Edward W. Evans

Ladybirds (Coleoptera: Coccinellidae) provide services that are critical to food production, and they fulfill an ecological role as a food source for predators. The richness, abundance, and distribution of ladybirds, however, are compromised by many anthropogenic threats. Meanwhile, a lack of knowledge of the conservation status of most species and the factors driving their population dynamics hinders the development and implementation of conservation strategies for ladybirds. We conducted a review of the literature on the ecology, diversity, and conservation of ladybirds to identify their key ecological threats. Ladybird populations are most affected by climate factors, landscape composition, and biological invasions. We suggest mitigating actions for ladybird conservation and recovery. Short‐term actions include citizen science programs and education, protective measures for habitat recovery and threatened species, prevention of the introduction of non‐native species, and the maintenance and restoration of natural areas and landscape heterogeneity. Mid‐term actions involve the analysis of data from monitoring programs and insect collections to disentangle the effect of different threats to ladybird populations, understand habitat use by taxa on which there is limited knowledge, and quantify temporal trends of abundance, diversity, and biomass along a management‐intensity gradient. Long‐term actions include the development of a worldwide monitoring program based on standardized sampling to fill data gaps, increase explanatory power, streamline analyses, and facilitate global collaborations.

Since the late 19th century, exotic ladybirds (Coleoptera: Coccinellidae) have been used extensively for suppressing herbivorous insects of economic importance. In recent decades, the introduction of non‐native biological control (BC) agents has been greatly limited due to the awareness of the potential non‐target effects of introductions. Nonetheless, recent episodes of biological invasions of economically important pests have raised the need to carefully consider whether the expected benefits of pest control go beyond the possible environmental risks of introduction. To better understand the factors that contributed to successful BC programs, here we review the literature behind classical and augmentative BC using exotic ladybirds. Additionally, by means of case studies, we discuss the BC efficacy of selected exotic species, e.g.,Coccinella septempunctataL.,Harmonia axyridis(Pallas), andHippodamia variegata(Goeze), and their position within the communities of predators in the introduced areas of USA, Canada, and Chile. In Europe, much of the research on exotic ladybirds has been conducted on the undesired impact ofH. axyridis. Therefore, we summarize the risk assessment data for this species and review the field research investigating the ecological impact on European aphidophagous predators. According to the BIOCAT database of classical BC programs, 212 ladybird species belonging to 68 genera have been released in about 130 years of BC activity, with 14.6% of introductions having resulted in partial, substantial, or complete control of the target pest. However, because post‐release evaluation of establishment and BC success has not always been conducted, this rate could underestimate the successful cases. Among other factors, ladybird establishment and pest suppression mostly depend on (1) intrinsic factors, i.e., high voracity, synchronized predator‐prey life cycle, and high dispersal ability, and (2) extrinsic factors, i.e., adaptability to the new environment and landscape composition. This review contributes to improved understanding of ladybirds as exotic BC agents.

The yearly timing of the life cycle of a parasitoid is a key element of its life‐history strategy. I examine here factors influencing the expression of partial bivoltinism in Tetrastichus julis Walker (Hymenoptera: Eulophidae), a specialist parasitoid introduced to North America to attack its univoltine host, the cereal leaf beetle, Oulema melanopus (L.) (Coleoptera: Chrysomelidae). The varying tendency was assessed of individuals of this gregarious larval parasitoid to either emerge as adults in the same summer they mature, or to enter diapause to emerge the following year. Parasitized hosts were obtained by rearing cereal leaf beetles collected as mature larvae from grain fields in northern Utah (western USA) throughout the growing seasons in 2013 and 2014. Cocoons spun by these beetles were held to determine patterns over the spring and summer in the tendency of the parasitoid to forgo larval diapause. A high percentage (nearly 90% in 2013) of parasitoid individuals were found to forgo diapause and emerge in the same summer from earliest maturing hosts. This percentage rapidly declined to 20% or less of individuals forgoing diapause and emerging from cocoons as the summer advanced. The percentage of parasitoid individuals forgoing diapause increased significantly at a given time of season (early or late) as the number of conspecifics with which an individual shared a host larva increased. These results may reflect a trade‐off for individual parasitoids in which greater success in finding – and ovipositing in – host larvae the following spring vs. in summer, is countered by reduced survivorship in diapausing over the winter vs. emerging in the same summer in which the parasitoid matures. Expression of partial bivoltinism of T. julis, as affected strongly by both season and within‐host density, results in high rates of parasitism of cereal leaf beetles both early and late in the season.

