Target For Classical Biological Control Research Articles

​Management Options of Mikania micrantha: A Review

The world’s problematic perennial weed Mikania micrantha hampers in crop production and causes enormous losses due to its interference. Management of M. micrantha by mechanical and chemical methods has not met with any reasonable success. So, it has become a target for classical biological control. Numerous natural indigenous plant species, fungi and insects were tried as bio-control agents for effective control of M. micrantha. However, along with bio-control, appropriate mechanical, chemical and cultural methods are required to be integrated for controlling it. Thus, integrated management approaches for control of M. micrantha should be evolved against this invasive weed in long run.

Host Specificity and Preliminary Impact of Lepidapion argentatum (Coleoptera, Brentidae), a Biocontrol Candidate for French Broom (Genista monspessulana, Fabaceae).

Simple SummaryFrench broom is a leguminous shrub that is an internationally significant invasive alien weed in California and nearby US states that competes with native vegetation and increases the risk of wildfires. French broom originates from the Mediterranean region and is the target for classical biological control. Exploration for prospective biological control agents in the native region of Western Europe resulted in the collection of the weevil Lepidapion argentatum. We conducted preliminary field studies showing that this weevil can impact seed production in the native habitat. We also measured the specificity of this candidate biocontrol agent in laboratory conditions on 36 plant species growing in California and Australia. Our data showed that, in no-choice tests, seven species were directly negatively impacted by gall formation induced on plant stems by the weevil, but at different levels, including two lupine species commonly distributed in California. Further experiments are needed to ascertain the safety of this candidate biocontrol agent prior to release.French broom (Genista monspessulana) (Fabaceae) is a perennial species native to the Mediterranean basin. Introduced in the 19th century as an ornamental plant, it is currently invasive in California and Australia. The current research is focused on biocontrol with the use of the phytophagous weevil Lepidapion argentatum (Brentidae). Its capacity to develop both in the stem galls and pods of French broom makes it a promising candidate. The impact on the reproduction of French broom was studied in Southern France and revealed that it could effectively reduce the number of viable seeds by 18.8%, but also increased the number of aborted seeds by 10% within the attacked pods. To evaluate the specificity of L. argentatum, choice and no-choice tests were performed in 2012 and 2015 on a total of 36 non-target closely related species. Results revealed the presence of galls and larvae in the stems of seven species, including two endemic Californian lupines; i.e., Lupinus arboreus blue and Lupinus chamissonis. In the future, new tests will be conducted to determine if L. argentatum is able to complete its entire development lifecycle on the non-target species where galls have previously been observed.

Cross-correlation analysis of invasive mango mealybug and its associated natural enemies in relation to meteorological factors: implications for biological control

ABSTRACTDamage caused by invasive downey snow line mealybug, Rastrococcus iceryoides Green (Hemiptera: Pseudococcidae) has been reported to vary between 30% to complete crop loss where no control measure is applied. The current studies seek to determine factors influencing R. iceryoides population outbreaks, parasitoid – host and predator–prey relationships as well as predict optimal management strategies through weather modelling over a period of 28 months from 2008 to 2010 in Tanzania. The highest incidence of R. iceryoides was recorded during the dry season coinciding with the major mango fruiting season. The relationship between R. iceryoides and the parasitoid was positive but not significant, which implies the influence on outbreaks was negligible probably due to low percent parasitism (<12%). However, the predator abundance was directly and significantly related to that of R. iceryoides. Average temperature, average relative humidity, rainfall, and R. iceryoides abundance were autocorrelated to each other. Cross-correlation coefficients vary significantly from −0.286 to 0.589 for the pair-variable between R. iceryoides, temperature, relative humidity, rainfall, parasitism and predators. Our findings showed that temperature was the key climatic variable that significantly influenced R. iceryoides outbreaks while rainfall was significantly negatively associated with the pest. Time series analyses show R. iceryoides population increased 4 months after an increase in average temperature in all the sites, 11 months after rainfall and 11 months after relative humidity in Kibaha and Dar es Salaam, respectively. Our findings revealed that R. iceryoides is an excellent target for classical biological control. Thus, the importation of promising co-evolved parasitoid specific to R. iceryoides from the aboriginal home is crucial in formulating an efficient and sustainable management approaches against the invasive mealybug pest in mango agro-ecosystems.

