Heliothrips haemorrhoidalis

Heliothrips haemorrhoidalis

The greenhouse thrips (Heliothrips haemorrhoidalis Bouché, 1833) is an insect belonging to the Thripidae family.

Systematics –
From a systematic point of view it belongs to:
Eukaryota domain,
Kingdom Animalia,
Subkingdom Eumetazoa,
Bilateria branch,
Phylum Arthropoda,
Subphylum Hexapoda,
Class Insecta,
Subclass Pterygota,
Exopterygota cohort,
Subcohort Neoptera,
Superorder Paraneoptera,
Section Thysanopteroidea,
Order Thysanoptera,
Suborder Terebrantia,
Family Thripidae.
The term is basionym:
– Thrips haemorrhoidalis Bouche, 1833.
The terms are synonyms:
– Dinurothrips rufiventris Girault, 1929;
– Heliothrips adonidum Haliday, 1836;
– Heliothrips haemorrhoidalis subsp. abdominalis Reuter, 1891;
– Heliothrips haemorrhoidalis subsp. angustior Priesner, 1923;
– Heliothrips haemorrhoidalis subsp. ceylonicus Schmutz, 1913;
– Heliothrips semiaureus Girault, 1928;
– Thrips haemorrhoidalis Bouche, 1833.

Geographic Distribution and Habitat –
Heliothrips haemorrhoidalis is an insect widely distributed in tropical and subtropical regions. It is hypothesized that this species is native to a tropical area and was introduced to other areas of the world.
It is also present in Mediterranean countries and in Italy.
It is a phytophagous insect that we find on the leaves of some plants but also on the fruits of citrus fruits (lemon) while on some flowering plants (such as the Gladiolus) it also affects the flowers. Furthermore, in the warmer southern environments and in greenhouses, it remains active even during the winter period, carrying out its biological cycle on cultivated plants.

Morphology –
Heliothrips haemorrhoidalis is a small insect of 1.2 – 1.8 mm in length.
Like other species of the Thripidae family, they have the typical flattened bodies with narrow, fringed, pointed wings and their ovipositors resemble a small saw.
On the head we find the antennae with 8 pale yellow segments, where the last segment narrows to appear needle-like. The head is hypognathous, pointed backwards; this connected to the prothorax via an articular membrane and also via cervical sclerites.
The eyes are compound and made up of 65-70 facets; there are also three ocelli; it also has asymmetrical mouth cones which contain an antheclipeus, lip, paired maxillary stylets and an unpaired left mandible which is well developed.
Adults have a black thorax and yellow to dark brown abdomen, but the tip of the abdomen is orange.
The abdomen is divided into 10 segments and the body is covered by cuticles which have an average thickness of 7.5 micrometres.
The epidermis is made up of flattened cells that are 3 micrometers thick.
The forewings are very narrow and contain a few short bristles on the veins.
The paws have only a single-segmented tarsier. The three pairs of legs of an adult are white.
The H. haemorrhoidalis also has two salivary glands. A pair of salivary glands consist of long tubular glands that run parallel to and attached to the midgut by the basal lamina of the midgut. This pair is composed of microvillated cells in the distal region and is lined by cuticle in the proximal region. The second pair of salivary glands is confined to the thorax and consists of ovoid glands. It seems that this gland produces a viscous type secretion while the tubular gland produces a watery type secretion.
The midgut of H. haemorrhoidalis lacks muscles and its unique feature is that it has a relatively low concentration of ganglia.
The larvae are yellowish-white with red eyes. They resemble a smaller version of an adult and are wingless. As these thrips reach their initial stages, they begin to darken in color.
The structure of the first instar larvae is similar to that of the adults. Their body length is between 430 and 480 micrometres, and their cuticles are about 1.1 to 2.5 micrometres thick. The internal structure of first instar larvae is not much different from that of H. haemorrhoidalis adult. They have only two spiracles and their ganglia are more densely packed than in adults.
The second instar larvae measure about 1.1 mm and are yellowish-brown in color with light gray antennae.
Prepupae look different than an adult as they begin to develop wings. The pupa physically differs from the prepupa in the growth of wings and the folding of the antennae above the insect’s head.

