Wheat is commonly stored together with other grains such as barley, rye, oats and triticale. It is important to assess the influence of smaller grains on progeny production and feeding preferences of
Adults of
Food preference of
The diet was loaded at random into the polythene covers. Each vertical pipe holding the polythene covers were numbered. Separate numbers were assigned to each diet, as well as each diet holder. The diet materials were assigned using a six numbered dice. For each diet holder the dice was rolled twice. The first number on the dice referred to the number of the diet and the second number referred to the number of the polythene dispenser. If the first number was 2, that referred to the rice grain and if the second number is 4, it indicated that the fourth dispenser be loaded with rice. If the same numbers were repeated, the dice was rolled again. Thus, wheat, rice, chickpea and their flours were loaded into the polythene bags and fastened to the vertical pipes. This system completely randomized the diet holders and thus the results obtained were without any bias as to the position of the feed material within the choice-based feeder paradigm. The vertical pipes were fitted with ‘T’ joints which were connected by horizontal pipes, about 2' long. The horizontal pipe structure was provided with a ‘T’ joint exactly in the middle, which was connected to a 2' long vertical pipe which served as the beetle vent. The beetle vent was closed with an end cap. The tunnel system was lengthy enough to ensure that the chemical signals from any of the diet materials were not available at the beetle inlet vent.
Exactly 200
Biological observations such as incubation, larval, pupal and total developmental periods, adult male and female longevities, fecundity and fitness were studied in detail. Examination of the influence of the different grain species on the emergence of the progeny of
Three pairs of newly emerged adults were transferred into glass petriplates. The pair that completed its development in a particular feed type was always allowed into the same feed type to understand the impact of that feed type on their biological characteristics. The beetles were allowed to mate and oviposit for about 15 days. Flour / grain and legume samples containing eggs were sieved carefully through a 90mm mesh and the eggs were separated out daily with the help of a fine brush by examining under a dissection microscope. Eggs deposited on the samples were transferred to petridishes using a fine brush and small debris, if any were removed carefully. Three replications of each feed type were maintained. Incubation period was recorded as the duration of time taken by the freshly laid eggs to hatch out, which was recognized by the dark extremities of the larva seen through the egg chorion.
The larval duration was recorded as the time (in days) taken from the hatching of the egg till the pupation of the last instar grub. To determine the number of larval instars and the duration of each instar, six replicates of six eggs on the same day were collected in petriplates. This was done to eliminate any error that may occur when eggs laid on different days were mixed. These eggs hatched almost on the same day. The growth of the grub was carefully noticed each day and the larvae were kept in separate petri dishes marked day-wise. The duration of the different instars were calculated by observing the moulted skin of the larvae in the feed. The process was carefully continued till all the larvae pupated
The pre-pupal stage does not involve moulting and can be distinguished from the fully mature larva by its elongated cylindrical shape and extended head. The corrected larval period was calculated by subtracting the pre-pupal period from the total larval period. The periodicity of six replicates of six pupae was followed to record the pupal period which extended from the formation of the pupa to the eclosion of the adult. Pupal period was recorded from the formation of pupa till the eclosion of the adult.
The life span of
Fecundity was recorded by counting the number of eggs laid during the oviposition period of a female. Oviposition started after the first mating took place. Mating initiated the ovipositional process. The eggs were laid singly in the flour material. The flour material was sieved and the eggs were recovered. From the grains and the legume, the eggs were collected using a small brush and a magnifying lens, after moving the grains carefully to one part of the container. The egg count in each diet was separately recorded. Egg counting was continued throughout the ovipositional period of a female. Counting was discontinued only after ascertaining that all the eggs to be laid are fully deposited. When eggs were not laid for a period of 10-12 days, it was presumed that the egg laying has fully stopped.
