a restricted host range, its reproductive performance on the indigenous Lippia scaberrima Sond. during the adult multiple-choice tests was unacceptably high. It was therefore concluded that B. parvisaccata was not sufficiently host-specific to be released against L. camarara in Africa.     

Physiological host range of two highly specialised mutualistic symbiotes: the fly Fergusonina turneri and its obligate nematode Fergusobia quinquenerviae,potential biocontrol agents of Melaleuca quinquenervia

In Australia, galls develop on Melaleuca quinquenervia (Cav.) S.T. Blake (Myrtaceae) as a result of the mutualistic association between the fly Fergusonina turneri Taylor (Diptera: Fergusoninidae) and its obligate nematode Fergusobia quinquenerviae Davies & Giblin-Davis (Tylenchida: Sphaerulariidae). The nematode induces gall formation, whereas the fly promotes gall maturation. Together they exploit M. quinquenervia buds and may inhibit stem elongation and flower formation. We delimited the physiological host range of this pair to determine their suitability as biological control agents of invasive M. quinquenervia populations in Florida, USA. Host use was assessed for eight species of Myrtaceae native to Florida, eight phylogenetically related ornamental species and oviposition alone on five non-myrtaceous species. Although oviposition was less specific, galls developed and matured only on M. quinquenervia. After establishment, galls are predicted to prevent flower and seed production, thereby reducing the regenerative potential of M. quinquenervia. This is the first example of an insect/nematode mutualism released as biological control agents of an invasive plant.     

Biology and host preference of the planthopper Taosa longula (Hemiptera: Dictyopharidae), a candidate for biocontrol of water hyacinth

Taosa longula Remes Lenicov (Hemiptera: Dictyopharidae) is a planthopper from the South American tropics that feeds on water hyacinth, Eichhornia crassipes (Mart.) Solms-Laubach (Pontederiaceae). The biology of T. longula was studied in the laboratory and field to evaluate it as a potential biological control agent for this widespread aquatic weed. The developmental time of nymphs was recorded at different temperatures (15, 19, 23, 25, 27 and 30 °C), and developmental threshold temperatures were obtained for the different instars. The host range was evaluated in terms of development and feeding preference. Development from instar I to adult was recorded in two no-choice trials, one with cut leaves of Pontederiaceae, and a second with growing whole plants. In the cut-leaf tests, adults were obtained from Pontederia cordata var. cordata, P. rotundifolia and water hyacinth. In the whole plant test, T. longula adults were obtained only from water hyacinth. Feeding preference was evaluated by means of a paired-choice test with 10 T. longula first instars on whole plants of P. c. cordata, P. rotundifolia and water hyacinth. The number of insects that fed on water hyacinth was significantly higher than on P. c. cordata and P. rotundifolia. Taosa longula showed a clear preference for water hyacinth and exhibited warm climate requirements, making it an attractive candidate for water hyacinth biological control in tropical and subtropical areas.