Eucalyptus Snout Beetle Research Articles

The Eucalyptus snout beetle in Colombia: Selection and evaluation of entomopathogenic fungi as bioinsecticides against Gonipterus platensis

The Eucalyptus snout beetles, which belong to the Gonipterus scutellatus species complex, cause heavy damage to Eucalyptus spp. worldwide. The species was reported in Antioquia, Colombia for the first time in 2016, threatening more than 115,000 ha of planted Eucalyptus spp. Elsewhere, its damage has been controlled using Anaphes spp. as classical biological control, but Anaphes spp. are not available in Colombia, where there are no documented control methods for this species to date. We identified the Gonipterus species using molecular methods and isolated entomopathogenic fungi from naturally infected beetles collected from the current distribution area in Colombia. We characterised the fungal isolates, selecting the best to develop a biological control agent. We considered insecticidal activity, UV-B radiation tolerance, yield, germination, and enzyme activity of conidia in making our selection. We confirmed the presence of G. platensis in Colombia, with adults naturally infected by Beauveria spp. and Metarhizium spp. From the isolated native fungi, M. brunneum (CA-3), M. robertsii (RI-1), B. bassiana (CA-1) and (CA-2), B. pseudobassiana (SP-1) were identified. We found remarkable differences in response to different variables between the selected isolates and SP-1 and CA-3 were the most virulent. The SP-1 isolate stood out from the rest for being the most tolerant to UV-B radiation, alkaline media, and low temperatures, germinating faster and producing elevated levels of lipases, chitinases, and proteases. The identified promising native fungus isolate, naturally occurring on field individuals, could be used to develop a biopesticide for controlling G. platensis in Eucalyptus spp. plantations in Colombia.

Anagonia lasiophthalma (Diptera: Tachinidae): Survey, identification, and biological traits of a new biological control agent of the Eucalyptus snout beetle, Gonipterus platensis (Coleoptera: Curculionidae)

The Eucalyptus snout beetle, Gonipterus platensis, is one of the main pests of eucalypts outside its native range. Among the available control methods for this pest, classical biological control with Anaphes nitens (Hymenoptera: Mymaridae) has been the most widely used, but it is not always effective. To identify other natural enemies that might provide further pest control, a field survey was conducted in Tasmania, Australia, in which Anagonia spp. were found to parasitize 7 % of Gonipterus spp. larvae. One species was subsequently identified as the solitary parasitoid Anagonia lasiophthalma, based on direct comparisons with research collection material in Australia. To assess the potential of this species as a biological control agent, A. lasiophthalma was reared on G. platensis larvae under quarantine conditions, and its biology and reproductive strategy were studied in the laboratory. Global mating success was 58 %, with 66 of the 114 A. lasiophthalma females analyzed mating within an established 10-day period. Most females mated within 48 h after emergence and started to parasitize about a week later. Dissections of mated females showed that this species is ovolarviparous, incubating its eggs in an ovisac, before inserting them “ready-to-hatch” directly into the host using a piercing structure derived from the modification of a sternite in the female terminalia. Over the course of their lifetime, females on average produced 35 offspring and post-mortem dissections revealed an additional 32 eggs in the ovisac. Longevity of females and males was similar, ranging between 55 and 84 days, but females maintained without host larvae lived longer than females exposed to host larvae. These results provide relevant information to improve laboratory rearing protocols and suggest that A. lasiophthalma may be effective against the snout beetle in its invaded range.

Screening five local entomopathogenic nematode species for their virulence against pupae of the Eucalyptus snout beetle, Gonipterus sp. n. 2, under laboratory conditions