Interactions of insect pests and their natural enemies increasingly are being considered from a metapopulation perspective, with focus on movements of individuals among habitat patches (e.g., individual crop fields). Biological control may be undercut in short-lived crops as natural enemies lag behind the pests in colonizing newly created habitat. This hypothesis was tested by assessing parasitism of cereal leaf beetle (Oulema melanopus) and alfalfa weevil (Hypera postica) larvae at varying distances along transects into newly planted fields of small grains and alfalfa in northern Utah. The rate of parasitism of cereal leaf beetles and alfalfa weevils by their host-specific parasitoids (Tetrastichus julis (Eulophidae) and Bathyplectes curculionis (Ichneumonidae), respectively) was determined for earliest maturing first generation host larvae. Rates of parasitism did not vary significantly with increasing distance into a newly planted field (up to 250–700 m in individual experiments) from the nearest source field from which pest and parasitoid adults may have immigrated. These results indicate strong, rapid dispersal of the parasitoids in pursuing their prey into new habitat. Thus, across the fragmented agricultural landscape of northern Utah, neither the cereal leaf beetle nor the alfalfa weevil initially gained substantial spatial refuge from parasitism by more strongly dispersing than their natural enemies into newly created habitat. Additional studies, including those of colonization of newly planted crops by generalist pests and natural enemies, are called for in assessing these results with a broader perspective.

Species invading new geographic regions may threaten continued existence of similar, indigenous relatives, particularly those species whose rarity may reflect an already tenuous existence. The spectacular colonization of North America in recent decades by Coccinella septempunctata L. has generated widespread concern over potentially adverse effects on population viability of native species of ladybird beetles (Coccinellidae). Coccinella novemnotata Herbst in particular has been hypothesized to be at great risk, as this species apparently dwindled in numbers across much of North America during the twentieth century. Here results of sampling diverse habitats over three decades are examined to address the fate of C. novemnotata in the intermountain region of western North America following the establishment of C. septempunctata during the 1990s. Alfalfa fields have served as a major habitat for C. novemnotata in the intermountain west. Sweep sampling in the late 1980s and early 1990s demonstated that C. novemnotata and C. septempunctata were both rare members of the alfalfa lady beetle community. Subsequent sampling in alfalfa over the next two decades revealed that populations of C. septempunctata increased greatly, while populations of C. novemnotata remained low but persistent. Similarly, modest numbers of C. novemnotata were found continuing to persist, often alongside large numbers of C. septempunctata, in a variety of other habitats, including sagebrush steppe and weed-infested rangeland and riparian sites. Morphological comparison of these individuals of C. novemnotata with museum specimens collected throughout the twentieth century revealed no significant difference in mean body size between these recently and previously collected individuals, nor any significant long-term decrease in body size following the arrival of C. septempunctata, as might reflect increasing food limitation for larval C. novemnotata. Collectively these results indicate that even in the face of invasion by a dominant competitor, C. novemnotata has maintained an ecological foothold in the intermountain west of North America, occurring in diverse habitats including both those supporting low and high numbers of the invader. The availability of these diverse habitats across a heterogeneous landscape may promote persistence less tenuous, even as confronted with invasion, than the low abundance of C. novemnotata alone might suggest.

The phenology of the stem-mining weevil Mecinus janthiniformis Toševski and Caldara (Coleoptera: Curculionidae) as adults attacking Dalmatian toadflax, Linaria dalmatica (L.) Miller (Plantaginaceae), was studied in 2014–2015 at two low elevation sites in northern Utah. The seasonal pattern of adult weevil abundance on the host plant at the two sites was most similar between years when described by degree-day accumulation, versus calendar date. Repeated censusing over the growing season revealed that males appeared first and subsequently peaked in abundance on the host plant earlier than females did, such that the adult population was dominated by males early in the season and by females late in the season. Peak female abundance on the host plant occurred at the time when Dalmatian toadflax stems reached their maximum height and density and when they began flowering widely. Maximum toadflax stem heights and densities, and flowering activity, were markedly reduced in 2015 compared to 2014. In contrast to these host plant parameters that vary between years, degree-day accumulation can be used readily for timing collection and survey efforts for adult weevils and female adult weevils in particular. Use of degree-day accumulation can thereby facilitate implementation of redistribution and monitoring programs for M. janthiniformis as a biological control agent of Dalmatian toadflax.

