INTENSITY AND EFFECT OF THE NEMATISM 347 



larger and averaged seventy per cent heavier than a similarly chosen twenty-five 

 from a fifty per cent infested lot. Anatomical evidence shows the infested female 

 beetles to be less fertile than the non-infested, doubt as to diminished fecundity 

 vanishing where the female host harbors a dozen or more adult nemas. In such 

 cases the mere relative volume of the parasites is convincing evidence of handi- 

 cap. See Fig. 1. Mr. Balduf in a letter speaks of beetles, many of which "died 

 of nemas." I have no rigid proof of such deaths, but believe them very probable 

 and at times numerous. Among the grubs the mortality may be heavy. 



In none of the numerous lots of beetles examined was the rate of infesta- 

 tion by any other zoo parasite as high as by Howardula, with the single excep- 

 tion of a forty-three per cent dipterous infestation; but no note was made of 

 degrees of phyto-infestation (cucumber-wilt organism, etc.). 



As many as thirteen thousand nemic larvae, by count, have been removed 

 from the body-cavity of a single Diabrotica vittata, and no doubt the number 

 may go much higher. On several occasions twenty or more adult Howardulas 

 were taken from a single beetle. Theoretically these should produce some forty 

 thousand larvae or more. The older female beetles, when nematized, deposit 

 from a few to upwards of fifty nemic larvae with each egg. See Fig. 3. These 

 soon mature on the eggs or in the soil (where they can live several weeks), moult 

 and copulate, the female developing a more perfect spear, and by its aid drilling 

 into the body-cavity of the beetle grubs soon after the latter hatch out. See Figs. 3 

 and 4. That it is most improbable the nemas enter the host by way of the 

 mouth and alimentary canal is well illustrated in Fig. 8. The active young beetle 

 larvae are armed with sharp-toothed, well developed mandibles. That the 

 fragile young nemas could, in any considerable numbers, pass so relatively small 

 a throat and mouth, armed as the latter is, one hesitates to believe. 



In plant-infesting triplonchs I have shown the devel- 

 opment of the so-called salivary glands to be greatest 

 in species noted for their efficiency in destroying the 

 tissues of the host, e.g., Tylenchus dipsaci, Caconema 

 radicicola, and suggested that these glands aid in dis- 

 solving the host tissues and thus supplement the mechani- 

 cal action of the spear or onchium, which therefore should 

 then act also as a spewing channel. In light of this, it 

 may not be without significance that the salivary glands 

 of Howardula benigna, at the time of entering its host, 

 appear better developed than in some of its nearest known 

 relatives. Conceivably this secretion is also antiseptic. 

 Nemas of very many kinds make their way through the Fig.3. Egg of a c 

 tissues of their hosts without causing fatal infections. ^ 



For instance, I have observed the most important abdomi- 

 nal and thoracic organs, heart excepted, of Dasyurus 



literally sewn through and through by long and slender nemas without apparent 

 infection. The existence of an antiseptic nemic secretion or excretion might ex- 

 plain this. In the case of Diabrotica, there is no known trace left of the relative- 

 ly large breach made by the parasite (see Fig. 4), a benignant result perhaps 

 facilitated by the parasite itself in the way indicated. 



