Direct competition occurs only among the betilids species, while indirect competition occurs with P. coffea. Gutierrez et al. considered symmetric competition among the betilids, but new data enables parametrization of asymmetric competition in dyadic contests the success rate of which depends on their biology . The different success rates are included in the model via the parameter ı , which weights the proportion of contest that are successful for the dif-ferent combinations of species. No information is available on rare triadic interactions, and hence is not considered in our analysis. When a second species of a betilid parasitoid enters a berry previously colonized by another parasitoid species, it attacks the immature stages of both CBB and the first parasitoid. Facultative oviposition and host-feeding interactions between betilid species are summarized in Table 4 .Simulations for Colombia had a five year time horizon corresponding to the normal crop cycle . In Brazil, the crop cycle is four years. In Colombia, two coffee harvests occur per year, a main one in September-November and a minor harvest in April-June . At Londrina PR , plastic flower pots only one coffee harvest occurs per year that may occur during June through September .
The ratio of parasitoid released was 1 per 1 CBB infested berry. In Colombia, the first berries colonized by CBB females appear around 5300 dd after planting , and at 7500 dd in Brazil. The times of berries first appear are reference times for parasitoid release. In Colombia, an initial release of 11 adults/plant of each betilid species occurs at 6790 dd and corresponds to a ratio of 1:1 parasitoid adults to CBB infested berries. For P. coffea, the initial release was 5 adults/plant corresponding to a ratio of 1:1 parasitoid females to CBB infested berries at time 5678 dd. For Brazil, the initial release of each of the betilid parasitoids at 8500 dd is 4 adults/plant corresponding to a 1:1 ratio of adult females of each betilid species to CBB infested berries. For P. coffea, 6 adults were released at 7500 dd for a 1:1 ratio of parasitoids to CBB infested berries. Single and multiple parasitoid releases during the crop cycle were also evaluated. Two strategies for multiple releases were evaluated: the first consisted of one release at the start of each coffee production cycle when CBB attack begins and the second in had releases at the start and end of each production cycle. The release rates were one female parasitoid per infested berry. The season long damage reduction for each scenario is computed as the ratio of CBB infested berries with control/CBB infested berries without control, while the proportion of parasitoid colonization rate by each species was computed as the ratio of CBB infested berries with parasitoid/total CBB infested berries. A constant immigration rate of 0.25 CBB females per day and plant was used in the model, while no immigration was assumed for the parasitoids. Dyadic contests, facultative host-feeding and facultative hyperparasiThism as appropriate for each species were examined for all combinations of parasitoid species interactions .
The effects of interspecific competition were analyzed using the number of adult parasitoids of each species produced per plant as affected by the presence of competing parasitoid species.The effects of weather at five locations on the coffee agroecosystem were analyzed for the 24 = 16 combinations of the four parasitoids including the null set. The different combinations in the model were characterized using Boolean presence , absence values. The efficacy of each parasitoid species on CBB control was further evaluated using permutations of the years of weather data from the five locations obtained using the allPerms procedure of the “permute” package in the statistical software R . For Colombia, this resulted in a random subset of 24 combinations of yearly weather data and 16 combinations of parasitoids . A similar procedure was used to generate 128 scenarios for Brazil.Negative binomial mixed regression models were fit to simulation outputs. This method accounts for over dispersion and skewness in the data, saThisfies the assumptions of the parametric analysis, and allows interpretation of the stochastic effect of the combinations of years of weather obtained by the shuffling procedure. In the analysis, the Boolean variables are the independent variables, while the cumulative number of CBB infested berries·year−1 in the simulation runs are the dependent variables. The effects of species-specific biology such as facultative host-feeding, facultative hyperparasiThism and dyadic contests were critical underlying factors affecting the output of the model .
The simulation runs were used to estimate the effects of parasitoid species on CBB infestation levels and oneachother.Akaike’s information criteria was used to select the final model for the different combinations of parasitoids, and chi-square goodness of fittests were used to assess the significance level.The dynamics of CBB infested berries in the absence of the parasitoids are depicted in Fig. 2a and predict CBB infestation of berries of 64.67%. Because parasitoid releases at the beginning and at the end of each harvest period for each species acting alone gave only slightly better control than the single release strategy , only the results for single releases are illustrated in Fig. 2. A single release of C. stephanoderis at 10 CBB infested berries/plant resulted in a 21.06% reduction of CBB infested berries on the plant and an 11.35% reduction in infestetation in shed berries on the ground. Compared to C. stephanoderis, a single release of C. hyalinipennis resulted in a 16.93% reduction in infestation on the plant and 8.23% reduction in infestation in shed berries, whilst a release of P. nasuta yielded 16.83% and 7.59% reductions respectively. In contrast, a single release of the eulophid P. coffea resulted in a 47.38% reduction in CBB infested berries on the plant and a 46.85% reduction in infestation in shed berries. Operating singly, the order of effectiveness of the parasitoids is P. coffea >> C. stephanoderis > C. hyalinipennis = P. nasuta , but none of the parasitoids provided high levels of control. Simulation of CBB infested berries available for attack by the betilid species shows asynchrony between seeking adult parasitoids and the low availability of CBB infested berries . The low level of control by single releases of the betilids is the consequence of the lag between the peaks of colonization of CBB infested berries attacked by the betilids and the late emergence of searching betilid females at the end of the ripening season . of Regressions of CBB infested berries·year−1 on the presence the parasitoid species under multiple climatic conditions shows that only P. coffea has a significant impact in reducing CBB infestation levels , a level of control that is clearly insufficient.From a human perspective, control of coffee berry borer using effective augmentative and/or classical biological control is desirable, but this outcome appears not to be possible in Central and South America using the three commonly introduced parasitoids . Of these parasitoids, only P. nasuta established in Colombia , and only C. stephanoderis and P. nasuta established in Brazil . A fourth parasitoid, C. hyalinipennis was considered for introductions, but laboratory studies revealed it is a facultative predator and hyperparasite on immature stages of the other betilids and conspecifics, plastic garden container it super parasiThism of CBB larvae, and it does not attack CBB adults . Our simulation results confirm the impact of these detrimental effects.We sought to determine why the establishment of the parasitoid species in the face of high CBB infestations in Colombia and Brazil has been difficult, and why no combination of the parasitoids shows promise for effective control of CBB. We first review the simulation results and then relate them to ecological theory. In sharp contrast to what is observed in the field, we assumed that all of the parasitoids established in the field and are attacking CBB and interacting with each other. This discrepancy with the facts suggests deficiencies in our knowledge of the biology of the species, and the omission in the model of the limiting effects of harvesting, crop management and cultural controls, and alternate hosts. For these reasons, our analysis of the parasitoids for control of CBB must be viewed as heuristic.
