Scale insect host ranges are broader in the tropics

The scale insects: Its status, biology, ecology and management in tea plantations

The scale insects reduce plant photosynthetic ability by sucking sap from leaves and causing significant damage to the tea crop in most tea-producing countries. They suck the sap from stems and tea leaves, which not only prevents further growth but also reduces the nutritional quality of the leaves by promoting the growth of sooty molds. However, due to the widespread use of organosynthetic pesticides in recent decades, most insect pests have developed high levels of pesticide resistance, reducing the effectiveness of insecticide application. Bio-control agents are environmentally safe and produce long-term results while reducing the use of chemicals and other pesticides without disrupting the natural equilibrium. The review includes a list of coccidicides discovered on tea in major tea-growing countries as potential tea pests. The scope of future studies and the plans for better management of this serious sucking pest of the tea plant are also discussed in this review.

Life table construction for crapemyrtle bark scale (Acanthococcus lagerstroemiae): the effect of different plant nutrient conditions on insect performance

Crapemyrtle Bark Scale (Acanthococcus lagerstroemiae; CMBS) is an invasive pest species that primarily infest crapemyrtles (Lagerstroemia spp.) in the United States. Recent reports have revealed the dire threat of CMBS to attack not only crapemrytles but also the U.S. native species with expanded host plants such as American beautyberry (Callicarpa spp.) and Hypericum kalmianum L. (St. Johnswort). A better understanding of plant-insect interaction will provide better and environmental-friendly pest management strategies. In this study, we constructed the first comprehensive life table for CMBS to characterize its biological parameters, including developmental stages, reproductive behavior, and fecundity. The indirect effects of three plant nutrient conditions (water, 0.01MS, and 0.1MS) on CMBS populations were examined using the age-stage, two-sex life table. The demographic analyses revealed that the plant nutrient conditions had significantly altered CMBS development in terms of the intrinsic rate of increase (r), the finite rate of increase (λ), the net reproductive rate (R₀), and mean generation time (T). Higher r, λ, and R₀ were recorded under nutrient-deficient conditions (water), while CMBS reared on plants with healthier growing conditions (0.1MS) had the most prolonged T. Overall, CMBS shows better insect performance when reared on plants under nutrient-deficient conditions.

The Box Tree Moth: An Invasive Species Severely Threatening Buxus Natural Formation in NW Italy

(1) The box tree moth (BTM), Cydalima perspectalis Walker, represents one of the recent examples of exotic insect pests native to Asia accidentally introduced in Europe by the nursery trade. In Europe, BTM develops on Buxus sempervirens L., causing significant damage to ornamental and natural plants. (2) Basic aspects of BTM biology were investigated at three sites in the NW Alps, where B. sempervirens occurs on rocky slopes, forming a protected habitat. In 2019–2021, we evaluated: (i) the seasonal flight activity with sex pheromone traps, (ii) the fecundity and the effects of food on the egg load, (iii) the potential adaptation of BTM on native secondary host plants, and (iv) the recruitment of natural enemies. (3) Our results revealed the presence of two generations per year. The number of mature eggs increased in fed adults and was higher in females of the first generation. No evidence of BTM shift on secondary plants was found in either laboratory or natural conditions, and no significant occurrence of natural enemies was recorded, except for one pupa of the tachinid Pseudoperichaeta nigrolineata. (4) Our findings provide valuable information to address and timely plan management strategies to preserve B. sempervirens as an essential component of rare forest ecosystems.

Four new species of Aspidiotini (Hemiptera, Diaspididae, Aspidiotinae) from Panama, with a key to Panamanian species

Four new species of armored scale insect, Clavaspisselvaticasp. nov., Clavaspisvirolaesp. nov., Davidsonaspistovomitaesp. nov., and Rungaspisneotropicalissp. nov., are described and illustrated from Panama. We also transfer two previously described species of Panamanian Aspidiotini to new genera, Hemiberlesiacrescentiae (Ferris) comb. nov. and Rungaspisrigida (Ferris) comb. nov., and report the first record of Selenaspidopsisbrowni Nakahara in Panama. A key to the species of Aspidiotini occurring in Panama is provided.

