Common St. Johnswort is widespread in eastern Canada but it seldom constitutes a serious weed problem. A demographic study conducted in 1993 and 1994 at four typical undisturbed sites indicated that 36 to 96% of established St. Johnswort shoots died during the growing season. Mortality was always associated with infection by a host-specific Colletotrichum gloeosporioides. The leaf-feeding beetle Chrysolina hyperici occurred at all sites and caused maximum midsummer defoliation of 27% in 1993 and 51% in 1994. Healthy plants readily recovered from defoliation during pupation of the fourth instar of the insect in June and following adult estivation in August. Although widespread, C. hyperici populations appear transient and alone do not cause sustained feeding pressure resulting in weed control. When Chrysolina larvae and adults were collected at six field sites and placed on healthy seedlings under controlled conditions, up to 36% of the plants became infected with C. gloeosporioides. Scanning electron micrographs commonly showed Colletotrichum conidia among the setae on legs, tarsal pads, and antennae of adults and larvae. In a series of three experiments conducted under controlled conditions in which Chrysolina larvae and adults were placed on healthy plants after feeding on diseased ones, the incidence of infection ranged from 63 to 100%. Hence, under favorable conditions Chrysolina adults may selectively transmit the pathogen in the field. This study demonstrated the potential of enhancing biological control of weeds by insects with the integration of an effective, host-specific pathogen.

The suitability of a target weed for classical biological control should be considered early in the process of plant invasion. Concerns have been raised about the recent arrival of Mikania micrantha Kunth in south Florida and its potential to spread and invade natural and managed ecosystems. This weed is native to the neotropics, and has been introduced into many Asian countries and, more recently, into Australia. In Asia, M. micrantha is particularly problematic in plantation crops, but also threatens natural areas and disturbed ecosystems. Several aspects of the biology and ecology of M. micrantha are discussed in this review to evaluate its suitability as a target of biological control in Florida. Based on an ecological niche model, the climate in southern and central Florida is highly favorable for the invasion of this weed. Previous biological control programs provide valuable information for Florida scientists about the availability of natural enemies and potential areas for future foreign surveys. Genetic comparison of the Florida population and native range populations, in addition to climate matching, should be considered when selecting areas for foreign exploration. Finally, the authors used a scoring system and risk-benefit–cost analysis to evaluate M. micrantha as a potential target for biological control in Florida. We suggest that similar feasibility evaluations should be conducted not only for well-established problematic weeds but also for new invaders with a known history of invasiveness.

We studied the response of naturalized kudzu plants to simulated herbivory at three locations: Delaware (DE), Pennsylvania (PA), and North Carolina (NC). At the DE and PA sites, plant mortality after the first yr was 14 and 50%, respectively, and was highest for plants that had a small starting root crown size. At both sites, 50 and 75% leaf and shoot clipping, and drilling one or two large holes from the root crown into roots, had no effect on aboveground biomass. In NC, all plants survived for 3 yr. Plants subject to 50% vine removal at this site showed significant decrease in aboveground biomass compared to the control, but 50% leaf cutting and root drilling had no effect. In the greenhouse, kudzu seedlings grown in 60 and 100% light compensated for 50% leaf removal, but 75% damage reduced aboveground biomass. Plants survived for 1 to 2 mo in 0% direct light, but only one of 53 plants survived to the end of the experiment. Results suggest that established kudzu plants are able to compensate for biomass removal, seedlings can survive for several weeks without light, and that effective biocontrol might require more than 2 to 3 yr of continuous damage.

