Tessaratomidae
Tessaratomidae is a family of true bugs. It contains about 240 species of large bugs divided into 3 subfamilies and 56 genera.
Tessaratomids resemble large stink bugs and are sometimes quite colorful. Most tessaratomids are Old World, with only three species known from the Neotropics. Some members of Tessaratomidae exhibit paternal care of eggs and offspring. The defensive chemicals of certain species can cause significant damage if they come into contact with human skin; they may also cause temporary blindness.
All species are exclusively plant-eaters, some of major economic importance as agricultural pests. A few species are also consumed as food in some countries.
Description
Larger species of Tessaratomidae are known informally as giant shield bugs, giant stink bugs, or inflated stink bugs, but they generally do not have a collective common name and are referred to mostly as tessaratomids.Tessaratomids are ovate to elongate-ovate bugs. They range in size from the smallest members of the tribe Sepinini at, to the large Amissus atlas of tribe Tessaratomini at. They are generally quite large and usually exceed in length.
The head of tessaratomids is generally small and triangular, with the antennae having 4 to 5 segments. The scutellum, the hard extension of the thorax covering the abdomen, is triangular. It does not cover the leathery middle section of the forewing but is often partially covered by the prothorax. The tarsi have 2 to 3 segments. Tessaratomids are most reliably distinguished from pentatomids by having six exposed abdominal spiracles instead of five.
Like all hemipterans, instead of mandibles for chewing, tesseratomids possess a piercing-sucking mouthpart for feeding. In tesseratomids, the rostrum has 4 segments.
Tessaratomids are often vividly colored, especially nymphs. Bright greens and reds are common colorations.
Ecology
All tessaratomids are phytophagous. They generally feed upon plants belonging to the plant orders Rosales and Sapindales, and spend most of their lives in tree leaves and stems. They exhibit incomplete metamorphosis and have lifespans that can be several years.Some tessaratomids guard their eggs and nymphs from predators which may include parasitoid wasps and assassin bugs.
Life cycle
The eggs of tessaratomids are barrel-shaped or globular. The eggs exhibit a ring of small protuberances, known as micropylar process, which permit entry of sperm for fertilization into the eggs. They also provide openings for air for the developing embryos.The eggs are laid in compact clusters glued to the leaves of a variety of plants. The laying arrangement can follow a pattern. For example, in Pygoplatys tenangau, the egg clusters are distinctively hexagonal; while in Piezosternum subulatum, they are arranged in two neat rows. The eggs are usually initially white, cream, or yellow in color but can change as the embryos inside mature.
Nymphs emerge from the eggs through peristaltic movements and with the help of an internal nearly H-shaped structure in the egg known as the 'egg burster'.
As in other hemipterans, tessaratomids are hemimetabolic, undergoing incomplete metamorphosis. This means that they do not possess larval and pupal stages. Instead, juvenile tessaratomids, hatch directly from the eggs. The nymphs resemble fully grown adults except for size and the absence of wings.
Nymphs usually undergo four to five successive stages of moltings, increasing in size and becoming more adult-like with each stage until the final molting. The stages are individually known as instars, with the earliest stage being known as the first nymphal instar. Nymphs may also differ significantly from adults in colors and patterns exhibited. In some species, nymphs often exhibit strikingly vibrant colors in contrast to the relative drabness of adults. The colors can also vary between instars.
Mating between adults can last for several hours, with the male and female attached end-to-end.
Maternal care
is a well-documented presocial behavior among tessaratomids. Egg guarding by adult females was first observed in 1991 by S. Tachikawa among Japanese species of the genera Pygoplatys and Erga.In 1998, Gogala et al. described Tessaratomines of the genus Pygoplatys from Thailand and Malaysia showing egg guarding behavior. In addition, they were also observed to exhibit another remarkable maternal behavior. A dense cluster of small nymphs were photographed being carried around by adult females. The nymphs were firmly clutching unto the bottom side of the abdomens of the adults and to each other, forming a compact mass. The females seemed unimpeded by their burden and were able to walk around normally and even fly. The nymphs, however, were not observed feeding. This behavior is known as "nymphal phoresy".
