Guiding Classical Biological Control of an Invasive Mealybug Using Integrative Taxonomy

Geographic Location, Population Dynamics, and Fruit Damage of an Invasive Citrus Mealybug: The Case of Delottococcus aberiae De Lotto in Eastern Spain

The invasive mealybug Delottococcus aberiae De Lotto (Hemiptera: Pseudococcidae) has rapidly spread in the Mediterranean basin since its detection in 2009 in the Valencia Community in eastern Spain. The use of sticky traps baited with its sex pheromone, (4,5,5-trimethyl-3-methylenecyclopent-1-en-1-yl)methyl acetate, has allowed to determine the geographical distribution of D. aberiae by means of the surveillance network described in the present work. The population monitoring of the pest over a five-year period (2019-2023) has revealed an increase from 31% to 70% of the affected citrus-growing area. The monitoring network has also allowed a better understanding of the pests' biological cycle throughout the year. The populations start growing from March to June and reach their maximum in July-August. During autumn, there is a gradual decline in the population. Although the highest annual populations were detected in 2022 and 2023, the greatest crop losses were recorded in 2020 and 2021, with mean values near 18%. Data suggest that the damage responsible for fruit deformation, and thus the economic losses, are related to the population levels in spring (April-May) rather than those in summer (July-August). The findings of this study can be valuable for future research and development of effective pest control strategies.

Exclusion of Mediterranean ant species enhances biological control of the invasive mealybug Delottococcus aberiae in citrus

BACKGROUND

Delottococcus aberiae is an invasive mealybug that produces severe damage in Spanish citrus. This mealybug has established a mutualistic relationship with native Mediterranean ant species that may limit biological control of this pest. Herein, we evaluated the effect of tending ants on the biological control of D. aberiae. To do this, we compared: (i) the density of D. aberiae, (ii) the density of its natural enemies, and (iii) the damage produced by the mealybug in trees with (control) and without ants (ants excluded with sticky barriers) in two citrus orchards across two consecutive years.

RESULTS

Lasius grandis was the most abundant ant species in both orchards and represented more than 95% of the ants tending D. aberiae in control trees. Spiders and lacewings were the most abundant predators observed in mealybug colonies, and the exclusion of mutualistic ants increased their abundance. Moreover, in control trees, ant activity throughout the year was negatively correlated with the relative abundance of predators (number of predators per mealybug). No parasitoids were recovered during field experiments. Ant exclusion reduced the density of D. aberiae and the ratio of damaged fruit at harvest across years and orchards.

CONCLUSIONS

This work corroborates the previous finding that D. aberiae benefits from its mutualistic relationship with L. grandis, probably because the presence of ants reduced the abundance of generalist predators. This mutualism can be disrupted using physical barriers on on the trunk. Further research should assess other methods of ant control that are more economic and feasible for citrus producers. © 2023 Society of Chemical Industry.

Taxonomy and Biological Control: New Challenges in an Old Relationship

Biological control and taxonomy are continuously developing fields with remarkable impacts on society. At least 80 years of literature have documented this relationship, which remains essentially the same in its mutualistic nature, as well as in its major challenges. From the perspective of Brazilian taxonomists, we discuss the impacts of important scientific and social developments that directly affect research in these areas, posing new challenges for this lasting relationship. The increasing restrictions and concerns regarding the international transit of organisms require improvements in research related to risk assessment for exotic biological control agents and also stimulate prospecting within the native biota. In our view, this is a positive situation that can foster a closer relationship between taxonomists and applied entomologists, as well as local surveys and taxonomic studies that are necessary before new programs and agents can be implemented. We discuss the essential role of molecular biology in this context, as an iconic example of the synergy between applied sciences and natural history. As our society comes to need safer and more sustainable solutions for food security and the biodiversity crisis, scientific progress will build upon this integration, where biological control and taxonomy play an essential role.

