EPPO Bull. 10 (4) : 491-498 (1980)

Colorado Beetle in the Channel Islands

by G. THOMAS' and F. WOOD2

An account of the Colorado beetle in the Channel Islands is given which records the successful results obtained there in preventing the establishment of this serious crop pest. This has been achieved by means of extensive efforts within the Islands and by sustained international cooperation with France, through the auspices of EPPO, to prevent sea-borne invasions from the Cotentin peninsula which threaten the Islands annually. This campaign has been amply justified and, as a result, no sea-borne invasions have occurred in the Islands from 1965 to 1975 and precautionary spraying of the potato crops there was discontinued in 1966.

Introduction

The advance of the Colorado beetle through France from 1922 to 1939 was viewed with considerable anxiety by the Channel Islands authorities because of the proximity of the islands to the Continent (fig. I). The prosperity of the Islands was threatened because, once the beetle became established, there would be serious repercussions on the important trade of agricultural produce between them and the United Kingdom. In Jersey, the agricultural economy was based chiefly on the export of early potatoes (3000 ha) and outdoor tomatoes, that of Guernsey mainly on the export of glasshouse tomatoes, but growing some 250 ha of potatoes, and the two governments were vitally interested in keeping the Islands free from Colorado beetle.

From 1933 onwards, considerable preparations were made to minimise the effect of possible beetle introduction, including special legislation, educational programmes involving films, leaflets and posters, the training of inspectors and laying in stocks of lead arsenate and carbon disulphide.

The first outbreak, an isolated case in Jersey, occurred in 1939, one year after the beetle became prevalent in the Cotentin, but the islands remained free from infestation thereafter until 1943, when five single beetles were found in separate areas near the south coast of Jersey. In 1944, four breeding colonies were discovered in this island but, because of the German Occupation (1 940-1 9451, the strict control measures which had been adopted previously were not possible and many beetle colonies became established, mainly within military fortifications.

After the liberation (May 19451, 46 colonies were present in Jersey but, by the end of 1946, these infestations were almost completely eradicated. This remarkable success was achieved only by energetic and costly measures applied under extreme difficulties. It had been found necessary in 1946 to strengthen legislation, allowing potato crops to be grown only under licence, and to prevent the crop being grown in private gardens. Growers were obliged to inspect their crops at least once every 14 days and all potato crops were given protective sprays and had to be examined by an official inspector within 3 days prior to lifting or destruction of the haulms. These and other measures allowed strict control to be applied, and total eradication of the Colorado beetle within the Islands by 1947 was envisaged with complete confidence. An account of the early infestations and the intensive and costly post-war measures is given by Small (1 947).

1) States Experimental Station, Howard Davis Farm, Trinity (Jersey). 2) Previously States Committee for Horticulture, St-Martin's (Guernsey)

49 1

Fig. 1. The Channel Islands.

Sea- borne Invasions At the end of May 1947, the Jersey authorities were suddenly faced with a

calamitous situation, when hundreds of live beetles appeared on potato crops and elsewhere inland and many thousands were found dead on the beaches. Large numbers of dead beetles were later found on the beaches of Guernsey, Sark, and Herm as well as a small number of live beetles inland. This first recorded and heavy sea-borne invasion of the Islands has been described in detail by Small (1 948, 1949) and Dunn ( I 949).

In Jersey, the effects of the invasion were serious and costly, delaying the lifting of the potato crop at the height of the season and interfering with labour, shipping and export organisations. At that time, there was no link with the French authorities but this was quickly achieved after the promotion of the European Colorado Beetle Committee in 1947- 1948, with the aim of preventing the spread of the beetle into new areas. This organisation

492

and its successor, the European Plant Protection Organization, were given whole-hearted support, from their inception, by the Channel Island authorities and a close liaison was established with the French authorities and scientific personnel.

Early accounts of the new, difficult problem of sea-borne invasions are discussed in papers by Small (1 9481, Dunn (1 9491, Small & Thomas (1 95 1, 1954). By 1949, and from then on, the Islands were able to benefit from international cooperation and understanding in dealing with the threat of Colorado beetle, and the French authorities left no stone unturned to solve and defeat the problem. An intensive campaign was started in the Cotentin peninsula in 1950, and special scientific studies were made by Trouvelot et al. (19501, LeBerre(1950, 1952)andLe Berre &Chevin(1952), Grison &LeBerre(1953). The campaign has continued annually as well as studies on many aspects of the problem.