Life cycle and host range ofPhycitasp. rejected for biological control of prickly acacia in Australia

Prickly acacia (Vachellia nilotica subsp. indica), a native of the Indian subcontinent, is a serious weed of the grazing areas of northern Australia and is a target for classical biological control. Native range surveys in India identified a leaf webber, Phycita sp. (Lepidoptera: Pyralidae) as a prospective biological control agent for prickly acacia. In this study, we report the life cycle and host-specificity test results Phycita sp. and highlight the contradictory results between the no-choice tests in India and Australia and the field host range in India. In no-choice tests in India and Australia, Phycita sp. completed development on two of 11 and 16 of 27 non-target test plant species, respectively. Although Phycita sp. fed and completed development on two non-target test plant species (Vachellia planifrons and V. leucophloea) in no-choice tests in India, there was no evidence of the insect on the two non-target test plant species in the field. Our contention is that oviposition behaviour could be the key mechanism in host selection of Phycita sp., resulting in its incidence only on prickly acacia in India. This is supported by paired oviposition choice tests involving three test plant species (Acacia baileyana, A. mearnsii and A. deanei) in quarantine in Australia, where eggs were laid only on prickly acacia. However, in paired oviposition choice trials, only few eggs were laid, making the results unreliable. Although oviposition choice tests suggest that prickly acacia is the most preferred and natural host, difficulties in conducting choice oviposition tests with fully grown trees under quarantine conditions in Australia and the logistic difficulties of conducting open-field tests with fully grown native Australian plants in India have led to rejection of Phycita sp. as a potential biological control agent for prickly acacia in Australia.

Phenology and dispersal of Larinus minutus Gyllenhal and Larinus obtusus Gyllenhal (Coleoptera: Curculionidae), two biological control agents of Centaurea stoebe ssp. micranthos (spotted knapweed) in Michigan

Centaurea stoebe L. ssp. micranthos (Gugler) (spotted knapweed) is an invasive plant that has been the target of classical biological control in North America for more than four decades. The seedhead-feeding weevils Larinus minutus Gyllenhal and Larinus obtusus Gyllenhal (Coleoptera: Curculionidae) are two of the most-widely released C. stoebe control agents, and have more recently been introduced into the eastern US. While there have been many studies focusing on their ability to impact C. stoebe in the western US and Canada, there have been few studies from eastern North America, and basic knowledge of important aspects of their biology is lacking. Here we report on the phenology and dispersal of L. minutus and L. obtusus in Michigan. We regularly sampled two established Larinus spp. populations in southern Michigan in 2012 and 2013, and found that while adult abundance fluctuates during the growing season, they remained at easily detectable levels from mid-June through the end of August. We also used previously established populations of L. minutus and L. obtusus released in 1996 (n=1), 2007 (n=2), and 2010 (n=5) to determine how dispersal of Larinus spp. into the surrounding landscape changes with time since release. Populations of Larinus spp. weevils showed little dispersal for 2years post-release. However, after initial establishment dispersal rates increased rapidly, resulting in average dispersal rates that increased exponentially with time since release. These findings can inform future biological control release and sampling programs for Larinus spp. in eastern North America.

Efficacy and host specificity compared between two populations of the psyllid Aphalara itadori, candidates for biological control of invasive knotweeds in North America