Classical biological control is a key method for managing populations of pests in long-lived crops such as plantation forestry. The execution of biological control programmes in general, as the evaluation of potential natural enemies remains, to a large extent, an empirical endeavour. Thus, characterizing specific cases to determine patterns that may lead to more accurate predictions of success is an important goal of the much applied ecological research. We review the history of introduction, ecology and behaviour of the parasitoid Ibalia leucospoides. The species is a natural enemy of Sirex noctilio, one of the most important pests of pine afforestation worldwide. We use an invasion ecology perspective given the analogy between the main stages involved in classical biological control and the biological invasion processes. We conclude that success in the establishment, a common reason of failure in biocontrol, is not a limiting factor of success by I. leucospoides. A mismatch between the spread capacity of the parasitoid and that of its host could nevertheless affect control at a regional scale. In addition, we suggest that given its known life history traits, this natural enemy may be a better regulator than suppressor of the host population. Moreover, spatial and temporal refuges of the host population that may favour the local persistence of the interaction probably reduce the degree to which S. noctilio population is suppressed by the parasitoid. We emphasize the fact that some of the biological attributes that promote establishment may negatively affect suppression levels achieved. Studies on established non-native pest–parasitoid interactions may contribute to defining selection criteria for classical biological control which may prove especially useful in integrated pest management IPM programmes of invasive forest insects.

Diadromus pulchellus Wesmael (Hymenoptera: Ichneumonidae) is a pupal parasitoid under consideration for introduction into Canada for the control of the invasive leek moth, Acrolepiopsis assectella (Zeller) (Lepidoptera: Acrolepiidae). Since study of the parasitoid outside of quarantine was not permitted in Canada at the time of this project, we assessed its efficacy via field trials in its native range in central Europe. This was done by simulating introductory releases that would eventually take place in Canada when a permit for release is obtained. In 2007 and 2008, experimental leek plots were artificially infested with pest larvae to mimic the higher pest densities common in Canada. Based on a preliminary experiment showing that leek moth pupae were suitable for parasitism up to 5–6 days after pupation, D. pulchellus adults were mass-released into the field plots when the first host cocoons were observed. The laboratory-reared agents reproduced successfully in all trials and radically reduced leek moth survival. Taking into account background parasitism caused by naturally occurring D. pulchellus, the released agents parasitized at least 15.8%, 43.9%, 48.1% and 58.8% of the available hosts in the four release trials. When this significant contribution to leek moth mortality is added to previously published life tables, in which pupal parasitism was absent, the total pupal mortality increases from 60.1% to 76.7%. This study demonstrates how field trials involving environmental manipulation in an agent's native range can yield predictions of the agent's field efficacy once introduced into a novel area.

The release of classical biological control agents has reduced the economic, environmental and social problems caused by water hyacinth, Eichhornia crassipes; however, additional control measures are needed in some locations. Water hyacinth plants were treated with different densities of eggs of the weevil Neochetina eichhorniae Warner, one of the main control agents, under different nutrient regimes in a controlled experiment. Plants were destructively sampled and the development of N. eichhorniae was assessed. The survival of first and second instars declined as larval density increased. Plant nutrient status did not directly affect the mortality rate of larvae, but at higher nutrient concentrations larvae developed faster and were larger at a given developmental stage. It is argued that the density dependence operating in N. eichhorniae occurs through an interaction between young larvae and leaf longevity. Consequently, events which disrupt water hyacinth leaf dynamics, e.g. frost or foliar herbicides, will have a disproportionately large effect on the control agents and may reduce the level of control of the host.

Surveys of the cereal stemborers and their natural enemies in Zambia were initiated in 1997. The surveys verified the presence of three stemborer species on maize, sorghum and pearl millet. These were the maize stalk borer, Busseola fusca Fuller (Lepidoptera: Noctuidae), the spotted stemborer, Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) and the African pink borer, Sesamia calamistis Hampson (Lepidoptera: Noctuidae). Occasionally, the sugarcane borer, Eldana saccharina Walker (Lepidoptera: Pyralidae) was also recovered especially around areas near the sugarcane plantation at Mazabuka, Southern province. Chilo partellus was the predominant stemborer in region I (areas with less than 600 mm of rainfall per annum). Three ‘hot spot’ areas, namely Luangwa, Buleya Malima and Kalobolelwa, were identified based on the abundance of Ch. partellus. The exotic parasitoid, Cotesia flavipes Cameron (Hymenoptera: Braconidae) was released in the three areas for the control of Ch. partellus. However, post-release surveys in these areas have not revealed any recoveries of Co. flavipes. Three indigenous natural enemies, namely Cotesia sp., Dentichasmias sp. and Dolichogenidea sp. emerged from the field-collected larvae.

