Abstract
The leaf miner (Coelaenomenodera elaeidis) is the major pest of the oil palm. Seasonality of C. elaeidis, its natural enemies and their relationship with temperature, rainfall and relative humidity were observed between January 2009 and December 2010 at the main station of the Nigerian Institute for Oil Palm Research. Leaf miner population estimates were obtained from NIFOR entomology division from 1976-1980. This study analyses temporal patterns in leaf miner abundance, and elucidates general patterns and factors influencing leaf miner abundance. Multiple linear regressions were used to analyse the relationship between abundance of leaf miner, its parasitoids and predators and the following climatic variables: maximum and minimum temperature (°C), rainfall (mm) and relative humidity (%). Climate variables from the month of pest collection (control variable) or from the month before collection (delayed variable) were used. The abundance of leaf miner and predatory ants peaked in the dry season, while parasitoids were most abundant in the rainy season. Significant correlations (P ≤ 0.05) were found between leaf miner, its natural enemies and both control and delayed weather variables. For all years, maximum temperature was the most dominant for all the leaf miner stages. This indicates that the weather variables at both the month of collection and with a delayed month in relation to collection are critical for pest-weather evaluation and important for leaf miner control. Temperature, rainfall and relative humidity had an effect on the population of C. elaeidis, and this effect is manifested primarily in seasonal fluctuations in oil palm agroecosystems. Weather influenced the seasonal population dynamics of C. elaeidis, facilitating early season build-up on the oil palm host crop. Dry season months with resultant higher temperatures recorded higher population of C. elaeidis.
Highlights
Seasonal variation in abundance of tropical insects is a common phenomenon [1,2]
The study site is located at the main station of the Nigerian Institute for Oil Palm Research (NIFOR)
There was a higher relationship between leaf miner and weather factors during the 2009-2010 periods (Table 1) in comparison with the 1976-1980 periods (Table 5). This could be attributed to higher mean temperatures prevailing at the 2009-2010 periods. This implies that progressively higher temperatures, lower rainfall and relative humidity values could be implicated in the increase in leaf miner abundance
Summary
Seasonal variation in abundance of tropical insects is a common phenomenon [1,2]. Insect abundance can change over time for a variety of reasons, including macroclimatic and microclimatic changes, and variation in the availability of food resources [1]. The effect of climate change in Nigeria is already contributing to extreme weather events: amount of rainfall, proliferation of pests, crop diseases and high temperature effects [3]. Insects are able to function faster and more efficiently at higher temperatures. They can feed, develop, reproduce, and disperse when the climate is warm, though they may live for a shorter time [4]. From an ecological point of view, particular variables such as the annual minimum temper-
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