G. W. Barber.
The Efficiency of Birds in Destroying Over-Wintering Larvæ of the European Corn Borer in New England.
Psyche 32:30-46, 1925.

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30 Psyche . [February
THE EFFICIENCY OF BIRDS IN DESTROYING OVER- WINTERING LARVB OF THE EUROPEAN CORN
BORER IN NEW ENGLAND.!
Cereal and Forage Crop Insect Investigations, Bureau of En- tomology, U. S. Dept. of Agriculture.
Several years ago, not long after investigations of the European corn borer (Pyrausta nubilalis Hiibn.) were begun by the Bureau of Entomology of the United States Department of Agriculture, it was frequently observed that cornstalks infested by the larvae of this insect showed in the spring of the year numerous holes along the stalks, the burrows of the insect beneath these holes being empty. This was the first evidence of any appreciable feeding by birds on this insect. Such evidence of bird feeding has been found each spring and it is now possible to associate this work with the downy woodpecker (Dryobates pubescens medianus Swainson) a winter resident in this region. In numerous instances, this bird has been observed at close range at work on the infested standing cornstalks. Plate IA, shows sections of cornstalks from which the larvae of the corn borer have been removed by this bird. This type of feeding by chickadees (Penthestes atricapillus atricapillus Linn.) has also been observed by Mr. F. H. Mosher.
Within the last few years observations have shown another type of feeding by birds on the overwintering larvae of this insect. This is the shredding of cornstalks illustrated in Figure lB, and is the result of feeding by grackles, blackbirds, starlings and probably several other species of migrating birds. These birds arrive in the latitude of Boston, Mass., from the middle to the last of April. Such work was especially noticeable in corn- stalks that had been piled in the fall or in stalks that had fallen over for one reason or another and lay on the surface of the soil. These birds have frequently been observed feeding in flocks in the spring, and in a short time .they are able to gather the larvae Contribution from the Bureau of Entomology, U. S. Department of Agriculture in cooperation with the Entomological Laboratory of the Bussey Institution, Hanard University, Bussey Institution No. 248. Pu&e 3k30.47 (1925). hup Ytpsychu einclub orgt12/32-030 html



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19251
Efficiency of Birds in Destroying Larvce of Corn Borer 31
from quite a number of cornstalks. They are able also to shred infested corn stubble and take the larvae in the more exposed positions, but apparently are not able to reach the larvae con- t,ained in standing stalks.
In the fall of 1922, when it was apparent that the birds were becoming a really important factor in the reduction of the num- bers of the corn borer, experiments were undertaken to determine how extensive such feeding was. These experiments were also carried on during the winter of 1923-1924. The object of this work was to obtain information on the extent of the combined feeding by all species of birds concerned rather than the extent of feeding of any particular species, the intention being to obtain as far as possible a picture of the present importance of birds as a group in relation to this insect rather than a study of the value of any one particular species.
The studies pursued during the fall of 1922 and the spring of 1923 may be treated under two heads; first, the extent of bird feeding on the larvae in infested cornstalks placed in the field for this purpose; second, the extent of feeding by birds on larvae in host plants that remained undisturbed in natural positions during the winter.
In the first part of this work twenty representative locations were selected throughout the infested area of eastern New Eng- land. In each of these locations ten stakes were set upright in the soil, there being six infested stalks fastened to each of these stakes. The three following types of corn were represented at each location: pop corn, sweet corn (Golden Bantam) and field corn (Longfellow Flint). Counts of the larval population of representative stalks during the fall gave an average figure as to the number of larvae expected from each stalk, and from this average the number of larvae expected from each station was computed. This series of experiments was placed in the field in November, 1922, after all larval activity had ceased, and the stalks were collected in April, 1923, before larval activity had commenced in the spring. The chance of losing an appreciable number of larvae by migration 'was small, since during this period the larvae were entirely dormant and inactive. Of these twenty experiments five showed extensive feeding by birds