This paper addresses the competitive interaction between Cotesia sesamiae, a gregarious larval endoparasitoid that is native to Africa, and Cotesia flavipes, an introduced parasitoid from southern Pakistan which has recently been established in East Africa for biological control of the exotic stemborer, Chilo partellus. The two parasitoids are morphologically similar, and they both attack medium-sized to large larval stages of gramineous lepidopteran stemborers. Based on previous work which suggested that Cotesia flavipes was competitively superior to Co. sesamiae, we speculated that Co. sesamiae may be locally extirpated in some areas of Africa. However, evidence from the field does not support this prediction. Recent field surveys in areas where both parasitoids occur, revealed that Co. sesamiae was still present, and densities were not declining. The interaction of the two parasitoids, as well as the influence of this interaction on host regulation, are discussed.

The various pests of the cassava plant, Manihot esculenta Crantz, were reviewed with particular reference to the two exotic pests viz: cassava mealybug,Phenacoccus manihoti, Mat-Ferr, and cassava green mite, Mononychellus tanajoa Bondar which were accidentally introduced into Africa without their natural enemies in the early seventies.

Classical biological control programme for these two pests initiated and championed by the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria was also reviewed and both successes and limitations of the programme highlighted. Suggestions on how to improve the efficiency of the programme are made.

Organic producers have traditionally understood the value of conserving the natural enemies of the pests of the crops they grow. An equal appreciation of the value of importing new species of natural enemies is also needed. Given this understanding, the interests of organic farmers could then be promoted by efforts to stimulate greater activity by government agencies in charge of such importations. Furthermore, the focus of such importations could be altered to target more precisely pests of crops most commonly grown by organic producers. This would benefit organic farmers by permanently solving or greatly reducing the intensity of problems from many introduced crop pests. The potential benefit of a coordinated federal and state program of classical biological control could be very large for organic farmers. There is an increasing interest nationwide in expanding the use of classical biological controls. Organic producers now have the opportunity to add their influence to this trend to reshape the country's pest control agenda away from chemicals and toward biological controls and to focus this at least in part on those pests of greatest concern to organic producers. To do so, however, organic producers will have to learn a new lesson, i.e., the difference between native and imported pests and the value of importation as a means to control the latter.

A programme to control the cassava green mite (CGM), Mononychellus tanajoa, using classical biological control was initiated in 1983 as part of the Africa-wide Biological Control Programme (ABCP). Basic studies on the field ecology and biotic potential of CGM, and surveys of CGM and associated indigenous natural enemies found on cassava throughout Africa are being used to develop ecologically sound release and follow-up strategies. Applied work includes colony maintenance of exotic phytoseiids, development of methodologies for mass producing, transporting and releasing natural enemies, plus experimental releases and post-release surveys. Important parts of the work are being done in collaboration with several institutes and agencies, including foreign exploration and preliminary screening of exotic natural enemies, international quarantine services, regional release and follow-up surveys, taxonomy of CGM and phytoseiids, simulation modelling of CGM in the cassava ecosystem, artificial diets for transporting CGM natural enemies, survey of entomopathogens of CGM and predatory behaviour studies of exotic phytoseiids.

Over 130 species of insects were found in association with the cassava mealybug (CM), Phenacoccus manihoti, and its newly introduced parasitoid Epidinocarsis lopezi in Africa. As the CM in SW Nigeria declined under the influence of E. lopezi, this introduced wasp maintained densities of 2.8–3 per CM-infested tip early in the dry season and 1.3–1.6 per infested tip late in the dry season, but declined overall from 1.3 to 0.2 per randomly collected tip within 1 year. The decline of CM led to a sharp reduction in numbers of indigenous coccinellids, particularly of Hyperaspis spp. and to a lesser extent of Exochomus sp., due to competition with E. lopezi for the common food source. Numerous species of other polyphagous predators and parasitoids of coccinellids were found in low numbers. Indigenous primary parasitoids, Anagyrus spp., were rare, but their 10 spp. of hyperparasitoids were often reared from E. lopezi, with Prochiloneurus spp. and Chartocerus spp. being the most common. Hyperparasitism declined from 41.3% in March 1983 to 16.9% in Dec 1984 and proved to be positively density-dependent. The effects of hyperparasitoids on this biological control programme are discussed.