Insect egg morphology: evolution, development, and ecology

Extracellular symbiont colonizes insect during embryo development

Insects typically acquire their beneficial microbes early in development. Endosymbionts housed intracellularly are commonly integrated during oogenesis or embryogenesis, whereas extracellular microbes are only known to be acquired after hatching by immature instars such as larvae or nymphs. Here, however, we report on an extracellular symbiont that colonizes its host during embryo development. Tortoise beetles (Chrysomelidae: Cassidinae) host their digestive bacterial symbiont Stammera extracellularly within foregut symbiotic organs and in ovary-associated glands to ensure its vertical transmission. We outline the initial stages of symbiont colonization and observe that although the foregut symbiotic organs develop 3 days prior to larval emergence, they remain empty until the final 24 h of embryo development. Infection by Stammera occurs during that timeframe and prior to hatching. By experimentally manipulating symbiont availability to embryos in the egg, we describe a 12-h developmental window governing colonization by Stammera. Symbiotic organs form normally in aposymbiotic larvae, demonstrating that these Stammera-bearing structures develop autonomously. In adults, the foregut symbiotic organs are already colonized following metamorphosis and host a stable Stammera population to facilitate folivory. The ovary-associated glands, however, initially lack Stammera. Symbiont abundance subsequently increases within these transmission organs, thereby ensuring sufficient titers at the onset of oviposition ~29 days following metamorphosis. Collectively, our findings reveal that Stammera colonization precedes larval emergence, where its proliferation is eventually decoupled in adult beetles to match the nutritional and reproductive requirements of its host.

Protective Geometry and Reproductive Anatomy as Candidate Determinants of Clutch Size Variation in Pentatomid Bugs

AbstractMany animals lay their eggs in clusters. Eggs on the periphery of clusters can be at higher risk of mortality. We asked whether the most commonly occurring clutch sizes in pentatomid bugs could result from geometrical arrangements that maximize the proportion of eggs in the cluster's interior. Although the most common clutch sizes do not correspond with geometric optimality, stink bugs do tend to lay clusters of eggs in shapes that protect increasing proportions of their offspring as clutch sizes increase. We also considered whether ovariole number, an aspect of reproductive anatomy that may be a fixed trait across many pentatomids, could explain observed distributions of clutch sizes. The most common clutch sizes across many species correspond with multiples of ovariole number. However, there are species with the same number of ovarioles that lay clutches of widely varying size, among which multiples of ovariole number are not overrepresented. In pentatomid bugs, reproductive anatomy appears to be more important than egg mass geometry in determining clutch size uniformity. In addition, our analysis demonstrates that groups of animals with little variation in ovariole number may nonetheless lay a broad range of clutch shapes and sizes.

A Triassic tritrophic triad documents an early food-web cascade

Endophytic oviposition behavior, the insertion of eggs into plant tissues, represents a sophisticated reproductive strategy of insects.1 This process is accomplished by employing a specialized egg-laying device, the ovipositor, that effectively protects eggs through plant tissue concealment.2,3 Endophytic oviposition behavior is currently common in many lineages of several major, extant insect orders, principally Odonata (dragonflies and damselflies), Orthoptera (katydids and grasshoppers), Hemiptera (cicadas, aphids, scale insects, whiteflies, leafhoppers, and bugs), Coleoptera (beetles), Lepidoptera (moths), and Hymenoptera (sawflies).3,4 Based on the occurrences of egg insertion damage and associated scar tissue expressed in fossil plant stems and leaves, endophytic ovipositional behavior is presumed to have emerged as early as the Early Pennsylvanian Period.5 However, for impression fossils, egg morphology and surrounding scar tissue can be difficult to discern on plants, often resulting in ovipositional damage that may be assigned to exophytic (eggs laid on plant surfaces) or to endophytic behavior.6,7,8,9 This ambiguity is due to the spatial relationships and histological mingling of ovipositional damage and enveloping scars with adjoining plant-host tissues. Here, we describe body fossils of insect eggs within ginkgophyte leaves from the Upper Triassic of China. Feeding damage from an egg-predatory insect commonly occurs on these eggs, as some eggs bear up to several feeding punctures. We provide exceptional body-fossil evidence for resource use of a host plant by an ovipositing insect and unravel the earliest-known tritrophic cascade of a host plant, an ovipositing insect, and an egg-predatory insect.

Evolution: Unveiling a hidden tripartite relationship

Endophytic oviposition is one of the most intricate insect reproductive behaviors. A new study characterizes Triassic insect eggs within ginkgophyte leaves, revealing the earliest known tritrophic association of a host plant, ovipositing insect, and egg-predating insect.

Star Polycation Mediated dsRNA Improves the Efficiency of RNA Interference in Phytoseiulus persimilis

RNA interference (RNAi) is one of the most widely used techniques to study gene functions. There is still a lack of RNAi techniques that can be applied in Phytoseiidae conveniently and efficiently. Star Polycation is a new nanomaterial commonly used as a carrier of dsRNA in RNAi. Five genes of P. persimilis (PpATPb, PpATPd, PpRpL11, PpRpS2, and Pptra-2) were selected to verify whether SPc promotes the delivery of dsRNA into P. persimilis through soaking. When each of the five genes were interfered using SPc-mediated dsRNA, the total number of success offspring produced per female in six days decreased by ca. 92%, 92%, 91%, 96%, and 64%. When PpATPb, PpATPd, PpRpL11, or PpRpS2 was interfered, both the fecundity and egg hatching rate decreased. In contrast, when Pptra-2 was interfered, reduction in the reproductive capability was mainly the result of the decreased egg hatching rate. Correspondingly, when the target gene was interfered, P. persimilis expression of PpRpL11 reduced by 63.95%, while that of the other four genes reduced by at least 80%. Our studies showed that nanomaterials, such as SPc, have the potential to be used in RNA interference of phytoseiid mites.