INTERESTING INSECTS

By N A Martin (2019)

Grass soldier aphid

Oregma panicola Takahashi, 1921

Oregma paniciola Tao, 1969

Neoceratovacuna panicicola Ghosh, Pal & Raychaudhuri, 1977

Neoceratovacuna paniciola (Tao, 1969)

This adventive soldier aphid is found living on grasses in many countries. In New Zealand it has been found on two native (indigenous, non-endemic) grasses. The aphid was first found by W. Cottier at Wesley Bay & Hunua Falls, Auckland in 1941. It is still common around Auckland. In summer and autumn, the distinctive white wax covered aphids cover the flower and seed heads of the grass host plants.

Conservation status: This adventive aphid does not appear to cause significant damage to the native host plants.

Soldier aphids have a stage, soldier, with structures that enables them to defend the colony against predators. In the Grass soldier aphid, the soldiers have enlarged and strengthened forelegs and special sharp horns on their head that enable them to pierce the skin of predators and their eggs. Most soldier aphids have a primary host with galls and a secondary host. In New Zealand the Grass soldier aphid is able to breed only on its secondary hosts, grasses. In New Zealand, the Grass soldier aphid only breeds non-sexually and has wingless and winged adult females. It is not certain that sterile soldier nymphs are present.

The adult female aphid may be winged or wingless. Both the wingless and winged females give birth to live nymphs. The adult females are dark coloured. The wingless female is mostly seen covered with powdery white wax that is produced by many large glands on the dorsal (top) side of the abdomen. The winged aphid is also dark coloured, but does not have prominent wax glands. Like other aphids it has two pairs of wings. The forewings have the distinctive pattern of veins typical of its subfamily.

The adults and nymphs have three pairs of legs and one pair of antennae. The wingless female and all nymphs have horns on the front of their head. The horns on the first and second stage nymphs are relatively long and pointed. On the underside of the head is the rostrum, that holds the stylets used for feeding. When not in use the rostrum points back between the legs. Near end of the abdomen aphids have a pair of siphunculae with an opening though which they excrete the honeydew. In the Grass soldier aphid these are small, with the openings are slightly raised. The cauda at the end of the abdomen is short and wide.

Adult females give live birth to nymphs that look like small wingless adults. The first instar and second instar (stage) nymph have long legs that may be pale or dark brown. The head is combined with the prothorax. The body has clearly marked short segments. On the dorsal (top) side there are wax glands like those on the wingless adult female. The wax is often lost when the nymph walks about. There are probably fourl nymphal stages. Nymphs go from one stage to the next by moulting, changing their skin. The mature nymph moults into the adult female. Nymphs that are going to develop into winged adults have wing buds.

If the Grass soldier aphid has an egg laying cycle, it is likely to involve tiny wingless males and sexual females. Each female is likely to lay only one egg. In the absence of a Primary host in New Zealand, eggs are unlikely to be produced in this country.

The Grass soldier aphid has developed the ability to on its secondary host all year and has spread to parts of the world where its primary host, a species Styrax (Styracaceae), does not live.

Feeding and honeydew

Like other Hemiptera, the Grass soldier aphid has sucking mouthparts. The two pairs of long stylets (specially shaped rods) are held in the rostrum. When it wishes to feed, the aphid moves the tip of the rostrum to the surface of the plant. The stylets are then gradually pushed into the plant. One pair of stylets, the maxillae, form two tubes; one through which saliva is injected into the plant and a second through which plants juices are sucked up into the insect. The Grass soldier aphid inserts the stylets into the phloem (the plant vessels for transmitting sap from the leaves to other parts of the plant). The sap has a high volume of water and sugars, more than the insect needs. Excess water and sugar is excreted from the siphuncles and called honeydew.

Two views of wingless adult female Grass soldier aphid, Pseudoregma panicola (Hemiptera: Aphididae) on a seed head of a native grass, Oplismenus hirtellus (Gramineae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30UM]

Photographs of the white wax on the bodies of two wingless female Grass soldier aphids, Pseudoregma panicola (Hemiptera: Aphididae). Creator: Miss M. J. Dahlberg. © Figure 91 in Cottier W. 1953. Aphids of New Zealand. N.Z. Department of Scientific and Industrial Research Bulletin. 106: 1-382. [Image: 30UZ]

© Figure 90 in Cottier W. 1953. Aphids of New Zealand. N.Z. Department of Scientific and Industrial Research Bulletin. 106: 1-382. [Image: 30UY]

Two views of wingless adult female Grass soldier aphid, Pseudoregma panicola (Hemiptera: Aphididae) on a seed head of a native grass, Oplismenus hirtellus (Gramineae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30UK]

Two views of nymphs and wingless adult female Grass soldier aphid, Pseudoregma panicola (Hemiptera: Aphididae) on a seed head of a native grass, Oplismenus hirtellus (Gramineae): note the long legs of the nymphs. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30UI]