Invasive knotweeds are large perennial herbs in the Polygonaceae in the genus Fallopia that are native to Asia and invasive in North America. They include Fallopia japonica (Japanese knotweed), F. sachalinensis (giant knotweed), and a hybrid species F. x bohemica (Bohemian knotweed). Widespread throughout the continent and difficult to control by mechanical or chemical methods, these plants are good targets for classical biological control. We examined the suitability of two populations of the psyllid Aphalara itadori from Japan as biological control agents by comparing their impact on the target weeds and assessing their fundamental host ranges. Both populations were capable of halting knotweed plant growth and reducing both above and below ground biomass by more than 50% in just 50days. Moreover, the psyllids caused mortality of several of the plants during this period. The two populations differed markedly in their reproductive potential on the different knotweed species. The Kyushu psyllid performed best on F. japonica and F. bohemica and the Hokkaido psyllid performed best on F. sachalinensis. Both were found to be specialized to knotweeds, with only very low occurrence of development on a small number of related non-target plant species. For the few non-target plant species that supported development, choice tests and multi-generational tests were used to further evaluate the likelihood of non-target host use. We conclude that A. itadori would be both effective and low risk as a biological control agent for invasive knotweeds and that both the Kyushu and Hokkaido populations may be needed to effectively control the entire knotweed species complex.

Laboratory and field experimental evaluation of host plant specificity of Aceria solstitialis, a prospective biological control agent of yellow starthistle

Centaurea solstitialis (yellow starthistle, Asteraceae) is an invasive annual weed in the western USA that is native to the Mediterranean Region and is a target for classical biological control. Aceria solstitialis is an eriophyid mite that has been found exclusively in association with Ce. solstitialis in Italy, Greece, Turkey and Bulgaria. The mite feeds on leaf tissue and damages bolting plants, causing stunting, witch's broom and incomplete flower development. Field experiments and laboratory no-choice and two-way choice experiments were conducted to assess host plant specificity of the mite in Bulgaria. Mites showed the highest degree of host specificity in the field and lowest in the no-choice experiments. In the field, highest densities of mites occurred on Ce. solstitialis and Ce. cyanus (bachelor's button), and either no mites or trace numbers occurred on the other test plants: Ce. diffusa (diffuse knapweed), Carthamus tinctorius (safflower) and Cynara scolymus (artichoke). In no-choice experiments, mites persisted for 60 days on Ce. diffusa, Ce. cyanus, Ce. solstitialis, Ca. tinctorius and Cy. scolymus, whereas in two-way choice experiments mites persisted on 25% of Cy. scolymus plants for 60 days and did not persist on Ca. tinctorius beyond 40 days. The eight other species of plants that were tested in the laboratory were less suitable for the mite. These results suggest that although A. solstitialis can persist on some nontarget plants for as long as 60 days in the laboratory, it appears to be much more specific under natural conditions, and warrants further evaluation as a prospective biological control agent.

Comparative life tables of leek moth,Acrolepiopsis assectella(Zeller) (Lepidoptera: Acrolepiidae), in its native range

Leek moth, Acrolepiopsis assectella (Zeller) (Lepidoptera: Acrolepiidae), is an invasive alien species in eastern Canada, the larvae of which mine the green tissues of Allium spp. This study was designed to construct and analyse life tables for leek moth within its native range. Stage-specific mortality rates were estimated for the third leek moth generation at three sites in Switzerland from 2004 to 2006 to identify some of the principle factors that inhibit leek moth population growth in areas of low pest density. The contribution of natural enemies to leek moth mortality was measured by comparing mortality on caged and uncaged leeks. Total pre-imaginal mortality on uncaged plants was 99.6%, 99.1% and 96.4% in 2004, 2005 and 2006, respectively. Variation in mortality was greater among years than among sites. Total larval mortality was greater than that in the eggs and pupae. This was due largely to the high mortality (up to 83.3%) of neonates during the brief period between egg hatch and establishment of the feeding mine. Leek moth pupal mortality was significantly greater on uncaged than on caged leeks, indicating an impact by natural enemies, and this pattern was consistent over all three years of study. In contrast, the other life stages did not show consistently higher mortality rates on uncaged plants. This observation suggests that the pupal stage may be particularly vulnerable to natural enemies and, therefore, may be the best target for classical biological control in Canada.

