Toxicity of diatomaceous earth on seed weevil, Sitophilus oryzae L. and its effect on agro-morphological characters of maize seeds

Sitophilus oryzae L. (Curculionidae; Coleoptera) is considered to be a serious internal feeder of stored cereals. The use of insecticides results in the development of resistance among the pests and residues in the produce. Diatomaceous Earth (DE) is from a natural source, environment-friendly, safe to humans and natural enemies. In addition, it is highly effective against a wide range of stored pest species and has no toxic residues on the treated seeds. The promising alternative to synthetic insecticides is the application of DE in storage pest management under physical control. With this background, the present study was aimed to find the efficacy of DE against rice weevil, S. oryzae L. and their effect on the agro-morphological characters of maize (Zea mays L.) seeds. Contact toxicity bioassays were carried out with different concentrations of DE against S. oryzae. The results of the bioassay studies revealed LD50 at the concentration of 1.27 mg/100 gm of maize seeds. Further, 100 per cent mortality was achieved at the dose of 15 mg/100 gm of maize seeds within six days of exposure. The effect of DE on the germination provided a significant increase in germinability of maize seeds (LD50= 94%, LD95= 98% and control= 96%). DE at the concentration of LD95 had a beneficial effect on the seedling parameters, especially germination% (98%) and seedling length (53.02 cm) of maize. The present study concluded that DE could be effectively utilised as an alternative management tool to chemical insecticides in the management of rice weevil under storage conditions.

Potential insecticidal activity of four essential oils against the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

Oils extracted from Cymbopogon citratus, Lantana camara, Artemisia camphorata, and Imperata cylindrica plants were used as potential insecticides against the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae). The phytochemical composition of the isolated oils was identified by gas chromatograph-mass spectrometry (GC-MS). Oil contact toxicities were evaluated against the adults of S. oryzae. The activities of acetylcholinesterase (AChE), alkaline phosphatase (ALP), and transaminases enzymes (AST) were measured. L. camara oil (LC50 = 9.81 mg/cm2) demonstrated the highest effect, followed by C. citratus oil (LC50 = 10.89 mg/cm2), A. camphorata EO (LC50 = 16.12 mg/cm2), and I. cylindrica oil (LC50= 36.85 mg/cm2) against the adults of S. oryzae. The inhibition percentages of AChE were 38.8, 41.7, 35.0, and 27.2%; ALP were 42.4, 49.3, 28.1, and 18.7%; AST were 33.9, 38.7, 20.8, and 11.8%; and ALT were 22.7, 30.5, 14.6, and 9.6% after treated S. oryzae with oils from C. citratus, L. camara, A. camphorata and I. cylindrica, respectively. The highest abundant compounds in C. citratus were geranial (25.95%), nerylacetal (8.85%), and neral (8.45%), in L. camara were caryophyllene (12.2%), and 3-elemene (8.89%), in A. camphorata were germacrene D-4-ol (20.83%), and borneol (19.47%), and in I. cylindrica were 5-phenylundecane (10.68%), and 6-phenyldodecane (8.70%).

Epizootological Significance of Rice Weevil as a Mycobacterium Bovis Reservoir

This article presents materials on the role of the rice weevil (lat. Sitophilus oryzae) in the process of transmission of Mycobacterium of tuberculosis. The relevance of the study is conditioned by the rapid spread of tuberculosis around the world and the need to develop more advanced methods for diagnosing this disease, which, for its part, is impossible without expanding knowledge on all possible reservoirs of the causative agent of infection. Long-term research around the world has proven that insects are carriers of various microflora, including pathogenic ones. Therefore the purpose of study was to establish the epizootological role of the rice weevil as a reservoir for Mycobacterium bovis in the process of occurrence and spread of tuberculosis. The study determined the duration of transfer and isolation of Mycobacterium of tuberculosis in the external environment by infected beetles. The museum dissociative strain of Mycobacterium bovis (118 passage) was used for the study, the subject of the study was rice weevils. For the furtherance of this goal, the culture, microscopic, and statistical studies were conducted, and the viability of mycobacteria was determined after passages through the beetle body by evaluating colony-forming units. The epizootological role of the rice weevil in the development and spread of tuberculosis has been established. It is proved that the beetle can keep mycobacteria in its body for 50 days with a gradual decrease in their number and is then able to secrete the pathogen for another 30 days, contaminating environmental objects. When evaluating colony-forming units of mycobacteria in the dynamics of the experiment, a decrease in their viability after persistence through the body of beetles was revealed from 5.3*108 in 1 g of the original crop up to 1.4*108 in 1 g of crop that grew from beetle homogenisate for 30 days. These study results will allow developing and improving existing measures for the prevention of tuberculosis and prevent the introduction of this infection into safe territory

Repellent Effect of the Pandanus (Pandanus amaryllifolius Roxb.) and Neem (Azadirachta indica) Against Rice Weevil Sitophilus oryzae L. (Coleoptera, Curculionidae)

The aim of this study was to determine the effect of Pandanus (Pandanus amaryllifolius 20 Roxb.) and Neem (Azadirachta indica) leaves powder on the repellency, mortality, and weight loss 21 of grains due to Sitophilus oryzae. The methodes of this study used a completely randomized design 22 (CRD) with 7 treatments and 4 replications. The results of this study indicate that the best treat- 23 ment in terms of causing repellency was the treatment of 10 grams of pandanus with a percentage 24 of 87.5%, while the best treatment in terms of causing pest mortality and was also able to reduce 25 the risk of rice weight loss due to Sitophilus oryzae was treatment 10 gram of neem with a mortality 26 percentage of 76.25% and weight loss of rice 3.14%. This research showed that neem leaf com- 27 pounds are better in terms of causing mortality, while Pandanus compounds are better in terms of 28 causing mortality of Sitophilus oryzae.