Ophionyssus natricis
Also know an: Snake Mite
Introduction
The life cycle of the snake mite Ophionyssus natricis (Camin, 1953) which is similar to other macronyssid and dermanyssid mites, can be completed in less than three weeks at 30ºC. The rate of maturation of the various stages is temperature dependent and one moult occurs between each stage.
- For information on the treatment of snake mites, see Snake Mite Infestation.
Average time span in each snake mite's life cycle stage at two different temperatures.
| Development Stage | 30°C (86°F) | 20°C (68°F) |
|---|---|---|
| Egg | 1-2 days | about 4 days |
| Lava (non-feeding) | less than 1 day | about 4 days |
| Protonymph (feeding) | 3 days | 14 days |
| Deuteronymph (non-feeding) | < 1 day | > 1 day |
| Adult (feeding) | 10 days | 32 days |
Development
Eggs
A gravid female leaves the host and finds a dark, moist crevice and lays eggs that are developed to the blastula or early gastrula stage. The rate of development is temperature dependent. Most eggs hatch into larva at relative humidity of 85% and greater. Desiccation resulting in ineffective hatching is a major cause of egg mortality.
Larva
An eggs hatches into a soft-bodied larvae that does not move after leaving the egg. The larval stage is very sensitive to desiccation and usually stays in the region of hatching until it matures and moults which usually requires 18-24 hours at 25-30ºC. Improper moulting is a major cause of mortality and effective moulting requires a relative humidity of at least 75%.
Protonymph
The larva mounts to the protonymph stage, which stay in the humid hatching area until its exoskeleton becomes sclerotised. A host is actively located and feeding begins within 24 hours. Numbers of unfed protonymphs may be found on objects within the cage and will attach to the snake when they are disturbed. They quickly crawl under scales and lacerate the soft skin between scales with their chelicerae. They remain attached to one spot until fully engorged. The duration of feeding is largely dependent on ambient temperature. The rate of engorgement is temperature dependent and typically requires three to seven days of feeding at 25ºC. When near full engorgement the posterior region of the body can be seen protruding from under the scale. While feeding is necessary for maturation and moulting to deuteronymphs, protonymphs can endure periods of starvation of up to one month. When full of blood, the protonymph drops off the host, finds a dark, moist crevice and moults. Approximately 10-20% of the nymphs die due to improper moulting even at optimum temperatures and relative humidities.
Deuteronymph
The protonymph moults into the deuteronymph stage. The deuteronymph is active but usually remains in the environment and not on the snake. The deuteronymph stage is of relatively short duration. The opposite sexes usually pair off in either the late protonymph or deuteronymph stage with the smaller male on the dorsum of the female. Ineffective moulting is a major cause of mortality.
Adult
The deuteronymph moults to the adult stage. Adults are sexually dimorphic and very active. Their life span is up to 40 days under favourable conditions. Both sexes will actively feed by telmophagy (compared to solenophagy) and use their well-developed chelicerae to lacerate the soft skin between scales. A blood meal is required for egg production but does not affect longevity. Mating takes place shortly after the mites reach adulthood. Upon locating a host the adult attaches under the scales.
Female adults are voracious feeders and can increase their body weight up by 1500% (from 0.05 mg to 0.75 mg) by feeding over a period of five to eight days. When near full engorgement the posterior region of the body can be seen protruding from under the scale. Fully engorged mites are frequently observed on the dorsolateral body before dropping from the host. Engorged females find a dark moist concealed area where they lay approximately 20 eggs over a five to 20 day period depending on the environmental temperature. Adult females will then feed again and reproduce two to three times at intervals of one to two weeks. A single female is capable of producing 60 to 80 eggs in her lifetime.
Males are frequently found on the dorsum of unfed adult or immature females. Mated females produce both fertilised and unfertilised eggs and viable egg production is not dependent upon successful mating. Fertilised eggs develop into females and unfertilised eggs develop into males from parthenogenesis.
