Studying the Combination Effect of Celery, Apium graveolens Extracts with Bt, Against Potato Tuber Moth Phthorimaea operculella

Potato tuber moth, Phthorimaea operculella is an important pest of potatoes which annually impose economic loss in potato production especially in stored places. Chemical control with spray in farms and fumigation in storages is a conventional method for depressing the population of this pest. In addition, with harmful effects of synthetic pesticides on environment and human health, developing resistant population of insects, compel researchers and plant protection institutions to utilizing new safe control methods. Delaying the resistance by keeping effectiveness of pesticides by using synergists and sublethal concentrations is a resistance management method. Bacillus thuringiensis is an effective microbial control agent against some insects. Its effectiveness decreased because of developing resistance in some population of insects. Combination of Bt with some botanical biopesticides increases its efficiency that reported in many studies. In this study combination of B. thuringiensis with hexane, ethyl acetate and methanol extracts of Celery, Apium graveolens were investigated on mortality and some biological parameters of PTM. Celery is a biennial plant in the apiaceae family, which is rich in some compounds such as phenolic and flavonoids. These compounds could affect biology and physiology of insects. Combination of sublethal concentrations of Bt with extracts of celery subjected for study of their effects on mortality, synergistic effects and some biological parameters on PTM larvae in this paper.

Potato tuber moth colony established by preparing larvae from a health colony in department of plant protection, Azarbaijan Shahid Madani university. Larva reared on potato tubers in plastic containers. Rearing carried out in controlled condition of 26±2ºC, 60% RH and a photoperiod of 16:8 (L: D) hrs.Foliage of celery after well washing with distilled water, dried in shadow in laboratory condition. Coarsely powdered dry plants used for extraction. Extraction carried out using the maceration method with three solvents, hexane, ethyl acetate and methanol respectively. Sub-lethal concentrations of both agents, including LC10, LC30 and LC50, individually and in combination, were assayed by the oral bioassay method. The same age and size of potato leaves were impregnated with sub-lethal concentrations of both experimental materials using the dipping method. The first larval instars of PTM were transferred on treated leaves, and mortality was recorded in 48, 96 and 144 hours’ intervals. Larval developmental period and adult’s emergence as an important biological parameterrecorded in all treatments. In addition, the inhibitory activity of extracts on α-amylase and protease enzyme of PTM larva was considered.Inhibitory activity of celery extracts in two concentrations 1 and 10%, on PTM larvae alpha-amylase activity was assayed by the dinitrosalicylic acid procedure, using 1% soluble starch as a substrate described by Bernfeld, (1955). And protease inhibitory activity assayed using azocasein as substrate, with comparing enzyme activity in controls and present of extracts in reactions.All experiments were replicated three times. On-way ANOVA analysis of variance in random design was used for statistical analysis. Duncan’s multiple range tests used for comparing means. For determining the synergistic, additive or antagonistic effects of combinations, chi-square test conducted between observed and expected results (df=1).

The results revealed that ethyl acetate extract of celery in combination with Bt synergistically increased the mortality of larvae. Compared to the control, the combination of methanolic extract with Bt didn’t affect larval mortality. However, the combination of sub-lethal concentrations significantly increased larval life span compared with the control and adult emergence decreased especially in LC50 combinations. Increasing the mortality with exposure time progressing, observed in all combinations and the most larval mortality recorded in 144 hours’ exposure time. Ethylacetate extract of celery alone and in combination with Bt more than other solvents affected biological parameters of PTM. Extracts in the concentration of 10 percent in reactions inhibited α-amylase and protease activity of PTM larvae by 27.97-37.77 and 11.48-25.51 percent, respectively.Numerous researchers have reported increased efficiency of Bt in combination with other plant extracts for controlling various insects. The observed synergistic effects can be attributed to factors such as disrupting midgut properties, inhibiting digestive enzyme activity, and disrupting the insect's immune system by plant extracts.Inhibitory activity of celery extracts on digestive enzymes activity of PTM larva, well documented in this research which is in alignment with other reports. Effects on larval life span that with prolonging it affects population dynamics of insect pests, reported in same studies. This biological effect has adverse effect on development and physiology of insects and asynchronies developmental stage with environmental variations which finally decrease the population of next generations or overwintering insect’s density. Adults and pupa emergence percentage decreased in combination of Bt with celery extracts that same results were reported in other researches.

This study aims to determine the effects of different extracts (prepared by different solvents) of celery in combination with Bt on potato tuber moth larvae. Effects of different solvents in separating effective compounds on PTM, was not same. In certain instances, the methanol extract of celery showed a minor effect in enhancing the potency of Bt. However, strong synergistic effects were observed with ethyl acetate and hexane extracts at various integrated concentrations. Time also played a crucial role in achieving the desired mortality results, with mortality and synergistic effects increasing over time in all extract combinations with Bt. Particularly, towards the end of the exposure period, a synergistic effect was notably observed in all integrations involving ethyl acetate extract of celery.In addition, with mortality, larval developmental period also affected by combinations. Increasing in life span observed in all treatments with different ratios. Adult emergence decreased strongly in different treatments and this is so important in decreasing the population of PTM. Because of importance of Bt as an effective and safe insecticide and increasing the resistance by different pests such as PTM, management of insects in integrated programs using plant extracts will improve the efficiency of Bt. Decreasing the sprayed concentrations in combination with other control methods are two important resistance management toll in IPM programs. Celery is a potent plant for this goal and additional studies are needed.