Species boundary and phylogeographical pattern provide new insights into the management efforts of Megacopta cribraria (Hemiptera: Plataspidae), a bean bug invading North America

BACKGROUND

Correct identification together with information on distribution range, geographical origin and evolutionary history are the necessary basis for the management and control of invasive species. The bean bug Megacopta cribraria is a crucial agricultural pest of soybean. Recently, M. cribraria has invaded the United States and spread rapidly, causing severe reductions in soybean yields. However, the species boundary and phylogeographical pattern of this invasive bean bug are still unclear.

RESULTS

The results of different species delimitation methods (Automatic Barcode Gap Discovery, Assemble Species by Automatic Partitioning, Bayesian Poisson Tree Processes and Bayesian Phylogenetics and Phylogeography) strongly demonstrated that M. cribraria and Megacopta punctatissima represent the same species. M. punctatissima should not be considered a distinct species but rather a variety of M. cribraria. Phylogenetic analyses revealed three well-supported clades (Southeast Asia [SEA], East Asia continent [EAC] and Japan [JA]) with distinct geographical structures in the M. cribraria-M. punctatissima complex. The SEA clade was at the base of the phylogenetic tree, and the sister relationship between the EAC clade and JA clade was strongly supported. The split between the EAC clade and JA clade occurred at approximately 0.71 Ma, corresponding to the submergence period of the East China Sea land bridge.

CONCLUSION

This study clarified the species boundary between M. cribraria and its closely related species and revealed the phylogeographical pattern and evolutionary history of M. cribraria. The species delimitation and phylogeography results achieved in this study could provide new insights into the monitoring and management of this agricultural pest. © 2022 Society of Chemical Industry.

Insecticide-contaminated honeydew: risks for beneficial insects

Honeydew is the sugar-rich excretion of phloem-feeding hemipteran insects such as aphids, mealybugs, whiteflies, and psyllids, and can be a main carbohydrate source for beneficial insects in some ecosystems. Recent research has revealed that water-soluble, systemic insecticides contaminate honeydew excreted by hemipterans that feed on plants treated with these insecticides. This contaminated honeydew can be toxic to beneficial insects, such as pollinators, parasitic wasps and generalist predators that feed on it. This route of exposure has now been demonstrated in three plant species, for five systemic insecticides and four hemipteran species; therefore, we expect this route to be widely available in some ecosystems. In this perspective paper, we highlight the importance of this route of exposure by exploring: (i) potential pathways through which honeydew might be contaminated with insecticides; (ii) hemipteran families that are more likely to excrete contaminated honeydew; and (iii) systemic insecticides with different modes of action that might contaminate honeydew through the plant. Furthermore, we analyse several model scenarios in Europe and/or the USA where contaminated honeydew could be problematic for beneficial organisms that feed on this ubiquitous carbohydrate source. Finally, we explain why this route of exposure might be important when exotic, invasive, honeydew-producing species are treated with systemic insecticides. Overall, this review opens a new area of research in the field of ecotoxicology to understand how insecticides can reach non-target beneficial insects. In addition, we aim to shed light on potential undescribed causes of insect declines in ecosystems where honeydew is an important carbohydrate source for insects, and advocate for this route of exposure to be included in future environmental risk assessments.

Improving Natural Enemy Selection in Biological Control through Greater Attention to Chemical Ecology and Host-Associated Differentiation of Target Arthropod Pests

Host-associated differentiation (HAD) refers to cases in which genetically distinct populations of a species (e.g., herbivores or natural enemies) preferentially reproduce or feed on different host species. In agroecosystems, HAD often results in unique strains or biotypes of pest species, each attacking different species of crops. However, HAD is not restricted to pest populations, and may cascade to the third trophic level, affecting host selection by natural enemies, and ultimately leading to HAD within natural enemy species. Natural enemy HAD may affect the outcomes of biological control efforts, whether classical, conservation, or augmentative. Here, we explore the potential effects of pest and natural enemy HAD on biological control in agroecosystems, with emphases on current knowledge gaps and implications of HAD for selection of biological control agents. Additionally, given the importance of semiochemicals in mediating interactions between trophic levels, we emphasize the role of chemical ecology in interactions between pests and natural enemies, and suggest areas of consideration for biological control. Overall, we aim to jump-start a conversation concerning the relevance of HAD in biological control by reviewing currently available information on natural enemy HAD, identifying challenges to incorporating HAD considerations into biological control efforts, and proposing future research directions on natural enemy selection and HAD.