What We Don't Know About Diet-Breadth Evolution in Herbivorous Insects

Half a million species of herbivorous insects have been described. Most of them are diet specialists, using only a few plant species as hosts. Biologists suspect that their specificity is key to their diversity. But why do herbivorous insects tend to be diet specialists? In this review, we catalog a broad range of explanations. We review the evidence for each and suggest lines of research to obtain the evidence we lack. We then draw attention to a second major question, namely how changes in diet breadth affect the rest of a species’ biology. In particular, we know little about how changes in diet breadth feed back on genetic architecture, the population genetic environment, and other aspects of a species’ ecology. Knowing more about how generalists and specialists differ should go a long way toward sorting out potential explanations of specificity, and yield a deeper understanding of herbivorous insect diversity.

The Evolutionary and Molecular Features of Broad Host-Range Necrotrophy in Plant Pathogenic Fungi

Necrotrophic fungal pathogens cause considerable disease on numerous economically important crops. Some of these pathogens are specialized to one or a few closely related plant species, whereas others are pathogenic on many unrelated hosts. The evolutionary and molecular bases of broad host-range necrotrophy in plant pathogens are not very well-defined and form an on-going area of research. In this review, we discuss what is known about broad host-range necrotrophic pathogens and compare them with their narrow host-range counterparts. We discuss the evolutionary processes associated with host generalism, and highlight common molecular features of the broad host-range necrotrophic lifestyle, such as fine-tuning of host pH, modulation of host reactive oxygen species and metabolic degradation of diverse host antimicrobials. We conclude that broad host-range necrotrophic plant pathogens have evolved a range of diverse and sometimes convergent responses to a similar selective regime governed by interactions with a highly heterogeneous host landscape.

Asexual parasites and their extraordinary host ranges

In diverse parasite taxa, from scale insects to root-knot nematodes, asexual lineages have exceptionally large host ranges, larger than those of their sexual relatives. Phylogenetic comparative studies of parasite taxa indicate that increases in host range and geographic range increase the probability of establishment of asexual lineages. At first pass, this convergence of traits appears counter-intuitive: intimate, antagonistic association with an enormous range of host taxa correlates with asexual reproduction, which should limit genetic variation within populations. Why would narrow host ranges favor sexual parasites and large host ranges favor asexual parasites? To take on this problem I link theory on ecological specialization to the two predominant hypotheses for the evolution of sex. I argue that both hypotheses predict a positive association between host range and the probability of invasion of asexual parasites, mediated either by variation in population size or in the strength of antagonistic coevolution. I also review hypotheses on colonization and the evolution of niche breadth in asexual lineages. I emphasize parasite taxa, with their diversity of reproductive modes and ecological strategies, as valuable assets in the hunt for solutions to the classic problems of the evolution of sex and geographic parthenogenesis.

A Neutral Model for the Evolution of Diet Breadth

Variation in diet breadth among organisms is a pervasive feature of the natural world that has resisted general explanation. In particular, trade-offs in the ability to use one resource at the expense of another have been expected but rarely detected. We explore a spatial model for the evolution of specialization, motivated by studies of plant-feeding insects. The model is neutral with respect to the causes and consequences of diet breadth: the number of hosts utilized is not constrained by trade-offs, and specialization or generalization does not confer a direct advantage with respect to the persistence of populations or the probability of diversification. We find that diet breadth evolves in ways that resemble reports from natural communities. Simulated communities are dominated by specialized species, with a predictable but less species-rich component of generalized taxa. These results raise the possibility that specialization might be a consequence of stochastic diversification dynamics acting on spatially segregated consumer-resource associations rather than a trait either favored or constrained directly by natural selection. Finally, our model generates hypotheses for global patterns of herbivore diet breadth, including a positive effect of host richness and a negative effect of evenness in host plant abundance on the number of specialized taxa.