In Situ Volatile Collection, Analysis, and Comparison of Three Centaurea Species and Their Relationship to Biocontrol with Herbivorous Insects

Centaurea solstitialis, commonly known as yellow starthistle, is an invasive plant listed as a noxious weed in the western areas of North America and is the target of classical biological control, which involves release of herbivores known to be specific to this plant. These insects often choose their host plant on the basis of the volatile organic compounds (VOCs) emitted. Accordingly, volatile analysis of host plants can provide insight into VOCs that may attract and/or repel the insect. To this end, solid-phase microextraction (SPME) and a customized collection bag were utilized to perform in situ volatile collection on intact and mechanically damaged leaves of Centaurea solstitialis, Centaurea cyanus, and Centaurea cineraria. Volatile identification was performed by GC-MS, and the VOC differences were determined. The plants C. solstitialis and C. cyanus have been reported to attract the weevil, Ceratapion basicorne, a candidate for biological control, whereas C. cineraria does not attract the weevil. Major VOCs unique to C. cineraria include the sesquiterpenes cyclosativene, alpha-ylangene, and trans-alpha-bergamotene. The compound trans-beta-farnesene was unique to C. solstitialis and C. cyanus.

The leaf‐tying moth Hypocosmia pyrochroma (Lep., Pyralidae), a host‐specific biological control agent for cat's claw creeper Macfadyena unguis‐cati (Bignoniaceae) in Australia

Abstract: Cat's claw creeper, Macfadyena unguis‐cati, a major environmental weed in coastal and sub‐coastal areas of Queensland and New South Wales, Australia is a target for classical biological control. Host specificity of Hypocosmia pyrochroma Jones (Lep., Pyralidae), as a potential biological control agent was evaluated on the basis of no‐choice and choice larval feeding and survival, and adult oviposition preference tests, involving 38 plant species in 10 families. In no‐choice tests, larval feeding and development occurred only on cat's claw creeper. In choice tests, oviposition and larval development was evident only on cat's claw creeper. The results support the host‐specificity tests conducted in South Africa, and suggest that H. pyrochroma is a highly specific biological control agent that does not pose any risk to non‐target plants tested in Australia. This agent has been approved for field release by relevant regulatory authorities in Australia.

The potential for biological control of invasive alien aquatic weeds in Europe: a review

A retrospective analysis shows that invasive, alien, free-floating and emergent aquatic weeds in Europe are good targets for classical biological control, and that genus-specific chrysomelid and curculionid beetles offer the most potential. Ludwigia spp., Azolla filiculoides, Lemna minuta, Crassula helmsii and Hydrocotyle ranunculoides should be prioritised as targets. Fungal pathogens have been under-utilised as classical agents but, whilst they may have some potential against free-floating weeds, they appear to be poor candidates against submerged species, although the suitability of arthropod agents against these difficult targets still merits investigation. The use of indigenous pathogens as inundative agents (mycoherbicides) shows some promise.

Factors Affecting Infection of Yellow Starthistle (Centaurea solstitialis) by Synchytrium solstitiale, Causal Agent of False Rust Disease.

Yellow starthistle (Centaurea solstitialis) is an annual invasive weed in the United States with Mediterranean origins. The expense of chemical control and the vast area of invasion make this weed an appropriate target for classical biological control. Observations of a field site in southern France revealed small orange galls on the leaves of yellow starthistle seedlings caused by the fungus Synchytrium solstitiale. Inoculation of yellow starthistle seedlings with a suspension of zoospores released from infected tissue resulted in infection. Ten days after inoculation, typical orange galls appeared on the exposed tissue. Preliminary host range testing showed up to 100% infection of C. solstitialis seedlings from both France and the United States and infection of Carthamus tinctorius, Centaurea americana, C. diffusa, C. rothrockii, C. squarrosa, and Helianthus annuus seedlings. No symptoms were observed on seedlings of Centaurea calcitrapa, C. maculosa, C. sulfurea, Cirsium californica, C. occidentale, Cynera cardunculus, and Taraxacum officinale. Zoospores were released in a pH range between 4.45 and 8.25 and optimally at temperatures between 5 and 15°C. Infection of yellow starthistle seedlings occurred after a minimum 1-h exposure to a zoospore suspension at 20°C.