In the Indonesian species Pygoplatys tenangau, females will cover the clutch of 70 to 120 eggs with their bodies after laying them, literally "standing guard" over them. When approached, they will spray defensive liquid at perceived attackers and may buzz their wings. They will not willingly abandon the eggs they are guarding, however, and if picked up will try to hold unto the leaf where their eggs are attached. It usually takes slightly more than two weeks for the eggs to hatch. The hatching process will take up 3 to 4 days, during which the newly hatched nymphs will immediately clamber onto their mother's abdomen. They were observed to remain phoretic for at least 17 days.
In the subfamily Oncomerinae, a predominantly Australian group of large colorful bugs, brooding behavior varies from species which do not practice it at all to adult females carrying first and second instar nymphs on their abdomens.
Adult female oncomerines of the genus Lyramorpha will guard nymphs at least to the second instar.
Oncomerines of the genera Cumare, Garceus, and Peltocopta exhibit the most advanced form of maternal care. Like the previously described Southeast Asian Pygoplatys individuals, the females actually carry young nymphs around on their abdomens. As the nymphs grow older, they eventually separate from their mothers, lose their bright colors, and become more solitary prior to molting into adults. Species which exhibit this behavior often have significantly flattened and expanded abdomens.
Of the Australian oncomerines, the bronze orange bug is the only species unequivocally documented to lack maternal brooding behavior. This peculiarity might be connected to the unreliability of the food plant availability for the species. Unlike other oncomerines who can only lay one egg clutch for the certain amount of time it takes to care for them, M. sulciventris can produce multiple egg clutches rapidly because females don't have to care for them. This allows M. sulciventris to rapidly expand their population when conditions are favorable.
Defenses
Tesseratomids, like many heteropterans, use chemical defenses, the source of the common name for pentatomoids - 'stink bugs'. When threatened, tessaratomids may squirt a strong jet of caustic liquid up to a distance of.The chemicals produced by heteropterans are usually alkanes and aldehydes from glands in the thorax. Compounds that are primarily for protection against fellow arthropods. However, the defensive chemicals of tessaratomids are notable for being one of the most debilitating to vertebrates, probably a defense specifically aimed against birds. They can cause damage to human skin and even cause temporary blindness if sprayed unto the eyes.
In Lyramoprha parens, nymphs are also known to be highly gregarious, forming massed feeding groups and moving to new feeding sites in close-packed groups. This behavior, along with their bright colorations and stink glands is believed to help in discouraging potential predators.
Aggregation behavior is also common in adults in some species. Aside from combined chemical defenses, other possible benefits of aggregation include better mating opportunities and shelter, greater retention of moisture and heat, and a possible sense of security. Lone bugs in some species were known to be more likely to be skittish than bugs in groups. However, aggregation can also increase the threats of diseases, parasites, and parasitoids.
If all these defenses fail, tessaratomids will escape predators either by flying away or dropping to the ground.
Natural enemies
of tessaratomids include several tiny parasitoid wasps as well as other hemipterans.Parasitoid wasps that parasitize tessaratomids usually come from the families Eupelmidae, Scelionidae, and Encyrtidae. Adult female parasitoid wasps will search out eggs laid by tessaratomoids. Upon finding some, they will thrust their ovipositors into them and lay eggs inside. The eggs of parasitoid wasps hatch and develop inside the tessaratomid eggs, feeding on the tessaratomid embryo and eventually killing it. Infested eggs characteristically turn darker in color as the wasp larva matures. After about a week, one or more adult wasps will then emerge from the now empty egg.
Musgraveia sulciventris is parasitized by the wasps Eupelmus poggioni and Telenomus spp.; Tessaratoma javanica by the wasps Anastatus colemani and Anastatus kashmirensis; and the lychee giant stink bug Tessaratoma papillosa by the wasps Ooencyrtus phongi, Anastatus spp., and Trissolcus spp..
In tessaratomids considered to be agricultural pests, the wasps that parasitize them are being studied as potential biological control agents. In the Fujian, Guangdong, and Guangxi provinces of China, mass-reared Anastatus japonicus are being released to combat Tessaratoma papillosa pests in lychee and longan crops. The same measures are also reportedly being done in Thailand.
Musgraveia sulciventris is also preyed upon by the predatory pentatomid Asopus and assassin bugs of the species Pristhesancus papuensis and Pristhesancus plagipennis.