A national collection

Diseases

Professional area | Diseases factsheet | Pests | Noctuid moths

Pests

Noctuid moths

These are caterpillars of moths and butterflies. In particular, the Small Mottled Willow Moth (Spodoptera exigua) and Silvery Moth (Autographa gamma) larvae do the most damage.

Voracious and mobile, the Silvery Moth caterpillar feeds at night and hides during the day. At its largest it can attack young leaves and the plant bulb.

The use of pheromone traps will give a warning when the adults are arriving on the wing, in time for precautionary chemical control measures which take the form of baited traps.

Biological methods work well in the case of the Small Mottled Willow Moth.

> Introduction

Noctuid moths are insects of the order Lepidoptera (butterflies and moths). These all have two pairs of membranous wings and a thick, furry body. Their long proboscis is useful for sucking their sustenance, and they fly quickly. Both moths and larvae are essentially active during the night.

 

Within this order, these moths belong to the family Noctuidae. This includes a group of moths which cause a very great deal of harm to many crops, and it is the voracious larvae (caterpillars) which do the damage.

We are concerned here with leaf-eating noctuids.

 

The kinds most often encountered under glass are Chrysodeixis chalcites (Tomato Looper, Green Garden Looper, or Golden Twinspot), Lacanobia oleracea (Tomato Moth or Bright-line Brown-eyes Moth), Mamestra brassicae (Cabbage Army Moth or Cabbage Moth), Autographa gamma (Silvery Moth), Spodoptera exigua (Small Mottled Willow Moth), and Heliothis armigera (Tomato Fruitworm, or Old World Bollworm).

> Life-cycle of butterflies and moths in general

Moths and butterflies have 4 stages of development:

  • egg: laid singly or in groups, on leaves or other objects such as the glass of greenhouses or their metal frames.
  • caterpillar (larva)
  • pupa
  • imago, butterfly or moth

It is only the caterpillar which harms plants; but they are voracious feeders, and get around fast. They have a head with highly developed chewing mouth parts, and can be between 2 and 4 mm long. They grow without stopping right up to the pupa stage and are always feeding heavily except when shedding a skin, when there is a temporary pause.

Once fully grown the caterpillar turns into a pupa, from which the adult emerges.

> The Small Mottled Willow Moth

This armyworm (Spodoptera exigua) is the main culprit when it comes to cyclamen damage.

 

It originates in the tropics and subtropics, where it feeds on a multitude of plant hosts. First appearance in Europe was in the Netherlands in 1976 following an import of infested plants from Florida (Chrysanthemum cuttings).

1 > Physical characteristics

1.1 > Adult moth :

  • only active at night, hidden during the day
  • small (15 mm long), living for 10 to 20 days
  • wingspan 20 to 30 mm
  • wings grey to chestnut
  • back wings have a characteristic bean-shaped yellow marking.

1.2 > Eggs :

  • scaly, 0.1 mm diameter
  • green, turning to grey then black (hard to see)
  • laid in the evening, groups of c. 150, underside of leaves
  • each female lays on average 500 to 600 eggs
  • egg stage lasts 2 to 4 days, depending on temperature.

1.3 > Caterpillars :

  • on hatching, greenish yellow and not very hairy
  • later colour turns chestnut, green or black, and so very easily mistaken for caterpillars of other species
  • side of the caterpillar has a yellow stripe with a black dot on each segment
  • 25 mm long when fully grown
  • 4 pairs of legs on abdomen
  • caterpillar stage takes 1 to 3 weeks, depending on temperature.
  • pupa a chestnut colour
  • pupal stage takes one week, in the ground.

 

At 25ºC (77ºF) the whole cycle of the Small Mottled Willow Moth takes 4 weeks.

2 > Damage seen on cyclamen

The caterpillars (or armyworms) are voracious feeders and can get through a great deal of plant material in a short time; the food they eat depends on their stage of development, but the damage they cause harms the plant a great deal and greatly reduces its market value. They feed mainly at night and stay hidden by day.

 

The young caterpillars eat only the underside of leaves; the older ones make holes in the leaves and also set upon flowers, flower buds and growing tips: they foul the flowers as well with their excreta; and they can get at the bulb by its upper surface.

 

Other noctuids also cause damage to cyclamen plants.

 

Damage on leave caused by caterpillars

 

 

Bulb and buds eaten by caterpillars

 

> Silvery Moth (Autographa gamma)

The Silvery Moth is a migrant moth which leaves southern Europe in summer for more northerly parts, returning in November.

This pest is to be found on brassica crops, but can also infest flower plants such as cyclamen.

There are two generations each year. From June onwards the adult visitors arrive and mate.