Parasitoids (Hymenoptera) of Mealybug Pests (Hemiptera: Pseudococcidae) from Southern Brazil: Molecular and Morphological Characterization

Parasitoids of three mealybug pests (Hemiptera: Pseudococcidae), Planococcus ficus (Signoret), Pseudococcus sociabilis Hambleton, and Pseudococcus viburni (Signoret) have been identified for the first time in Brazil. Mealybugs were collected in fruit-growing areas along southern Brazil during 2013-2016. An integrative approach, combining morphological and molecular methods, was used to identify the Brazilian parasitoids to the species level. Fifteen species were recorded, including 14 primary parasitoids belonging to Encyrtidae and Platygastridae and a single secondary parasitoid species belonging to Signiphoridae. The encyrtid parasitoids Acerophagus flavidulus (Brèthes), Anagyrus calyxtoi Noyes and Zaplatycerus sp., and the signiphorid secondary parasitoid Chartocerus axillaris De Santis are reported for the first time in Brazil.

Evidence for a cryptic parasitoid species reveals its suitability as a biological control agent

Uncertainty about the taxonomic status and the specificity of a species commonly prevent its consideration as a candidate for biological control of pest organisms. Here we use a combination of molecular analysis and crossing experiments to gather evidence that the parasitoid wasp Ganaspis brasiliensis, a candidate for biological control of the invasive spotted wing drosophila Drosophila suzukii, is a complex of at least two cryptic species. Complementary experiments demonstrate that individuals from one genetic group readily parasitize several drosophila species regardless of their food source while individuals from the other one are almost exclusively specific to larvae feeding in ripening fruits. Because only D. suzukii attacks ripening fruits in its area of invasion, parasitoids from this second group appear to be well suited as a biological control agent. Our study demonstrates the need for a combination of biosystematics with biological and ecological investigations for the development of safe and efficient biological control programs.

Sex Pheromone of the Invasive Mealybug Citrus Pest, Delottococcus aberiae (Hemiptera: Pseudococcidae). A New Monoterpenoid with a Necrodane Skeleton

Native to sub-Saharan Africa, Delottococcus aberiae De Lotto (Hemiptera: Pseudoccidae) is an invasive mealybug that has been recently reported in Europe, seriously damaging citrus production in eastern Spain. In this study, we isolated and determined the structure of the sex pheromone of D. aberiae, to provide a highly specific and effective lure for detecting, monitoring, and potentially controlling this pest. The volatile profile of D. aberiae virgin and mated females was studied by aeration and collection of effluvia in Porapak-Q. The resulting extracts were analyzed by gas chromatography coupled to mass spectrometry (GC-MS), revealing a candidate compound specific of virgin females. GC-MS and nuclear magnetic resonance spectroscopy data evidenced a new compound, (4,5,5-trimethyl-3-methylenecyclopent-1-en-1-yl)methyl acetate, with an unusual β-necrodol skeleton. This compound was synthesized and shown to be attractive to male D. aberiae in both laboratory and field experiments. A GC analysis using an enantioselective stationary phase and polarimetry analyses of the synthetic enantiomers showed the natural compound emitted by virgin females to be the - enantiomer.

