Biological studies on Trioza erytreae
Intensive studies on the ecology of Trioza erytreae (EPPO Al pest) have been carried out in South Africa. Investigated were mating, fertility and oviposition of adults as well as settling and the general behavior of nymphs.
Under field conditions first instar nymphs usually settle on the ventral side of leaves. Many of these nymphs are able to disperse over a distance of 300 mm before settling. Compared to nymphs that developed on stems, those that developed on leaves moved around less, completed their development in a shorter period and when they became adults, the males had larger forewings. First instar nymphs apparently orientate themselves by the leaf roughness to settle on the ventral surface. Light seems to help them but gravity plays no role in this. Of psylla nymphs on the ventral side of leaves, 7.2 % ·vacated their galls and 11.8 % moved their positions in the gall per day indicating that nymphs are only partially sedentary. Significantly less nymphs completed their development on young branches than on either the ventral or dorsal sides of leaves.
Males of Trioza erytreae are the aggressors during mating. From time to time they become restless and wander around on the plants, presumably in search of females. During these periods a male often searches a number of leaves and attempts to mate with any adult psylla, male or female, or with mating pairs which it encounters. He may also try to mate with aphids and can become stuck to the aphid's siphunculi. Copulation lasts on average 5 min 32 s at 21°C to 26°C. It takes 29 s to lay an egg, followed by a delay of 23 s before the next egg is oviposited.
Males become sexually mature on the same day that they become adults, and females on the second and third day after the final moult. A female can mate without leading to fertilization. In most cases the duration of mating does not determine whether a female is fertilized or not. A single successful mating enables a female to lay eggs for 16 + 1.5 days (S.E.) or to fertilize a mean of 591 ± 60.8 eggs. As females lay from 102 to 2335 eggs (mean 982), they will have to mate twice on average, but up to four times to be fertilized fully. There are indications that overwintering females will have to mate within about a month previously for the eggs to be fertile. One male has the ability of fertilize one but not more than four females to their full capacity. A 95,9 % hatching was observed in field collected eggs. On citrus, eggs are mostly laid on the tips of shoots, young leaves, stems and thorns. They may also be deposited on citrus flower buds and on lemon fruit.
Sources
Van den Berg, M.A. ; Deacon, V.E. ; Thomas, C.D. (1991) Ecology of the citrus psylla, Trioza erytreae (Hemiptera : Triozidae). 3 Mating, fertility and oviposition.
Phytophylactica 23, 195-200
Van den Berg, M.A. ; Deacon, V.E. ; Thomas, C.D. (1991) Ecology of the citrus psylla, Trioza erytreae (Hemiptera : Triozidae). 4. Settling and general behavior of nymphs
Phytophylactica 23, 201-208