PARASITIZATION OF LYGUS LINEOLARIS (HEMIPTERA: MIRIDAE) BY LEIOPHRON UNIFORMIS (HYMENOPTERA: BRACONIDAE): HOST DEFENSE AND HOST ACCEPTANCE.

Abstract

The ability of Leiophron uniformis (Gahan) to parasitize 4 Lygus spp. was determined. While L. uniformis readily attacked Lygus hesperus (Knight), L. lineolaris (Palisot de Beauvois), L. elisus Van Duzee, and L. desertinus Knight, only 6.7% of the L. lineolaris attacked were parasitized compared to 84-87% parasitization of the other species. Two factors were found to cause the low rate of parasitism of L. lineolaris. L. uniformis oviposited in (accepted) few of the L. lineolaris nymphs attacked and most eggs found were encapsulated by the host. Nymphs less than 48-hr old were readily parasitized because they were accepted by the wasps and the hosts encapsulated few of the parasitoid eggs. As nymphal age increased, parasitism dropped rapidly as the acceptance of the host decreased and the host's encapsulation ability increased. Different strains of L. lineolaris were found to differ greatly in their susceptibility to parasitism, their ability to encapsulate, and their acceptance by the parasitoids. A host strain from Arizona was very resistant to parasitism, whereas a strain from Delaware (NJLBR) that had been in culture for 7 years was easily parasitized. The NJLBR strain had no encapsulating ability and it was readily accepted by L. uniformis. A recently established host strain from Delaware (DELBR) encapsulated 23-27% of the parasitoid eggs while an Arizona strain (FILBR) encapsulated 66-76% of the eggs. The DELBR nymphs were accepted in 42-43% of the attacks while the FILBR nymphs were accepted in only 5-14% of the attacks. Delaware and California parasitoid strains did not differ in their acceptance of L. lineolaris or in their ability to resist encapsulation. Rearing L. uniformis for only 1 generation on L. lineolaris did not precondition the wasps to accept that species as a host in preference to L. hesperus. L. uniformis, which had been reared on L. lineolaris for 5 or more generations, did accept that host 2.5 times as often as wasps reared on L. hesperus. The parasitoids did not known any increase in resistance to encapsulation even after they had been reared on L. lineolaris for 11 generations.