Annotation and seasonal incidence of insect pests on fennel (Foeniculum vulgare mill)

Introduction

Fennel (Foeniculum vulgare Mill.) is an important seed spice crop belonging to the family Apiaceae and is valued for its aromatic fruits, culinary applications and medicinal properties. In India, fennel is cultivated extensively in different agro-climatic regions and contributes substantially to the seed-spice sector. The crop is mainly cultivated during the rabi season and is adapted to moderately cool and dry conditions. In Maharashtra, fennel is cultivated on a limited scale, while its cultivation has expanded in parts of the Vidarbha region. However, productivity and quality of fennel can be affected by several insect pests belonging to different taxonomic groups. The pest complex associated with fennel comprises predominantly sucking insects and defoliating caterpillars. Aphids, leaf hoppers and other sap-feeding insects can affect plant growth by removing plant sap, whereas caterpillars may cause damage by feeding on foliage. The occurrence and abundance of these insects vary with crop stage and prevailing environmental conditions. Knowledge of the pest complex and its seasonal abundance is essential for identifying periods of pest build-up and planning appropriate management measures. Regular monitoring can also help avoid unnecessary calendar-based pesticide applications. Meena et al. (2020) [5] emphasized the importance of rational pest-management practices in fennel cultivation. Therefore, the present investigation was undertaken to document the insect-pest complex and determine the seasonal incidence of insect pests and associated natural enemies on fennel under the local conditions of Vidarbha.

Materials and Methods

2.1Experimental site

The investigation was conducted during rabi 2025-26 at the Experimental Farm, Department of Agricultural Entomology, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola, Maharashtra. Fennel variety AF-101 was sown line sowing method at 60 cm × 45 cm spacing. For seasonal incidence observations, a separate fennel plot was maintained without insecticidal protection so that natural pest infestation could be followed throughout the crop period.

Annotation of insect pests

For annotation of insect pests on fennel a field survey was conducted at six locations within the jurisdiction of Dr. PDKV, Akola. The survey locations included the Department of Entomology field, Chilli and Vegetable Research Unit field, Agricultural Technology Information Centre field and farmer fields at Barsi takli, 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 fennel. 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.

Seasonal incidence

For seasonal incidence studies separate fennel plot was maintained under natural infestation at the Entomology Research 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) [7] . Aphid population was recorded on the apical 5-cm twig and expressed as number per 5 cm twig. Tree hopper, leaf hopper and red cotton bug populations were recorded per plant, while hairy caterpillar, twig looper and cabbage looper populations were recorded as larvae per plant, while seed wasp population was recorded as number per umbel. Ladybird beetles, predatory spiders and hover 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

Annotation of insect pests and beneficial insects associated with fennel

The survey conducted at six locations revealed a diverse arthropod assemblage associated with the fennel ecosystem (Table 1). The recorded fauna comprised 17 species, including 12 pest species, 3 predator species, 1 pollinator species and 1 decomposer species. Among the pest complex, aphid (Hyadaphis spp.) was the most consistently occurring insect and was recorded at almost all surveyed locations. Other sucking pests included, leaf hopper (Empoasca sp.), tree hopper, plant hopper, stink bug (Nezara viridula) and seed bug (Nysius spp.) and defoliating insects included cabbage looper (Trichoplusia ni), tobacco caterpillar (Spodoptera litura), hairy caterpillar, twig looper (Ectropis excursaria). In addition, red cotton bug (Dysdercus cingulatus) and seed wasp (Systole albipennis) were recorded during the survey. The occurrence of pest groups varied among locations, indicating variation in the arthropod assemblage within the local fennel ecosystem. The predominance of aphid in the present investigation agrees with previous observations on fennel and other seed spices. Meena et al. (2020) [5] recorded a diverse pest complex on fennel under an organic production system in Rajasthan and reported aphids as one of the most persistent and important pest groups. They recorded Hyadaphis coriandri, along with other sucking pests, seed-associated insects and defoliators. Shewale and Borad (2020) [8] also reported several insect pests on fennel. The beneficial arthropod fauna observed in the fennel ecosystem comprised ladybird beetles and their grubs, hover fly larvae and predatory spiders. Honeybees were also observed and were considered as pollinators rather than predatory natural enemies.

