Insecticidal Efficacy of Conventional and Botanical Insecticides against Potato Tuber Moth (Phthorimaea operculella (Zeller) Lepidoptera: Gelechiidae)

Essential oils and synthetic insecticides

Insect cultures and rearing conditions

Bioassays

Statistical analysis

Table 2: Percentage of tubers infested and effectiveness of insecticides in preventing infestation by PTM (%) (Mean±SE)^*.

As shown in table 2, the tested products indoxacarb, spinetoram and Gamma-T-ol were 100 percent effective up to 7 days of treatment and were significantly superior even after 72 days of the treatment with an average infestation of 37.5% as compared to control (100%). It was determined that two concentrations (15 and 20ml) of spinetoram were effective in preventing the damage to potato tubers by PTM during 42 days. It was revealed that the lowest doses of spinetoram protected tubers for 35 days under laboratory conditions. Similarly, it was determined that the second and third doses of Gama-t-ol were effective in prevented the damage to potato tubers for 42 days. The data suggested that Fungatol and deltamethrin offered no protection to tubers against PTM. The treatments of Fungatol, deltamethrin and control obtained similar efficacy results. Indoxacarb treated tubers had no sign of infestation after 112 days. In addition, spinetoram and Gamma-t-ol treated tubers had no sign of infestation after 42 days but there were 27.5% and 22.5% damage respectively after 49 days. This is in contrast to Fungatol and deltamethrin treated tubers, which offered no protection and infestations were similar to that of the control.

The results show that the medium and high doses of Gamma-T-ol treated tubers had no sign of infestation and prevented damage to potato tubers by PTM for 42 days. All of doses Fungatol treated tubers had infestation at after seven days and not effective. The Gamma-T-ol and Fungatol are new extracts which have been tested against a few insect pests before. Only there was a study on effect of PTM. The effect of extract L. petersonii on larva of PTM was investigated. In this study, the highest mortality (100%) occurred at concentration of 0.4% while the smallest mortality was at 0.05% the extracts of L. petersonii[23]. There are references of using an extract of L. petersonii against other insects. For example, the efficacy of LSO against the diamondback moth P. xylostella L. was evaluated. According to this study the feeding activity and development were significantly reduced of larval stages on broccoli leaves that had been dipped in LSO. Oviposition deterrence was also found when an adult stage was exposed to treated leaves. Fecundity dropped by 50% at concentrations of 0.5%. The LC₅₀ value for third instar larvae was estimated to be 2.93% at 7 days after treatment. In addition, the oil was also tested at concentrations from 0.5 to 6% for oviposition deterrence of an egg parasitoid of the diamondback moth, Trichogramma pretiosum (Riley) (Hymenoptera: Trichogrammatidae). LSO deterred parasitisation in choice tests but not in no-choice tests. LSO did not cause mortality of T. pretiosum during 24 hours in a contact toxicity test.

It was concluded that LSO had no significant effects on the parasitoid, and therefore LSO is compatible with this biocontrol agent for integrated management of the diamondback moth [18]. Similarly, Erdogan and Hassan [19] revealed that the extract of L. petersonii caused 100% mortality of the two-spotted spider mite at 6 days after treatment.