Invasions of one or more of the Islands, recorded from 1947-1 980, have occurred no fewer than 26 times in Jersey, 14 in Sark, 8 in Guernsey and occasionally Herm, and 2 in Alderney. Live beetles were last found on the beaches in 1965. Three periods can be defined : Period I : 1947 to 1952. The number of beetles arriving on the shores was, except in 1949, massive, amounting to many thousands and, as a result of live beetles getting inland, was followed by breeding colonies on crops. Period I1 : 1953 to 1965. For these 13 years, the numbers of beetles arriving were never more than around 1000, in most years less than 100, and in three of those years none were found. This remarkable improvement began three years after the commencement of the Cotentin campaign. Period I11 : 1966 to 1974. During this 9-year period, apart from a single dead beetle in 1969, no beetles have been found on the Channel Island beaches.

No breeding colonies were found after 1952, and the absence of these during the period 1953-1 965, though undoubtedly related to the smaller number of beetles arriving on the beaches, was also due to thorough beach inspection, conscientious hand collecting, and treatment with DDT when beetles were found. Protective spraying of the whole of the potato crop was also practised annually.

Time and Duration of Beetle Arrivals

The recorded dates of arrival, duration and incidence of sea-borne beetles are given in tables 1-4. With one exception, 195 1 C in Jersey, when the beetles arrived on the north- west and south-west shores of the Island, the invasions were first detected on the north- east and east beaches at times when easterly winds (often 20 knots or more) were blowing and soon after the maximum shade temperatures in Jersey reached 20OC. The numbers of beetles given in the tables are derived from observations and collections and are shown to give the relative incidence from one year to the other. It is impossible to assess exact numbers, the distribution of the beetles on the shores being extremely uneven, many intermingled with seaweed or cast up in rock crevices or among boulders and stones. In the days following arrival, the beetles are carried along the south and north coasts by tidal movement. The duration of an invasion depends on the persistence of easterly winds but normally the period is 5- 10 days. An immediate improvement or cessation of the invasion was experienced when the wind became westerly.

The beetles arrive during May and June (apart from some usual findings in Sark, table 2) first in Jersey, which has experienced most invasions, 3-9 days later in Guernsey, Sark and Herm, and 1 1 - 18 days later in Alderney.

A general deduction from the records is that the mass of beetles falling on the sea was so reduced from 1952 onwards that the numbers were insufficient to invade Alderney

493

Table 1. Sea-borne arrivals of Colorado beetle in Jersey.

Year I Duration I Total beetles I Live beetles I Infested areas

1947 1948 1949 1950 A

B C

1951 A B C

1952

1953 1964 1955 A

B C

1956 1957 1958 1959 A

B 1960 1961 1962 1963 1964 1965

Period I - massive invasions, 1947-1952 May28 - June 4 May 16 - May 23

June 15 - June 17 May 1 1 - May 18 May26 - June 2 June 9 - June 16 May29 - June 1 June 7 - June 10 June 23 - June 26 May 17 - May20

many 1,OOO's many 1,000's

369 + 1716 + 1268 +

25,000 + many 1,000s many 1,000's many 100s 2,000 +

Period I1 May28 - June 9 June 3 - June 24 June 1 - June 3

June 10 - June 15 June 18 - June 21 May27 - May28 May 25 - June 21

nil May 17 - May 21

June 15 May 18 - June 2

May 27, only nil

May 30 - June 10 nil

May21 - May24

- reduced invasions, 78 20 34 700 150 39 26

37 1

79 7

338

42

-

-

-

Table 2. Sea-borne arrival of Colorado beetle in Sark.

