Evaluation of augmentative biological control options against fruit and shoot borer, Conogethes punctiferalis (Guenée) (Lepidoptera: Crambidae) in guava in India

Conogethes punctiferalis (Guenée) (Lepidoptera: Crambidae) has emerged as one of the important pests of guava in Punjab, India. Chemical insecticides have been used for its management, which could have serious implications on environmental and human health. As an alternative to chemical insecticides, biocontrol is the most appropriate alternative for its eco-friendly management. Two field experiments were therefore, conducted to evaluate efficacy of two biocontrol agents, Trichogramma chilonis Ishii (Hymenoptera: Trichogrammatidae) (egg parasitoid) and Chelonus blackburni Cameroon (Hymenoptera: Braconidae) (egg-larval parasitoid) against the borer during rainy season, 2020 and winter season, 2020–21. Four releases of both parasitoids at various dosages were carried out at weekly intervals starting from first week of July in rainy season and first week of October in winter season. Trichogramma chilonis @ 2000 parasitized eggs per tree was the best in reducing the fruit damage and increasing yield and net income over check in both rainy as well as winter season crops. There was 73.6% reduction in damage over control, 1.70 Metric tons (MT) increase in yield over control and 258.36 US $ per acre increase in net income over control in rainy season crop. During winter season, there was 62.5% reduction in damage, 1.98 MT increase in yield and 488.23 US $ per acre increase in net income over control. Four augmentative releases of T. chilonis @ 2000 parasitized eggs per tree successfully controlled the fruit and shoot borer incidence in guava during rainy and winter season.

Kinnow in terms of area under production.In Punjab, it was grown on 9730 hectares of land with a total production of 219,850 MT during 2020-21 (Anonymous 2021).
In India, around 80 species of insect pests have been reported on guava.Among these, nine major insect pests, viz.fruit flies; Bactrocera dorsalis (Hendel) and B. zonata (Saunders); bark eating caterpillar, Indarbela quadrinotata Walker); striped mealybug, Ferrisia virgata Cockerell; scale insect, Pulvinaria psidii Maskell; fruit borer, Deudorix isocrates (Fabricius)' shoot and fruit borer Conogethes punctiferalis (Guenée), rugose spiralling whitefly, Aleurodicus dispersus Russell; tea mosquito bug, Helopeltis antonii V. Signoret and stem borer, Aristobia testudo (Fabricius) cause significant losses to the guava growers (Rai et al. 2019).One of the major threats to the production and productivity of various fruit crops are the lepidopteran borer pests.They cause damage to the stem, fruits, roots, inflorescences, etc., thereby reducing the quantity as well as quality of the produce.Crambids are known worldwide for their extensive damage to various agricultural and horticultural crops, C. punctiferalis being one of them (Kumar et al. 2021).
Among the major pests of guava, the fruit and shoot borer, C. punctiferalis (Lepidoptera: Crambidae) is widely distributed in Asia and Australia (Rai et al. 2019).C. punctiferalis is a highly polyphagous borer pest, known to feed on more than 120 species of wild and cultivated plants.It is known by various common names such as yellow peach moth, maize moth or peach pyralid moth, castor shoot and capsule borer, castor seed caterpillar, durian fruit borer, durian husk borer, Queensland bollworm, smaller maize borer and cone moth in various parts of the world.The female moths feed, oviposit and develop primarily in buds and fruits of all kinds of host plants (Li et al. 2015).Among the fruit crops, it has been reported on apple, banana, citrus, grape, guava, litchi, mango, peach, pear, plum, pomegranate and sapota (Reddy et al. 2020).C. punctiferalis is observed to cause fruit damage ranging from 10-12% on guava in Punjab, India.
In the past few decades, there has been excessive use of chemical pesticides for the control of insect pests on various crops which has caused serious complications such as persistence of pesticide residue in crop products, pest resistance development, and secondary pest outbreaks in general (Wytinck et al. 2020).Apart from this, the chemical insecticides have a negative impact on the natural control of insect pests by killing their natural enemies (Crowder et al. 2010).For eco-friendly management of insect pests, biological control is the most preferred one for a sustainable alternative to the chemical insecticides (Barratt et al. 2018).Therefore, the objective of the present study was to evaluate two biocontrol agents, Trichogramma chilonis Ishii, an egg parasitoid and Chelonus blackburni Cameroon, an egg-larval parasitoid (both native to India) for the management of C. punctiferalis in guava, and its impact on yield of guava fruits and economics of their releases.

