DINODERUS OCELLARIS STEPH.* Part III
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STUDIES ON THE COMMON BAMBOO-BORER, DINODERUS OCELLARIS STEPH.* Part III. Biology BY N. L. SITARAMAN [Technical Development Establishment Laboratory (Stores), Kanpur] Received September 12, 1950 (Communicated by Dr. T. S. Subramanian, F.A.SC.) 1. INTRODUCTION THE bamboo-borer, Dinoderus ocellaris Steph. is a serious pest of bamboos in India and hitherto no detailed work has been described on the biology of this pest. In Parts I and II of this series of papers x, 2 a short account of the egg, sex differentiating structures of the pupae and a technique for rearing larvae under laboratory conditions have been described. Apart from Beeson's account3 on the general biology of this pest and a short note on the subject by Sen, 7 no definite information has been available hitherto on the mode of oviposition, the egg-laying capacity of the beetles, the number and the dura- tion of the larval instars, etc. In order to devise ways and means for the effective control of this pest, a systematic study of the biology of this pest was undertaken in these Laboratories and the results are described in the present paper. For the sake of providing complete information, short summaries of work described earlier in Parts I and II 1, ~ have been included at appro- priate places. 2. SYSTEMATICPOSITION D. ocellaris Steph. belongs to the order Coleoptera, sub-order Polyphaga, superfamily Bostrichoidea and family Bostrychidce. Lesne~ included it in the subfamily Dinoderime, but BSving and Craighead ~ considered Psoicke (including Dinoderus), Bostrychidte and Lyctidce as distinct families and made two groups--the first consisting of Lyctinat, Psoime, Dinoderinae and Apoleonime and the second Bostrychince. 3. TYPE OF DAMAGE The beetles attack bamboo culms within 24 hours of felling by boring in at cut ends. The entrance tunnel is extended towards the centre in a solid culm and between the walls in a hollow culm, where the fibrovascular bundles are widely spaced and there is an abundance of the * Parts I & II of this series were reportedpreviously under the caption "Studies on the Dinoderus Borer in Bamboo". 148 Studies on Common Bamboo-Borer, D. ocellaris Stepk.--lll I49 nutritious pithy tissue. This tissue contains starch and the richer it is in starch the heavier is the attack. The beetles enter longitudinally but bore transversely after a short distance from the entrance holes. Scn 7 has reported that "the entry hole of the adult beetle is carried in a zig zag fashion, more horizontal than vertical and is always found full of frass" 4. LIFE-HISTORY (i) Precopulation period.--Adults mate outside the bamboos within 18 hours after emergence,1 one mating being sufficient for the fertilisation of all the eggs laid by a female. (ii) Preoviposition period.--The interval between copulation and ovi- position shows much variation depending upon the type of food available. Eggs were observed on the third or fourth day, when freshly emerged adults were released on bamboo-strips (3" long, 1" wide and 89radius of curvature) having high starch content. In crushed maize, which is not the natural food of the beetles, though it provides a suitable oviposition medium,~ the preoviposition period varied from 7-16 days. In bamboo-strips, eggs were observed at the site of the entrance holes when thin layers of the strip were removed. According to Sen, 7 the eggs were found lying burried in the moist and soft frass towards the end of the tunnel. In maize,, the eggs were laid loosely in the powder resulting from the beetles boring into the grains. Table I records the observations on the preoviposition period. TABLE I. Preovipositionperiod of D. ocellaris Steph. Temp. 86~ / R.H. 75% Bamboo-strips Maize Preovi position Copulating Preovi positio~ Copulating Eggs period adults Eggs period adults observed on observed on released on (in days) released on (in days) 13-9-1947 16--9-1947 3 3-3-1948 16-3-1948 13 16-9-1947 20-9-1947 4 6-3-!948 22-3-1948 16 20-9-1947 24-9-1947 4 11-3-1948 18-3-1948 7 23-9-I 947 27-9-1947 4 I5-3-1948 29-3-1948 14 26-9-1947 29-9~1947 18-3-1948 28-3-1948 10 12-3-1948 16-3-1948 20-3-1948 31-3-1948 11 Average 3.7 l1.8 150 N.L. Sitaraman (iii) Location of eggs: oriposition period.