Larval populations of the sagebrush defoliating moth Aroga websteri Clarke (Lepidoptera: Gelechiidae) were sampled in a montane stand of big sagebrush ( Artemisia tridentata Nutall) in northern Utah during 2008–2012 to develop degree-day (DD) estimates for moth phenology (single-sine method, base temperature 5°C). Degree-day estimates were determined also for populations studied previously (in 1972–1975) in a lowland valley stand of big sagebrush on the Utah–Idaho border. Peak larval abundances (of mostly first and second instars, and ranging from 0–2.8 larvae per 15 cm of terminal stem at individual locations in northern Utah in 2008–2012) occurred on average at 239 DD (accumulated beginning 1 January). Differences in DD accumulation and precipitation among years with endemic (low) and population irruption levels of the Aroga moth were examined using data from these sites and from historical accounts from Alturas, CA, during 1962–1964. The DD accumulation during mid-May through mid-June (when early instars of the moth are developing) was intermediate in years of population irruptions versus in endemic years with cooler or warmer late springs–early summers. Years with population irruptions were also characterized by high precipitation in June and July during late stage larval development. Thus, it appears that periodic population irruptions of the defoliator are associated with distinctive weather conditions. Additional research is needed to test whether these conditions can promote increased larval survivorship as associated with high nutritional value and palatability of sagebrush foliage for the moth.

Increasing concern over worldwide loss of biodiversity has led ecologists to focus intently on how ecosystem functioning may depend on diversity. In applied entomology, there is longstanding interest in the issue, especially as regards the importance of natural enemy diversity for pest control. Here I review parallels in interest, conceptual framework, and conclusions concerning biodiversity as it affects ecosystem functioning in general and classical biological control in particular. Whereas the former focuses on implications of loss of diversity, the latter focuses on implications of increase in diversity as additional species of natural enemies are introduced to novel communities in new geographic regions for insect pest and weed control. Many field studies now demonstrate that ecosystem functioning, e.g., as reflected in primary productivity, is enhanced and stabilized over time by high diversity as the community increases in its efficiency in exploiting available resources. Similarly, there is growing field support for the generalization that increasing species and functional diversity of natural enemies leads to increasing pest suppression. Nonetheless a central concern of classical biological control in particular, as it seeks to minimize non-target effects, remains as to whether one or a few species of natural enemies can provide sufficient pest control.

In North America host-specific flea beetles (Aphthona spp.; Coleoptera: Chrysomelidae) from Europe have been introduced to suppress invasive populations of the exotic forb, leafy spurge, Euphorbia esula L. (Euphorbiaceae). Long term outcomes of such introduction were examined in 2013 for a spurge infested site (managed as elk winter range) in the mountain foothills of northern Utah where three species of flea beetles had been released two decades earlier, in the 1990s. The abundance of leafy spurge at the site had declined by 2013 to only 4% of its abundance in 1995. The three species of flea beetles (dominated by A. lacertosa Rosenhauer) persisted in low numbers at the site in 2013 [peaking at 7-8 adults (all species combined) per 100 stems and inflicting aboveground feeding damage to all spurge stems by late summer]; flea beetle abundance had declined by 89-97% from high numbers as sampled in 2001. Another biocontrol insect, the stem borer Oberea erythrocephala Schrank (Coleoptera: Cerambycidae), had immigrated on its own to the site (as first detected in 2008) and, by mid-July in 2013, had damaged all spurge stems (typically causing total loss of the inflorescence on flowering stems). With the collapse of the spurge population at the site, the biomass of grasses [dominated by the exotic Bromus inermis Leyss and Arrhenatherum elatius (L.)] and forbs increased by 269% and 507%, respectively, from 1995 to 2013. These increases in grasses and forbs at the site with insect suppression of leafy spurge have resulted in more favorable habitat for elk and other wildlife.