Biology of Anagrus optabilis (Perkins) (Hymenoptera, Mymaridae), an egg parasitoid of delphacid planthoppers.
Anagrus optabilis is an important biological control agent of delphacid planthoppers in Asia. The author reports that he has reared it for the first time in Japan from Saccharosydne procerus, Zuleika nipponica and Nilaparvata muiri and describes all the immature stages. The mymarid was reared in the laboratory in Japan in N. lugens on rice seedlings. Pairing occurred immediately after adult emergence and the females actively sought host eggs; they parasitized all eggs in a mass of host eggs, laying 1 egg in each. Mated females laid 27-66 eggs each (average 46.1) and unmated females laid 20-54 eggs each (average 34.2); the progeny of unmated females were exclusively male. Development from egg to adult averaged about 49.5 days at 15°C, 24.3 days at 20°C, 14.5 days at 25°C and 10.8 days at 30°C. The threshold for development was 11.3°C for females, and the thermal constant above this threshold was calculated to be 199.6 days-degrees. At 15, 20, 25 and 30°C, males and (in brackets) females of A. optabilis provided with honey and water survived for 11.2 (14.2), 6.7 (7.1), 4.4 (5.7) and 3 (3.3) days, respectively, but when provided with water only they survived for 10.6 (9.5), 5.4 (3.7), 4.1 (2.2) and 2.4 (1.8) days, respectively. Evidence was obtained that the parasite overwinters as an egg or 1st-instar larva in a host. In the laboratory, A. optabilis parasitized 86.7% of the eggs of N. lugens provided, 79.6% of those of Sogatella furcifera and 70.5% of those of Laodelphax striatella. In the field, the percentage parasitism was 5.4 for Saccharosydne procerus and 22.5 for Z. nipponica (both on Zizania latifolia) and 17.3 for N. muiri (on Leersia japonica). In the laboratory, A. optabilis did not complete its development beyond the pupal stage when provided with eggs of Nephotettix cincticeps.