Exploiting host preference and botanicals for The management of Bruchid Beetle ( Callosbruchus maculatus Fab. (Bruchidae: Coleoptera)

Abstract

Bruchid Beetle, Callosbruchus maculatus Fab. (Coleoptera: Bruchidae) is one of the most destructive insect pest of stored pulses such as Mung beans, Cow peas and Adzuki beans, etc. The research project was carried out in the Entomological Laboratory at the University of Haripur, Khyberpakhtunkhwa, Pakistan during 2018-2019. In the present experiments free choice and no choice tests were conducted to study the biology of C. maculatus on five hosts, i.e. Phaseolus vulgaris L., Vigna radiata L., Vigna unguiculata L., Cicer arientinum L., and Pisum sativum L., under controlled conditions at 27±5°C, 60%±5 Relative Humidity and 12h:12h (L: D) photoperiod. The experiments were laid out under Completely Randomized Design with four replications. The results of both the experiments showed significant differences in C. maculatus oviposition, percent adults emergence, infestations and seed weight loss (P ≤ 0.05). Highest mean oviposition (166.8 and 178.75 eggs/female) were recorded on P. vulgaris. Maximum percentage of adults (96.0 and 92.16 adults) were emerged on V. radiata. Highest mean percent infestations (69.0 and 82.96) were noted on V. unguiculata. Highest host seed weight loss (53.0 and 53.88%) due to C. maculatus infestations were recorded on V. unguiculata while sex- ratio was non-significant in both the tests. Proximate analysis of the five selected hosts seeds yielded ash (2.64- 4.17%), moisture (6.95-10.05%), protein (21.75-25.96%), fibre (2.80-6.48%), fat (0.81- 5.04%) and carbohydrate (51.25-63.257%). Percent host damages were positively correlated with the number of eggs, host weight loss and adult emergence but negatively correlated with fat and fibre. The preferred hosts V. radiata was selected for further experiments. Each of the five different plants species Azadirachta indica A., Nicotiana tabacum L., Melia azedarach L., Nicotiana rustica L. and Thuja orientalis L. were tested each at six different concentrations of 0.5%, 1%, 1.5%, 2%, 2.5% and 3% in the form of powder, crude, ethanol and crude (leaves and fruits) plant extracts to find comparative biology of C. maculatus. The experiments with plant extracts yielded dose dependent effects on oviposition, percent adult emergence, percent infestations of C. maculatus and percent host seed weight loss (P ≤ 0.05). Experiments with ethanol gave significant results. In ethanolic extracts lowest and highest mean oviposition (84.54, 117.17 eggs/female), adult emergence (58.40, 82.01%), infestations (16.65, 25.60%) and percent host seed weight loss (7.85, 26.73%) were recorded on A. indica and T. orientalis, respectively. All plant extracts had no significant effect on male: female sex ratio, however males ratio were slightly higher than females. The repellency of five plant species at six different concentrations were recorded after 1, 2, 3, 6, 24, 48, 72 and 96 hour’s exposure. In case of plant crude extracts, overall maximum mean percent repellency (39.75, 43.87, 48.25, 54.16, 61.14, 68.29, 72.00 and 67.54%, Class II-IV) was recorded with A. indica and minimum mean percent repellency (28.00, 34.12, 39.95, 42.16, 49.42, 57.46, 59.04 and 45.87%, Class- II-III) with T. orientalis. In ix case of ethanolic extracts, the highest mean percent repellency (57.08, 62.32, 66.70, 74.44, 76.45, 82.02, 76.74 and 64.06%, Class- III-V) was recorded with A. indica, while lowest mean percent repellency (25.34, 27.64, 29.26, 39.00, 46.00, 49.36, 56.03 and 37.00%, Class- II-III) with N. rustica. Phyto-chemical analyses of crude and ethanolic extracts of five plants species yielded variable amounts of phytochemicals, i.e. of alkaloids, flavonoids, saponins, di-terpenes, phyto-sterol and phenols. However, A. indica and N. tabacum yielded highest amounts of most of the phyto-chemicals. Overall results showed that ethanolic extracts were more effective than crude extracts. The toxicity of selected plant species was tested at six different concentrations in the form of powder, crude and ethanol to find the mortality of C. maculatus after 24, 48, 72, 168, and 336 hour’s exposure. The results of toxicity experiments with the five plant powders extracts revealed highest mean toxicities (15.42, 20.42, 31.14, 61.26 and 92.65%) with A. indica while lowest mean toxicities (6.67, 11.67, 20.18, 40.09, and 69.12%) with T. orientalis. Crude and ethanolic plant extracts were tested in contact, residual and topical applications methods. Both crude and ethanolic plant species extracts showed significant differences in C. maculatus mortalities (P ≤ 0.05). Among the crude and ethanoic extracts of different application methods contact application gave promising results. In case of crude extracts through contact method maximum mean mortalities of 26.25, 33.00, 49.12, 69.05 and 9.054% were observed with N. tabacum while minimum mean mortalities of 15.00, 20.00, 39.04, 50.95 and 57.14% with T. orientalis. Highest mean mortalities with ethanolic extracts through contact method were of 29, 49, 61, 63 and 87% with A. indica while minimum mean mortalities of 27, 30, 27, 43 and 67% with N. rustica. V. radiata and V. unguiculata were found susceptible hosts for C. maculatus. Among the five plant species, A. indica, N. tabacum and M. azedarach suppressed C. maculatus populations in powder, crude extracts and ethanol form, due their repellent and toxic effects at 3% dose rate, which make them potential botanical insecticides for the management of C. maculatus. The findings of the present research will lay down a base for developing efficient management strategies against the C. maculatus.