Determination of thermal constant and development threshold of Bihar hairy caterpillar, Spilarctia obliqua Walker

Effect of six constant temperatures viz., 18±1, 21±1, 24±1, 27±1, 30±1 and 33±10C was studied on the egg hatchability, larval pupal development and adult survival of Spilarctia obliqua. Development rate of egg, larva and pupa gradually increased with increase in temperature, while total developmental period decreased. Mean developmental period of the pest decreased from 93.73 days at 18±10C to 31.20 at 33±10C. The lowest and the highest temperatures at which no development took place were found to be 12±10C and 39±10C, respectively. Regression equations between development rate and temperature were found to be Y= 0.0189 X -0.1998 (R2=0.88) for egg, Y=0.00122 X -0.0248 (R2=0.84) for small larva (1-3rd instar), Y=0.0058 X -0.0675 (R2=0.76) for large larva (4-6th instar), Y=0.0074 X-0.1075 (R2=0.94) for pupa and Y=0.0142 X-0.4363 (R2=0.79) for adults. Developmental threshold were determined to be 10.57, 11.27, 11.55, 15.28 and 10.92oC for egg, small larva, large larva, pupa, and adult respectively with corresponding thermal constant being 52.91, 344.82, 243.90, 142.85 and 70.42 degree days (DD). Thermal constant to complete a generation was found to be 854.90 DD. This was the first studies on this aspects, these estimated thermal thresholds and degree days could be used to predict the S. obliqua activity in the field for their effective management through pest forecasting.

Young Larvae of Veromessor Pergandei (Hymenoptera: Formicidae: Myrmicinae)

Time was when it seemed every myrmecologist wanted to work on Veromessor pergandei, but we can find no mention of it in the last eight years of Zoological Record. When we lived with it in Death Valley and southern Nevada it became one of our favorite ants.To differentiate instars we would like the following specimens: a first instar inside an egg; a second instar inside a first instar that is ready to moult; a third instar inside a second ready to moult; etc; a mature larva; a prepupa. Fortunately our V. pergandei material meets all the requirements, except the first. V. pergandei is polymorphic, which presents another problem: when does subcaste differentiation begin? How can one tell whether a small larva is the young of a major or a mature of a minim; or whether a mediumsized larva is the mature of an intermediate worker or the halfgrown larva of a major? In V. pergandei subcaste differences apparently begin in the fourth instar and are manifested only in size.V. pergandei presents another problem: there are two body shapes for mature worker larvae. We have no explanation for this.

Experimental work on reproduction in the tsetse fly,Glossina palpalis

1. The reproductive cycle of the female fly was worked out at an average temperature of 24° C. The lowest egg of the right ovary develops first, and is ripe in 7 days. Ovulation never occurs earlier than the 8th day, and frequently later; it bears some relation to fertilization, for eggs in virgin females failed to ovulate for weeks. The first larva was produced in a variable time after fertilization (because of delayed ovulation), but the succeeding larvae were produced very regularly, with an average period of 9·9 days between them.2. Pupae produced in the laboratory usually weigh less than those collected in the field. The reason for this is nutritional, and flies must take large meals at the right stage in gestation to produce large pupae. It is impossible to ensure that this happens with all flies in the laboratory.3. Abortions are caused in captivity by flies obtaining too little blood. They may be induced in pregnant females by allowing them to take only small meals, when either an egg or a small larva is extruded. When these flies were properly fed later, they produced normal larvae.4. A constant temperature of 30° C. causes sterility in females. Ovaries develop abnormally, embryos fail to hatch from eggs, but young larvae (in the uteri) are not adversely affected.5. A constant temperature below 22° C. slows down the rate of development of the eggs in the ovaries and lengthens the larval period. Experiments at this temperature are complicated by inactivity of males, which leave many females unfertilized. The length of the combined embryonic and larval periods is 17½ days.6. Experiments performed outside in the laboratory compound suggest that the period between each larva in the field (during December in Uganda) will be about 13½ days (min. temp. 16° C.; max. temp. 27° C.).7. Flies appear to be able to breed equally well with relative humidities of 47, 88 and 100 per cent. In the drier air care must be taken with feeding, or the flies die from desiccation.8. A temperature of 20° C. can cause pregnant females to retain their larvae for an extra 12 hours, but not longer.

A NEW LEPIDOPTEROUS INSECT INJURIOUS TO VEGETATION

In the months of June and July the Red Pine (Pinus resinosa) and the white Pine (Pinus strobus) show by the exuding pitch that they are suffering from the attacks of an insect. The wounds occur on the main stem below, the insertion of the branch. On cutting into the bark the injury is found to be caused by a small larva, which, when full grown, measures 16 to 18 millimetres. The head is shining chestnut brown with black mandibles. The body is livid or blackish green, naked, with series of black dots, each dot giving rise to a single, rather stout, bristle.