What is Nasonia, the Parasitoid Jewel Wasp?

Nasonia is a genus of small parasitoid wasps, often measuring only a few millimeters long. Commonly called jewel wasps, their name reflects a metallic, gem-like sheen on their bodies. These insects belong to the Hymenoptera order, which also includes ants and bees. While harmless to humans, they have a specialized reproductive strategy that has captured the attention of researchers.

Life as a Parasitoid Wasp

The life of a Nasonia wasp is defined by its parasitoid nature, a strategy where its larvae develop on another organism, ultimately consuming and killing the host. A female wasp seeks a suitable host, the pupa of a fly like a blowfly or flesh fly, often found in carrion or bird nests. Upon locating a host puparium, the hard outer casing of a fly pupa, she uses her ovipositor—a sharp, tube-like organ—to drill through its wall.

After penetrating the casing, the female injects a potent venom that paralyzes the developing fly and halts its growth, preserving it as a fresh food source. She then lays a clutch of 20 to 50 eggs directly onto the host’s surface. The female also uses her ovipositor to feed on the host’s nutrient-rich fluids, known as hemolymph, which aids in producing more eggs.

The wasp eggs hatch in approximately 36 hours. The newly emerged larvae feed on the immobilized fly pupa for about nine days, progressing through several growth stages within the protective host puparium. Once development is complete, the larvae pupate and transform into adult wasps. The new adults then chew an exit hole through the host casing to emerge and repeat the cycle.

A Wasp with Extraordinary Genetics

Nasonia possesses a genetic system called haplodiploidy. In this system, the sex of an individual is determined by the number of chromosome sets it has. Females develop from fertilized eggs and are diploid, meaning they have two sets of chromosomes, one from each parent. Males develop from unfertilized eggs and are haploid, possessing only a single set of chromosomes from their mother.

This haplodiploid system is an advantage for genetic studies. Because males are haploid, any recessive genes they carry are immediately expressed, as there is no second chromosome to mask their effects. This allows researchers to more easily identify the function of genes and how traits are inherited.

The genetics of Nasonia are further complicated by an intracellular bacterium called Wolbachia. This inherited bacterium manipulates the wasp’s reproduction. Its most notable effect is cytoplasmic incompatibility, a phenomenon where sperm and eggs from different populations become incompatible, creating a reproductive barrier. However, these bacteria can be eliminated with antibiotics, making different species interfertile in a lab setting.

Intricate Behaviors of Nasonia

The behaviors of Nasonia are finely tuned to their parasitoid lifestyle. Mating occurs almost immediately upon emergence from a host. Males emerge first and wait for the females, which leads to intense local mate competition as brothers from the same clutch vie to mate with their sisters. Brief, stereotypic courtship displays precede mating, after which females disperse to find new hosts.

Host selection is a key behavior for a female Nasonia, as her progeny’s success depends on finding a suitable host. This involves detecting chemical cues associated with fly pupae. The family of odorant binding proteins, which are involved in detecting smells, has expanded in the Nasonia genome, enhancing its ability to locate hosts in complex chemical environments.

Venom plays a multifaceted role beyond simple paralysis. The complex cocktail of proteins not only subdues the host but also manipulates its physiology to prevent immune responses that could harm the developing wasp larvae. This chemical manipulation ensures the host remains a viable, non-reacting food source throughout the wasps’ development.

Why Scientists Study Nasonia

Nasonia is a model organism for research across several scientific disciplines, including evolution, genetics, and developmental biology. The ease of rearing these wasps and their short two-week generation time make them a practical system for laboratory experiments. Their ability to enter a dormant larval stage, known as diapause, also allows for the long-term storage of genetic strains.

The haplodiploid sex determination system simplifies the study of complex traits and the genetic basis of behavior. Scientists can map genes involved in species differences by taking advantage of the interfertility between species after antibiotic treatment. This has made Nasonia a tool for studying speciation and the genetic underpinnings of traits like courtship behavior and host preference.

The interaction between Nasonia and the Wolbachia bacterium provides a model for understanding host-symbiont relationships and their evolutionary consequences. Research on their venom composition sheds light on the rapid evolution of proteins and the molecular arms race between a parasitoid and its host. The availability of sequenced genomes for three Nasonia species has further accelerated this research, enabling detailed genetic comparisons.