Attitude and biological cycle –
Heliothrips haemorrhoidalis is an insect that in the warmer southern environments and in greenhouses remains active even during the winter period; in the coldest environments it winters as an adult, in shelters among the vegetation or under the bark.
It is a parthenogenetic insect, therefore male individuals in greenhouses are rare. Females have a reproductive system consisting of two ovaries, two lateral oviducts, and an accessory gland. The reproductive accessory gland consists of an apical bulb and a thin glandular duct. At the base of the ovipositor is a sebum gland.
The life cycle of this insect consists of egg development, two nymphal stages, a non-feeding prepupal stage and a pupal stage. A single thrips could produce up to seven generations when living in favorable temperate conditions and more than twelve generations when living in favorable tropical conditions. The average life span of an H. haemorrhoidalis is about one month.
The female independently lays eggs under the surface of leaves or on fruits. If there are exposed areas, females carry the eggs in accessory gland secretions and in feces. The eggs hatch to release the larvae after 14-15 days in environments at 26-28°C and hatch in 16-22 days at 21-25°C.
Some larvae tend to carry fecal droplets on the tip of their abdomen to act as a repellent against predators. After emergence, the female takes about 4-6 days to start oviposition. They produce up to 47 eggs when conditions are right.
The first and second larval stage lasts 9 to 16 days depending on the temperature of the area they live in.
In the prepupal and pupal stages the insect does not feed. The prepupal and pupal stage lasts 3-6 days depending on the temperature of the area they live in. The prepupal and pupal stage will last 3-6 days depending on the temperature of the area they live in.
This thrips completes, depending on the environments, up to 6-7 generations per year.

Ecological role –
Heliothrips haemorrhoidalis is a polyphagous species which adapts to warm climates and consequently very common in greenhouses; it lives mainly on the underside of the leaves.
The damage occurs both on the leaves but also on fruits, such as in the lemon, while on some flowering plants, such as the gladiolus, it also affects the flowers.
The damage is determined by the trophic bites and by the punctiform and blackish excrements that smear the leaves and fruits; on the leaves it manifests itself with silvering of the leaf, necrosis and subsequent phylloptosis.
On citrus fruits, especially lemon, it causes a characteristic rustiness, following the suberification of the tissues; the russeting takes on a whitish color on ripe fruit, while it is brownish on green fruit.
Rusting can also be caused by the attack of mites such as Panonychus citri and others.
The fight against this thrips has been carried out up to now with chemical and agronomic systems, following the criteria of the guided fight.
The agronomic fight consists essentially in pruning practices which tend to thin out the foliage, to limit the swarming of the phytophagous avoiding the stagnation of humidity which favors it.
In the event of heavy infestations, and especially on lemons, chemical control has been used, through treatments in the spring (when the petals fall) and in the autumn which are the most favorable to infestations.
The interventions were performed when the intervention thresholds were exceeded, which were established in:
– 2-3% of infested fruitlets, out of a survey of 20 fruits per plant;
– 5-10% of infested leaves, on a survey of 4 shoots per plant.
However, it should be considered that adults can be monitored by applying blue chromotropic traps, placing one every 50 square meters approximately.
Furthermore, the treatments against scale insects, carried out with white oils, may contain the pullulations of the phytophagous, in these cases, to carry out a joint fight, we intervened with white oils activated with organic phosphorus.
However, Heliothrips haemorrhoidalis has numerous predators; among these we remember two parasitoids: Megaphragma spp. and Thripobius javae. Megaphragma attacks the eggs of H. haemorrhoidalis while T. javae attacks the larvae of H. haemorrhoidalis. It appears that the presence of Thripobius javae in greenhouse plants is an indicator of the presence of H. haemorrhoidalis in the greenhouse. However, one of the Megaphragma species, Megaphragma mymaripenne, is not effective in treating these thrips despite a study showing that 50% of H. haemorrhoidalis eggs showed parasite emergence holes when exposing these thrips to that particular Megaphragma species. .
Other predators that prey on H. haemorrhoidalis are the wasp species Spilomena emarginata and S. nozela. These wasps attack adult and larval thrips and paralyze them to feed on their own larvae.
Furthermore, the specialization of the crops on which it feeds is a determining factor in the proliferation of this thrips, therefore, in addition to the evaluation of its parasitoids, it is necessary to reconsider the production systems, avoiding excessive specializations.

Guido Bissanti

Sources
– Wikipedia, the free encyclopedia.
– GBIF, the Global Biodiversity Information Facility.
– Russo G., 1976. Agricultural entomology. Special Part. Liguori Publisher, Naples.
– Pollini A., 2002. Handbook of applied entomology. Edagricole, Bologna.
– Tremblay E., 1997. Applied entomology. Liguori Publisher, Naples.

Photo source:
– https://inaturalist-open-data.s3.amazonaws.com/photos/12962849/original.jpg