Abstract
Sitophilus oryzae (L.), Sitophilus zeamais (Mots.) and Sitophilus granarius (L.) are major pests of stored grain, especially on cereals. Sitophilus linearis (Herbst) a congeneric of the afore-listed species was obtained from seeds of a wild plant, Tamarindus indica L. The development of S. linearis on some selected crop seeds as well as tamarind seeds was investigated in the laboratory at 25.3-30.3 °C and 75.0% ± 5.0 RH. One hundred grammes each of heat sterilized maize, rice, sorghum, millet, cowpea and tamarind seeds were infested with 100 unsexed adults of S. linearis and observed to determine the suitability of the different substrates for the development of the weevil. Sitophilus linearis bred and multiplied on the tamarind seeds but not on the selected crop seeds in the laboratory. Mean developmental period on the tamarind seeds was 32 days. The highest number (51) of adults that emerged on the first day of emergence was from cultures set up with one-week old adult insects. The highest mean weight (3.9mg) was also recorded on the cultures set up with one-week old insects. However, both mean number of emerged adults and mean adult weight were not significantly different (P>0.05). A significant difference was recorded in the mean percentage survival period of S. linearis on the different substrates (P<0.05) with the longest survival recorded on tamarind seeds. It can therefore be concluded that Sitophilus linearis, though a member of the family of grain weevils, could not reproduce on the cereal substrates or the cowpea seeds presented to it in the laboratory. If further studies confirm these findings, then Sitophilus linearis may pose no threat to cereal production due to its inability to survive and reproduce on them.
Highlights
IntroductionOther species in the same genus include Sitophilus oryzae (L.), Sitophilus zeamais (Mots.) and Sitophilus granarius (L.) which are stored grain pests
The results of the developmental study revealed the inability of Sitophilus linearis to develop and breed on the various crop seeds under the laboratory conditions of 25.3-30.3 °C and 26.7-75.0% RH
The highest number of emerged insects was recorded on the first day of emergence, with a mean of fifty-one (51) adult insects from the jars seeded with one-week old insects, whilst the highest number of insects was recorded on the second day of emergence, with a mean of twenty seven (27) adult insects from the jars infested with two-weeks old insects
Summary
Other species in the same genus include Sitophilus oryzae (L.), Sitophilus zeamais (Mots.) and Sitophilus granarius (L.) which are stored grain pests. The fourth instar larva lives within the chamber and moults into a prepupa (Cotton, 1920).This is followed immediately by a pupal stage which lasts for seven days before reaching the adult stage The adult does not immediately leave the seed but remains within to harden and feed for a few days (about 3-4 days) (Cotton, 1920) These weevils are among the most serious cosmopolitan pests of stored cereal grains in the tropic and sub-tropic regions (Throne, 1994). This study sought to investigate and compare the development of S. linearis on some crop seeds as well as the tamarind seed under laboratory conditions, so as to determine the extent to which S. linearis could pose a threat to food grains in storage
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