Wm. E. Bickley.
Inheritance of Some Varietal Characters in Chrysopa oculata Say (Neuroptera: Chrysopidae).
Psyche 59(2):41-46, 1952.

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PSYCHE
Vol. 59 June, 1952 No. 2
INHERITANCE OF SOME VARIETAL CHARACTERS
IN CHRYSOPA OCULATA SAY (NEUROPTERA :
CHRYSOPIDAE) *
BY WILLIAM E. BICKLEY
College Park, Maryland
Varieties of Chrysopa oculata Say are distinguished by the degree of darkness of wing veins and by color patterns, chiefly markings on the genae, vertex, and pronoturn. Most of the varieties are species synonyms. C. albicornis Fitch, which has dark cross veins, and C. chlorophana Burm., which has green cross veins, were placed under C. oculata Say by Smith (1922). One of several reasons for doing so was the fact that the forms readily cross. Smith (1932 and 1934) recognized five varieties which have different color patterns on the vertex. In carei Smith, spots on the vertex are absent. In xanthocephala Fitch there are two black or brown spots in the antennal band or closely connected with it; but if the two spots are not connected with the antennal band the form is called bipunc- ata Fitch. Variety oculata Say has four dark spots on the vertex (pi. 5, A). In illepida Fitch there are two elongate bands; in other words the spots on each side are fused (~1. 5, B).
When large numbers of Chrysopa oculata are examined it is found that some specimens cannot be placed in the recognized categories. A good example is a form in which the vertex has two spots on one side and an elongate band on the other (pi. 5, C). In an attempt to clarify the status of some of the varieties, an investigation was made of the inheritance of some characters upon which varieties are based.
* Scientific Art. No. A357, Contribution No. 2338 of the Maryland Agricultural Experiment Station, Department of Entomology. Dr. Sumner 0. Burhoe, Professor of Zoology, University of Maryland aided in interpreting the possible genetic status of the varieties. 4 1




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42 Psyche [me
Field-collected gravid females were put in separate fruit jars with cheese-cloth coverings, and eggs obtained from them were isolated in one-ounce bottles with absorbent cotton plugs. Larvae were given about a dozen field- collected aphids every day or every other day. Sometimes larvae were fed termite workers. They spun cocoons, pupated, and emerged in the small bottles. Adults lived and reproduced satisfactorily in fruit jars. They were given a few aphids and a little water daily. The average duration of the egg stage was approximately three days and the larval stage, 14 days. Adults usually emerged 14 days after the cocoon was spun.
Two varieties were reared, inbred and inter-bred, namely the common ocuhta, which has four spots on the vertex, and illepidu, which has two elongate bands on the vertex. Seven ocdata females of unknown ancestry, some from different localities in Maryland, produced 103 offspring. Of these, 101 or 98% were oculata. There were one illepida and one xanthocephala (a form with only two spots). The progeny of two wild illepida, females consisted of 83 in- dividuals, 58 of which were octdata and 25 of which were illepidaÌÔreapectivel 70% and 30%.
Twelve pairs of first generation individuals were mated so that offspring- of nearly all possible combinations could be studied. To determine whether or not there was any sex lhkage, duplicate crosses were made in which the sexes with given characters were reversed. Results of second generation pairings are given in Table 1. It is obvious that the genes responsible for oeidata are more prevalent. This appears to be true not only in the populations reared but also throughout the range of the species, It is unlikely, however, that oeulata is a dominant character in the Mendelian sense, because of its occurrence in offspring from illepida parents. Pairing F as given in the table shows that one pair of illepida from an illepida female produced 50 % oculata off spring, indicating that they carried the oculata gene. This high percentage fur- EXPLWATION OF PLÌöT 4
Markings on the vertex of Chrysopa ocutata. A. Variety oculata. B. Variety iilepida.. C. "Borderline" individual.



