Whitefly control
Eret-line e
Eretmocerus eremicus
Eretmocerus eremicus
Eret-line e is a proprietary product containing pupae of the whitefly parasitoid Eretmocerus eremicus Rose and Zolnerowitch, Aphelinidae, Hymenoptera. This species was known as Eretmocerus nr sp. californicus until the taxonomy of the genus was revised in 1997 by Rose and Zolnerowitch.
The initial commercial development of this beneficial was in response to the increasing problems caused by the Tobacco Whitefly (Bemisia tabaci or Bemisia argentifolia) in various countries. Eretmocerus eremicus will parasitise both Bemisia tabaci and the Glasshouse Whitefly Trialeurodes vaporariorum, and is produced using the latter as a host.
Unlike Encarsia formosa, Eretmocerus eremicus is unable to turn within the host integument, and so does not emerge well when attached to cards. Syngenta Bioline havehas developed a Blister Pack as an alternative method of distribution. This can be suspended oin the crop in the same way as an Encarsia card. It makes the product clearly visible, and allows the grower to judge quality and emergence more easily.
The product is also available in a bran base for distribution around the crop.
Eretmocerus eremicus originates in the desert regions of Arizona and California, and is able to tolerate higher temperatures than Encarsia formosa.
Eretmocerus eremicus is available for release in the United Kingdom under licence from DEFRA.
Eretmocerus eremicus is a parasite of Trialeurodes vaporariorum and Bemisia tabaci. It is in the same family as Encarsia formosa, and is similar in size and shape, but does not have the familiar black and yellow coloration. Instead it is a pale yellow or orange, and can be quite difficult to see amongst whitefly larvae. Unlike Encarsia, in which almost all the individuals are female, Eretmocerus populations consist ofhas males and females in almost equal numbers.
Eretmocerus eremicus females search leaves for the larvae of either Bemisia or Trialeurodes. On finding a suitable host, they palpate it with their antennae, and then turn and to insert an egg between the host and the leaf surface. The larva thatwhich hatches from this egg burrows into the host larva, and a capsule forms around it. The larva initially lives within this capsule, but is not apparently damaged by it. Thus the capsule is different from those formed as part of the hosts’ normal immune response to parasitism. The host continues to feed and grow, and is only killed once it hasis fully grown fully grown and has ceased to feed.
Females select mainly second instar host larvae for parasitism, but will lay eggs under other instars. Egg laying is influenced by the leaf structure of the whitefly host plant: hairy leaves lift the margins of the whitefly larvae and make it easier for Eretmocerus to insert eggs under beneath them. The host plant also influences the success of parasite development.
Whitefly parasitised by Eretmocerus do not develop the black colour so characteristic of Encarsia parasitism. They are harder to detect within the crop, and so more careful examination of the host is necessary. Using a microscope, it is possible to see one or both of the yellow ‘mycetomes’, which are normally symmetrically placed either side of the midline, displaced to the side. As the pupa reaches maturity the darker yellow or orange of the adult can be seen with the naked eye.
Although Eretmocerus females cannot penetrate the host cuticle with their ovipositors, they nevertheless kill large numbers of host larvae whichthat do not develop into parasites. Females have been observed probing around the vasiform orifice of whitefly larvae, and it is believed this is host feeding behaviour isat they are host feeding when they do this. Up to 40% of the mortality which occurs has been attributed to this host feeding.
Eretmocerus eremicus (Previously Eretmocerus nr californicus)
Eret-line e is supplied as pupae in a bran carrier, or within ‘Blister Packs’.
For the bottled product:-
On receipt, place the bottles in a cool shaded area. DO NOT EXPOSE TO DIRECT SUNLIGHT OR TEMPERATURES ABOVE 8°C.
Apply the product in the early morning or evening when light levels and temperatures are low.
Do not apply in full sun.
Immediately before use, lay the bottle on its side and rotate gently to mix the contents thoroughly.
Open the bottle in the glasshouse.
Sprinkle the product directly onto leaves, onto the growing medium, or into universal release boxes, in areas with whitefly populations.
Apply at 0 5/m˛ (up to 20/m˛ in areas where whitefly areis already present in the crop).
For the Blister Packs’
Separate the blisters from each other by gently folding and tearing along the perforations.
Bend the card forward slightly at the top of the blister, and pull the tab outwards.
Hang the opened blister onto leaf petioles within the crop, so that it is in a shaded position.
STORAGE:
Use within 18 hours of receipt.
Keep at 5°- 810°C until use.
Eret-line e should be used wherever Bemisia is present. It can also be used to control the Glasshouse Whitefly Trialeurodes vaporariorum, so is useful in mixed populations.
Eretmocerus eremicus is better adapted to high temperatures, and those which that fluctuate strongly from day to night, than is Encarsia formosa. Where the two are used together to control Trialeurodes, the former becomes dominant during periods of hotter weather. It is also reported to perform poorly at low temperatures. . This does not mean that it does not establish and exert control at moderate temperatures: it is simply behaviourally and physiologically adapted to deal with wide fluctuations in temperature, and exploit those times when temperatures are suitable for activity. This section seems unclear to me. It sounds as though it's saying that 'the former', (i.e. Eretmocerus performs better at high temps but poorly at low temps., but then it says that 'it' (Eretmocerus?) is adapted to deal with wide temp ranges.
The use of the two species in combination provides improved control of Trialeurodes throughout the season. Eret-line e should always be used preventively, before whitefly populations become established. High release rates may be able to reduce existing populations, but the cost will be high, and it may be more appropriate to use a compatible insecticide to reduce initial numbers.
Eret-line e is supplied in two forms: a bottle product containing 3000 pupae mixed into a bran carrier material, and a blister pack containing 5,000 in total, as 20 blisters each producing 250 adult Eretmocerus eremicus.
The blisters should be opened by gently flexing the card until the tab on the back of the blister can be pulled open. This tab then needs to be bent so that it does not re-close the blister. Opened blisters are then hung amongst foliage in the crop.
The bottle product should be laid on its side and rolled gently to ensure uniform distribution, and portions of the bran emptied out into Universal Release Boxes or other small containers that which are distributed around the crop.
Use of Eretmocerus eremicus is not recommended as a first option where there is a substantial risk of virus transmission from invading adult Bemisia. Other available biological controls are also not recommended in this situation, and use of an appropriate chemical remains the solution of choice. Eretmocerus may then be introduced when the risk of invasion is lower.
Where Trialeurodes is the pest and Bemisia is not present, consider using Encarsia formosa alone. . On tomato (not Cherry tomatoes) and Aubergine crops in Northern Europe the Mirid Bug Macrolophus caliginosus provides excellent control of both whitefly species after an initial period of establishment. It should be used in conjunction with Encarsia and Eretmocerus.
Used as recommended, Eret-line e will provide season long control of Bemisia and Trialeurodes.
Eret-line e will not control existing high populations of either Bemisia or Trialeurodes when used alone. It will not directly reduce adult populations of whitefly, and cannot protect crops from virus infection carried by invading adult whitefly. It may reduce the subsequent spread of viral infection by reducing the numbers of larvae which reach maturity.
A range of chemical insecticides may be successfully integrated with the use of Eretmocerus. Where the insecticide used affects the development of whitefly larvae, there will inevitably be an indirect effect on Eretmocerus populations because ofdue to the death of hosts. Thus young parasite larvae may die because of the death of the host, but in most cases mature larvae and pupae will survive, and the population will recover rapidly.