Annotation and seasonal incidence of insect pests on Ajwain (Trachyspermum ammi L.)

Introduction

Ajwain is cultivated on a limited scale, while its cultivation has expanded in parts of the Vidarbha region. Like other seed spice crops, Ajwain is attacked by several insect pests. Aphids, leaf hoppers and seed bugs have been reported among the important sucking pests, while defoliators and other insects may also occur under field conditions. Previous studies have demonstrated variation in the insect pest complex of Ajwain according to genotype and agro-climatic conditions. Ranjeetha et al. (2020) [9] , for example, recorded aphid and other insect pests associated with Ajwain genotypes under the eastern dry zone of Karnataka. Information on the local insect pest complex is essential for determining the pest species requiring regular monitoring. Equally important is knowledge of seasonal population development because the timing of pest appearance and peak abundance determines the period during which management interventions are most likely to be effective. Studies conducted on related seed spice crops have shown that aphid populations generally increase during the later rabi period and that predator abundance may increase concurrently with pest abundance (Purti and Anuradha, 2017; Kanjiya et al., 2018; Swami et al., 2018; Dadhich and Pandey, 2022) [8,2,10,1] . Despite the increasing importance of Ajwain in Vidarbha region, information on its insect pest assemblage and seasonal incidence under local conditions remains limited. Therefore, the present investigation was undertaken to annotate the insect pests associated with Ajwain and to study their seasonal incidence under local conditions.

Materials and Methods

The investigations were conducted during the rabi season of 2025-26 at the Research Farm of the Department of Agricultural Entomology, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola, (MS). Ajwain variety AA-01-19 was sown by line sowing method at 60 cm × 30 cm spacing. All the requisite agronomical practices were followed to ensure good crop growth. For annotation of insect pests on Ajwain a field survey was conducted at six locations within the jurisdiction of Dr. PDKV, Akola. The survey locations included the Department of Entomology field, Integrated Farming Research System field, Agricultural Technology Information Centre field and farmer fields at Seloo (Distt. Wardha), Vivara and Akot (Distt. Akola). The observations were recorded at regular interval at these places from vegetative stage through crop maturity to know the infestation of insect pests on Ajwain. The insect specimens from each places were collected and identified using insect catalogues, identification keys and pictorial resources. The recorded arthropods were grouped according to their ecological status as pests, predators, pollinators or decomposers. For seasonal incidence studies separate Ajwain plot was maintained under natural infestation at the Entomology field of Dr. PDKV, Akola. Observations were initiated at crop establishment and continued until harvest. Ten randomly selected and tagged plants were used for weekly observations. Pest and natural enemy populations were recorded at weekly intervals following the methodology adopted by Ranjeetha et al. (2020) [9] . Aphid population was recorded on the apical 5-cm twig and expressed as number per 5 cm twig. Leaf hopper, plant hopper, mealy bug and plant bug populations were recorded per plant, while hairy caterpillar and semilooper populations were recorded as larvae per plant. Ladybird beetles, predatory spiders and syrphid flies were recorded as number per plant. Meteorological observations corresponding to the observation weeks were obtained for maximum and minimum temperature, bright sunshine hours, wind speed, morning and evening relative humidity, evaporation and rainfall. The seasonal trend was interpreted in relation to the observed pest and natural enemy populations. The relationship between the seasonal population of insect pests and natural enemies and prevailing weather parameters was determined using Pearson's correlation coefficient (r). Weekly population observations corresponding to the meteorological weeks were paired with the respective weekly weather observations. The weather variables considered were maximum temperature, minimum temperature, morning relative humidity, evening relative humidity, sunshine hours and evaporation. Correlation coefficients were calculated separately for each insect pest and natural enemy to determine the direction and strength of association with the individual weather parameters.