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44 Psyche [JUM
nishes proof that oculata is not a simple dominant. Further- more, in E, C, and E oculata, presumably heterozygous if illepida is recessive (because they were the offspring of illepida females) produced low percentages of illepida, If oculata were dominant the expected proportions of ilkpida would be 25% in I3 and C, and 50% b E.
The high percentage of ocuhta offspring in all the crosses occurs in a manner showing close approximation to the results expected from segregating recessives with a rare production of illepida, which could be explained by the presence of two or more pairs of recessive genes either of which in the homozygous recessive state could produce ocuhta. Thus, if there are two genes any one of which in the recessive state would produce o&ta, a cross like those in D (Table I) could theoretically produce 25% ilm'da, provided that the illepida parent is heterozygous for both pairs of genes. The actual number obtained was 19F. If it is assumed that any one of three genes in the recessive state might produce ocwlata, the actual ratios of the five crosses will conform more closely with the theoretical. Whatever the genetic mechanism may be, it can be concluded that illepida is not a simple recessive. If such were the case, inbreeding could not possibly produce any- thing except illepida, but actually the result is 50% ocviata. (Table 1, F.) Conversely, the fact that inbreeding of five pairs of oculata from an oculata. female gives only oculata suggests that this character may be a recessive. There are of course the other patterns on the vertex to be considered, but no attempt is being made to explain their occurrence. Even though the manner in which the variations are produced cannot be explained easily and regardless of the percentages of the two varieties obtained from the dif- ferent crosses, the important point is that the characters which have caused the naming of ocvluta and illepida are inherited. Moreover this appears to be true for the other varieties previously mentioned, including those with dif- ferences in darkness of wing venation.
An eighth variety recognized by Smith (1932) is separata Banks which "is distinguished by the absence of a connec- tion between the black loop under the antennae and the black genal band." If the connection is very faint the



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19521 Bickle Mnheritance in Chrysopa 45
form is still called separata. There are various degrees in reduction of width of this connecting band, and in this case it appears that the character is so subtle that it is not reliable.
Because of inconsistencies and intergradations in color patterns and because the genetic status of some of the varietal characters is at least partially understood, it seems reasonable to conclude that the varietal names are no longer of any value. The avoidance of the term variety where it lacks real meaning is one of the principles set forth by Ferris (1928). If this principle is applied the work of the taxonomist will be simplified. He no longer has
a problem when he is confronted with borderline cases such as individuals with spots on one side of the vertex and a band on the other, and specimens with the face as in separata, the vertex as in illepida, and the wings as in albi- cornis.
Pairing No. of
Pairs
A CC(OC) x OC(OC) 5
B oc(o'c) x oc (ill) 2
C oc(il1) x oc(i1l) 1
D oc(oc) x ill(i1l) 2
E oc(il1) x ill(i1l) 1
F ill(il1) x ill(il1) 1
Total oculata illepida Borderline
Off- No. % No. % No. %
Spring
84 84 100
83 78 94 4 5 1 1
11 10 91 1 9
59 48 81 11 19
60 39 65 21 35
18 9 50 8 44 1 6
Table 1. Inbreeding and crossing of two varieties of Chrysopa oculata (Say) ; oc(oc) indicates oculata from an oculata female; oc(il1) indi- cates cculata from an illepida female; ill(il1) indicates illepida from an illepida female.
Two varieties of Chrysopa oculata Say were reared, in- bred, and interbred, namely, the common oculata, which has four spots on the vertex, and illepida, which has two elongate bands on the vertex. Twelve second generation pairings were made and 315 offspring obtained. All of these pairings resulted in high percentages of oculata. It is, therefore, concluded that the genes responsible for this character are more prevalent. However, oculata is not a



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46 Psyche [June
simple dominant, and there is evidence which suggests that there are two or more genes, any one of which in the re- cessive state produces oculata. Because of inconsistencies and intergradations in color patterns and because the genetic status of some of the varietal characters is partially understood, it may be concluded that the varietal names are no longer of any value.
LITERATURE CITED
FERRIS, G. F.
1928. The principles of systematic entomology. Stanford Univ. Publications. Univ. Series. Biol. Sci., 5 (3) :103-268. SMITH, R. C.
1922. The biology of the Chrysopidae. Cornell Univ. Agr. Exp. Sta. Memoir 58: 1291-1372.
1932. The Chrysopidae (Neuroptera) of Canada. Ann. Ent. So;. Amer., 25 :579-601.




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