--Eggs are deposited singly into the ends of the severed fibrovascular bundles (Plate VI). It is prob- able that this is the usual method of oviposition in bamboos since the beetles did not oviposit either in bamboo dust filled in glass tubes or packed between two glass plates. The distance from the entrance hole and the site of ovi- position is about 0.67 mm. For the determination of the number of eggs laid by the female and the oviposition period, beetles (pairs) were released in small Petri dishes containing crushed maize grains and counts of eggs were made daily. In bamboo strips, a single female was released on each and thin layers of the strip were then removed by a sharp razor and the larva present (both living and dead) were collected at regular intervals, care being taken not to disturb the female beetle. Since it was not possible to count the exact number of eggs laid by a female beetle, the total number of larvae collected as above gave an approximate indication of the number of eggs laid. Tables II and III record data on the egg-laying capacity of D. ocellaris Stpeh. in bamboo strips and crushed maize grain respectively. It would appear, therefore, that the number of eggs laid ranges from 50-52 when the food is bamboo. In the case of crushed maize, the number of eggs laid is variable and in any case less than that laid on bamboo strips. The duration of the oviposition period ranges from 12-16 days in the case of crushed maize, and from 46-51 days when the food is bamboo. TABLE II. Egg-laying capacity of D. ocellaris Steph. Food ........ Bamboo Strips Temperature ........ 86 ~ F. / R.H. 75~ Strips examined on and number of larva removed Single female Oviposition o2~ after copulation released on began on 29.3 30.3 5.4 8.4 il 2.4 16.4120.4 2t.4 28.4 1.5 6.5 12.5 [~ ~....q 12-3-1948 .. 16-3-1948 13 I 3 4 5 3 6[ 21 3 21 1 3 Ag:a, 52 (1) / (I) (1) (I) (2) (I) I 13-3-1048 * -V-T-7 2 Adul, I 5i (1) [(I)' ' i d,ead ,. ;2 13-3-1948 .~ -- -V -V -7 Adu,t / r (1) (1) dead * Not observed. Figures in brackets denote number of larvae found dead. Studies on Common Bamboo.Borer, D. (~cellaris Steph.--ll[ 151 TABLE III. Egg laying capacity of D. ocellaris Steph. Food ........ Crushed maize grains Temperature ........ 85 ~ F. ] R.H. 75~ -Number of eggs per day C opulati ng Oviposi- adults tion began on released on 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 3-3-1948.. 16-3-19~8 3 2 4 1 5 .. 7 2 1 .... 4 .. 9 ,~ 29 6-3-1948.. 22-3-1948 2 5 3 6 4 1 5 4 2 1 .. 2 3 2 1 Q ~ 41 11-3-1948.. 18-3-1948 1 3 2 5 1 3 6 3 1 4 2 8 5 .. 2 1 9"~ 47 15-3-1948.. 29-3-1948 4 2 1 5 7 6 2 1 5 1 3 2 3 2 1 ~ ~ 45 (iv) Post-oviposition period.--Females which failed to oviposit after having laid eggs regularly were considered as having passed the oviposition period. The post-oviposition period varied from 6-7 days at 86 ~ F. and 75~ R.H. (v) The egg.--The egg has been described earlier? The egg of Dinoderus minutus is 0.81 mm. long and 30.20 mm. broad.* (vi) Incubation period.--The incubation period of 46 eggs was studied at 86 ~ F./75~ R.H. It varied from 3-5 days and the average was 4.2 days. Sen 7 has reported that the incubation period of 20 eggs ranged between 2 to 4 days at a temperature of 84 ~ F. The incubation period of the eggs of D. minutus varies from 3-7 days. 4 (vii) Hatching.--The mode of hatching is rather peculiar. The larva breaks through the broader end of the egg with the tip of its abdomen, which is armed with three dorsally located spines. The chorion is almost com- pletely cut open and the broader end remains fastened like a lid. The larva gradually wriggles out and the hatching is completed within 24 hours. (viii) The larva.--The freshly hatched larva is pale white in colour and almost cylindrical in shape and does not possess a greatly enlarged thorax-- a characteristic of the Bostrychid larva. Head is slightly curved and the body is sparsely clothed with hairs. The larva assumes the shape of a grub only after the second moult. (a) Moulting.--Forty-eight hours before moulting, the larva becomes ~ompletely inactive and ceases to feed. The skin of the body looks dry and 152 N, L. Sitaraman dull. The cuticle ruptures on the median line of the prothorax and the larva wriggles out by muscular contractions of the body. When the moulted skin is adhering to the last few abdominal segments, the larva curves and detaches itself from the skin by holding it in its mandibles.