The Eucalyptus snout beetle, Gonipterus sp. n. 2, is an important pest of eucalypt trees in South Africa and other countries. The pest is partially controlled with a mymarid egg parasitoid, Anaphes nitens. Identifying additional biological control agents that target other developmental stages of Gonipterus sp. n. 2 is necessary to improve control. Entomopathogenic nematodes (EPNs) are used as biological control agents for numerous soil pests and thus have the potential to be used against the pupal stage of Gonipterus sp. n. 2, which occurs in the soil. In this study, five South African EPN species were screened for their virulence on uncased pupae of Gonipterus sp. n. 2. At a concentration of 200 IJs/pupa in 50 μl of sterile water, Steinernema jeffreyense, S. fabii, Heterorhabditis noenieputensis and H. safricana caused pupal mortality of less than 40 %, while S. yirgalemense caused the highest pupal mortality of 100 % two days post-inoculation. Steinernema yirgalemense was selected and applied at different concentrations, namely 0, 12, 25, 50, 100, 200, and 400 IJs/pupa to determine its lethal concentration. Probit analysis indicated that the LC50 and LC90 of S. yirgalemense were 48.29 and 260.63 IJs/pupa, respectively. The study also showed that the pupal cases do not affect the efficacy of S. yirgalemense as it caused more than 90 % mortality of cased pupae of Gonipterus sp. n. 2 in soil bioassays. In addition, pupal age did not affect the efficacy of S. yirgalemense. Based on our findings, S. yirgalemense is a potential candidate for the biological control of pupae of Gonipterus sp. n. 2.

Presence of the Eucalyptus snout beetle in Ecuador and potential invasion risk in South America.

Eucalyptus snout beetles are a complex of at least eight cryptic species (Curculionidae: Gonipterus scutellatus complex), native to mainland Australia and Tasmania, that defoliate Eucalyptus trees and are considered important pests. Since the 19th century, three species of the complex have been introduced to other continents. Here, we document the presence of Eucalyptus snout beetles in Ecuador. We used DNA data for species identification and unambiguously demonstrated that the Ecuadorian specimens belong to the species Gonipterus platensis, which has low genetic diversity compared with other species in the complex. We analyzed G. platensis' potential distribution in South America with ecological niche models and found several areas of high to intermediate climatic suitability, even in countries where the pest has not been registered, like Peru and Bolivia. Accurate identification of species in the G. scutellatus complex and understanding of their potential distribution are essential tools for improved management and prevention tactics.

Susceptibility of Eucalyptus trees to defoliation by the Eucalyptus snout beetle, Gonipterus sp. n. 2, is enhanced by high foliar contents of 1,8-cineole, oxalic acidand sucrose and low contents of palmitic and shikimic acid.

Gonipterus sp. n. 2 (Coleoptera, Curculionidae) is an invasive, commercially important weevil that causes large-scale defoliation of Eucalyptus trees. The weevil specifically feeds on young leaves and new shoots, thus reducing tree growth. The weevil displays a very strong preference for certain Eucalyptus genotypes, however, this behaviour and the chemistry underlying it is poorly understood, thereby complicating the selection of resistant trees. To elucidate the feeding preference of Gonipterus sp. n. 2, we assessed the relative levels of susceptibility of 62 Eucalyptus genotypes from 23 species using a laboratory choice assay. This revealed large intraspecific variation in susceptibility to weevil feeding, which for certain species, exceeded the interspecific variation. A semiquantitative metabolite profile analysis on 13 genotypes revealed strong correlations of 10 metabolites to feeding damage. The behavioural effects of the identified compounds were assessed through an in vitro feeding preference assay using artificial diets as well as under field conditions. This revealed three phagostimulants (1,8-cineole, oxalic acidand sucrose) and two feeding deterrent compounds (shikimic acid and palmitic acid) for Gonipterus sp. n. 2. These chemical markers can be applied to tree breeding programmes for the selection of resistant genotypes to reduce damage caused by Gonipterus weevils.

Molecular identification and phylogeography of Gonipterus spp. (Coleoptera: Curculionidae) in Brazil

AbstractThe identification of the Gonipterus scutellatus complex species, known as the eucalyptus snout beetle, remained confusing for several years worldwide. Currently, the species Gonipterus platensis and Gonipterus pulverulentus are cited as present in Brazil. However, precise Gonipterus species identification, geographic distribution and economic importance in Brazil are unknown. Thus, our objectives were (i) to confirm the identification of Gonipterus species from different localities in Brazil using the sequencing of COI gene fragment, (ii) design a specific multiplex PCR marker for rapid molecular identification of Gonipterus species present in Brazil and (iii) apply a phylogeographic approach to assess the genetic diversity, demographic parameters and genetic structure of G. platensis population in Brazil. We confirmed the presence of G. platensis and G. pulverulentus in Brazilian territory. The species show different distribution, where G. platensis is widely distributed and G. pulverulentus is restricted to the south region. Gonipterus platensis populations are in spatial expansion, probably associated with the growth of Eucalyptus‐cultivated areas in Brazilian territory. Significant regional genetic population structure reinforces that the long dispersion processes of G. platensis within Brazilian territory is mediated by human activities. Thus, quarantine practices must be maintained and implemented to prevent new domestic and international introductions of Gonipterus specimens in Eucalyptus fields in Brazil.

