Danger of Chemical Pesticides

 

 Natural Enemies

Bio-control agents can be integrated in the management techniques to avoid abusive use of chemical pesticides. The agents include parasites, parasitoids and natural enemies of the pest. Natural predators of Tuta absoluta are Macrolophus pygmaeus and Nesidiocoris tenuis (Arno & Gabarra, 2011). According to Arno and Gabarra (2011), Indoxacarb increases the mortality of Macrolophus pygmaeus and Nesidiocoris tenuis. They also state that azadirachtin and spinosad have a negative effect on the reproduction of the predatory insects of tomato leaf miner. Trichogramma pretiosum and Trichogramma brassicae are popular egg parasitoids of tomato leaf miner (Mirhosseini, Fathipour, Holst, Soufbaf, & Michaud, 2019). They report that the egg parasitoid Trichogramma pretiosum, when applied together with predatory bug Nesidiocoris tenuis in a tomato leaf miner field, affects the performance of the predator. They also suggest the augmentation of predatory agents’ pre-infestation but never along with the egg parasitoids. Simultaneous application of both the predator and parasitoid affects the predation since the palatability of the pest decreases due to the presence of the parasitoid inside the prey. Phthorimaea operculella granulovirus (PhopGV) have also proven effective against Tuta absoluta (Tiba et al., 2018).

Interaction between multiple pest control factors Faria, Torres, Fernandes & Farias (2007) reported that plant structure was not associated with the efficiency of Trichogramma pretiosum, however, pest infested plant apexes had a healthy pest population. They also state that the pest population is highest in the upper portion of the plant stem; the pest infestation decreases with plant height from the ground level. Use of insecticides like cartap, phenthoate, lambda-cyalothrin, abametin, tebunozide and teflubenzuron to control Tuta absoluta affects the natural enemy Trichogramma pretiosum with slight to large negative effects (Consoli, Parra & Hassan, 2009). Using biocontrol requires sharp entomological knowledge and the understanding of pest management. We cannot always be technically right. If not right at crucial decision-making stages, a small mistake can cause a heavy loss of produce and resources. Hence, a simpler method of pest control can be used that includes luring and/ or trapping. Batalla-Carrera, Morton and Garcia-del-pino (2010) report the successful larval parasitism of nematodes namely Steinernema carpocapsae, Steinernema feltiae and Heterorhabditis bacteriophora over Tuta absoluta. Metarhizium anisopliae anisopliae (Metsch.)is effective against tomato leafminer\'s pupa (Contreras et al., 2014). Inanil, Yoldas and Birgucu (2012) report that both Beauveria bassiana (Bals.) and Metarhizium anisopliae (Metsch.) can effectively use to control the eggs and larvae of Tuta absoluta. Bacillus thuringiensis kurstaki is effective against tomato pinworm under open as well as greenhouse conditions (Sabbour & Soliman, 2012).

 Lure and Traps

Megido, haubruge & Verheggen (2013) suggest that the use of virgin females as lure is more convenient and economical as compared to light trapping. Delta traps with appropriate lure and a sticky portion inside the trap is used to trap the pest. The trap height should be set according to the plant height and around the height with relatively higher infestation (Megido et al., 2013). Russell IPM suggests at most 4-5 traps per ha for monitoring of the pest whereas a huge number of traps (10-20) per ha for monitoring as well as mass trapping. Two more traps can be added on all four sides to deduce the direction of insect entry (Megido et al., 2013).

Cultural Measures

Prevention is an important measure to manage tomato fields from Tuta absoluta. The farmland should be free from the crop residue of last season. Mono cropping of the tomato should be avoided and crop rotation with non-host crops can be done. Fine screening nets can be used to surround the fields. Greenhouse is an appropriate setting to maintain the biodynamics of the confined agro-ecology. ‘Push and Pull’ strategy can be utilized to maintain the delicate balance between the populations of natural predators and the pest. Boundary cropping, trap cropping, mixed cropping and intercropping can be of use.

 Hormonal Pesticides

Insect growth regulators are the latest group of pesticides. They do not leave any persistent residue, nor do they have any hazardous effect on human health. Pyriproxyfen is a juvenile hormone mimic causing mortality of half the population of early larva under exposure (Tome, Cordeiro, Rosado & Guedes, 2011).

 Botanical Pesticides

The development of insect resistance to pesticides compels us to search for safer ways of pest management. The methods have already existed unexplored in the deep roots of our traditional farming system. Botanicals are the answer to most problems invited by abuse and overuse of pesticides. Ghanim (2014) has reported that chinaberry, geranium, onion and garlic prove effective against tomato leaf miner. According to him, the effectiveness of the botanicals decreases in the sequence of Chinaberry, Geranium, onion and garlic respectively. Azadirachtin, also a botanical, is an alkaloid obtained from Neem tree (Azadirachta indica) having an anti-feedent, repellent and sterility induction effect over the instars of Tuta absoluta (Berxolli & Shahini, 2017). It interferes with vital life processes of the pest like oviposition, molting and feeding resulting in growth disorders of the insect (Berxolli & Shahini, 2017). Application of azadirachtin is relatively more effective in the early two instars of the larva than during the later stages (Berxolli & Shahini, 2017). According to Abdel-Baky and Al-Soqeer (2017), Simmondsin extracts from jojoba seeds (Simmondsia chinensis) is effective against the second instar larvae of Tuta absoluta.

Conclusion

Tuta absoluta is a dangerous invasive pest for Nepalese agriculture. Chemical pesticides like Spinosad, Abamectin, Emamectin benzoate, Triflumuron and Diafenthiuron were found successful initially. However, researches on the negative effects of synthetic chemicals on the environment made the scientific community look for sustainable and eco-friendly alternatives. The use of natural enemies, hormones, botanical pesticides, physio-mechanical traps etc. are among the most effective alternatives in the current scenario. Scientists concerning the field are carrying studies to evaluate and determine the optimum pest management. Recently introduced, insect hormones seem to have no residual side effect. Furthermore, the hormones prove to be effective