Seasonal incidence of insect pests

The observations on seasonal incidence (Table 2) revealed that insect pest incidence was commenced during the 46th standard meteorological week. At the beginning of the observation period, insect populations were generally very low or absent. Only cabbage looper was recorded at 0.1 larva per plant during the initial observation. Pest activity commenced during the 46 th MW and increased progressively with crop development. Sucking pests were predominant during the observation period. Aphid was the most prominent insect pest observed during the seasonal incidence obsevation period. Its population increased progressively from 1.2 aphids per 5 cm twig during the 47th SMW and attained a peak of 39.1 aphids per 5 cm twig during the 9th SMW. The marked increase during the later part of the crop season clearly indicated the predominance of aphid in the fennel pest complex under the prevailing conditions. Tree hopper appeared at a relatively low population during the initial period, recording 0.2 per plant during the 47th SMW. Its population increased progressively and reached a maximum of 5.8 per plant during the 8th SMW, after which it declined slightly to 5.1 per plant during the 9th SMW. Leaf hopper population was initially low, with 0.2 per plant during the 48th SMW. It subsequently increased and reached a maximum of 5.1 per plant during the 3rd SMW. Thereafter, the population gradually decreased and reached 2.9 per plant by the 9th SMW. Hairy caterpillar population increased from 0.1 per plant during the 47th SMW and attained its maximum population of 4.4 per plant during the 5th SMW. Following the peak, its population declined and reached 2.3 per plant by the 9th SMW. Cabbage looper was recorded at comparatively low density. Its population increased from 0.1 per plant during the initial period to a maximum of 1.5 per plant during the 5th SMW and subsequently declined to 0.9 per plant by the 9th SMW. Twig looper remained at a comparatively low population throughout the observation period. Its population increased gradually and reached 1.0 per plant during the 6th and 7th SMWs, followed by a decline to 0.7 per plant by the 9th SMW. Red cotton bug appeared relatively later during crop development. Its population increased and reached 2.4 per plant during the 8th and 9th SMWs. Seed wasp was not recorded during the initial period. It appeared from approximately the 4th SMW and gradually increased to 1.9 per umbel by the 9th SMW. The gradual increase towards the later crop period indicates a distinct seasonal pattern compared with the early-appearing defoliators.

Seasonal incidence of natural enemies:

The natural-enemy population increased progressively with crop development and increasing insect abundance. Ladybird beetles increased from 0.2 per plant during the 47th SMW and reached a maximum of 4.3 per plant by the 9th SMW. Predatory spiders first appeared during the 49th SMW, attained a maximum of 1.7 per plant during the 6th and 7th SMWs, and recorded 1.6 per plant towards the end of the observation period. Hover fly larvae also appeared during the 49th SMW and increased gradually to 2.3 per plant by the 9th SMW. Similar increases in coccinellid and other predator populations during periods of higher aphid abundance have been reported in coriander and fennel (Purti and Anuradha, 2017; Kanjiya et al., 2018; Dadhich and Pandey.,2022) [1,2,6] .

Overall seasonal pattern

The data clearly identify aphid as the predominant pest, followed by tree hopper and leaf hopper in terms of maximum population recorded. Among defoliators, Hairy caterpillar recorded the highest population. The complete seasonal dataset confirms that pest abundance changed substantially during crop development and that individual pest species followed different seasonal patterns.

Association with weather parameters

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, Wind speed and evaporation were positively and significantly associated with the populations of all the insect pests and natural enemies, whereas bright sunshine hours and relative humidity did not show significant associations with any of the organisms. [1,3,4,9] , who demonstrated varying associations between weather parameters and insect pest populations under different agroecological conditions.

Conclusion

The present investigation demonstrated that fennel supported a diverse arthropod community comprising insect pests, predators, pollinators and decomposers under the agro-climatic conditions of Vidarbha. Twelve pest taxa were recorded during the survey, with Aphid (Hyadaphis coriandri) emerging as the predominant pest and Other pests included tree hopper, leaf hopper, planthopper, red cotton bug, stink bug, seed bug, seed wasp and several foliagefeeding caterpillars.

The seasonal study showed that pest activity increased progressively as the crop advanced towards flowering, seed formation and maturity. Aphid was the dominant pest, appearing during the 47th meteorological week and reaching its highest population of 39.1 aphids per 5 cm twig during the 9th meteorological week. Other pests showed speciesspecific periods of peak activity. Regular monitoring of aphids and other sucking pests, together with conservation of naturally occurring predators, should receive particular attention during the period of increasing pest abundance The seasonal activity of the pests was not uniform. Leaf hopper and twig looper attained their peaks relatively early, whereas aphid, tree hopper, red cotton bug and seed wasp showed greater abundance during the later part of the crop season. Cabbage looper and hairy caterpillar remained comparatively low in abundance. The later crop period, particularly January and February, was therefore identified as an important period for regular pest surveillance.

Ladybird beetles, predatory spiders and hover flies were the major natural enemies recorded in association with the fennel pest complex. Their populations increased with increasing pest abundance, suggesting an important ecological association between pests and their natural enemies. Weather analysis indicated that maximum temperature, minimum temperature and evaporation were showed significant positive associations with pest and natural-enemy populations, while morning and evening relative humidity showed predominantly significant negative relationships. The findings indicate that weather-based monitoring, particularly during the late rabi period, can help in identifying periods of increased pest risk. The information generated from the present investigation provides a useful baseline for future studies on pest forecasting, economicthreshold development and conservation-based integrated pest management of fennel under Vidarbha conditions.

References

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