INFLUENCE OF HOST STAGE ON OVIPOSITION, DEVELOPMENT, AND SEX RATIO OF Anagyrus lopezi (DE SANTIS) (HYMENOPTERA: ENCYRTIDAE), A PARASITOID OF THE CASSAVA MEALYBUG, Phenacoccus manihoti MATILE-FERRERO (HEMIPTERA: PSEUDOCOCCIDAE)

Abstract

Influence of host stage on oviposition, development, and sex ratio of Anagyrus lopezi (De Santis) (Hymenoptera: Encyrtidae), a parasitoid of the cassava mealybug, Phenacoccus manihoti Matile-Ferrero (Hemiptera: Pseudococcidae). The parasitoid Anagyrus lopezi (De Santis) (Hymenoptera: Encyrtidae) was introduced from Thailand into Indonesia in early 2014 to control the invasive cassava mealybug, Phenacoccus manihoti Matile-Ferrero (Hemiptera: Pseudococcidae). Because of the need to produce large numbers of high-quality females, research was conducted in the laboratory to determine host stage preference for A. lopezi on different instars of P. manihoti. Individual female wasps were exposed to first, second, third instar nymphs, and pre-reproductive adult mealybugs. In the no-choice test, the frequency of parasitized hosts and the number of eggs laid per host was significantly higher in second and third instar nymphs as well as adult mealybugs compared to first instar nymphs. In the two-choice test, third instars nymphs and adult mealybugs were the most preferred host for oviposition. Immature development of parasitoids was faster and the ratio of female to male parasitoids was higher following oviposition in second and third instar nymphs and pre-reproductive adult hosts, compared to the first instar nymphs. Our findings indicate that the use of pre-reproductive adults as hosts in a mass-rearing program would be the most productive and fastest way to produce A. lopezi populations with a female-biased sex ratio. Field release of parasitoids should be conducted when the host’s third instar nymph is the most abundant because the period during which preferred and suitable host stages are available would be the longest.

Parasitoid of cassava mealybug, Anagyrus lopezi (Hymenoptera: Encyrtidae): Mummy size, adult emergence, sex ratio, and parasitization level

“…The host instar also affects the parasitoid's pupa size of the resulting progeny. The proportion of male parasitoids will decrease as the host's size or stage increases (Adriani et al 2020). Female and male A. vexans emerging from parasitized hosts at the third instar were significantly larger than in other stages.…”

“…The rearing of mealybugs follows the rearing method of Adriani et al (2020). One imago of P. manihoti is infested on cassava cuttings aged two weeks.…”

“…The host stage affects parasitoid progeny, with the first instar of the mealybug producing a male parasitoid proportion value of 0.90. As the host stage increase, the female progenies are produced in a proportion value of 0.74 (Adriani et al 2020). The offspring sex ratio (male ratio) decreases with increasing host size.…”

“…Some biological factors as the sex ratio of A. lopezi; in the field, the sex ratio of Epidinocarsis lopezi became more male-biased at higher host densities (Dijken et al 1991). The capability of A. lopezi cassava mealybugs has been recorded since the host entered the 2 nd stage instar, and most prefer the 3 rd instar (Adriani et al 2020). The cassava mealybugs which have been successfully parasitized will be formed as pupae.…”

“…The mummy helps protect the developing larval parasitoid (Daane et al 2008). Adult parasitoids will appear through an opening of the tip of the mummy, while the size of the mummy will determine the sex of the parasitoid (Adriani et al 2020). However, the measurement has not been done to differentiate the sex.…”