Morphology
Egg
The eggs are about 300-400 µm in length and 200-300 µm in width. They are off-white to tan ovoid structures that darken at one pole. The eggs are visible to the unaided eye and do not change in size as they develop. Unfertilised eggs are somewhat smaller than fertilised eggs.
Larva
The larval stage is a small, white, fragile, non-feeding, six-legged mite (400 µm x 250 µm). The integument is poorly scleritised and bears numerous papillae that gives a cobblestone. The developing fourth leg of the later nymphal and adult stages may be observed as a crescent shaped structure under the lateral integument posterior to leg Ill.
Protonymph
The unfed protonymph is similar in size to the larva. The body is posteriorly tapered and there are four pairs of legs and well-developed chelicerae. The dorsal and ventral surfaces are partially covered with scleritised plates and a number of setae. Leg I is slightly shorter than leg IV and legs II and Ill are shorter again. The posterior three pairs of legs are used for locomotion. Pair 1 bears sensory receptors in the tarsal segments and may be waved in front of the body. The body of the fully engorged protonymph is ovoid in shape and is approximately twice as long as it is wide. Engorged male protonymphs average 530 by 275 µm whereas females average 688 by 360 µm.
Deuteronymph
The bodies of the deuteronymphs are approximately the same size as engorged protonymphs or unfed adults of the same sex and are typically dark red to black in colour. The dorsal and ventral integument lacks the scleritised plates found on protonymphs and adults and has a striated texture. The density of setae is markedly reduced in comparison to protonymphs and adults and the chelicerae are soft and underdeveloped in comparison to those of the protonymph and adult. The legs are longer than those of the protonymph with pair II the shortest.
Adult Male
Unfed adult males are ovoid with a posteriorly tapered body (500 µm x 200-250 µm). Legs I & IV are approximately 50 µm longer than II & III. The body is covered with scleritised plates and has a hairy appearance due to numerous setae. Engorged males are posteriorly ovoid and are wider (300-350 µm) than unfed males. The colour of the engorged male is dependent upon the amount of ingested erythrocytes and the degree of digestion.
Female Adult
Unfed adult females are ovoid (600 µm x 300-400 µm). Legs I and IV are approximately 100 µm longer than II and Ill. The body is covered by scleritised plates and has a hairy appearance due to numerous setae. Fully engorged females are posteriorly globose and may measure over 1300 µm in length. They are dark red or black in colour.
Definitions
- Archenteron - Surface cells of the gastrula invaginate to form mesoderm and endoderm. The invagination is the archerteron, the primitive gut.
- Blastopore - The blastopore is the opening that forms as a result of invagination of the surface layer of the gastrula to form
the archenteron.
- Blastula - The blastula stage follows the morula and is produced by the cleavage of the fertilised ovum. It consists of the blastoderm, a single layer of cells that surrounds the blastocoele, a fluid-filled cavity.
- Chelicerae - Chelicerae are the mouthparts of ticks and some blood-feeding mites and consist of a pair of chelicerae lateral to a central hypostome.
- Dermanyssid mite - Dermanyssid refers to parasitic mites of the family Dermanyssidae. Species include Dermanyssus, Ornithonyssus and Pneumonyssus.
- Gastrula - The gastrula stage follows the blastula and consists of ectoderm and endoderm. These have invaginated to form the anchenteron and an opening, the blastopore.
- Macronyssid mite - Macronyssid refers to parasitic mites of the family Macronyssidae.
- Scleritise - Scleritisation is the hardening of exoskeleton.
- Setae - Setae are hairlike projections.
- Sexually dimorphic - Sexually dimorphic species are those where the different sexes have different physical appearances.
- Solenophagy - Solenophagy is the method of feeding employed by mosquitoes and some other insects. Blood vessels are directly fed from after they have been penetrated.
- Telmophagy - Telmophagy is the type of feeding where the blade-like distal ends of the chelicerae mechanically lacerate host tissue. The hypostome is then inserted into the wound and is attached to host tissue. The mite feeds from a pool of blood that forms around the embedded mouthparts. Blood is taken in through the feeding channels located between the chelicerae and hypostome by capillary action through the activity of a pharyngeal pump.