Little is known about the effects of Fungatol (tea tree terpinene-4-ol) and Gamma-T-ol (tea tree oil, 75% Terpene) obtained from the tea tree on insects. Studies on the effect of Fungatol and gamma on insects are limited. The first study the effects of Fungatol and Gamma-T-ol was carried out by Iramu [24]. In this study, the insecticide effect of Fungatol, Gamma-T-ol, Fungatol + Neem and Gamma-T-ol + Neem extracts on A. gossypii was investigated in laboratory conditions. The leaf disc dipping method was used in laboratory tests. The highest insecticidal effect showed Fungatol + Neem and Gamma-T-ol + Neem extracts on A. gossypii. In addition, it has been reported that these extracts have no effect on the reproduction and development of A. gossypii. In another study, researchers have reported that Fungatol + Neem spray (50.0-001) had the highest efficacy on T. absoluta Kasap, et al., investigated the toxic effects of Fungatol and Gamma-T-ol extracts on A. gossypii and T. urticae under laboratory conditions [25,20]. The researchers reported that extracts of Fungatol (3.50%) and Gamma-T-ol (3.60%) resulted in 42% and 48.9% of mortality, respectively, after 48 hours on A. gossypii because of their different concentrations of extracts. The same concentrations of extracts were reported to cause 94% and 93.3% of mortality on T. urticaeadult females after 72 hours. Kok and Kasap found that the effects of insecticides on Myzus persicaeSulzer, (Hem: Aphididae) which cause economic losses in many cultivated plants under laboratory conditions in the same extracts [26]. They reported that extracts of Fungatol (3, 50%) and Gamma-T-ol (3, 60%) resulted in 72% and 80% mortality treatment after 72 hours on M. persicae respectively. Gamma-T-ol and Fungatol have been used against other arthropods. For example, it was revealed that the highest mortalities were observed at concentrations of 3.5% of Fungatol and 3.6% of Gamma-T-ol, and the mortalities caused by 3.5 and 3.6% concentrations of Fungatol and Gamma-T-ol, respectively, at 1, 24, 48 and 72 hours, were 0, 52, 74, 94%, 0, 52, 78 and 94% on two spotted mite respectively [27]. In addition, Kasap, et al., revealed that after 1, 24 and 48 h, the highest concentration of Fungatol (3.5%) and Gamma-T-ol (3.6%) obtained from M. alternifolia had caused 0, 18, 42% and 0, 20, 48.9% mortality of cotton aphid respectively. moreover, Fungatol and Gamma-T-ol showed the high repellent effect against T. urticaeunder laboratory conditions [20,28].

There are many studies the insecticidal about effect of plant extracts on PTM. For instance, Sharaby, et al., revealed that vapors of Cymbopogon citrates Stapf., Myristica fragrans Houtt., Mentha citrate and a-l on one caused highly significant reductions in the life span of exposed PTM [29]. In another study, Treated potato tubers by methanolic extract of lavender elicited the lowest percentage of first larval PTM penetration, and studying of oviposition-preference demonstrated that the largest number of eggs was laid on control and fumitory with 28 and 10 eggs after three days, respectively [30]. Moreover, it was determined that dried powders of Allium cepa, Curcuma longa, Colocasia antigurum, Ocimum basilicum, Dodonaca viscose and Thuja orientalis played a highly significant role in reducing egg deposition on PTM [31]. Lal found that the leaves of Lantana aculeate provided most protection to the tubers, reducing damage than Eucalyptus globulus and Bacillus thurungiensis [32]. It was observed that extracts of Piper nigrum and Matricaria chamomile showed high mortality, anti feeding and repellent effect on larva of PTM [33].

Results from this laboratory testing showed that indoxacarb provide efficient control for 112 days. These results confirmed the data presented by Dobie who mentioned about a slower, but at the same time the most continuous, effect of indoxacarb against young larvae of the PTM compared with other tested compounds [34]. Gecheva and Dimitrov revealed that indoxacarb and deltamethrin caused 100% larvicidal mortality 14 days after treatment [35]. The same authors found that after indoxacarb and deltamethrin treatment ovicidal mortality was 38.8 % and 49.6% respectively. Das and Rahman determined that deltamethrin (K-obiol DP2) treatment kept potato tubers free of the pest [36]. The best control over the PTM can be exercised by indoxacarb. In our experiments deltamethrin showed some effect on PTM as Das and Rahman revealed in their studies [36]. In Tunisia Das, et al., found that deltamethrin, granulosis virus and B. thuringienses were equally effective in reducing pest damage, and after 3 months storage the treatments showed no significant effect on sprouting [37]. Collantes, et al., who found that deltamethrin was most toxic for adult of PTM [38]. This may be explained that deltamethrin used in our experiments could be a different formulation.

According to our results, spinetoram (15 and 25ml) have been found to be effective in preventing damage to potato tubers by PTM for up to 42 days. In parallel with our results, Dobi revealed that when larvae were exposed to spinetoram mortality increased directly with time of exposure [34]. Mortality was noticed quickly at the 5 minute mark with 10% mortality. This mortality more than doubled at the next time interval of 15 minutes. Between 15 minute and 30 minute intervals, the mortality rate had the highest increase from 28% to 72% mortality. The mortality rate then started to plateau between the 30 minute and the 60 minute interval. By 120 minutes, the evaluation timing, spinetoram had caused 100% mortality. In addition, it was determined that spinetoram was effective in controlling PTM in field conditions, which is in accordance with our results [39].