Actions for Monitoring the Gonipterus Pest in Eucalyptus on the Cantabrian Coast

Forests are a natural resource of great importance for sustainable development. They represent the primary use of Spanish territory and cover 36% of its area. Eucalyptus shrublands are the most productive, particularly on the Cantabrian coast, occupying a total area of 406,566 ha. Since 1991, some of these shrublands have been affected by the eucalyptus snout beetle (Gonipterus platensis), a coleoptera (weevil) from the Curculionidae family that feeds on eucalyptus leaves and produces significant damage. The innovation project of the Supra-regional Operational Health Group on Gonipterus in Eucalyptus was developed (2019–2020) to establish a global approach to the serious problem it causes in Asturias and Galician Eucalyptus stands. A group of experts devised two action protocols to unify the methods and variables measured in the field: a protocol for measuring and estimating damage (degree of defoliation) and a parasitism protocol to establish actions to monitor the degree of parasitism (collection of oothecae, management of the sample, laboratory procedure). In the results, in addition to establishing the sampling protocol, an analysis of the data (from 2017 to spring 2020) provided by the different administrations of the Autonomous Communities studied has been carried out. The data analysis reveals an improvement in the impact of the damage on the Cantabrian coast (29.8% reduction in damage in Galicia and 14.7% in Asturias). In Galicia, the number of adult insects decreased from 2017 to 2019, increasing in the spring (from April to June) of 2020 above the mean values of previous years in that period. The number of larvae in the different larval stages showed similar development in all cases. The mean larvae (in their different stages) and mean oothecae showed a significant decline in the year 2018 compared to the spring of 2017, with an upturn in 2019 and again similar values to 2018 in the spring of 2020. In Asturias, similar mean values of the order of 0.5 insects per plot on dates (May–June) in spring were observed in 2019. While in 2020, a progressive increase could be seen in the mean number of insects throughout March, up to 1.9 insects per plot. Results of research on the biological treatment of parasitisation of oothecae with A.nitens were also collected to adjust the number of oothecae per bag deposited in the field and the number of Anaphes released per ha. Based on the field observations, the appropriate release time was determined to succeed in controlling the Gonipterus population.

Mitigation Measures for Invasive Insect Pests on Eucalyptus Spp. in East Africa: A Review

Eucalyptus spp. plantation forestry is expanding rapidly to meet wood and fibre demands internationally, including in Eastern Africa (especially Kenya, Uganda and Tanzania). However, Eucalyptus spp. plantations in eastern Africa are increasingly being damaged by invasive insect pests. In particular, the Australian invasive pests; Gonipterus scutellatus complex (Eucalyptus snout beetle), Leptocybe invasa (Blue gum chalcid), Thaumastocoris peregrinus (Bronze bug), and Glycaspis brimblecombei (Red gum lerp psyllid) pose a serious threat to Eucalyptus spp. plantations in eastern Africa. This is a trend that has also been noted in other parts of Africa and globally. Factors that influence introduction, establishment and spread of Australian invasive insect pests include: the expanding planting of Eucalyptus in intensive plantations over large areas, increased human trade and transport, natural dispersal mechanisms across borders, and a growing pool of established exotic pests in the neighbouring regions. Therefore, there is increasing pressure to develop more effective management strategies for the invasive pests and more rapidly than in the past. Some of the strategies that are employed in pest management and require improvement include: strengthening phytosanitary and quarantine measures at ports of entry, selection and deployment of resistant/tolerant host tree genotypes, and international and regional collaborations to prevent the entry and management of invasive species. In this review we assess on the knowledge generated in recent studies concerning forest pests and further consider methods/policies that could be employed or improved to mitigate the threat of invasive pests associated with Eucalyptus spp. in the Eastern Africa region. Key words: Eucalyptus spp, Pest management, Gonipterus scutellatus, Thaumastocoris peregrinus, Leptocybe invasa, Glycaspis brimblecombei

First record of a new microsporidium pathogenic to Gonipterus platensis in Brazil

