Life History of Cactoblastis cactorum
Department of Biological Sciences
Mississippi State University
Last updated: July 3, 2009
Egg. Cactoblastis cactorum lays its eggs in linear chains, commonly referred to as egg sticks, that are affixed to the spines or areoles of cactus cladodes (Dodd 1940, Pettey 1948, Mann 1969, Robertson 1987). Eggs are off-white in color when first laid and darken until they become almost black at the time of hatching (Pettey 1948). The length of the egg stage is influenced by temperature (Legaspi & Legaspi 2007). In Australia, the incubation period for the eggs can be as short as 23 to 28 days in the winter and last as long as 60 to 70 days in the winter (Dodd 1940). In South Africa, the duration of the egg stage is approximately 35 to 40 days in the summer and 45 to 55 days in the winter (Pettey 1948).
Larva. Once hatched, first-instar larvae collectively work to penetrate the cuticle and epidermis of a plant cladode through the creation of an entry hole. Upon entering the cladode, larvae feed internally for the duration of the larval phase of the life cycle (Dodd 1940, Pettey 1948). Larvae rarely leave the plant upon which they have hatched and when they do they are frequently unsuccessful in finding new host plants (Dodd 1940, Pettey 1948). In laboratory experiments, larvae have reliably detected host plants only within a distance of 6 to 8 inches (Dodd 1940, Pettey 1948). Larvae have been observed to vacate the cladode in search of shade on the underside of the plant during especially hot times of the day (Dodd 1940, Pettey 1948, personal observations) and to congregate on the upper side of the plant on cold days (Pettey 1948). In Australia, the larval stage lasts approximately 50 days in the summer generation and approximately 180 days in the winter generation (Dodd 1940). In South Africa, the larval stage takes on average 56 to 75 days to complete in the summer and 122 to 145 days in the winter (Pettey 1948).
Pupa. Upon completion of the larval phase, C. cactorum typically pupate at the base of the plant in the leaf litter, beneath dead cladodes or rocks, or in the soil (Dodd 1940). In Australia, the pupal phase lasts approximately 21 to 28 days in the summer and 35 to 42 days in the winter (Dodd 1940). In South Africa, the pupal phase generally lasts 24 to 29 days in the summer and about 62 to 77 days in the winter (Pettey 1948).
Adult. Adults typically emerge one to three hours after sunset and mate in the early morning hours of the first or second day after emergence (Dodd 1940, Pettey 1948). The moths are usually active only between sunset and shortly after sunrise (Pettey 1948). While a short proboscis with sensilla is present in the adult stage of C. cactorum (R. Brown, personal communication), the adults are not known to feed (Dodd 1940, Pettey 1948). In Australia, adults lived on average nine days but may live up to 18 days (Dodd 1940). In South Africa, adults lived on average five to nine days (Pettey 1948).
Oviposition has been reported to begin the night after emergence in Australia (Dodd 1940) and South Africa (Pettey 1948), but during a field experiment in Florida laboratory-reared females were observed to oviposit only between the third and sixth days of the adult stage (Legaspi et al. 2009).
Estimates of number of eggsticks and total number of eggs per female vary widely. In Australia, females typically oviposit on average 100 eggs divided among three to four eggsticks (Dodd 1940). In South Africa, females generally oviposit between one and four eggsticks. In the winter in South Africa, females lay on average between 86 and 97 eggs in total. During the summer in South Africa, females lay on average between 160 and 172 eggs in total (Pettey 1948). While uncommon, females have been observed to lay 300 eggs or more eggs (Dodd 1940, Pettey 1948). In Florida, laboratory-reared females lay on average 4 eggsticks (Legaspi et al. 2009).
Estimates of the number of eggs per egg stick also vary widely. Dodd (1940) reported that 70 to 90 eggs per egg stick was common in Australia. Pettey (1948) also noted averages of 68 to 97 eggs per egg sticks in South Africa. However, Robertson (1985) reported a lower average of 54 eggs per egg stick in South Africa. In Florida, an average of 23 eggs per egg stick has been reported (Legaspi et al. 2009). In addition, eggs are not always distributed evenly among egg sticks. Dodd (1940) and Pettey (1948) noted that the first egg stick to be laid usually contains the most eggs. Legaspi et al. (2009) found that in Florida females laid the most eggs per egg stick on the third day after emergence (mean = 43 eggs).
Dodd (1940) noted that adults may disperse up to 15 miles to oviposit. In a flight mill experiment, C. cactorum adults on average flew the equivalent of 1.2 miles within a 24-hour period and the maximum distance flown was greater than 13 miles (Sarvary et al. 2008).
Number of Generations. Cactoblastis cactorum generally has two to three generations per year. In the native range of C. cactorum in South America, there are two generations per year, except in southern Uruguay where there may only be one generation per year (Dodd 1940). In Australia, there are two generations a year, except in central to southern Queensland where there may be three generations per year (Dodd 1940). There are also two generations per year in South Africa (Pettey 1948). There are three generations per year in Georgia, South Carolina, and most of Florida. In the Florida Keys and Puerto Rico there are overlapping generations (Hight & Carpenter 2009).