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32 Psyche [February
when examined in the spring, mostly the work of woodpeckers. Of the remaining fifteen experiments one was destroyed by an over-anxious farmer, one was partly destroyed by a tractor and the others showed only very slight traces of feeding by birds or no evidence of bird feeding whatever. Table Number 1 shows the extent of bird feeding on the five experiments at,tacked, and the recovery of larvae from stations that escaped noticeable bird feeding. The average recovery of larvae from experiments not attacked by birds was 1,090 larvse per station as compared with the average expectancy of 1,223.2. This apparent loss of 10.8 per cent of expected larvae per station was undoubtedly TABLE I
Extent of Feeding by Birds on Experimental Material in the Spring of 1923. Experiments on which birds fed.
Location
-
Scituate, Mass.
Newbury, Mass,
Rockport, Mass,
Medford, Mass
Arlington, Mass
Experiments on which birds did not feed. iV-20
IV-29
IV-28
IV-10
IV-7
IV- 1 1
i V-6
IV-14
!V-6
1V-14
V-8
IV-7
IV-I I
Bristol, N. H.
Framington,N.H.
Wells, Me.
Concord, Mass.
Falmouth, Mass.
Quincy, Mass.,
Harwich, Mass.
Methuen, Mass.
Manomet, Mass.
Tyngsboro, Mass.
Wareham, Mass.
Wellfleet, Mass.
Worcester, Mass.,
Xl-8
XI-7
XI-7
XI-4
X-31
XI-4
XI-I
XI-2
X-30
X 1-8
XI-I
X-31
X-26




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192.51
Efficiency of Birds in Destroying Larvae of Corn Borer 33
caused by migration of a few larvae and the loss of small pieces of stalks containing larvae during transportation of the corn- stalks used in the experiment.
The average winter mortality in the 18 experiments listed in table No. 1 was 10.5% per cent. The average per cent of larvae credited to bird feeding in the five stations where stalks were attacked, was 61. The average per cent of larvae credited to bird feeding in the 18 stations recovered was 17. The stations that showed extensive feeding by birds (Fig. 1) are all within the area most heavily infested by the European corn borer and localities where infestation has been severe for several years. Because of this fact and because no marked evidence of bird feeding was found in areas slightly infested or areas that had become heavily infested by the insect within the last year or two, it would appear that woodpeckers are aware of the fact that infested cornstalks contain desirable food only in this heavily infested area, and that in more sparsely infested regions or in areas where infestation had but recently become severe they are for the most part still unfamiliar with the exis- tence of this source of food.
Several of the more commonly infested weeds and cul- tivated plants were also tied to stakes to observe possible feeding by birds on larvae contained in such plants. These were placed with the experiment at Medford, Mass., mentioned in Table 1, where birds took 69 per cent of the larvae from the cornstalks tied to stakes.
Of the several plants thus observed, common sunflower (Helianthus annuus L.), Princesplume (Pol'ygonum orientate L.), Polygonum sp., and cocklebur (Xanthium spp.) showed extensive feeding by birds of the same sort attributed to woodpeckers while no evidence of such feeding was noticed in Abutilon (Abutilon theophrasti Medic,), pigweed (Amaranthus retroflexus L.), rag- weed (Ambrosia sp.,) beggar-ticks (Bidens sp.), pot-marigold (Calendula officinalis L.), aster (Callistephus sp.), feather cocks- comb (Celosia argentea L.), Cosmos bipinnatus Cav., Dahlia sp., barnyard grass (Echinochloa crusgalli L.), Japanese millet (Echi- nochloa sp.) , Gladiolus sp., strawflower (Helichrysum bracteatum



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34 Psyche [February
Andr.), geranium (Pelargonium hortorum), lirna bean (Phaseolus lunatus, L.), and African marigold (Tagetes erecta L.) . The field examinations of cornstalks showed much the same evidence as was obtained from the experimental work described in the preceding paragraphs. Numerous instances were found where birds had removed a high percentage of the larval content of cornstalks and such instances were found only in heavily Fig. 1.
Map of the area known to be infested by the European Corn Borer in New England in 1922.
Circles show localities where experiments were placed in the fall of 1922 ; clear circles indicate that no feeding by birds was found, while circles having a cross in the center indicate localities where birds fed on larvae contained in the corn stalks of the experiment. A white line surrounds the area known to be infested up to July 1, 1919. 1-Arlington, Mass. 8-Tyngsboro, Mass. 14-Quincy, Mass. 2-Medford, Mass. 9-Bristol, N. H. 1 5-Scituate, Mass. 3-Rockport, Mass. 10-Concord, Mass. 16-Wareham, Mass. 4-Newbury, Mass. 11-Worcester, Mass. 17-Falmouth, Mass. 5-Wells, Me. 12-Walpole, Mass. 18-Manomet, Mass. 6-Methuen, Mass. 13-Taunton, Mass. 19-Harwich, Mass. 7-Farmington, N. H.