Seasonal Distribution and Movement of the Invasive Pest Delottococcus aberiae (Hemiptera: Pseudococcidae) Within Citrus Tree: Implications for Its Integrated Management

Delottococcus aberiae (De Lotto) (Hemiptera: Pseudococcidae) is the most recent species of mealybug introduced to Spain that is affecting citrus. The feeding behavior of D. aberiae causes severe direct damage to citrus fruits, distorting their shape and/or causing reduction in size. There is no information available regarding its distribution within the citrus trees. The main objective of this study was to describe the seasonal distribution of D. aberiae within citrus trees and its migration patterns on the plants. Ten citrus orchards from eastern Spain were periodically sampled during 3 yr. In each orchard, the mealybug was sampled in different infested strata (canopy, trunk, and soil) and canopy structures (flower, fruit, leaf, and twig). Results showed that, within the sampled strata, D. aberiae was mostly in the canopy. Within the canopy, the feeding location of D. aberiae changed throughout the year. D. aberiae overwintered in the twigs and moved to the flowers and fruits in spring. Once there, its populations started to increase exponentially until August. From February to September, 5-30% of the mealybugs migrated to the trunk and soil. These results will facilitate an early detection of the pest in the areas where it is spreading and improve sampling protocols and pesticide applications.

Defensive behaviors of the new mealybug citrus pest, Delottococcus aberiae (Hemiptera: Pseudococcidae), against three generalist parasitoids

Delottococcus aberiae De Lotto (Hemiptera: Pseudococcidae) is an invasive mealybug that has become a citrus pest in Europe. This mealybug species causes serious damage because it deforms the fruits. Here, we studied the defensive behavior of D. aberiae when it was attacked by three parasitoid species: Acerophagus angustifrons (Gahan), Anagyrus sp. near pseudoccoci (Girault), and Leptomastix algirica Trjapitzin (Hymenoptera: Encyrtidae). Anagyrus sp. near pseudoccoci and L. algirica detected and accepted nymphs and adult females of D. aberiae, whereas A. angustifrons only accepted adults. We recorded four defensive responses of D. aberiae to parasitoid attacks: abdominal flipping, swiveling around the inserted stylet, withdrawing the stylet and walking away, and, occasionally, they secreted ostiolar fluids. Despite these defensive behaviors, the mealybug did not escape parasitism from any of the tested parasitoids, even though A. angustifrons needed more than 15 min to parasitize. We also analyzed the nutritional value of the honeydew excreted by D. aberiae for A. angustifrons and A. sp. near pseudococci. Females and males of these parasitoids lived more than 28 d when fed sucrose, but they lived fewer than 3 d when fed D. aberiae honeydew. Therefore, D. aberiae excretes honeydew of poor quality for parasitoids. The consequences of these biological traits of D. aberiae for its biological control are discussed.

Integrative taxonomy methods reveal high mealybug (Hemiptera: Pseudococcidae) diversity in southern Brazilian fruit crops

The Serra Gaúcha region is the most important temperate fruit-producing area in southern Brazil. Despite mealybugs (Hemiptera: Pseudococcidae) infesting several host plants in the region, there is a lack of information about the composition of species damaging different crops. A survey of mealybug species associated with commercial fruit crops (apple, persimmon, strawberry and grapes) was performed in Serra Gaúcha between 2013 and 2015, using both morphology and DNA analyses for species identification. The most abundant species were Pseudococcus viburni (Signoret), found on all four host plant species, and Dysmicoccus brevipes (Cockerell), infesting persimmon, vines and weeds. The highest diversity of mealybug species was found on persimmon trees, hosting 20 different taxa, of which Anisococcus granarae Pacheco da Silva & Kaydan, D. brevipes, Pseudococcus sociabilis Hambleton and Ps. viburni were the most abundant. A total of nine species were recorded in vineyards. Planococcus ficus (Signoret) and Pseudococcus longispinus (Targioni Tozzetti) were observed causing damage to grapes for the first time. A single species, Ps. viburni, was found associated with apples, while both Ps. viburni and Ferrisia meridionalis Williams were found on strawberry. Four of the mealybug species found represent new records for Brazil.