Top 20 environmental weeds for classical biological control in Europe: a review of opportunities, regulations and other barriers to adoption

SummaryClassical biological control remains the only tool available for permanent ecological and economic management of invasive alien species that flourish through absence of their co‐evolved natural enemies. As such, this approach is recognized as a key tool for alien species management by the Convention on Biological Diversity (CBD), the European and Mediterranean Plant Protection Organization (EPPO) and the European Strategy on Invasive Alien Species (ESIAS). Successful classical biological control programmes abound around the world, despite disproportionate attention being given to occasional and predictable non‐target impacts. Despite more than 130 case histories in Europe against insect pests, no exotic classical biological control agent has been released in the EU against an alien invasive weed. This dearth has occurred in the face of increasing numbers of exotic invasive plants being imported and taking over National Parks, forests and amenity areas in this region, as well as a global increase in the use of classical biological control around the world. This paper reviews potential European weed targets for classical biological control from ecological and socioeconomic perspectives using the criteria of historical biological control success, taxonomic isolation from European native flora, likely availability of biological control agents, invasiveness outside Europe and value to primary industry and horticulture (potential for conflicts of interest). We also review why classical biological control of European exotic plants remains untested, considering problems of funding and public perception. Finally, we consider the regulatory framework that surrounds such biological control activities within constituent countries of the EU to suggest how this approach may be adopted in the future for managing invasive exotic weeds in Europe.

Prospects for the biological control of the groundnut leaf miner, Aproaerema modicella , in Africa.

Abstract The groundnut leaf miner, Aproaerema modicella , is a pest of groundnut and soyabean in South and Southeast Asia that has recently invaded Africa. It was first found in Uganda in 1998 and is now recorded in Mozambique, Malawi, Democratic Republic of Congo and South Africa. In all African countries where A. modicella has been found, the pest has reached outbreak densities and severe yield losses have been observed on groundnut. In this paper, we review the natural enemies of A. modicella in Asia and evaluate their potential for biological control in Africa. The main natural enemies of A. modicella in Asia are parasitoids. Over 30 primary parasitoid species have been recorded with mean parasitism rates fluctuating between 20% and 50% and peak parasitism reaching 53-91%. The most often cited parasitoids belong to the genera Goniozus (Hym.: Bethylidae), Apanteles , Bracon , Chelonus and Avga (Hym.: Braconidae), Brachymeria (Hym.: Chalcididae), and Stenomesius , Sympiesis and Tetrastichus (Hym.: Eulophidae). Predators and pathogens have been poorly studied. A. modicella is a promising target for classical biological control using natural enemies from Asia. Damage levels are, on average, higher in Africa than in Asia, where parasitoids, and possibly predators and pathogens, probably play an important role in the natural control of the pest. However, surveys are needed in Asia to better study natural enemies of A. modicella before selecting the most suitable agents. Until now, most studies on natural enemies were carried out in India, where A. modicella is considered a serious pest. New surveys should focus on other regions, where the moth causes little damage and very little is known on its natural enemy complex.

Mouth Parts and Alimentary Canal of Opsius stactogalus Fieber (Homoptera: Cicadellidae)

Opsius stactogalus Fieber (Homoptera: Cicadellidae) is a small (0.81^.5 mm long) leafhopper native to Europe (Harding, 1930) in the subfamily Deltocephalinae (Arnett, 1993). It is abundant in western North America on the introduced, halophytic, shrubby tree tamarisk, Tamarix spp. (Tamaricaceae) (Harding, 1930; Hopkins and Carruth, 1954; Liesner, 1971; Wiesenbom, 2003). Most tamarisks naturalized in the United States are hybrids between the Eurasian Tamarix ramosissima Ledebour and Tamarix chinensis Loureiro (Gaskin and Schaal, 2002). Tamarisk's invasiveness, water uptake, and low diversity of dependent wildlife (Brock, 1994; Di Tomaso, 1998) have made it the target of classical biological control (Fornasari, 1997; Sobhian et al, 1998). Feeding by O. stactogalus can reduce tamarisk growth. Stem growth was reduced on caged Tamarix plants exposed to increased O. stactogalus densities (Liesner, 1971). Effects on tamarisk growth likely depend on the plant tissues or fluids O. stactogalus consumes. Species of Cicadellidae feed on mesophyll, phloem, or xylem preferentially or in combination (Backus, 1985). Several species of Deltocephalinae feed primarily on phloem (Backus and McLean, 1983). I examined the mouth parts and alimentary canal of O. stactogalus to better understand how the insect feeds and its effects on tamarisk. Opsius stactogalus adult females were collected from T. ramosissima trees at Boulder City, Clark County, Nevada (site description in Wiesenbom, 2003), and chilled for 10 min at ?18?C. To examine and photograph mouth parts, leafhopper heads were excised, digested 1 h in 10% NaOH heated to 100?C, dehydrated in ethanol, and mounted in euparal posterior-aspect upward on microscope slides. I used an ocular reticle to determine photomicrograph scale and measure (?0.01 mm) the length of the longest maxillary and mandibular stylet from their convergence at the tip of the hypopharynx on each specimen. Alimentary canals were dissected from leafhoppers in physiological saline, transferred with a pipette onto microscope slides, and photographed in dark field illumination.

