On the Hawkmoth Deilephila nerii and its Braconidous Parasite

ON THE HAWK-MOTH DEILEPHILA NERII.

ON THE HAWK-MOTH DEILEPHILA

221

NERII,

L., AND ITS BRACONIDOUS PARASITE.

BY COL. W . G . BROUGHTON HAWLEY,

D.S.O.

One day in mid-July 1935, my attention was called to a large Sphingid larva that was crawling across the road in heavy rain at Pachmarhi in Mahadeo hills of Central India at 3500 feet.

The insect was orange-yellow on its first five segments above, and yellow throughout beneath. Lateral lines on the remainder,' with a large black spot on fourth segment and blackish-olive on the back of the sixth to thirteenth, with many small pale spots ; the anal horn was short, yellow and much down-curved. I guessed it to be D. nerii and put it into a small box with some grass-roots, wherein it at once spun a loose web and pupated.

Unfortunately the moth emerged at night, in early August, and was discovered by a cat who tore off the gauze and ate the insect, of which I found the remains on the floor next morning, confirming the caterpillar's identity.

Upon returning to Jubbulpore in October, I searched some Oleander-shrubs and found about eight, and subsequently many more, larva; varying from \ to 1> inches in length. These all appeared to have been parasitised. For, one after another on attaining I i inches or so in length, they suddenly turned brown in the middle, the anterior half dropped off, and the rear half remained firmly fixed to leaf or twig by its claspers. This residue then became quite hard, forming an external protection of the enclosed parasitic pupa. I have retained several of these, whence the perfect Braconids (cp. Trans, iii, 196) emerged in due course.

Shortly after this catastrophe and in the same month, I heard that D. nerii larvae were also to be had upon another species of garden shrub, which I consequently searched, finding five caterpillars. Of these three (a) were in their last skin, one (b) made its final change of skin on 25-6 October, and one (c) was parasitised and died. A sixth (d) was later discovered upon O l e a n d e r — T h e three (a) larvae were normal in colour, i.e. bright green with white stripes and dots, a large pale-blue spot within a black circle on the fourth segment, and a yellow anal horn. This larva (b) when found was a pinkish-grey colour, with pink lateral stripes, and suffused with purple above the stripes : spot and horn normal.

After changing skin on 26 October, a process occupying just fourT i ! W C n t y h ° U r S ' k P r e s e n t e d a totally different appeairance : now the head and first five segments were bright rusty-red, a narrow black band ran behind the head, eye-spot in 4 segment was n o r m a l ;

222

ON THE HAWK-MOTH DEILEPHILA NERII.

its back was rust-red with four black transverse stripes running into blotches laterally, and a flesh-pink patch on the sides that extended over segments ten and eleven : with the usual white dots.

Of (a) the first to cease feeding did so on night of 26-7 October turning colour immediately ; the other two did so the next night, spinning a rough shelter of leaves and rubbish on earth. (b) after changing skin, fed incessantly for four days and nights, and grew at an incredible speed, becoming lighter in colour tili morning of 1 November, when he appeared quite dark, just the colour of a Cossus-larva, betook himself to the dead leaves and there pupated, producing a fine male on 11 December following.

The earliest imago emerged on night of 1-2 December, the second came out a cripple on 4 December, and the third two days later : all from (a). Shade temperatures at this time varied from 50° to 75°, i.e. distinctly cold when compared with October or earlier.—(d) was a later brood than the above and would touch nothing but Oleander, refusing that shrub upon which a. b. and c. were found and reared. d. refused to settle at all well, but eventually pupated when apparently about half grown : stränge to say, he emerged in good ccndition the day after c., i.e. on 12 December, of which he was hardly more than half the size.

Summary : Saw full-grown larva in Pachmarhi in mid-July ; four large ones at Jubbulpore in October, with great numbers of small ones that were all parasitised. Imagines emerged from four pupas in December ; one female flew to light in veranda about 11.30 p.m. on 7 March 1936, and two or three more during the course of that month.

Other kinds of Hawk-moths met with in Jubbulpore during 1935-6 were a very large and battered female of Acherontia Atropos, L., or closely allied species.—Two Sphinx convolvuli, L., at dusk in early February at Petunia blossoms.—Deilephila celerio, L., at late dusk in January and end of Dcember at Petunia, Phlox and Verbena; probably plentiful in autumn.—Small Goldstriped Hawk (Theretra Clotho, Fab.) December, January and early February, with a small fresh emergence on 2 March.

Apparently plentiful on above flowers at dusk in autumn after rains.—Green White-spotted Hawk (T. Oldenlandice, Fab.): Very common from autumn to March, then scarcer, at flowering shrubs and plants : and earlier flyer, before and during dusk.— Rayed Hawk (Nephele didyma, Fab.) apparently a later Aver at late dusk or after it, at above three plants in early March.—Mango Hawk (Hippotion Bcerhavice, Fab.) : one specimen in late March or April at flowers, chiefly Petunia, after dark in the orange gardens.—Macroglossa gyrans, Walk., an early flyer about sunset or before, at all flowers in autumn, later in poor condition, but did not disappear tili February.

223

THE HYMENOPTERA OF SUFFOLK.

[Colonel Hawley kindly presented us with a dozen cocoons, each pierced near one extremity by the circular hole whence had emerged singly both sexes of the above parasitic Braconid, which proves upon examination to be a species of Rhogas as anticipated (Trans, iii, 196 where read Jubbulpore throughout for Tubbulpore) and has been described (Entom. 1937, p. 255) by us as Rhogas siccitesta, sp. nov., because it emerges from the indurated husk of its host's larva. It is a solitary parasite of D. nerii, L., showing no indication of its presence tili the laiter's Caterpillar is or two inches in length : " I saw no parasite laying eggs in these larvae," the Colonel says in lit. Sept. 1936, but they were already attacked when I found them about one or \ \ inches long and looking quite healthy. Soon after that they collapsed suddenly and became brown over the three or four central segments, but remained fixed to their fulcrum. In a few hours the anterior five or six segments became detached and feil to the ground, leaving the posterior ones still in situ to form the ' cocoon ' for the parasite's pupa, whose larva is a greenish-white creature fully a quarter-inch in length." T h e whole process is obviously analogous to that of British species of this genus, especially Rhogas prertor, Reinh., which thus slays the allied Smerinthus populi, Linn.—Ed.]

THE

HYMENOPTERA PORTIO TERTIO ET

Subfamily

OF

SUFFOLK.

ULTIMO.

OPHIONINJE.

Plectücus collaris, Gr.—Finbro (Tuck), Lackford, Walberswick.

P• terebrator, Fst.—On Monks Soham House window, 30 August.

P. melar.ocerus, Fst.—Beaten from poplar in Bentlev Woods on 23 May 1931.

Aperileptus albipalpus, Gr.—Rarelv seen [reccrded from Norfolk].

Proclitis prcetor, Hai.—Swept at Claydon bridge, September.

P. socius, Hai.—Brobablv not uncommon : on nettles at Wherstead.

Megastylus cruentator, Schd.—Tostock (Tuck); common at Monks Soham, &c.

M. conformis,Fst.—Taken at Palmers Heath, Brandon, May. Helictes erythrostomus, G m — S w e p t at Mildenhall on 19 June 1915.

H. mediator, Schd.—Not uncommon : on nettles at Wherstead.

H. borealis, Hlg.—Abundant everywhere throughout the County.

Ponzon exhaustator, Fab.—Quite rare : in a Wherstead lane, 28 October 1898.