R2103 3.2 Cabbage white and Black bean aphid

Question 1

How do insects breath?

Answer 1

A system of tubes, called tracheae which penetrate right through the insect’s body. Air enters the tracheae by pores called spiracles on each side of the insect’s abdomen. Each segment of the abdomen has a pair of spiracles.

Question 2

What shrubs are hosts for black bean aphid?

Answer 2

Viburnum opulus and Euonymus europaeus

Question 3

When should barrier netting be used to prevent damage from cabbage white butterfly?

Answer 3

Before April

Question 4

Describe caterpillars of large white butterfly.

Answer 4

Yellow and black and hairy, whereas for the small white they are green.

Question 5

What does complete metamorphosis mean?

Answer 5

Complete change through stages of egg, larva (caterpillar), pupa (inactive) and adult.

Question 6

Describe life cycle of cabbage white butterfly.

Answer 6

Two generations per year with caterpillars emerging from late spring until early autumn.

1. Eggs laid in batches 20–100 underside of cabbage leaves May/June.
2. Larvae hatch after 1–2 weeks; feed on leaves for about 5 weeks, then pupate.
3. Pupa attached by silk; 3–4 weeks hatches into adult butterfly in July/August.
4. Adult emerges in July/August.

Question 7

Describe the black-bean aphid life cycle.

Answer 7

1. Eggs overwinter on Viburnum opulus and Euonymus europaeus.
2. In spring, eggs hatch out into wingless females, which reproduce without mating (parthenogenesis).
3. From time to time, winged daughters are produced and these fly away to colonise new plants such as beans or other summer hosts in May/early June. They continue to breed there, feeding on and damaging the crop.
4. During the summer months, the aphid continues to produce wingless daughters by parthenogenesis. More winged females are also produced and these will spread to new plants.
5. From winged females, wingless females are produced.
6. Only in the autumn (in response to decreasing daylight and temperatures) are both sexes produced which are winged and fly to the winter host plants. The females then give birth to egg-laying females (wingless daughters). The winged males then mate with the egg-laying females (wingless) who then lay eggs and start the cycle all over again.

Question 8

Glasshouse whitefly: facts

Answer 8

• Difficult pest to control under glass because breeding is very rapid.
• Best way to control is through using biological controls.
• Breeding is continuous under glass but development time is dependent on temperatures. Less than 3 weeks if conditions are ideal, this lengthens over the winter months. Prefer warm conditions and develop very quickly when temperatures are between 26–32°C.
• The damage is caused by the feeding activities of both adults and immature stages, via the piercing mouthparts where they withdraw copious amounts of sap.

Question 9

Describe the life cycle of glasshouse whitefly.

Answer 9

1. Egg
2. First instar (immature)
3. Second instar (immature)
4. Third instar (immature)
5. Fourth instar (immature)
6. Adult

• April: parthenogenic egg laying starts; females lay about 200 very small elongated oval eggs on the lower leaf surface over a period of several weeks.
• These hatch to produce nymphs which then become flat and immobile. Green.
• This then results in a series of instars.
• The last stage (fourth instar) involves a scale stage which is a thick walled ’pupa’ (although it is not a true pupa). From which the adult female or male emerges.
• The adults are tiny (1.5mm), with four wings, and scatter when disturbed. The white colour is due to deposits of white wax.
• 3 days later and the newly hatched female will start laying eggs.
• The whole cycle takes about 32 days in spring and 23 days in the summer. Huge numbers can occur, resulting in a serious outbreak.
• The skins of the eggs and pupa stages are very thick and are therefore hard to control.

Weeds such as nettles are suitable host species and should be controlled where they grow near glasshouses.

Question 10

Vine weevil quick facts

Answer 10

Affects: ornamental plants and some fruits, especially those grown in containers

Main symptoms: Adult weevils notch leaf margins (particularly on thick-leaved evergreen plants such as rhododendron); grubs eat roots

Most active: Adult weevils: spring to late summer; grubs: summer to spring

Control:

1. Mild spring or summer evenings: pick off the adult weevils. Shake shrubs over an upturned umbrella, newspaper or similar to dislodge and collect more. In greenhouses, look under pots or on the underside of staging benches where the beetles hide during the day
2. Trap adults with sticky barriers
3. Encourage wildlife – birds, frogs, toads, shrews, hedgehogs and predatory ground and rove beetles
4. Remove as many larvae as possible from compost infested with grubs