Gene expression plasticity across hosts of an invasive scale insect species

For plant-eating insects, we still have only a nascent understanding of the genetic basis of host-use promiscuity. Here, to improve that situation, we investigated host-induced gene expression plasticity in the invasive lobate lac scale insect, Paratachardina pseudolobata (Hemiptera: Keriidae). We were particularly interested in the differential expression of detoxification and effector genes, which are thought to be critical for overcoming a plant's chemical defenses. We collected RNA samples from P. pseudolobata on three different host plant species, assembled transcriptomes de novo, and identified transcripts with significant host-induced gene expression changes. Gene expression plasticity was pervasive, but the expression of most detoxification and effector genes was insensitive to the host environment. Nevertheless, some types of detoxification genes were more differentially expressed than expected by chance. Moreover, we found evidence of a trade-off between expression of genes involved in primary and secondary metabolism; hosts that induced lower expression of genes for detoxification induced higher expression of genes for growth. Our findings are largely consonant with those of several recently published studies of other plant-eating insect species. Thus, across plant-eating insect species, there may be a common set of gene expression changes that enable host-use promiscuity.

Micro- and Macroevolutionary Trade-Offs in Plant-Feeding Insects

A long-standing hypothesis asserts that plant-feeding insects specialize on particular host plants because of negative interactions (trade-offs) between adaptations to alternative hosts, yet empirical evidence for such trade-offs is scarce. Most studies have looked for microevolutionary performance trade-offs within insect species, but host use could also be constrained by macroevolutionary trade-offs caused by epistasis and historical contingency. Here we used a phylogenetic approach to estimate the micro- and macroevolutionary correlations between use of alternative host-plant taxa within two major orders of plant-feeding insects: Lepidoptera (caterpillars) and Hemiptera (true bugs). Across 1,604 caterpillar species, we found both positive and negative pairwise correlations between use of 11 host-plant orders, with overall network patterns suggesting that different host-use constraints act over micro- and macroevolutionary timescales. In contrast, host-use patterns of 955 true bug species revealed uniformly positive correlations between use of the same 11 host plant orders over both timescales. The lack of consistent patterns across timescales and insect orders indicates that host-use trade-offs are historically contingent rather than universal constraints. Moreover, we observed few negative correlations overall despite the wide taxonomic and ecological diversity of the focal host-plant orders, suggesting that positive interactions between host-use adaptations, not trade-offs, dominate the long-term evolution of host use in plant-feeding insects.

Plant defences on land and in water: why are they so different?

BACKGROUND

Plants (attached photosynthesizing organisms) are eaten by a wide variety of herbivorous animals. Despite a vast literature on plant defence, contrasting patterns of antiherbivore adaptation among marine, freshwater and land plants have been little noticed, documented or understood.

SCOPE

Here I show how the surrounding medium (water or air) affects not only the plants themselves, but also the sensory and locomotor capacities of herbivores and their predators, and I discuss patterns of defence and host specialization of plants and herbivores on land and in water. I analysed the literature on herbivory with special reference to mechanical defences and sensory cues emitted by plants. Spines, hairs, asymmetrically oriented features on plant surfaces, and visual and olfactory signals that confuse or repel herbivores are common in land plants but rare or absent in water-dwelling plants. Small terrestrial herbivores are more often host-specific than their aquatic counterparts. I propose that patterns of selection on terrestrial herbivores and plants differ from those on aquatic species. Land plants must often attract animal dispersers and pollinators that, like their herbivorous counterparts, require sophisticated locomotor and sensory abilities. Plants counter their attractiveness to animal helpers by evolving effective contact defences and long-distance cues that mislead or warn herbivores. The locomotor and sensory world of small aquatic herbivores is more limited. These characteristics result from the lower viscosity and density of air compared with water as well as from limitations on plant physiology and signal transmission in water. Evolutionary innovations have not eliminated the contrasts in the conditions of life between water and land.

CONCLUSION

Plant defence can be understood fully when herbivores and their victims are considered in the broader context of other interactions among coexisting species and of the medium in which these interactions occur.