Microsporidia are naturally occurring fungal-related parasites that can infect nearly all animal hosts, but their biocontrol potential of insect pests is routinely overlooked in agriculture and forestry. This research brings the first report describing the natural occurrence of a microsporidium causing disease in field-collected populations of the invasive eucalyptus snout beetle, Gonipterus platensis (Coleoptera: Curculionidae), a major destructive pest of eucalyptus plantations in Brazil. Adult beetles were collected during field surveys in commercial eucalyptus plantations in southern Brazil to be examined and dissected with typical symptoms to verify presence of microsporidian spores in haemolymph. From 14 plantations in different sites, the natural infection occurrence in these populations ranged from 0 to 65%, while a lab colony exhibited an infection incidence of 70%. Spore density in haemolymph of symptomatic insects averaged 2.1 (± 0.4) × 107 spores/beetle. Symptoms in infected adults were identified by an abnormal abdomen with malformation of the second pair of wings, impairing their flight activity. Electron transmission microscopy of the pathogen showed morphological features similar to species belonging to the genus Nosema or Vairimorpha. Phylogenetic analysis of the full-length small subunit ribosomal RNA gene suggests this pathogen’s placement in the genus Vairimorpha, but with a sequence identity of ~ 94% with the nearest neighbours. The low level of sequence identity suggests this pathogen may represent a novel taxon in the genus and further requires whole genome sequencing for definitive taxonomic resolution. These findings provide insights on the natural occurrence of this novel pathogen of this invasive pest in Eucalyptus plantations in Brazil. Further studies are needed to determine potential of this microsporidium in the design of conservative or augmentative biological control programs for this invasive pest.

Entomopathogenic fungi as the microbial frontline against the alien Eucalyptus pest Gonipterus platensis in Brazil

The eucalyptus snout beetle (ESB), Gonipterus platensis, is endemic to Australia but has become a major invasive, destructive pest of Brazilian eucalyptus plantations. Efforts to develop insecticides based on entomopathogenic fungi against ESB are limited by the lack of known virulent strains. We therefore explored the virulence of indigenous Brazilian strains of major entomopathogenic fungi—Beauveria spp. and Metarhizium anisopliae—against ESB adults. We found widely varying virulence and later capacities for conidial production on infected adult cadavers. Two strains stood out, B. bassiana IBCB-240 and M. anisopliae IBCB-364, as especially lethal for ESB adults under laboratory conditions, sporulated abundantly on infected insects, and also outperformed comparable strains used in commercial mycoinsecticides. Notably, B. bassiana IBCB-240 exhibited lower LT50 values at low inoculum levels (≤ 107 conidia mL−1) and smaller LC50 values than M. anisopliae IBCB-364. Taken together, this study emphasizes natural variation in virulence among indigenous Beauveria and Metarhizium strains against ESB adults and identifies fungal strains with superior lethality to existing commercialized strains for managing this eucalyptus pest in Brazil.

Identification and genome sequencing of RNA viruses in the eucalyptus snout beetle Gonipterus spp. (Coleoptera: Curculionidae).

The genomes of two putative new RNA viruses (macula-like virus and bunya-like virus) were identified in total RNA extracted from dead eucalyptus snout beetles (Gonipterus spp.) from a laboratory colony. However, only bunya-like virus was detected in field-collected insects. The macula-like virus has a monopartite single-stranded RNA genome that contains three open reading frames (ORFs) encoding an RNA-dependent RNA polymerase (RdRp), a capsid protein (CP), protein with unknown function. The bunya-like virus genome was predicted to consist of two RNA segments: a large segment (L) encoding a single protein (RdRp) and a small segment (S) encoding a putative nucleocapsid protein.