Chelonus blackburni
Adults of C. blackburni were released by hanging 4, 6 and 8 perforated vials per tree containing 25 adults in each vial for treatments 4, 5 and 6, respectively.
Four releases were made at weekly interval from first week of July in rainy season, 2020 and first week of October in winter season, 2020-21.The research study was conducted on ' Allahabad Sufeda' cultivar of guava.There were 5 replications (3 trees per replication) for each treatment.

Observations recorded
Fruit infestation was recorded by counting number of infested fruits out of hundred randomly selected fruits at 7, 14 and 21 days after the fourth release.The per cent reduction in damage over untreated control was also calculated.The impact on yield of guava fruits was assessed by counting number of marketable fruits from each tree in each replication.Average weight of 50 fruits was taken, which was 96 g/fruit.Fruit yield (kg/tree) was calculated by multiplying average weight of fruit (96 g) with number of fruits/trees and multiplied by 1000 to convert it into kg/tree.Yield/acre (metric tons) was calculated by multiplying fruit yield (kg/tree) with total number of trees in one acre (132 trees) and dividing by 1000.The gross income over control was calculated by multiplying increase in yield over check by market price of guava, which was 0.18 US $ per kg in rainy season and 0.27 US $ per kg in winter season.Net income over control was calculated by subtracting cost of biocontrol agents and labor cost of their production from the gross income over control.

Data analysis
The data were subjected to analysis of variance (ANOVA) using Randomized Block Design (RBD).Similar results were recorded during both the years and therefore, results were pooled.The significance of differences between treatment means was compared using F test at 5% probability.Before statistical analysis, percentage data were subjected to square root transformation to meet normality test and homogeneity of variances (Panse and Sukhatme 1954).
The economic benefits in T. chilonis-2000 parasitized eggs/tree was maximum wherein, the net income of 258.10 US $ per acre was achieved over control as compared to its lower doses, i.e. 1500 parasitized eggs/tree (206.39US $) and 1000 parasitized eggs/tree (165.52 US $).The releases of C. blackburni (100, 150 and 200 adults/ tree) were not economical at all, causing economic losses of 910.21 US $, 1363.82US $ and 1799.36US $ per acre, respectively during rainy season, 2020 (Table 3).