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19251
Efficiency of Birds in Destroying Larvce of Corn Booer 35
infested areas and in localities that had been infested for several years. In sparsely infested localities or in areas where infesta- tion had been severe only recently, no extensive feeding was noticed although in some cases there were traces of feeding by birds. The following table shows the condition as found in certain heavily infested fields that were found to be attacked by birds.
TABLE 11.
Extent of Feeding by Birds on Material Undisturbed by Man in the Spring of 1923.
Locality
Watertown, Mass,
Milton, Mass.
Marblehead,
Mass.
Melrose, Mass.
Date
examinee
--
IV-2-23
IV-6-23
Iv-13-23
v-3-23
v-11-23
Type
Estimatec
number
of larvee
taken by
birds
I 86,480
26,957
.........
140,946
.........
Estimated
per cent
of larvae
taken by
birds
--
92 %
78%
30%
97%
80%
Condition
I 3 acre;
1 acre
I acre
acre
.......
=Standing
and broken
over
' standing and
--
The figures mentioned in this table were obtained by counting the number of cornstalks in the several fields, estimat- ing the fall infestation of the stalks, and comparing this figure with the average infestation found on the date of the examina- tion. The spring infestation per cornstalk was obtained by averaging several series of counts made in different parts of each field. In all these instances both types of bird feeding shown in figure 1 were found, the feeding attributed to woodpeckers being extensive in standing stalks and the stalks lying on the ground being shredded by other birds.
In weeds instances were found of the removal of considerable numbers of larvae from cocklebur (Xanthium sp.) and barnyard grass (Echinochloa crusgalli L.). In one field several score of Size
cz:n of corn-
stalks
"
"
of are;
broken over
Lying on
soil
standing and
broken over
' In piles
partly burn-
1 ed




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36 Psyche [February
dahlia plants were found from which birds had removed nearly all the larvae of the European corn borer that these plants had harbored.
Although birds (particularly the downy woodpecker) feed to a limited extent on the larvae of this insect in the fall and winter, most of the feeding is done in the spring, especially the shredding of stalks lying on the ground. The experiment placed
in Medford, Mass.,
(table I), showed on April 9, 1923, that birds had by that time taken 65 per cent of the larvae from the cornstalks. A similar experiment in the same locality was continued until June 27, 1923, a date when most of the insects had transformed to adults. At that time examination showed that birds had apparently taken 82 per cent of the insects from - the cornstalks.
In the fall of 1923 a series of experiments much similar to those previously described was placed in the field for the purpose of obtaining information on the extent of feeding by birds on this insect. However, this time fifty stations were chosen instead of twenty as in the previous work. Each station was composed of four stakes to each of which was fastened five infested corn- stalks, the larval expectancy as obtained from stalk counts being on an average of 15.5 larvae per stalk.
These stations were so selected as to cover the entire area infested by this insect in New England and were run out in lines as straight as possible from Arlington, Mass., as a center as fol- lows: first line comprising 12 stations in a northeasterly direction as far as Sebago, Me.; second line comprising 5 stations in a northerly direction as far as Farmington, N. H.; third line com- prising 8 stmations in a direction north by northwest as far as Bristol, N. H.; fourth line to the northwest as far as Gardner, Mass. comprising 3 stations; fifth line comprising 4 stat'ions to the west as far as Worcester, Mass.; sixth line to the southeast as far as Touisset, Mass., composed of 4 stations; seventh line to the south as far as Mattapoisett, Mass., composed of 4 sta- tions; eighth line composed of 9 stations to the southeast and extending on Cape Cod as far as Provincetown, Mass. Fig. 2.