Many 100's Majority

112 902 102

5,000 + 20

500 + 1 1 2 0

500 +

53-1965 8 1 6 1

60 nil nil

6 1 3 1

135

nil

-

-

-

I nil

Year 1 Duration I Total beetles I Live beetles I Infested areas

1947 1948 A

B 1949 1950 A

B 'C

1951 A B

1952 A 'B

1955 1960 A

B 1961

Other years

June 4 - June 9 May20 - May23

Early June nil

May 14 - May 19 June 1 - June 17

August 27 - Sept 2 June 7 July 30 May 23 July 24

June 10 - June 18 May 30 - May 31 June 1 - June 12 May 16 - May 17

Period I, 1947-1952 large numbers large numbers large numbers

many 1,OOO's small numbers small numbers

few 100s few ? 60 7

Period 11, 1953-1965

-

3 nil

few nil nil

? few few

+ 30 per cent ? 1 4

-

4 nil nil

nil nil nil nil nil nil 1

-

19 4 nil 1 nil

nil nil nil nil nil

Unusual discoveries on beaches. In 1952, an infested area was present on this Island on July 21

494

Table 3. Sea-borne arrivals of Colorado beetle in Guernsey.

1962 1963 June 5

Other years

Year I Duration I Total beetles I Live beetles I Infested areas

1 nil nil 28 1 nil nil nil nil

1947

1948 1950 A

B 1952

1950 1951

May 29 June 9

May 20 - May23 May 14 - May 19 May30 - June 13

May 23

May 29-30 600 ? nil June 10-1 1 Several 100s ? nil

Period I, 1947-1962

Some nil nil nil

Period 11, 1953-1 965

7 -

6 -

5 -

4 -

3

2 -

I -

- 1963

1961

1956

1960 1953

Ig59 1969 1951 1977 1959

1952 1965 1950 1955 1951 i955

f948 7957 1947 7954 1950 1955 1949

- - - -- s----- __-

A ( I ) A ( 1 ) B

6 A 8 - C

C B

No beetles found on beaches in 1949. Similar numbers to those in Guernsey were found in Herm, on June 9, 1947.

1-5 '6-1 '19-15 16-20214?5'26-X)

Tableau 4. Sea-borne arrivals of Colorado beetle in Alderney (1947-1952).

31-4 5-9 10-14 15-19 20-2425-29'304

f a r I Duration 1 Total beetles I Live beetles I Infested areas I

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The relevance of the invasion period to the Jersey potato industry can be seen by reference to fig. 3, which shows a fairly typical cumulation curve for the export of the crop. The optimum period for invasion by beetles is near to 50 % lift of the crop, a time at which maximum disruption could be caused, and is a sound reason for the great importance paid to sea-borne invasions by Colorado beetle. Observations on many occasions have shown that some of the insects can walk or fly immediately they are cast up on shore and, at times, egg laying has been observed on seaweed or even on the hands of collectors when beetles were picked up on the high water mark. Many potato crops in the Islands are grown at a short distance from the shore, in some cases only a few metres, and surviving Colorado beetles can easily gain a foothold.

I

50-

45 -

40- c

I

U

t" 0 35- 0 0

30-

25- L

lnvosion period 1947- 65 ___--__-__ --_-------- .+ f _59% Exporfed

/ optimum time for invasions

I , I I I I I I I I I

5 4 b 20 25 30 5 jo 35 20 2; 40

f ig. 3. Cumulative curve for potato exports, Jersey

Prkutions Taken by the Islands Drastic measures have been taken in the Islands to prevent beetle establishment and

to obviate the effect of invasion, and considerable assistance has been given to the anti- beetle campaign in the Cotentin peninsula. It is not intended here to give an account of the costs of anti-beetle measures taken in the Islands but to summarise systems which have proved valuable in the control and eradication of the pest. Overall spraying of the total potato crop to give insecticidal cover throughout the growth of the early and late crops was carried out in early programmes when beetle colonies were established. The insecticide, at first lead arsenate, later DDT, was mixed with a copper fungicide, since it was necessary to protect the crop against potato blight, and was applied at first by contractors, later by the growers themselves. When dithiocarbamates became the preferred blight control fungicides, in 1962, it was decided to issue growers with DDT alone and, as the situation improved, sprays were reduced to one treatment, applied during an officially specified period, to protect the crops against sea-borne invasions. The costs of materials for protective spraying and other anti-beetle measures and for staff to carry out various duties in the scheme were met, throughout, by public funds.

