Effects of feeding frozen mealybugs on the growth, development, and reproductive capacity of Cryptolaemus montrouzieri Mulsant

Cryptolaemus montrouzieri is one of the most widely used natural enemies in the field of biological control. To clarify the feeding effects of frozen mealybugs on C. montrouzieri and provide a scientific basis for the development of artificial feed, the following experiments were carried out: C. montrouzieri populations were fed with fresh mealybugs (CK) and frozen mealybugs (T), and their pupation and emergence rates were measured and compared. Individual C. montrouzieri were similarly fed with fresh (CK) and frozen mealybugs (T), and the developmental periods of larvae and pupae, as well as the body weights of adult males and females, were measured and compared. Adults obtained from the aforementioned experiment 2 were paired within their groups and then each divided into two subgroups, each fed with different combinations of fresh and frozen mealybugs during larval and adult stages: fresh/fresh (CK), fresh/frozen (T1), frozen/fresh (T2), and frozen/frozen (T3). The pre-oviposition periods and 10-day oviposition amounts of female beetles in these groups were then compared. The results showed that for the C. montrouzieri fed with frozen mealybugs, the pupation and emergence rates (90.00% and 87.00%, respectively) showed no significant difference compared to the control group (92.00% and 90.00%, respectively). However, the developmental periods for larvae and pupae (15.42 d and 11.48 d, respectively) were significantly longer than those of the control group (13.51 d and 10.88 d, respectively), and the body weights of adult males and females (10.82 mg and 9.54 mg, respectively) were also significantly lower than those in the control group (11.39 mg and 9.94 mg, respectively). The pre-oviposition periods for CK, T1, T2, and T3 were 7.20 d, 8.29 d, 7.42 d, and 8.31 d, respectively, and the hatching rates were 83.56%, 81.50%, 83.78%, and 81.91%, with no significant differences among the four groups. The 10-day oviposition amounts for CK (157.73) and T2 (140.33) showed no significant difference, while T1 (57.30) and T3 (58.77) showed no significant difference. However, significant differences were observed between CK and T1/T3, as well as between T2 and T1/T3. These results indicated that feeding C. montrouzieri with frozen mealybugs did not adversely affect their pupation rates, emergence rates, pre-oviposition periods, or hatching rates. However, it significantly negatively impacted the developmental periods of larvae and pupae, the body weights of adult males and females, and the quantity of eggs produced. Although frozen mealybugs could not fully replace fresh mealybugs as feed for large-scale production of C. montrouzieri, they still demonstrated good potential for use. Future improvements in formulation processing of frozen mealybugs and the use of artificial oviposition media might enhance their growth, development, and reproductive performance.