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19251
Efficiency of Birds in Destroying Larvce of Corn Borer 37
Fig. 2.
Map of the area known to be infested by the European Corn Borer in New England in 1923.
Circles show localities where experiments were placed in the fall of 1923;-clear circles indicate that no feeding by birds was found, while circles having a cross in the center indicate localities where birds fed on larvae contained in the corn stalks of the experiment. A white line surrounds the area known to be infested up to July 1, 1919. 1-Arlington, Mass.
2-Medford, Mass.
3-Saugus, Mass.
4-Beverly, Mass.
&-Marblehead, Mass.
6-Rockport, Mass.
7-Newbury, Mass.
8-Hampton, N. H.
9-Kittery, Me.
10-Wells, Me.
1 1-Biddeford, Me.
12-Scarboro, Me.
13-Woburn, Mass.
14-Andover, Mass.
1 5-Methuen, Mass.
16-Kingston, N. H.
17-Farn~ington, N. H.
18-Bedford, N. H.
19-Hillsboro, N. H.
20-Concord, N. H.
21ÌÔFranklin N. H.
22-Bristol, N. H.
23-Concord, Mass.
24-west ford, Mass.
25-Harvard, Mass.
26-Leominster, Mass.
2 7-Gardiner, Mass.
28-Natick, Mass.
29-Southboro, Mass.
30-Worcester, Mass.
31-Medfield, Mass.
32-Foxboro, Mass.
33-Attleboro, Mass.
.34-Touisset, Mass.
35-Needham, Mass.
36-Bridgewater, Mass.
37-Mattapoisett, Mass.
38-Milton, Mass.
39-W. Hingham, Mass.
40-Cohasset, Mass.
41-Marshfield, Mass.
42-Kingston, Mass.
43- Falmouth, Mass.
44-Sandwich, Mass.
45-Brewster, Mass.
46-well fleet, Mass.
47-Provincetown, Mass.




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38 Psyche [February
Examinations of the cornstalks of these experiments in the spring of 1924 showed that 16 of these stations exhibited feeding by birds to a noticeable extent, while the remainder showed either a mere trace of bird feeding or no evidence of such feeding at all. In Table 3 those stations that showed bird feeding are listed together with the number and percentage of larvae ap- parently removed from the stalks by birds. The average winter mortality for the 38 stations listed in table no. 3 was 4 per cent.
The average per cent of larvae apparently taken by birds in the 16 stations that showed bird feeding (based on the average recovery per stalk in experiments not touched by birds) was 54. The average per cent of larvae apparently taken by birds in the total number of 47 experiments (based on the average recovery per stalk in experiments not touched by birds) was 19. Three stations were lost or destroyed, leaving 31 that showed either a mere trace of bird feeding or none at all. The infestation in the fall was on an average 310 larvse per station. Spring ex- aminations of the 31 stations that showed no important feeding by birds proved that the average infestation at that time was 14.7 larvae per stalk or 294 larvae per station, an apparent loss per station of 16 larvae or approximately 5 per cent of the ex- pected larvae. This loss is slight when it is remembered that in some stations birds apparently did take a few of the larvae, and that the cornstalks were necessarily handled several times and were transported for considerable distances, so that small pieces were sometimes broken off and lost. These figures, however, are offered to show that the findings as regards bird feeding, shown in Table no. 3, present a fair picture of the extent to which birds fed on this material.
These results show a considerable increase in the area in which birds fed extensively, (Fig. 2 and 3) over the results ob- tained in the spring of 1923. This may be due to the fact that the larger number of stations provided a much more accurate test of conditions and so gave a much better picture, or it may indicate a widening field over which birds have become aware of an existing food supply. There is also a possibility of the element of chance entering to the extent that if the right species of birds



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19251
Efficiency of Birds in Destroying Larvce of Corn Borer 39
found the stations, feeding would result, whereas if the experi- ments remained undiscovered by birds able to take larvae from the cornstalks no evidence of feeding would be found. Whatever the reason, however, the fact of evidence of bird feeding on over- wintering larvae of this insect in cornstalks over a much more extended area during the spring of 1924 than was observed previously remains, and it is the writer's belief that birds were a more important factor in reducing the numbers of the European