Use of digital images to differentiate reactions of collections of yellow starthistle (Centaurea solstitialis) to infection by Puccinia jaceae

Yellow starthistle (YST) (Centaurea solstitialis) is an invasive weed in the USA and a target of classical biological control. However, the precise geographical origin(s) of YST in the USA is not known. This study was conducted to learn whether the origin(s) of YST in California, USA could be determined on the basis of digital image analysis (DIA) of YST reactions to isolates of the rust Puccinia jaceae. One trial was conducted with two isolates of P. jaceae and another trial with only one of these isolates. Six different YST collections were tested. The DIA consistently detected and measured rust pustules on YST leaves. Compared to visual assessment, DIA was a fair predictor of the number of rust pustules per leaf. There were no differences between isolates of P. jaceae in reactions of different YST collections in the first trial. Differences in plant reactions between trials were predominately due to more disease incidence and severity in the second trial, which was probably from the greater amount of inoculum. Based on analyses of variance and canonical discriminative analyses, YST from California appeared most closely related to the YST collection from Erzurum, Turkey. In examination of squared Mahalanobis distances, all collections, except the collection from Turkey, were significantly distant from the California collection in both trials. More studies are necessary to determine the precise area(s) of origin (within Turkey and neighboring countries) of YST in the USA. Digital image analysis of rust reactions can be a powerful tool to do this.

PROSPECTS FOR THE CLASSICAL BIOLOGICAL CONTROL OF MAJOR INSECT PESTS AND WEEDS IN SOUTHERN CHINA

Abstract This paper deals with the prospects for the classical biological control of major insect pests and weeds in southern China. One hundred and seventy‐four species of insect pests in southern China are nominated and their broad distribution and origin or possibly origin in other countries are discussed. An attempt is made to draw together information relevant to where a search might be made for natural enemies if an arthropod pest is being considered as the target for classical biological control. The success of classical biological control of the six insect pests and five weeds elsewhere in the world has been indicated. It is recommended to take urgent measures to strengthen and expand projects in classical biological control in China.

Biological Control of Alfalfa Weevil in North America

Alfalfa weevil, Hypera postica (Gyllenhall) (Coleoptera: Curculionidae), is of Eurasian origin. This destructive pest of alfalfa (lucerne) was accidentally established in North America on three separate occasions. These introductions are commonly identified in the literature as biological strains: western alfalfa weevil, Egyptian alfalfa weevil (=Hypera brunneipennis Boheman), and eastern alfalfa weevil. Alfalfa weevil has been the target of classical biological control almost since its discovery in North America more than 90 years ago. These efforts have resulted in establishment of at least nine exotic parasitoids and egg predators: Bathyplectes curculionis (Thomson), B. anurus (Thomson) and B. stenostigma (Thomson) (Hymenoptera: Ichneumonidae); Microctonus aethiopoides Loan and M. colesi Drea (Hymenoptera: Braconidae), the latter of undetermined origin; Oomyzus incertus (Ratzenberg) (Hymenoptera: Eulophidae); Dibrachoides dynastes (Forester) and Peridesmia discus (Walker) (Hymenoptera: Pteromalidae); and Anaphes luna (Girault) (Hymenoptera: Mymaridae). A fungal pathogen, Zoophthora phytonomi Arthur (Phycomycetes: Entomophthoraceae), of undetermined origin, is becoming an increasingly important alfalfa weevil mortality factor. Most major USA alfalfa production areas now benefit from a complex of alfalfa weevil biological control agents. Collectively, these agents have effected substantial reduction in the economic importance of alfalfa weevil across the northern USA However, biological agents provide only partial control of alfalfa weevil, and importance of their contribution differs considerably with production area. Still, the benefits achieved, especially from reduced need for insecticides in alfalfa production, mark this as one of the great success stories of classical biological control in North America.