Estimating defoliation impact of Gonipterus platensis on Eucalyptus globulus stands productivity using a forest simulator based on 3-PG

Growth losses due to insect defoliations are difficult to estimate. The lack of appropriate tools that account for defoliations in growth simulations makes difficult the task of forest managers to project growth, and thus, the expected economic income. The present work integrates defoliations in the 3-PG forest growth model in order to provide a tool that allows forest managers to estimate Eucalyptus globulus stands growth losses under a set of defoliation scenarios by simulating attacks of the Eucalyptus snout beetle Gonipterus platensis. To mimic these attacks, different amounts of the upper third of the canopy were removed, from 0 to 100%, depending on the scenario intensity, and considering only spring season attacks or both spring and autumn attacks in the same year. A set of E. globulus virtual stands, representing a range of site productivities, were submitted to constant yearly consecutive defoliations since age 2 up to 10. Simulation results showed that, for scenarios that removed 50, 75 and 100% of the upper third of the canopy, volume losses averaged 54, 74 and 83%, respectively, at age 10 with just the spring attack, reaching 69, 82 and 88%, respectively, with also the autumn attack. Removing only 25% of the upper third of the canopy produced relevant losses only if the stands were attacked in both seasons. Lighter defoliations tested seemed to have a marginal effect on stand growth regardless of site quality. The tool was also used to evaluate a field assessment methodology of G. platensis defoliation attacks on a set of real stands by comparing observed and estimated volumes at age 10. Estimations showed increasing volume losses with increasing defoliation intensities. When evaluating the field assessment methodology, results suggest that a single field visit to assess the G. platensis attack level in the whole lifetime of a stand is insufficient to make reliable growth loss estimations. The integration of the impact of defoliations in the 3-PG growth model revealed to be potentially useful as a forest management decision tool.

Assessing the competitive interactions between two egg parasitoids of the Eucalyptus snout beetle, Gonipterus platensis, and their implications for biological control

The Eucalyptus snout beetle, Gonipterus platensis (Marelli), is an important pest of Eucalyptus globulus Labill. This insect is partially controlled by the egg parasitoid Anaphes nitens (Girault) in many regions, but the introduction of additional natural enemies can potentially increase pest control. In this study, we evaluate intra- and interspecific competitive interactions between the incumbent A. nitens and the new egg parasitoid Anaphes inexpectatus Huber and Prinsloo. The effects of temperature, order of parasitism, number of parasitoid ovipositions, time interval between ovipositions, and host egg age were analysed. Distinct outcomes of competition were found at different temperatures, with benefit to A. inexpectatus at 20 °C. The first species to parasitise generally prevailed over the second, indicating exploitation competition. However, interference competition was also apparent, namely when A. inexpectatus laid multiple eggs, outcompeting A. nitens, and when the first parasitism occurred six days before. In this case, the second species was able to eliminate the first. Anaphes nitens tended to reject eggs parasitised by A. inexpectatus, whereas A. inexpectatus showed no interspecific host discrimination behaviour towards eggs parasitised by A. nitens. Overall, A. nitens parasitised more hosts and is expected to contribute more to pest control, but it was found to be more susceptible to intraspecific competition. Results suggest that A. inexpectatus and A. nitens should be able to coexist, as asymmetric competition was found to depend on temperature. However, A. inexpectatus establishment in the field in areas where A. nitens is already present may be delayed or even prevented due to interspecific competition. As such, the introduction of A. inexpectatus in a classical biological control programme against G. platensis is advised to be carried out by releasing large numbers of parasitoids in consecutive occasions.

Economic Outcome of Classical Biological Control: A Case Study on the Eucalyptus Snout Beetle, Gonipterus platensis, and the Parasitoid Anaphes nitens

Despite the importance of invasive pests, few studies address the costs and benefits of the strategies used to control them. The present work assesses the economic impact of the Eucalyptus snout beetle, Gonipterus platensis, and the benefits resulting from its biological control with Anaphes nitens in Portugal, over a 20-year period. Comparisons were made between the real situation (with A. nitens) and three scenarios without biological control: 1) replacement of Eucalyptus globulus by resistant eucalypts; 2) insecticide use; and 3) offset of yield losses by imported wood. A cost-benefit analysis was performed to evaluate a programme that aimed to accelerate A. nitens establishment. Although A. nitens provides adequate pest control in several regions, 46% of the area planted with eucalypts is affected by the beetle, causing wood losses of 648 M euros over 20 years. Losses in the three hypothetical scenarios were estimated at 2451 M-7164 M euros, resulting in benefits from biological control of 1803 M–6516 M euros, despite the fact that only partial success was achieved. Anticipating biological control by just one, two, or three years resulted in benefit-cost ratios of 67, 190, and 347, respectively. Because nonmarket values were not accounted for, these figures are likely underestimated.