1 > Physical features

1.1 > Adult moth :

  • body and wings chestnut to grey in colour
  • front wing brownish to grey, with a velvety centre crossed by a white mark like the letter gamma (y)
  • wingspan 30 to 40 mm
  • back wings light brown, darker brown at the edges.

1.2 > Eggs :

  • white
  • hatch after about 6 days

1.3 > Caterpillars :

  • 40 mm long when fully grown
  • colour green with a lighter side stripe and a dark spot beneath for each segment
  • short stiff hairs
  • a looper, with 2 pairs of abdominal legs that have a typical looping gait (the back is lifted as the rear legs are placed just behind the front, then lowered as the front legs are moved on)
  • three pairs of false legs
  • undulating head movement while moving along.

 

The life cycle takes a little less than one month. The second generation appears in August, and the caterpillars and pupae of these will over-winter in heated glasshouses.

They are particularly fond of stalks and will bite through leaf stems.

 

Perforation of flower stems caused by caterpillars

 

 

Damage in heart of plant caused by Duponchelia

 

> Tomato Looper, Green Garden Looper, or Golden Twinspot (Chrysodeixis chalcites)

This moth also comes from the tropics and subtropics and has been present in French glasshouses since 1973; it may be found on cyclamen. Under glass a number of generations may overlap.

1 > Physical characteristics

1.1 > Adult moth :

  • wingspan 32 to 37 mm
  • wings and bodies golden chestnut
  • front wings have two small characteristic drop-shaped marks.
  • adult lives for 5 to 10 days

1.2 > Eggs :

  • each female lays 3000 to 4000 eggs
  • eggs hatch after 2 to 4 days

1.3 > Caterpillars :

  • very similar to those of the Silvery Moth
  • up to 50 mm long
  • green with a yellow stripe on the side
  • each segmenthas a black dot above the yellow line
  • greenhead
  • two pairs of legs on abdomen (looper)
  • lighter line on the back
  • caterpillar stage takes 4 to 6 weeks

> Tomato Moth or Bright-line Brown-eyes Moth (Lacanobia oleracea, syn. Mamestra oleracea)

Widespread in Europe and of Eurasian origin, the Bright-line Brown-eyes Moth is a fairly common pest of herbaceous plants, especially ornamentals under glass.

1 > Physical characteristics

1.1 > Adult moth :

  • wingspan 30 to 45 mm
  • front wings reddish brown with a wide white stripe near the end
  • rear wings chestnut or grey/chestnut with a more or less visible chestnut patch

1.2 > Eggs :

  • greenish, hemispherical, slightly ribbed
  • laid in groups of 30 to 200 on the underside of leaves.
  • each female can lay 1000 eggs in a lifetime
  • eggs hatch after 1 to 2 weeks

1.3 > Caterpillars :

  • 40 to 50 mm long
  • brown yellowish green or brown flecked with white and (less densely) black
  • lighter stripe on and just below the back
  • yellow side stripes
  • 4 pairs of legs on abdomen
  • brown head
  • caterpillar stage takes 22 to 28 days

1.4 > Chrysalis :

  • 16 to 19 mm long
  • dark brown to black

 

Outdoors, the moths appear from late May onwards, but in a heated glasshouse they may be seen as early as January.

The caterpillars are generally at their most numerous from July to September.

Under glass there may be up to 3 generations in a year.

2 > Damage observed

The young caterpillars do little harm, only gnawing the underside of leaves, producing an intaglio effect. Older caterpillars, on the other hand, consume the whole organ. Leaves, stalks and also flowers may be severely damaged.

> Cabbage Army Moth or Cabbage Moth (Mamestra brassicae)

This is a native European butterfly, and a common pest of ornamental herbaceous plants. In France there may be 2 or 3 generations a year. The adults appear in May or June.

1 > Physical characteristics

1.1 > Adult moth :

  • wingspan 45 mm
  • front wings grey/chestnut with an oval patch with white edges
  • rear wings a light grey/brown with a patch in the middle

1.2 > Eggs :

  • 0.8 mm, spherical, with a slight protuberance
  • transparent when laid, turning chestnut/black
  • laid in groups of 20 to 100 on the underside of leaves.
  • eggs hatch after 12 to 18 days

1.3 > Caterpillars :

  • 35 to 45 mm long
  • colour develops from green to yellow and then chestnut
  • yellow stripe along the body
  • pupa glossy and black or chestnut
  • pupates in the ground
  • pupa over-winters

 

THIS IS NOT AN EXHAUSTIVE LIST. OTHER NOCTUIDS MAY BE FOUND ON CYCLAMEN, EVEN THOUGH THIS IS NOT THEIR PRIMARY HOST (for instance, Turnip Moth, Agrostis segetum)

> How armyworms spread

These are moths that fly, usually by night, and can therefore lay eggs in many spots at some distance from each other.

