Callosobruchus Maculatus - Life Cycle

Life Cycle

A female C. maculatus beetle can lay over a hundred eggs during her adult life, and most of them will hatch. She lays these eggs on the surface of the bean (the type of bean is variable), where they remain. The larvae hatch out of the egg and burrows straight into the bean about 4–8 days after oviposition (the laying of the eggs). During maturation, the larvae chew near the surface of bean, leaving behind thin, window-like layers in the seed coat. The larvae emerge from this thin window after 20–35 days from first burrowing into the bean.

Larval crowding can get quite impressive as 8-10 larvae can develop within the same bean. The larval crowding limits the amount of resources available to each individual. This results in longer development time, higher larval mortality, lower fecundity in survivors, and smaller adult size.

Once the beetles emerge from the bean as adults, they mature within 36 hours. Adults have a mean lifespan 7 days in a lab environment, but some have been able to live up to 14 days. C. maculatus adults do not need to feed, and spend their time as adults mating and laying eggs. Despite not needing to eat, if offered sugar water, yeast, or plain water, adult beetles will partake. This replenishes spent resources and affects how many eggs the female will lay. In one study, females were provided with water, sugar, or nothing. The females with access to sugar lived longer and laid more eggs than those without that access.

C. maculatus can live in a range of humidity levels and temperatures, which has made its invasion of multiple continents successful. Variation in developmental time can be affected by a number of factors, including humidity, environment temperature, type of legume, number of larvae in the same bean, and amount of inbreeding experienced in the population. A bean that is too dry will be impossible for the larva to bore into, and a bean that is too wet will have too much fungal growth for the larva to survive. When experimenters kept temperature constant at 30°C and varied the humidity (0-3%, 21%, 44%, 63%, 80% and 91%) they found a wide variance in acceptable humidity ranges. In general, a humidity range of 25% to 80% was acceptable, but each life stage had a different optimal humidity level. The most eggs hatched at 44% and 63% humidity, while 21% and 80% humidity caused significantly fewer eggs to hatch. Larval and pupal development could not be studied separately, as they both take place inside the bean, but 44% humidity produced the highest survival. Adults, in contrast, lived much longer at higher humidity levels (81% and 90%). In another experiment, researchers manipulated the temperature (17°C, 27°C and 37°C) while keeping humidity constant. While larvae developed in a range of temperatures, 17°C and 37°C stressed the organism. The ideal temperature range is 24-28°C.

The age of the mother also significantly affects the development and survival of the offspring. When mothers lay eggs later in life, the eggs are less likely to hatch, the larvae will take longer to develop, and there will be higher larval mortality.