Notes on the Egg-Parasites of the Apple Tree Tent-Caterpillar (Malacosom Americanum)
International Journal of
BY I. T. WILLIAMS 0
Omaha 0
Nebraska. 0
0 Contribu.tions from the Entomological Laboratory of the Bussey Institution, Harvard University , No. 117
behind the middle, apices separately rounding, surface minutely alutaceous, finely punctate in rather obscure rows which fade at tip so that the apical area becomes almost smooth and shining. Abdomen above with four full dorsal segments, as well as the basal lateral portion of another, exposed behind the elytral tips, this uncovered surface being strongly shining and sparsely punctate. The segmental edges have a peculiar laminate appearance, as if folded over. The terminal segment is nearly semicircular in outline and strongly hairy. Underside very shining, sparsely and finely punctured, the prosternal and abdominal apices tinged with yellow. Legs rather slender, the femora and tibim flattened, front tibim wider, denticulate and strongly hairy, all the tarsi slender, hairy and with large simple claws. Length, if straightened out, nearly 5.00 mm. Compared with the description of the Guatemalan specimen, this insect is considerably larger, attaining a length of about 5.00 ram., against 3.5 of the southern form. The coloration is also different and there are some diversities in sculpture and structure, which, however, may perhaps be due to unlike interpretation. I think that the funiculus has six joints in C. championi, though Dr. Sharp, while admitting difficulty in counting, allows only five in C. mollis. He makes no mention of a groove on the posterior half of the head nor of a marginal prothoracic bead.
-
NOTES ON THE EGG-PARASITES OF THE APPLE TREE
TENT-CATERPILLAR (MALA COSOMA AMERICANUM)
points of possible interest noted, a list of the parasites found,
together with some comment on their behavior and relative
abundance, seemed to be worthy of publication.
The eggs used for one experiment were separated into four lots,
according to the dates of collection and the conditions under which
they were kept. Box No. 1 contained ab,out 850 egg-masses,
collected between February 0 and March in the immediate
vicinity of the Bussey Institution, and kept in a greenhouse until
the caterpillars and parasites emerged. Box No. contained
about 180 egg-clusters, collected in a locality a few miles south
of the first (Stony Brook Reservation, near Hyde Park, Mass.)from
June 19 to June 9 (mostly on the earlier date). Box No. 8
contained about 50, collected at the same place as those in Box No. 1,
but kept out of doors, so that the exact date on which they were
gathered is immaterial. Box No. 4 contained about 60,
accumulated in the laboratory from time to time, but, for one reason or
another, not placed in the other boxes. The results in these last
three boxes were almost indentical.
In addition to these, about 80 egg-masses were collected in early
spring and placed in cold storage for the months of April, May, and
June. The box containing these was known as No. 5. Six more
masses were isolated in test-tubes for individual records.
Caterpillars hatched from the eggs in the greenhouse about two
weeks after collection, and the first parasites emerged March 9, or
about five weeks after collection. Under natural conditions the first
caterpillars appeared April 19 and the first parasites, June 19. An
attempt was made to rear the early hatched caterpillars in order to
secure their eggs for experiment, but they contracted the wilt disease,
and perished to the last individual. It was, therefore, necessary to
rely on pupae collected in the field, and as these were heavily
parasitized the number of adults reared from them was small. The
first female emerged and laid her eggs on June 9, probably a day
or two earlier than it would have done under natural conditions.
Six species of parasites were bred from the eggs, They will
be taken up in the order of emergence.
place to others. May 31 was the date of the last specimens to
appear in this box. In all, twenty-two males, twenty-four females
and five or six which escaped before their sex was determined
issued from this box.
Under natural conditions this parasite was, oddly enough, the
last to make its appearance. In Box No. four males and one
female issued between July 6 and July 31, over two weeks after
all the other species (except for those in the cold-storage box) had
ceased to emerge, and in Box No. 3 six females and four males
appeared, at about the same time. The total from all the boxes
was thus about 66, and the percentage of parasitism, counting 00
eggs to the cluster, was only 0.06 per cent. This is, of course,
economically negligible, supposing it to represent typical
conditions.
As its name shows, this insect was described as a caterpillar
parasite, but as the Aphelinine, the subfamily to which it belongs,
are otherwise exclusively parasites of the Coccide, and as it was
afterwards reared by Howard and others from Aspidiotus and
Chionaspis, it was naturally assumed that Ashmead had been
mistaken. (...truncated)