Discussion
So far, there have been very few studies on Trichogramma being used as biocontrol agent for the management of C. punctiferalis.Zhang (2007) observed higher rate of parasitism of C. punctiferalis eggs by Trichogramma dendrolimi Matsumura in chestnut (Castanea crenata Mill.) orchards in Beijing, China.He et al. (2008) evaluated T. chilonis for management of C. punctiferalis on litchi in Beijing, China and found that 28.8% of C. punctiferalis eggs were parasitized.Ballal et al. (2018) suggested that augmentative release of Trichogramma spp.and C. blackburni can be helpful for the control of this borer in south India.However, this was first ever use of T. chilonis for the management of this pest on guava in Punjab.In field crops, it is possible to measure actual egg parasitism as crops are of less height.But in fruit crops, it is very difficult to locate eggs of C. punctiferalis.So, in the present study, we conceded per cent reduction in fruit damage as evaluation indicator.
Augmentative biological control, which involves mass production and release of large quantities of biocontrol agents, has shown promising results in terms of reduction or even elimination of the insecticidal use (Eilenberg et al. 2001).The trichogrammatids have widely been used as egg parasitoids for the management of lepidopteran pests.Trichogramma releases have been carried out on about 32.0 million ha area annually in more than 50 countries including India (van Lenteren et al. 2017).The genus Trichogramma, having their ability to parasitize eggs of multiple pest species, make them good egg parasitoids for biocontrol program (Zucchi et al. 2010).In the  Comprehensive studies have been conducted in India for evaluation of various trichogrammatids against tissue borers in various crops indicating their importance for the management of lepidopteran pests.Shenhmar et al. (2003) conducted a large-scale field demonstration using T. chilonis against Chilo auricilius Dudgeon (Lepidoptera: Crambidae) in Punjab, India during 2000-01 and found that there was reduction in damage over the control by 52.04% during 2000, while 60.03% during 2001.Kumar et al. (2004) concluded that five inundative releases of T. chilonis-1,00,000 parasitized eggs/ha at weekly intervals in Punjab Chhuhara cultivar of tomato caused 62.19% reduction in damage caused by Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) over control in their studies conducted at PAU, Ludhiana, Punjab.Shera et al. (2017) assessed on farm impact of inundative releases of T. chilonis against maize borer, Chilo partellus Swinhoe (Lepidoptera: Crambidae) in various districts of Punjab, India and found that there was 56.86 and 56.10% reduction in damage over control in Kharif maize in 2014 and 2015, respectively, which translated into net returns of 93.18 US $ and 112.79 US $ over control in year 2014 and 2015, respectively.Sangha et al. (2018) also reported the releases of trichogrammatids resulted in the reduction in damage caused by lepidopteran pests of basmati rice over control up to an extent of 61.50% in the farmers' field.Sharma et al. (2020) evaluated T. chilonis against lepidopteran tissue borers of sugarcane crop in various districts of Punjab, India and reported 57.4 and 61.4% reduction in damage over control in case of Chilo infuscetallus Snellen (Lepidoptera: Crambidae) and C. auricilius, respectively.Benefit: Cost ratio of 1.68 and 1.70 was achieved in biocontrol treatments against C. infuscetallus and C. auricilius, respectively.

Conclusion
Four augmentative releases of egg parasitoid T. chilonis-2000 parasitized eggs/tree at weekly interval caused lesser percentage of damage fruits and significant reduction in damage over control in both rainy and winter season guava, which thereby resulted in higher fruit yield and net returns over control in both seasons.Thus, the use of biocontrol-based technologies involving inundative releases of this trichogrammatid is an alternative to chemical insecticides for sustainable and eco-friendly management of C. punctiferalis in guava orchards, Punjab, India.

Fig. 1
Fig. 1 Per cent reduction in C. punctiferalis damage due to release of biocontrol agents during July-August 2020 (rainy season) in guava

Fig. 2
Fig. 2 Per cent reduction in C. punctiferalis damage due to release of biocontrol agents during winter season, 2020-21

Table 1
Evaluation of biocontrol agents against C. punctiferalis in guava during rainy season, 2020 Data were subjected to square root transformation and original values are given; Means followed by different letters within column differ significantly (p < 0.05) * Mean (± SE) of 5 replications; **4 releases at weekly intervals;

Table 2
Impact of release of biocontrol agents against C. punctiferalis on number and yield of marketable guava fruits during rainy season, 2020 * Mean (± SE) of 5 replications; **no. of trees/acre = 132; average weight of fruit = 96 g; Means followed by different letters within column differ significantly (p < 0.05)TreatmentsNo. of marketable fruits/tree* Fruit yield (kg/tree)** Yield/acre (MT)

Table 3
Cost of release of biocontrol agents for the management of C. punctiferalis in guava during rainy season, 2020 * Cost of protection (cost of tricho card = 0.60 US $ per card; cost of C. blackburni culture = 1.81 US $ per 100 adults; labour charges = 4.36 US $/person/day); # Market price of guava = 0.18 US $ per kg

Table 4
Evaluation of biocontrol agents against C. punctiferalis in guava during winter season, 2020-21

Table 5
Impact of release of biocontrol agents against C. punctiferalis on number and yield of marketable guava fruits during winter season, 2020-21 Mean (± SE) of 5 replications; **no. of trees/acre = 132; average weight of fruit = 96 g; Means followed by different letters, (p < 0.05) within column differ significantly *

Table 6
Cost of release of biocontrol agents for the management of C. punctiferalis in guava during winter season, 2020-21 * Cost of protection (cost of tricho card = 0.60 US $ per card; cost of C. blackburni culture = 1.81 US $ per 100 adults; labour charges = 4.36 US $/person/day; # Market price of guava = 0.27 US $ per kg