Environmental risk assessment of the egg parasitoid Anaphes inexpectatus for classical biological control of the Eucalyptus snout beetle, Gonipterus platensis

Classical biological control is a valuable tool against invasive pests, but concerns about non-target effects requires risk assessment studies. Potential non-target effects of Anaphes inexpectatus Huber and Prinsloo (Hymenoptera: Mymaridae) were assessed for a classical biological control programme against the Eucalyptus snout beetle, Gonipterus platensis (Marelli) (Coleoptera: Curculionidae). No-choice tests were conducted with 17 non-target species to assess host specificity, including 11 curculionids. In behavioural observations, A. inexpectatus showed no interest in any of the non-target species, but two weevil species were parasitised within five days of exposure, although at significantly lower rates than G. platensis. In choice tests, only one non-target, Hypera postica (Gyllenhal) (Coleoptera: Curculionidae), was parasitised, at a rate of 0.6%, while 50.0% of G. platensis eggs were parasitised. Based on the host specificity test results and the potential host fauna found in the target area, the likelihood of non-target effects resulting from the release of A. inexpectatus is considered to be negligible.

Pre-selection and biological potential of the egg parasitoid Anaphes inexpectatus for the control of the Eucalyptus snout beetle, Gonipterus platensis

The Eucalyptus snout beetle, Gonipterus platensis (Marelli), causes severe damage to eucalypt plantations in several countries, despite the presence of the parasitoid Anaphes nitens (Girault). Climate and/or host–parasitoid mismatch may explain A. nitens shortcomings in some areas in Portugal, Spain, Chile, South Africa, or Australia. Because additional parasitoids may be needed to achieve reliable control of this pest, Anaphes inexpectatus Huber and Prinsloo, retrieved from field surveys conducted in Tasmania (the pest’s native habitat), was selected for pre-release studies in Portugal. Life history traits of A. inexpectatus and A. nitens were compared at six temperatures (5, 10, 15, 20, 25, and 30 °C), including development times, thermal constants, viability, parasitism, and behaviour. Temperatures ranging from 10 to 20 °C were adequate for development, while at 25 and 30 °C, deleterious effects of temperature were detected, particularly in A. nitens. Development thresholds were similar for A. inexpectatus and A. nitens (6.0 and 5.4 °C, respectively), but A. nitens needed 313 degree-days to complete development, while A. inexpectatus needed 263 degree-days. Globally, A. nitens produced more progeny, parasitised more eggs, and lived longer than A. inexpectatus. Net reproductive rates were higher for A. inexpectatus at lower temperatures (10 and 15 °C), and higher for A. nitens at moderate temperatures (20 and 25 °C). In addition, A. inexpectatus evidenced higher tolerance to the highest temperature tested (30 °C). Anaphes inexpectatus is likely to establish under field conditions and may enhance parasitism of G. platensis.

Genetic Recombination Potential ofGonipterus scutellatus(Gyllenhal) (Coleoptera: Curculionidae), a Pest of Eucalyptus Plantations in South Africa

The eucalyptus snout beetle, Gonipterus scutellatus (Gyllenhal), introduced to South Africa from Australia, causes extensive damage to eucalyptus plantations in colder regions where biological control is less effective. A cytogenetic study was undertaken to assess the weevil's genetic recombination potential and thereby its ability to adapt to changing environmental conditions. During this study we investigated: (i) the sequence of meiosis; (ii) the weevil's karyotype; and (iii) the number and position of chiasmata on the bivalents. Squashes of male testes revealed a normal, chiasmate meiosis, a sex chromosome complement of Xyp and an autosome complement of three large, and two medium-sized, sub-metacentric pairs and seven small acrocentric pairs. The diploid chromosome number (2n = 26) is marginally higher than the ancestral chromosome number of the Curculionidae (2n = 22). Chiasmata were absent from the proximal regions of the bivalents, occurring mostly in the distal regions and less frequently in the ...