Results and Discussion

The survey conducted at six locations revealed a diverse arthropod assemblage associated with the Ajwain ecosystem (Table 1). The recorded fauna comprised 20 groups/species, including 10 pest groups, six predator groups, three pollinator groups and two decomposer groups. Among the pest complex, aphid (Myzus persicae) was the most consistently occurring insect and was recorded at almost all surveyed locations. Other pest groups included mealy bug, leaf hopper, tree hopper, plant bug, grasshopper, black field cricket (Teleogryllus commodus), cotton seed bug, hairy caterpillar and semilooper. The occurrence of pest groups varied among locations, indicating variation in the arthropod assemblage within the local Ajwain ecosystem. The predominance of aphid in the present investigation agrees with previous observations on Ajwain and other seed spices. Ranjeetha et al. (2020) [9] identified aphid as an important pest of Ajwain and recorded substantial variation in aphid infestation among Ajwain genotypes. Seed spice literature also identifies sucking pests, particularly aphids, as important pests of the crop group. The beneficial arthropod community comprised ladybird beetles, big-eyed bugs (Geocoris spp.), syrphid flies, spiders, green lacewings (Chrysoperla spp.) and great black wasps. Honey bees and butterflies were recorded as flower visitors, while green bottle flies and chironomid midges were associated with decomposing material. The observations on seasonal incidence (Table 2) revealed that no insect pest incidence was recorded until the 47 th meteorological week (MW). Pest activity commenced during the 48 th MW and increased progressively with crop development. Sucking pests were predominant during the observation period. However, aphid was the earliest and most prominent pest observed on Ajwain. It appeared during the 48 th MW at 0.2 aphids per 5-cm twig and increased to 6.8 aphids per 5-cm twig by the 52 nd MW. Thereafter, the population increased rapidly and reached a maximum of 18.3 aphids per 5-cm twig during the 9 th MW. Leaf hopper and plant hopper populations also increased progressively from the 48 th meteorological week. Their maximum populations were 5.7 and 5.8 individuals per plant, respectively, during the 8th meteorological week. Plant bug attained a maximum population of 6.1 individuals per plant during the same week. Mealy bug remained at a comparatively low level, appearing during the 50th meteorological week and fluctuating between 0.1 and 0.4 individuals per plant. Hairy caterpillar and semilooper also occurred at low densities, with maximum populations of 0.3 and 0.4 larvae per plant, respectively. The weekly data show a clear shift from negligible pest abundance during early crop establishment to increasing pest pressure during January and February. Aphid abundance was particularly pronounced during the later crop period, whereas defoliators remained at low densities. This pattern indicates that the local Ajwain crop during the study season was more favourable for sucking pests than for foliage-feeding larvae. Natural enemies appeared shortly after the establishment of pest populations and increased concurrently with pest abundance. Ladybird beetles were first recorded during the 49th meteorological week and reached a maximum of 3.4 individuals per plant during the 9th meteorological week. Predatory spiders appeared during the 50 th meteorological week and reached a maximum of 2.5 individuals per plant during the 8 th meteorological week. Syrphid flies were first observed during the 51 st meteorological week and reached a maximum of 1.9 individuals per plant during the 9 th meteorological week. Similar increases in coccinellid and other predator populations during periods of higher aphid abundance have The correlation coefficient between the insect pests, natural enemies and different weather parameters were worked out (Table 3). The correlation analysis revealed that maximum temperature, minimum temperature and evaporation were positively and significantly associated with the populations of all the insect pests and natural enemies, whereas bright sunshine hours and evening relative humidity did not show significant associations with any of the organisms. Wind speed showed significant positive relationships with most of the populations, except leaf hopper and plant bug. Morning relative humidity also showed significant negative correlations with most of the populations, except semilooper. The present findings are in agreement with the earlier results of Kumar et al. (2016) [3] , Dadhich and Pandey (2022) [1] , Parveen and Samyuktha (2026) [7] , Kumar et al. (2023) [4] , Nayak et al. (2019) [6] , and Nabil and Hegab (2019) [5] , who demonstrated varying associations between weather parameters and insect pest populations under different agro-ecological conditions. The present investigation demonstrated that Ajwain cultivated under local conditions supported a diverse arthropod community consisting of insect pests, predators, pollinators and decomposers. Ten pest groups were recorded, with aphid (Myzus persicae) being the most widespread and predominant pest. Pest incidence commenced during the 48th meteorological week and increased progressively during crop development, with aphid attaining its maximum population during the 9 th meteorological week. Leaf hopper, plant hopper and plant bug reached maximum abundance during the 8 th meteorological week, whereas mealy bug, hairy caterpillar and semilooper remained at comparatively low densities. The abundance of ladybird beetles, predatory spiders and syrphid flies increased concurrently with pest populations. These findings provide useful baseline information for pest surveillance and indicate that the later crop period, particularly January-February, represents an important period for monitoring insect pest populations and associated natural enemies in Ajwain under Vidarbha conditions. Maximum and minimum temperature and evaporation showed significant positive associations with pest and natural-enemy populations, while morning relative humidity showed predominantly significant negative relationships.

The study identified the later crop period, particularly January-February, as the period of greater pest activity, providing useful baseline information for seasonal monitoring and timely management of insect pests on Ajwain under Vidarbha conditions.

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