Nymphs of Grass soldier aphid, Pseudoregma panicola (Hemiptera: Aphididae) on a seed head of a native grass, Oplismenus hirtellus (Gramineae): note their long legs. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30UJ]

Microscope slide of a first instar (stage) nymph of Grass soldier aphid, Pseudoregma panicola (Hemiptera: Aphididae): note the sharp horns on its head. Creator: Nicholas A. Martin. © Landcare Research. [Image: 30YM]

Microscope slide of a second instar (stage) nymph of Grass soldier aphid, Pseudoregma panicola (Hemiptera: Aphididae): note the sharp horns on its head. Creator: Nicholas A. Martin. © Landcare Research. [Image: 30YN]

Microscope slide of a second instar (stage) nymph of Grass soldier aphid, Pseudoregma panicola (Hemiptera: Aphididae): note the sharp horns on its head. Creator: Nicholas A. Martin. © Landcare Research. [Image: 30YP]

White wax covered Grass soldier aphids, Pseudoregma panicola (Hemiptera: Aphididae) on a seed head of a native grass, Oplismenus hirtellus (Gramineae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 30YQ]

Flower and seed head of a native grass, Oplismenus hirtellus (Gramineae) with white wax covered Grass soldier aphids, Pseudoregma panicola (Hemiptera: Aphididae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 30UW]

Flower head of a native grass, Oplismenus hirtellus (Gramineae) with white wax covered Grass soldier aphids, Pseudoregma panicola (Hemiptera: Aphididae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30UD]

Nymphs and wingless females of Grass soldier aphid, Pseudoregma panicola (Hemiptera: Aphididae) on a seed head of a native grass, Oplismenus hirtellus (Gramineae): note some of the large nymphs have wing buds. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30UN]

Nymphs of Grass soldier aphid, Pseudoregma panicola (Hemiptera: Aphididae) on a seed head of a native grass, Oplismenus hirtellus (Gramineae): note some of the large nymphs have wing buds. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30UH]

Recently moulted nymph of Grass soldier aphid, Pseudoregma panicola (Hemiptera: Aphididae) on a seed head of a native grass, Oplismenus hirtellus (Gramineae): note the wing buds and the pale areas on the abdomen that might be wax secreting glands. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30UL]

A colony with a winged adult female Grass soldier aphid, Pseudoregma panicola (Hemiptera: Aphididae) on a seed head of a native grass, Oplismenus hirtellus (Gramineae): note the white wax coating the non-wnged aphids. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30UP]

Two views of a colony of Grass soldier aphids, Pseudoregma panicola (Hemiptera: Aphididae) on a seed head of a native grass, Oplismenus hirtellus (Gramineae): note the winged female and the white wax coating the other aphids. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30UQ]

Drawing of the forewing of an adult female Grass soldier aphid, Pseudoregma panicola (Hemiptera: Aphididae). © Figure 4 in Cottier W. 1953. Aphids of New Zealand. N.Z. Department of Scientific and Industrial Research Bulletin. 106: 1-382. [Image: 30UX]

Two views of the upper side of a winged adult female Grass soldier aphid, Pseudoregma panicola (Hemiptera: Aphididae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30UR]

Two views of the underside of a winged adult female Grass soldier aphid, Pseudoregma panicola (Hemiptera: Aphididae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30US]

Normally aphids require specialist skills for their identification, However, in summer, colonies of the Grass soldier aphid are easy to recognize when it is inhabiting its two native grass host plants in summer. The young shoots, flower and seed heads of the grasses are covered by these white wax covered aphids. The winged adult female has the wings folded flat over her abdomen unlike other winged aphids that hold their wings vertically.

Flower and seed heads of a native grass, Oplismenus hirtellus (Gramineae) with white wax covered Grass soldier aphids, Pseudoregma panicola (Hemiptera: Aphididae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 30UT]

Flower and seed head of a native grass, Oplismenus hirtellus (Gramineae) with white wax covered Grass soldier aphids, Pseudoregma panicola (Hemiptera: Aphididae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 30UV]

A colony of Grass soldier aphids, Pseudoregma panicola (Hemiptera: Aphididae) on a seed head of a native grass, Oplismenus hirtellus (Gramineae): note the white wax coating the aphids. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30UE]

A colony of Grass soldier aphids, Pseudoregma panicola (Hemiptera: Aphididae) on a stem of a native grass, Oplismenus hirtellus (Gramineae): note the white wax coating the aphids. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30UG]

Two views of a colony of Grass soldier aphids, Pseudoregma panicola (Hemiptera: Aphididae) on a seed head of a native grass, Oplismenus hirtellus (Gramineae): note the winged female and the white wax coating the other aphids. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30UQ]

No natural enemies of this soldier aphid have been recorded in New Zealand.

The Grass soldier aphid has been found on two species of native grasses in New Zealand. Normally, soldier aphids have a primary host on which they induce galls in which they live and breed. In New Zealand the Grass soldier aphid has no primary host, it just has ‘secondary’ host plants on which it breeds and completes its annual cycle.