Earlier simulation results by Gutierrez et al. and here suggest that only the eulophid adult endo-parasitoid can reduce CBB populations significantly but not sufficiently. Unlike the betilids, P. coffea attacks multiple CBB females as they are boring into coffee berries and effectively stops CBB reproduction. Furthermore, P. coffea does not host-feed on siblings, allowing rapid growth of its populations during the berry-ripening period. Studies with P. coffea in Costa Rica and Mexico using sleeve and field cages support our simulation results. In Costa Rica, Espinoza et al. released a 1:10 ratio of P. coffea adults to CBB infested berries in entomological sleeves and obtained 95% parasitization of CBB adults and a 3 − 5.6 fold decrease in berry damage. In a similar study in México, Infante et al. obtained P. coffea parasiThism rates of 79%. Unfortunately, cage results cannot be compared with open field releases such as those of Castillo et al. who obtained a very low progeny from the original number of female adults liberated. In a two year survey of CBB parasitoids in Western Kenya, only 17 P. coffea adults were reared from 69,500 CBB infestedberries . These differences in the field studies suggest that crop management, harvest intensity, weather and other unexplored factors must play large roles that will be explored in a forthcoming report.Gutierrez et al. found that the betilids released singly or in combination assuming high immigration and search rates gave poor control of CBB. They attributed the result to a low numerical parasitoid response relative to CBB as each betilid female colonizes only one berry and only partial mortality of the available hosts may occur. Our results confirm this interpretation. Further, the oviposition rate of betilids estimated from field data ranged from 0.055 to 0.076 eggs·female−1·dd−1 which is about six fold lower than the oviposition rate of 0.348 eggs CBB female−1·dd−1 . In addition, host-feeding by betilid adults on CBB eggs and larvae is common and reduces the future availability of preferred stages for parasiThism. Under laboratory conditions, C. stephanoderis females fed honey had 80% greater longevity and decreased host feeding, and this practice has been proposed to improve the survival in the field after release and to improve control of CBB, especially when preys are scarce . In Colombia, high densities of betilid females emerge at the end ofthe berry ripening seasons when CBB infested berries are in short supply. Thus, despite predicted high parasitization rates, a bottleneck occurs between harvests that reduces adult betilid densities to levels that are slow to rebuild in the face of rapidly increasing CBB populations. This result was verified by Benassi in the states of Espiritu Santo and São Paulo, Brazil who observed that low densities of wasps at the beginning of the harvest period required several months to increase significantly. Benavides et al. suggested that parasitoid releases should be made during the middle of the ripening season, but high CBB damage rates normally occur by this time.Whatever strategy a species evolves, it must assure its continuity in time, and hence its traits must assure “adaptedness” to the biotic and abiotic conditions to minimize the likelihood of extinction . Further, Gutierrez and Regev proposed that evolved strategies may have little to do with maximizing the commonness of the species in the environments. Rather, adapted individuals and the species they comprise must via their genetics, take a long-term view of their resource management problem, and that tradeoffs are based on sufficiency or constrained optimization behavior rather than maximization rules. On the theoretical r-K continuum , coffee and CBB have r-selected strategies, while the parasitoids have intermediate ones. The well-documented biology of coffee, CBB and its parasitoids suggests that poor control of CBB is not unexpected because coffee is a long-lived shrub that produces high numbers of fruit, and few seeds need survive CBB attack to provide replacements . Furthermore, CBB is polyphagous in its home range in Africa with coffee being but one of its hosts . Similarly, the linkages of the parasitoids to CBB are not particularly tight because the parasitoids also have other hosts and CBB and the parasitoids spread the risk of extinction through polyphagy . As a result, little by way of regulation of CBB occurs resulting in high infestation levels in coffee in the Americas and in its native range in Africa.