The employment and training of staff to record the potato fields (over 5000 plots were grown at first), to inspect these crops, to deal with beach inspection and treatment and to carry out the special requirements to control breeding colonies was also essential.

496

Breeding colonies in growing crops were given special treatment, as follows : 1) Lifting stopped if in progress, and the outbreak officially declared to be an infested area. 2 Thorough hand picking of all stages of the beetle and surrounding fields searched. 3) The crop and surrounding potato crops given insecticidal treatment. 4) The crop lifted under official supervision leaving selected rows to act as trap plants, the

5) The crop and trap plants inspected daily until no traces of Colorado beetle are found and

6 ) Widely-spaced, late seed potatoes interplanted to continue trap-cropping and inspected

7) The whole area soil-injected with carbon disulphide during the winter. 8) In the following year, the grower is obliged to plant a further potato crop which is then

Thorough and conscientious hand collection of the pest, as an adjunct to insecticidal treatment in crop outbreaks and on the beaches, was considered to be extremely important.

At times, breeding colonies have been found on the weed Sofunurn nigrum L. and on tomato crops. Similar measures, modified according to circumstances, were used in these cases.

When conditions for sea-borne invasions became better understood, weather and tide conditions were watched daily during May and June with the assistance of the Jersey Meteorology Department. These records, plotted onto a control chart, are continued annually. Together with information from the staff of the French Ministry of Agriculture, including alerts and warnings from a series of observation posts set up in the Cotentin peninsula, it is possible to pin-point danger periods for sea-borne invasions and inspectors are immediately deployed to examine the tide-mark on the beaches. Using these methods, it is considered that all beach invasions can be detected and measures can be taken to prevent the escape of beetles inland, when necessary. Beetle outbreaks can, if occurring in the future, be dealt with using modified, but similar tactics- to those mentioned above.

The main effort must still, however, be concentrated on the source of the sea invasions since, in contrast to the appearance of occasional summer adult Colorado beetles on aircraft, ships and cargoes, these are potentially the most dangerous. Therefore, the study of the ecology and population dynamics of the beetle now being carried out in the Cotentin peninsula, together with the active field campaign to reduce beetle populations there carried out by our French colleagues, constitute the most fruitful measures in controlling future Colorado beetle invasions.

Since this paper was written a resurgence in the beetle population in the Cotentin, following ideal weather conditions during 1976 resulted in further arrivals of beetles on the beaches in Jersey only, 5 dead adults during 1976, 23 (2 live) in 1977 and 4 dead beetles in 1980. These are included in the histogram (fig. 2).

crop to be sold locally and not exported.

frequently thereafter.

frequently.

given frequent inspection.

Le doryphore dans les Iles Anglo-Normandes

Larticle resume la situation doryphorique des Iles Anglo-Normandes ; le ravageur n’a jamais reussi a s’y installer grice aux mesures prises sur place e ta la cooperation etroite avec la France, realisee en vue de prevenir l’invasion doryphorique par la mer, a partir de la presqu’ile du Cotentin. Cette cooperation est patronnee par I’OEPP et, depuis 1965, aucune invasion par voie marine n’a ete observee si bien qu’il a ete possible d’abandonner les traitements prophylactiques des cultures de pommes de terre a partir de 1966.

497

K O J I O P A O C K M R HYK H A A H r n O - H O P M A H O C K M X OCTPOBAX

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LE BERRE, J.R. (1950). Action des facteurs climatiques sur I'incitation au vol du doryphore. C.R. Aced. Sci. 237 :

LE BERRE, J.R. (1952). Contribution a I'etude du determinisme de I'envol du doryphore, Leptinofarsa deeemlineafa

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SMALL, T. (1947). Colorado beetle in Jersey, 1939-46. Agriculture 53 : 450-453. SMALL, T. (1948). Colorado beetle in Jersey, 1947. Agriculture 54 : 569-574. SMALL. T. (1949). Colorado beetle in Jersey, 1948. Agriculture 56 : 115-1 76. SMALL, T. & THOMAS, G.E. (1951). Colorado beetle in Jersey, 1949 and 1950. Agriculture 57: 582-586. SMALL, T. & THOMAS, G.E. (1954). Colorado beetle in Jersey. A study of the problem of sea-borne invasions.

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