The caterpillars also can cover fairly large distances; they have normal walking capabilities and can cause damage elsewhere than at the original site of infestation.

> Countermeasures

Current practices, the use of selective controls and the less frequent recourse to soil disinfecting, have resulted in more widespread appearances by these pests among cultivated plants.

> Management measures and prevention

Caterpillars can be picked off by hand while there are still few enough of them. Additionally, steam disinfecting of soil can be a useful way of destroying any pupae that may be there.

 

UV lamp traps (heat source) are useful for estimating the size of the population and can provide some measure of control of adult numbers, which reduces egg laying.

 

Outdoor pheromone traps (sexual trapping) permit detection of flights, and with good forewarning chemical methods of control can be deployed at the best moment. These traps are available for various noctuids (Mamestra oleracea, Chrysodeixes chalcites,...), but not for the Small Mottled Willow Moth.

> Biological control

1 > Using a virus

Good results are obtained against the Small Mottled Willow Moth with the virus Spod-X GH.

This is a polyhedric virus of the Baculovirus family: it is selective for the Small Mottled Willow Moth, and is therefore not toxic for any other organism (insect, animal or human). It infects the larval stage, and young caterpillars are particularly susceptible. 6 days after treatment the disease develops and the caterpillar dies.

The treatment suits cyclamen. It is used in some parts of Holland, though it does not figure on the province’s Index of plant medication, nor the French (1997).

Treatment is recommended immediately the first butterfly appears in the glasshouse or outside; ensure that the underside of the leaves is well wetted (treatment should be repeated at least once a week for 3 weeks). For dosage, see the manufacturer’s instructions.

2 > With a bacterium

Bacillus thuringiensis var. kurstaki may be used for biological control of many lepidoptera, including noctuids. The bacterium contains a pro-toxin of crystalline structure. Once the caterpillar ingests plant matter where the bacterium is present, the enzymes in its gut release the toxin. The bacterium is therefore only effective on the larvae, so it is important to pick the right moment to act. Some hours after ingestion, the caterpillar stops feeding, so damage is limited; the caterpillar then starves to death (by general metabolic disturbance and paralysis of mouth parts) in 2 to 5 days.

There are a number of varieties of the bacterium, each with a toxin that acts specifically on certain insects. This is a method which does no harm to other, untargeted insects such as the beneficial ones.

This bacterium was the very first biological insecticide to be used, back in the 1960s.

There are many commercial preparations, which are to be used in accordance with the manufacturer’s recommendation.

The quantity of active ingredient that the caterpillar needs to absorb depends on the plant concerned and on the size of the caterpillar; so it is important to understand and recognise the various stages of development.

 

In France, this technique is little used on cyclamen because climatic conditions are not humid enough.

It is important to realise also that the Small Mottled Willow Moth (Spodoptera exigua) is unaffected by these bacterial products.

3 > With natural predators of the caterpillars

Introduction of Trichogramma, an egg parasite, can reduce caterpillar populations: these lay their eggs inside a noctuid’s egg and it develops there; this also stops the caterpillars hatching. On the other hand, it does nothing to the caterpillars already present.

> Chemical control

Chemical control is a tricky business. At the time of its introduction into Europe the Small Mottled Willow Moth already had some resistance to certain insecticides, and the problem has got worse since.

The young caterpillars are more susceptible to the active ingredients of chemical controls, which emphasises the importance of timely intervention.

 

The constant development of the regulations and homologations of phytosanitary treatment products, and the differences in regulations according to each country make it impossible for us to include updated information on homologations. Each producer will have to contact his local plant protection bureau to obtain the latest updates concerning the regulations and use of phytosanitary products. We strongly advise testing beforehand on a plant sample in order to measure the chemical’s activity (establishing the dose) and any effect on the plant (plant poisoning).



Caution

This advice sheet is based on the methods used at the SCEA at Montourey (Fréjus, France). These procedures may need some modification to adapt them to other climatic situations. Before starting to grow cyclamen there needs to be a review of precautions against pests and diseases.   We must point out that our advice and suggestions are offered for information purposes and therefore cannot include any guarantee of specific results; it is a good idea to carry out trials beforehand.

 

Pests :

S.A.S Morel Diffusion

2565, rue de Montourey
83600 Fréjus - France

International telephone : +33 (0)4 94 19 73 04
Switchboard : + 33 (0)4 94 19 73 00
Fax : +33 (0)4 94 19 73 19

Contactez notre <br />Responsable technique
Contact our
Technical Adviser