Heterodera humuli
Encyclopedia
Heterodera humuli is a plant pathogenic nematode, the hop cyst nematode. It is an obligate parasite and infests hop plants, Humulus lupulus.
with a body length 0.7 to 0.96 mm. The eggs
are oval, 0.09 x 0.04 mm and the first two instar
larva
e are vermiform. The second instar larvae are mobile in damp soil and invade suitable roots. Here they develop further and become sedentary, burying their heads in cells and feeding on the cell sap. The central part of their bodies swells, and after moulting again they develop into bottle-shaped third instar larvae and then thicker lemon-shaped fourth instar larvae. At this stage they either become male or female depending on the food supply. The swollen larval bodies break out of the root and the mobile males travel through the soil while the females remain attached to the root tissues by their heads. After insemination, the females continue feeding and lay eggs. These remain inside the bodies of the females which die and turn into cysts. A single generation lasts 34 to 56 days depending on environmental conditions.
, Urtica dioica. Infection with this nematode can lead to a poor quality crop and a decrease in yield of hops of 50%. Mortality in hop cuttings is higher in the presence of this nematode.
In a research study in England, cysts of H. humuli were found in every sample taken in a hop garden. The largest number occurred in the top fifteen centimetres of soil but some were found at much greater depths. The numbers of second instar larvae fluctuated in a pattern which indicated that there were probably two or three generations in a growing season, each lasting about six weeks. Under controlled conditions of 20°C and a sixteen hour day, the life cycle lasted forty days and this was the optimal temperature for development. Most second stage larvae invaded hop roots at 15°C but the egg hatch was greater at 20°C. In moist soil, the second-stage larvae survived for at least fifty four days and were still capable of invading roots and reproducing. It is uncertain how long the eggs remain viable in the cysts but in hatching trials using root diffusates of H. lupulus, Cannabis sativa
, Urtica dioica, Urtica urens
and Ficus
sp., only the diffusate of H. lupulus had any effect on the hatching rate of the larvae.
Description
The female hop cyst nematode is white and lemon-shaped with a body length of 0.3 to 0.7 mm and a width of 0.3 to 0.6 mm. The male is transparent and vermiformWorm
The term worm refers to an obsolete taxon used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, and stems from the Old English word wyrm. Currently it is used to describe many different distantly-related animals that typically have a long cylindrical...
with a body length 0.7 to 0.96 mm. The eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
are oval, 0.09 x 0.04 mm and the first two instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e are vermiform. The second instar larvae are mobile in damp soil and invade suitable roots. Here they develop further and become sedentary, burying their heads in cells and feeding on the cell sap. The central part of their bodies swells, and after moulting again they develop into bottle-shaped third instar larvae and then thicker lemon-shaped fourth instar larvae. At this stage they either become male or female depending on the food supply. The swollen larval bodies break out of the root and the mobile males travel through the soil while the females remain attached to the root tissues by their heads. After insemination, the females continue feeding and lay eggs. These remain inside the bodies of the females which die and turn into cysts. A single generation lasts 34 to 56 days depending on environmental conditions.
Distribution
The hop cyst nematode occurs in many European countries, the USA, Canada, South Africa and New Zealand.Biology
The optimal soil temperature for the development of this nematode in plant roots is about 25°C. It prefers heavy soils. The main host plant is the hop, Humulus lupulus, but the nematode can also survive in the roots of the stinging nettleStinging nettle
Stinging nettle or common nettle, Urtica dioica, is a herbaceous perennial flowering plant, native to Europe, Asia, northern Africa, and North America, and is the best-known member of the nettle genus Urtica...
, Urtica dioica. Infection with this nematode can lead to a poor quality crop and a decrease in yield of hops of 50%. Mortality in hop cuttings is higher in the presence of this nematode.
In a research study in England, cysts of H. humuli were found in every sample taken in a hop garden. The largest number occurred in the top fifteen centimetres of soil but some were found at much greater depths. The numbers of second instar larvae fluctuated in a pattern which indicated that there were probably two or three generations in a growing season, each lasting about six weeks. Under controlled conditions of 20°C and a sixteen hour day, the life cycle lasted forty days and this was the optimal temperature for development. Most second stage larvae invaded hop roots at 15°C but the egg hatch was greater at 20°C. In moist soil, the second-stage larvae survived for at least fifty four days and were still capable of invading roots and reproducing. It is uncertain how long the eggs remain viable in the cysts but in hatching trials using root diffusates of H. lupulus, Cannabis sativa
Cannabis sativa
Cannabis sativa is an annual herbaceous plant in the Cannabaceae family. Humans have cultivated this herb throughout recorded history as a source of industrial fibre, seed oil, food, recreation, spiritual enlightenment and medicine...
, Urtica dioica, Urtica urens
Urtica urens
Urtica urens, commonly known as Annual Nettle, Dwarf Nettle or Small Nettle, is a herbaceous annual plant species of the genus Urtica. It is native to Eurasia and it can be found in North America and New Zealand as an introduced species...
and Ficus
Ficus
Ficus is a genus of about 850 species of woody trees, shrubs, vines, epiphytes, and hemiepiphyte in the family Moraceae. Collectively known as fig trees or figs, they are native throughout the tropics with a few species extending into the semi-warm temperate zone. The Common Fig Ficus is a genus of...
sp., only the diffusate of H. lupulus had any effect on the hatching rate of the larvae.