After 24 hours of introducing the
Fecundity is high in wheat (427 eggs) and wheat flour (425 eggs) and about 15 percent less in rice flour. The total larval period in rice was 27±4 and the highest larval period of 45± 4 days was recorded in the legume chickpea. The highest pupal periodicity was recorded in chickpea (13±2) and the lowest pupal periodicity was recorded in wheat grain and its flour (8±1.87 & 8±1.04). The incubation period was lowest (7days) in wheat and highest (10days) in chickpea flour. The total developmental period was 55 percent higher in chickpea compared to wheat grain (
Feed type |
Interval after release (in h) |
|||
24 |
48 |
72 |
96 |
|
Wheat |
b 36 ± 4 (18 ) |
b 41 ± 4 (20) |
b48 ± 3 ( 24 ) |
c 51 ± 2 (26 ) |
Rice |
a14 ± 4 ( 7 ) |
a 18 ± 4 ( 9 ) |
a 22 ± 3 (11) |
a24 ± 3 (12) |
Chick pea |
a 16 ± 3 ( 7 ) |
a 16 ± 2 ( 8 ) |
a 18 ± 0.8 ( 8 ) |
a 21 ± 2 (10.50) |
Wheat flour |
b30 ± 6 ( 15) |
b38 ± 6 ( 14 ) |
b46 ± 4 ( 23 ) |
c 50 ± 3 ( 25 ) |
Rice flour |
a14 ± 3 ( 7 ) |
a 15 ± 3 ( 7 ) |
a 17 ± 3 ( 8 ) |
a 21 ± 2 ( 10 ) |
Chick pea flour |
a15 ± 3 ( 7 ) |
a16 ± 3 ( 8 ) |
a 17 ± 3 ( 8 ) |
a21 ± 2 ( 10 ) |
Stray beetles |
c76 ± 8 ( 38 ) |
c 56 ± 7 ( 28 ) |
c 32 ± 5 ( 16 ) |
b 12 ± 2 ( 6 ) |
Feed type |
Incubation period |
Total Larval period |
Pupal period |
Total developmental period |
Fecundity |
No. of eggs hatched |
Adult longevity (Days) |
|
Male |
Female |
|||||||
Days |
||||||||
Wheat |
a7 ± 2 |
a27 ± 6 |
8 ± 2 |
a45 ± 7 |
a427 ± 6 |
a406 ± 11 (95) |
242 ± 5 |
244± 5 |
Rice |
c9 ± 2 ( 31 ) |
a27 ± 4 ( –56 )* |
12 ± 1 ( 57 ) |
a51 ± 2 ( 13 ) |
b375 ± 15 (–12 ) |
b362 ± 18 ( 97 ) |
214 ± 10 ( -11 ) |
212±3 ( 13 ) |
Chick Pea |
c9 ± 2 ( 33 ) |
b45 ± 4 ( 57 ) |
13 ± 2 ( 73 ) |
b69 ± 3 ( 55 ) |
b373 ± 16 (–13 ) |
b360 ±14 ( 97 ) |
210 ±10 ( -13 ) |
210±6 ( 14 ) |
Wheat flour |
b8 ± 2 ( 15 ) |
a28 ± 3 ( – 4 )* |
8 ± 1 (0) |
a44 ± 3 ( 1 )* |
a425 ± 26 (– 0.4)* |
a390 ± 13 ( 92 ) |
234 ± 8 ( -3 )* |
235 ±4 (- 4 ) |
Rice flour |
b7 ± 1 ( 13 ) |
a30 ± 3 ( 4 )* |
9 ± 1 ( 17 ) |
a49 ± 3 ( 9 )* |
b365 ± 14 (–15 ) |
b352 ± 13 ( 96 ) |
234 ± 8 ( - 3 )* |
231± 4 (-5 ) |
Chick pea flour |
c10 ±1 ( 51 ) |
b40 ± 3 ( 40 ) |
10 ± 1 ( 31 ) |
b63 ± 6 ( 39 ) |
b378 ± 9 ( –11 ) |
b365 ± 10 ( 97 ) |
193 ±8 (-20 ) |
185 ±7 (-24 ) |
Mechanisms of acceptance of cereal grains or legumes by insect pests of stored products are complex and depend on many factors, such as the physicochemical and biochemical grain properties as well as the insects’ capacity for biochemical and physical adaptation to post-harvest conditions
The results of an earlier study showed that the highest progeny was found in wheat, which is one of the softest grains. According to
A study by
Initially the choice - food chamber, perhaps was not familiar to
The incubation period is lowest (7 ± 2 days) for eggs laid by
The highest fecundity was recorded in
Hatchability of eggs varied from 92 percent (wheat flour) to 97 percent (Rice grain). Minimum statistically non significant variation was recorded with reference to hatchability of
TS conveys sincere gratitude to the Principal, Scott Christian College Nagerciol, Tamilnadu, India, Head, Department of Zoology, for the laboratory facilities extended.