Bionomics of Codling Moth: Eco-biology

Bionomics of Codling Moth

Eco-Biology (Field Biology)

The eggs are deposited on the upper surface of the leaves or fruits and take 5 - 12 days to hatch, depending upon the temperature and humidity. A female can oviposite an average of 25 - 60 eggs singly or in groups of two to three. The spring brood (females emerging from the overwintering populations) produce fewer eggs than the summer broods; with an average fecundity of approximately 25 - 35 and 40 - 70 eggs per female, respectively. Occasionally, a female lays more than 100 or less than 12 eggs (Carter 1984). Natural mortality of eggs ranges from 25 - 50%. Temperature above 27 °C decreases the fecundity and increases the sterility (Isley 1937). Adult codling moths do not copulate or lay eggs as the evening temperature falls below 15 °C. If chill lasts 2-3 weeks, the females die without laying any eggs. A relative humidity of 75% is optimum for oviposition (Balachowski and Viennot-Bourgin 1939). Average hourly temperatures and the amount and duration of rainfall between 5 and 7 p.m. significantly influence oviposition in the first generation, but oviposition by the second generation is affected only by temperatures (Hagely 1976).

Studies on within-tree egg distribution in undamaged apple orchards showed that the average number of eggs per spur were positively correlated with the number of apples but negatively correlated with the number of eggs per apple (Jackson 1979, Tadic 1963). Also 57% of eggs laid in the field were within 7.5 cm and 91% within 20 cm from the fruit.

The time from egg hatch to successful entry into the fruit is critically important period in the field biology of the codling moth. Hagely (1972) found that rainfall was the most important cause of mortality of the first instar larvae when they were just beneath the epidermis of the fruits. Geier (1963) suggested that mortality of the first instar occurred because of increasing water contents of the fruits and consequent flooding of tunnels. The second and third instar larvae in the fruits also are affected by rainfall. Rainfall during late spring and early summer could be a critical factor affecting larval survival (Hagely 1972). Exposure of the eggs and first instar larvae to short photoperiod decreases the reproductive activity of adults (Deseo 1973, Deseo and Saringer 1975).

The codling moth has five larval instars, the first four of which are spent in the fruit. The fifth (prepupae) exists the fruit and searches for site either to pupate or overwinter (Smotavac 1957). The length of the larval feeding period is approximately 16-24 days, but it is a function of temperature and apple variety in which they feed (Goonewardene at el. 1984). Rock and Shaffer (1983) found a positive correlation between temperature and survival rate of codling moth, and 27°C was the optimum temperature for development. No significance difference has been found in the developmental rate of males and females as influenced by temperature. The average cocooning and pupal period is about 18.45 days and it too is dependent on temperature.

The codling moth overwinters as a diapausing mature larvae in the cocoon under the bark or in the ground near the base of the tree. Dickson (1949) first showed that decreasing photoperiod induce diapause in the larvae of codling moth. Although the diapause appears to be facultative and influenced by the prevailing photoperiod and temperature, the propensity for univoltinism seems to be present in this species as some individuals do not respond to photoperiodic changes and enter diapause (Riedl 1983).