Egg resorption behaviour by the solitary egg parasitoid Anaphes nitens under natural conditions

AbstractWe investigated under outdoor conditions and inside a climate chamber: (i) whether Anaphes nitens Girault (Hymenoptera: Mymaridae), an egg parasitoid of the Eucalyptus snout beetle, Gonipterus scutellatus Gyllenhal (Coleoptera: Curculionidae), experienced egg resorption, and (ii) how various treatments (location, food, and/or host supply) and body size influenced egg load, egg resorption, fecundity, and longevity. One‐day‐old females were mated and randomly assigned to five groups: (A) honey + hosts, (B) water + hosts, (C) only honey, (D) only water, and (E) control females killed at emergence. We compared the egg load of the newly emerged females, which represent the control group (egg load = ovarian eggs present at emergence), with the lifetime egg load (i.e., ovarian eggs + emerged offspring + not emerged offspring) of the females with various host and diet treatments, by dissection of the ovaries to find evidence of egg resorption. All groups reared outdoors had fewer eggs than the control, while indoors there was no significant difference. Outdoors, starved but host‐provided wasps (B) experienced the highest reduction of the lifetime egg load (51%). Groups without access to food (B + D) resorbed more eggs than groups provided with honey (A + C). Females with honey and hosts (A) had the highest lifetime fecundity, but those with water and hosts (B) showed a higher daily realized fecundity. Host‐deprived females with access to food (C) attained the longest lifespan. Our results suggest that under stress conditions, such as low temperature and food shortage, A. nitens females practice egg resorption, probably to save energy.

Thermal requirements and phenology of the Eucalyptus snout beetle Gonipterus scutellatus Gyllenhal

Abstract: Laboratory experiments and field surveys were carried out to study the thermal requirements and phenology of the Eucalyptus snout beetle Gonipterus scutellatus (Curculionidae) and its parasitoid, Anaphes nitens (Mymaridae). Developmental times were recorded for G. scutellatus life stages: egg to first instar larva, first instar to pre‐pupal larva, prepupae to adults and the complete life cycle. Experiments were performed in temperature‐controlled chambers maintained at 10, 15, 20, 25 and 30°C with a photoperiod of 11 : 13 h of light : darkness and 50–60% RH. To calculate the minimum threshold temperature of the parasitoid, parasitized egg capsules were kept under similar conditions. During 1998 and 1999 we studied the phenology and the day‐degree (DD) accumulation of G. scutellatus and its parasitoid in plots of Eucalyptus globulus at six different sites in NW Spain. Every 2 weeks, the numbers of snout beetle adults and egg capsules were counted in each plot. The rate of parasitism was estimated by collecting 90 egg capsules from each plot on each sampling date. We recorded the temperatures in each plot to test whether differences in temperature alone could account for the phenology of this snout beetle. To complete a full life cycle from egg to adult, the weevil required a mean of 1119.83 ± 20.59 DD above a base temperature of 6.11°C. The parasitoid had a base temperature of 5.09°C and needed 318.16 DD to complete a life cycle. Our model indicated that three generations of snout beetle could develop each year, corresponding to peaks of snout beetle numbers in the field in March–April, June–July and November. In some years only one generation of G. scutellatus was recorded due probably to the effectiveness of the parasitoid. Differences in numbers of adults and egg capsule were recorded between neighbouring ‘coastal plots’ and between neighbouring ‘inland plots’. Hence, climate alone does not appear to explain the phenology of G. scutellatus.

The present status ofAnaphes nitens(Hymenoptera: Mymaridae), an egg parasitoid of the Eucalyptus snout beetleGonipterus scutellatus, in the Western Cape Province of South Africa

The egg parasitoid Anaphes nitens (Girault) was successfully introduced into South Africa in 1926 to control the Eucalyptus snout beetle, Gonipterus scutellatus Gyllenhal. However, outbreaks of the beetle on the Highveld in the 1980s questioned the efficacy of the parasitoid as a biological control agent and a programme was instituted to determine its present status. This study represents the Western Cape programme where 20 host egg-capsules were collected at fortnightly intervals for five years from three localities and the percentage parasitism was recorded. The mean parasitism rate varied between Cape Town (76%), George (82%), and Grabouw (89%). The highest parasitism occurred in spring (October) at Cape Town (96%) and (September) Grabouw (92%); and in autumn (May) at George (78%), coinciding with that of maximum host egg production, which in turn was dependent on the availability of fresh foliage. More host eggs were present in Cape Town (42%) than at either George (30%) or Grabouw (28%). Parasitism occurred consistently throughout the year at George which experiences all year rainfall, but the winter rainfall Cape Town and Grabouw localities experienced distinct peaks in parasitism in spring. Biological control of G. scutellatus remains effective in the Western Cape, from where A. nitens could be procured for release in Highveld regions in spring.