Sigaus Minutus

''Sigaus minutus'' is a species of short-horned grasshopper in the family Acrididae. It is one of the smallest and rarest species of grasshopper in New Zealand, found only in the Mackenzie district of South Island. There are 13 species within the genus ''Sigaus'' described by Bigelow (1967), all endemic to New Zealand. The population status of ''Sigaus minutus'' is declining according to threat assessments made by orthopteran experts in 2010.

Habitat and distribution

''Sigaus minutus'' is found near Lake Tekapo, Lindis Pass and in the Mackenzie district, South Island, New Zealand. It has also been observed near Alexandra in Otago. This grasshopper is very well camouflaged on stony surfaces and amongst lichen. It is absent in areas of dense vegetation as it needs to bask.

Morphological characters

''Sigaus minutus'' is one of the smallest ''Sigaus'' species but very similar to the Otago species ''S. childi.'' Genetically, ''S. minutus'' is sister to the alpine species ''S. campestris'' from central and southern South Island mountains. As seen in most New Zealand grasshoppers, these species are all without functioning wings and their cryptic colouring is variable within populations but always aids camouflage. Females are larger than males.

Dimensions

Adult male: length 9–10 mm, pronotum length 1.6-1.9 mm, pronotum width 1.80-2.20 mm, femur length 4.90-5.60 mm, femur width 1.60-1.90 mm.

Adult female: length 14 –16 mm, pronotum length 2.50-2.65 mm, pronotum width 3.05- 3.30 mm, femur length 7.00-7.20 mm, femur width 2.10-2.50 mm.

External characters

FEMALE

The fastigium is concave with upraised margins and bumps laterally on posterior margin. Posterior margin of pronotum sinuate with broad indent medially, sometimes with small v within the broad indentation (Bigelow, 1967). The character differentiating ''S. minutus'' from ''S. childi'' is the absence of a second pronotum suculus.

MALE

Genitalia: principal lobes of lophi tongue-shaped, Mesal lobes very round projecting medially. Ancorae present, with bulbous swelling when viewed dorso-caudally narrowing to an inwardly directed point. Dorsal sclerite well developed as in other members of this genus, with broad lateral arms converging to form a broad, blunt, upturned projection with swelling at apex projecting caudal. Large swollen shell-shaped supraramus closely flanking the aedeagus. Dorsal aedeagal sclerites large and swollen, ventral aedeagal sclerites long.
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File:Sigaus minutus, seen near Lake Tekapo, New Zealand 2018.jpg, alt=
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Behavior

As with other New Zealand grasshoppers, ''S. minutus'' is a diurnal herbivore, requiring open ground to bask. Males are smaller than females when adult and will remain on the back on the females (in copula) during prolonged mating. Eggs are laid in the soil.

Areas for conservation

The majority of populations of ''S. minutus'' are on small isolated patches of privately owned farmland where land management practices will ensure their extinction. In a survey of 20 sites on Crawford Hills Rd, Alexandra (Jamieson & Manly 1997), no ''Sigaus childi'' or ''S. minutus'' were found on land which is in pasture, used for growing orchards, or being irrigated. Experiments have shown that acridids cannot tolerate insecticides or herbicides and are very sensitive to heavy metals and fertilizers in the soil.

References

External links

*''Sigaus minutus'' discussed on RNZ ''Critter of the Week''
27 May 2022

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Acrididae of New Zealand
Acrididae