Distribution, life history and host specificity of Chrysolina picturata and Chrysolina sp. B (Coleoptera: Chrysomelidae), two biological control agents for Chrysanthemoides monilifera (Compositae)

AbstractThe southern African shrubs Chrysanthemoides monilifera monilifera and C. m. rotundata (Compositae) are serious weeds of native vegetation in Australia and are targets for classical biological control. In host specificity tests using 69 species from 25 families, two leaf-feeding chrysomelid beetles, Chrysolina picturata (Clark) and Chrysolina sp. B, were able to complete development on only Chrysanthemoides monilifera and C. incana. The subspecies Chrysanthemoides m. monilifera was the superior host for both Chrysolina picturata and Chrysolina sp. B. Feeding and limited development of both species occurred on Calendula officinalis; limited development by Chrysolina picturata larvae occurred on Helianthus annuus, Tussilago farfara and Cymbonotus priessianus. Chrysolina picturata and Chrysolina sp. B are considered to be Chrysanthemoides-specific and have been approved for release in Australia. Potential release sites for both Chrysolina species were chosen by comparing the climate of the insects' African distribution with climate stations within the range of Chrysanthemoides monilifera in Australia. Chrysolina picturata and Chrysolina sp. B are suited for release within the western distribution of Chrysanthemoides m. monilifera in coastal areas of south eastern South Australia.

Biological Control of Obscure Scale (Homoptera: Diaspididae) in California: An Experimental Approach

Obscure scale, Melanaspis obscura (Comstock), is native to the eastern half of the United States where it is associated with hosts in the genera Quercus, Carya, and Castanea. In its native home, the scale is exploited by a complex of natural enemies, including predators, parasites, and pathogens. Although obscure scale is generally maintained at low levels in natural habitats (presumably by natural enemies), it is a major pest of pin oak in urban areas and a minor pest of pecan. In 1962, an infestation of obscure scale was detected on oaks in Capitol Park in Sacramento, CA; efforts to eradicate the infestation were not successful, and this population became a target for classical biological control in 1981. Because the infestation was restricted and spread slowly, there was sufficient time for preintroductory investigations. Exploration for candidate natural enemies for importation into California was directed at parasites associated with obscure scale on pecan in southern Texas. Eleven species in 8 genera were recovered; the major species were Ablerus clisiocampae (Ashmead), Coccophagoides fuscipennis (Girault), Encarsia aurantii (Howard), and Physcus varicornis (Howard). Instead of releasing all of the major primary parasites (empirical approach), a more experimental approach was employed--that is, single-species release of E. aurantii. This species was chosen because of its thelyotokous reproduction, high egg load at emergence (highest among major primary parasites), and abundance in the native home of obscure scale. Over 11,000 females were released in 1988 and establishment was confirmed in 1990. From 1992-1994, the parasite population increased steadily while the abundance of scale crawlers declined by 3-fold; the crawler-to-parasite ratio declined from approximately 25 to approximately 7. Through selective pruning, parasitization by E. aurantii, and timing of insecticide treatments, obscure scale is now under integrated pest management (IPM) in Capitol Park, and it may eventually come under complete biological control. This project illustrates how preintroductory investigations both in the native home of the target pest and under quarantine conditions can be used to derive an introduction strategy in classical biological control. Some additional aspects of introduction strategy are discussed.