Diversity spices richness of pollinators in cashew

Abstract

The study entitled "Diversity and Species Richness of Pollinators in Cashew" (November 2023–March 2024) conducted at the Regional Agricultural Research Station (RARS), Pilicode, investigated pollinator diversity, species richness, and foraging behaviour in cashew (Anacardium occidentale Linn.), a vital insect-pollinated cash crop. Observations were made on early (Nov–Dec), mid (Dec–Jan), and late (Feb Mar) flowering types through hourly monitoring of 10 inflorescences from 6:00 AM to 5:00 PM. Pollinator species were identified and analysed for abundance, foraging behaviour (peak foraging hours, foraging rate and foraging speed), and correlations with weather conditions. A bagging experiment was done to assess their role in fruit set. Nesting sites and bee pasturage were also documented. The study identified 12 pollinator species, including 11 hymenopterans from Apidae (Apis cerana indica Fabricius, Tetragonula sp., Ceratina hieroglyphica Smith, C. binghami Cockerell), Halictidae (Halictus sp. 1, Halictus sp. 2, Lasioglossum sp., Hoplonomia sp.), and Megachilidae (Megachile cephalotes Smith, M. lanata Fabricius, M. laticeps Smith), along with one dipteran (Mesembrius sp., Syrphidae). Halictidae had the highest distribution (49%). Species abundance varied with flowering type: Tetragonula sp. dominated early flowering (30.435%), A. c. indica Fabricius mid flowering (41.176%), and Lasioglossum sp. late flowering (46.296%). Overall, A. c. indica Fabricius was most abundant (21.85%). It also exhibited the highest foraging rate (15.4 flowers/trip), while Tetragonula sp. had the lowest (2.8 flowers/trip). Tetragonula sp. showed the highest foraging speed (6.19 sec/flower), while Hoplonomia sp. had the lowest (1.49 sec/flower). Peak activity of most pollinators were during the forenoon, aligning with flower anthesis. Diversity indices showed variations in species richness, diversity, and evenness by flowering type and time. Mid-season flowering types displayed the highest richness and diversity, while early types had greater evenness. Highest diversity was recorded between 11:00–12:00 AM. The overall species richness was 12, with high diversity indicated by Shannon-Weiner and Simpson indices. The Berger-Parker index suggested high evenness, with no single species dominating the pollinator population. 101 Weather significantly influenced pollinators. A. c. indica Fabricius and Tetragonula sp. were negatively correlated with maximum temperature and wind speed but positively with relative humidity. Tetragonula sp. also showed a negative correlation with bright sunshine. Halictus sp. 1 and Halictus sp. 2 positively correlated with relative humidity, with Halictus sp. 2 also negatively correlated with wind speed. Mesembrius sp. showed a negative correlation with wind speed, while Lasioglossum sp. positively correlated with maximum temperature, bright sunshine, and wind speed but negatively with relative humidity. Hoplonomia sp. was negatively correlated with relative humidity and positively with wind speed. The bagging experiment underscored essential role of pollinators in fruit set, as open-pollinated inflorescences achieved 7.17% fruit set, while bagged ones had none. This highlights the importance of pollinator conservation for enhancing cashew productivity and sustainability. Nesting sites for C. hieroglyphica Smith and C. binghami Cockerell were found in pruned cashew stumps, with stages separated by powdered wood. Weeds like Stachytarpheta jamaicensis Linn., Mimosa pudica Linn. and Rungia sp. in orchards attracted pollinators, offering crucial bee pasturage. This pioneering study at RARS, Pilicode, provides foundational insights into cashew pollinators, acknowledging variations in pollinator diversity across different locations. It underscores the critical role pollinators’ play in boosting cashew productivity and advocates against using chemical pesticides between 8:00 AM and 3:00 PM to avoid disrupting their activity. Preserving pollinator populations is vital for maintaining cashew production and addressing the increasing demand for cashew nuts.