14 



BRITISH LEPIDOPTEEA. 



the early . larval stage of lepidopterous insects. It may be that 

 natural selection protects one species more perfectly in one stage, 

 another species in another stage, but, so far, young larvae appear to be 

 the particular form against which destructive agencies are most active. 



However well eggs may be protected, it is evident that consider- 

 able destruction does take place in this stage, and it must be admitted, 

 especially in the case of eggs laid in large batches, that if an attack 

 thereon be made by some voracious entomophagous enemy, the de- 

 struction is absolutely complete. Scudder records that ants destroyed 

 the eggs of a Pyrantels cardui, that he had enclosed on a thistle. 

 Spiders, ants and mites, are great offenders in this direction, but 

 probably their combined destructive efforts fall much below those of 

 the true egg parasites— minute Hymenoptera of the genera Tricho- 

 gramma and Telenomus — which lay their eggs in the ova of lepidopterous 

 insects, and whose larvae find sufficient nourishment therein to enable 

 them to reach the imaginal condition. Nicholson mentions the rearing 

 of 30 Telenomus phalaenarum from some eight eggs of Macrothylacia 

 (Lasiocampa) rubi ; Bacot records the destruction of a whole batch of 

 Arctia caia eggs by the same species, whilst Bignell states that he 

 bred 2,100 imagines, of the same parasite, from 200 eggs of M. rubi, 

 an average of more than ten to each egg ; Dimmock mentions the 

 breeding of 30 hymenopterous parasites from a single egg of Smerinthus 

 excaecatus. Numbers of parallel cases have been recorded in the 

 various entomological magazines. 



The duration of the egg-stage varies greatly in different species. 

 Buckell, Fenn and Prout have given comprehensive lists of the 

 duration of the egg-state in a great number of Geometric! species. 

 The shortest periods recorded are two days, in the case of Acidalia 

 virgularia, four days for Timandra amataria and other species. On 

 the other hand, many species, that hatch the same year, pass a much 

 longer period in the egg-state, e.g., Selenia tetralunaria, 23 days; 

 Amphidasys strataria, 30 days ; Boarmia abietaria, 19 days ; B. gem- 

 maria, 20 days ; Hybemia leucop>haearia, 38 days ; Larentia caesiata, 24 

 days, etc. In some species the length of time varies in different years, 

 probably depending on meteorological conditions. Thus, Biston Mrtaria 

 may take from 17 to 37 days ; Hemerophila abruptaria, from 14 to 26 

 days ; Selenia lunaria took 7 days in 1865, 12 days in 1861, and 15 

 days in 1886 — all of the first brood. Selenia bilunaria has the 

 following record : — 1880, first brood, 16 days ; 1883, first brood, 28 

 days, second brood, 16 days; 1890 and 1891, second brood, 15 days. 

 But different broods of the same species may vary in the same year ; 

 thus, in 1865, one batch of Camptogramma fluviata took 5 days, another 

 10 days, and a third 21 days. 



Of those species which pass the winter in the egg stage, the time 

 is so great that the combined larval, pupal, and imaginal periods are 

 comparatively very short. Thus the egg stage of Epione apiciaria 

 lasts as long as 9f months ; of Ennomos autumnaria, 7f to 10 months ; 

 of Him era pennaria, 5 months; of Oporabia fil iyrammaria, 4f months ; 

 of Cidaria testata, 8 months ; of Ckesias spartiata, i.\ months. The 

 egg stage of Thecla w-album. and Zephyrus quercus lasts from July to 

 early May ; of Tliecla pruni, from June until late April ; of Plebeius 

 aegon, from July to April ; of Tricldura cyataegi, from September to 

 * Entom. Record, etc., iii., pp. 175-176; iv., p. 255; iv., p. 292. 