The primary host is likely to be a species in the genus Styrax (Styracaceae). An example of this genus is the ornamental species grown in New Zealand, Styrax japonica, Japanese snowdrop tree, Japanese snowbell tree.

Feeding and honeydew

Like other Hemiptera, the Grass soldier aphids have sucking mouth parts. The long stylets, special shaped rods, are held in the rostrum. When it wishes to feed the aphid moves the tip of the rostrum to the surface of a leaf or stem. The stylets are then gradually pushed into the plant. The inner pair of stylets, form two tubes, one through which saliva is injected into the plant and a second through which plants juices are sucked up into the insect. Grass soldier aphids insert its stylets into the phloem, the plant vessels for transmitting sap from the leaves to other parts of the plant. The sap has a high volume of water and sugars, more than the insect needs. Aphids excrete the excess water and sugar, which is called honeydew.

Flower and seed heads of a native grass, Oplismenus hirtellus (Gramineae) with white wax covered Grass soldier aphids, Pseudoregma panicola (Hemiptera: Aphididae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 30UU]

Flower and seed heads of a native grass, Oplismenus hirtellus (Gramineae) with white wax covered Grass soldier aphids, Pseudoregma panicola (Hemiptera: Aphididae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 30UT]

Flower and seed head of a native grass, Oplismenus hirtellus (Gramineae) with white wax covered Grass soldier aphids, Pseudoregma panicola (Hemiptera: Aphididae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 30UW]

A colony of Grass soldier aphids, Pseudoregma panicola (Hemiptera: Aphididae) on a seed head of a native grass, Oplismenus hirtellus (Gramineae): note the white wax coating the aphids. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30UF]

A colony of Grass soldier aphids, Pseudoregma panicola (Hemiptera: Aphididae) on a stem of a native grass, Oplismenus hirtellus (Gramineae): note the white wax coating the aphids. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30UG]

Two views of a colony of Grass soldier aphids, Pseudoregma panicola (Hemiptera: Aphididae) on a seed head of a native grass, Oplismenus hirtellus (Gramineae): note the winged female and the white wax coating the other aphids. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 30UQ]

Research Project

In New Zealand, several aspects of the annual cycle of the Grass soldier aphid are uncertain. For example, are soldier castes present, are they sterile, and when are they produced. Other nymphs also have horns on their head. Can these be used in defence of the colony?

Also it would be useful to know how the populations survive the winter, i.e. what is their annual cycle in New Zealand.

Soldier aphids

The existence of ‘soldiers’ in aphid colonies was only discovered in 1977. This section summarises information from two recent publications (Aoki & Kurosu 2010, Stern & Foster 1996) that are listed in Information Sources.

Species of aphids with ‘soldiers’ have only been found in two subfamilies of aphid, Eriosomatinae and Hormaphidinae and are usually associated with a primary host plant on which they induce galls in which they live. The gall formers have a second host plant that is colonised by winged aphids. On each host there are parthenogenetic generations, before winged aphids produced. The defensive morph (soldier) is usually first or second instar (stage) nymph. They are usually sterile, that is they cannot moult and grow into adult females. It is believed that most species evolved the soldier morph to defend the colony in the gall on the Primary host plant. Soldiers are also present on the secondary host plants.

A general distinguishing characteristic of soldiers is that they tend to attack, rather than run away from, predators. They will attack and kill predator eggs as well as larvae. Soldiers with enlarged forelegs and sharp horns on their head, repeatedly pull the predator onto their horns, tearing the predator’s cuticle (skin). Other soldiers use their stylets to attack predators. They may also have enlarged forelegs, hind legs, the middle leg or all three. Soldier aphids have been shown to be effective against larvae of Syrphidae (hoverflies), Coccinellidae (ladybirds), Chrysopidae (green lacewings), Anthocoridae and Lycaenidae (predatory sucking bugs).

Aoki A, Kurosu U. 2010. A Review of the Biology of Cerataphidini (Hemiptera, Aphididae, Hormaphidinae), Focusing Mainly on Their Life Cycles, Gall Formation, and Soldiers. Psyche, A journal of Entomology 2010: 1-31.

Cottier W. 1953. Aphids of New Zealand. N.Z. Department of Scientific and Industrial Research Bulletin. 106: 1-382.

Singh G, Singh R. 2018. Updated check-list of Indian Hormaphidinae (Aphididae: Hemiptera) and their food plants). Journal of entomology and zoology studies 6(2): 1345-1352.

Stern D L, Foster W A. 1996. The evolution of soldiers in aphids. Biological Review 71: 27-79.

Plant-SyNZ: Invertebrate herbivore-host plant association database. plant-synz.landcareresearch.co.nz/.

The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.

Landcare Research New Zealand Limited (Landcare Research) for permission to use photographs.